バイオマス

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バイオマスは、電気を生成するための燃料として使用される植物ベースの材料です。例としては、木材および木材残留物、エネルギー作物、農業残留物、および産業、農場、家庭からの廃棄物があります。[1]バイオマスは直接燃料として使用できるため(たとえば、木材の丸太)、バイオマスとバイオ燃料という言葉を同じ意味で使用する人もいます。他の人は、ある用語を他の用語に包含します。[a]米国およびEUの政府当局は、バイオ燃料を輸送に使用される液体または気体燃料と定義しています。[b] [c]欧州連合の合同調査センターはコンセプトソリッドを使用していますバイオ燃料とは、薪、木材チップ、木質ペレットなど、エネルギーに使用される生物由来の生または加工された有機物と定義します。[d]

2019年には、57 EJ(exajoules)のエネルギーがバイオマスから生産されたのに対し、原油から190 EJ、石炭から168 EJ、天然ガスから144 EJ、原子力から30 EJ、水力から15 EJ、風力、太陽光から13 EJと地熱の組み合わせ。[2] [e]現代のバイオエネルギーの約86%は暖房用途に使用され、9%は輸送に使用され、5%は電気に使用されます。[f]世界のバイオエナジーのほとんどは森林資源から生産されています。[g] バイオマスを燃料として使用する発電所は、太陽光発電所や風力発電所によって生成される断続的な電力とは異なり、安定した電力出力を生成できます。[h]

IEA(国際エネルギー機関)は、バイオエナジーを再生可能エネルギーの最も重要な供給源として説明しています[i] IEAはまた、現在のバイオエナジー展開率は将来の低炭素シナリオで必要とされるレベルをはるかに下回っており、展開の加速が緊急に必要であると主張している。[j] [k] 2050年までのIEAのNetZeroシナリオでは、従来の[l]バイオエナジーは2030年までに段階的に廃止され、総エネルギー供給に占める現代のバイオエナジーの割合は2020年の6.6%から2030年には13.1%、2050年には18.7%に増加します。 。[3] IRENA(国際エネルギー機関)は、2030年にバイオマスから生産されるエネルギーが倍増すると予測していますが、従来のバイオエナジー(6 EJ)からの貢献はわずかです。[m]IPCC 気候変動に関する政府間パネル)は、バイオエナジーが正しく行われれば、気候を緩和する可能性が非常に高いと主張しています[n] [o]。IPCCの緩和経路のほとんどには、2050年のバイオエナジーからの実質的な貢献が含まれています(平均200EJ)。 p] [q] [4]一部の研究者は、排出量の節約が少なく、初期炭素強度が高く、気候へのプラスの影響が現れるまでの待ち時間が長いバイオエナジーの使用を批判しています。[5]

将来最大の可能性を秘めている原材料の原料は、リグノセルロース系(非食用)バイオマス(たとえば、銅や多年生のエネルギー作物)、農業残渣、および生物学的廃棄物です。これらの原料はまた、気候上の利益を生み出す前に最短の遅延を持っています。熱生産は電力生産よりも気候に優しく、他の再生可能エネルギー源に置き換えるのは困難です。固体バイオ燃料は、液体バイオ燃料よりも気候にやさしいです。石炭をバイオマスに置き換えることは、天然ガスを置き換えるよりも気候にやさしいです。小規模または古いバイオマスのみの発電所よりも、大規模または最新の石炭プラントでバイオマスを燃焼させる方が気候にやさしいです。研究者の炭素強度の推定値は、炭素の会計方法が異なるため、大きく異なります。

バイオマスカテゴリー

バイオマスは、エネルギーのために直接収穫されたバイオマス(一次バイオマス)、または残留物と廃棄物のいずれかに分類されます:(二次バイオマス):[r] [s]

エネルギーのために直接収穫されたバイオマス

エネルギーのために直接収穫される主なバイオマスの種類は、木材、一部の食用作物、およびすべての多年生エネルギー作物です。

エネルギーのために直接収穫される木質バイオマスは、主に伝統的な調理と暖房の目的で収穫された木と茂みで構成されています(主に開発途上国で)。[ 6] IEAは、従来のバイオエナジーは持続可能ではなく、2050年までのネットゼロシナリオでは、2030年にすでに段階的に廃止されていると主張しています提供されるエネルギー含有量は4EJです。[6]これらの作物は持続可能なものと見なされており、その可能性は(多年生のエネルギー作物と合わせて)2050年までに少なくとも年間25EJと推定されています。[6] [v]

エネルギーのために収穫される主な食用作物は、砂糖生産作物(サトウキビなど)、デンプン生産作物(トウモロコシなど)、および石油生産作物(菜種など)です。[7]サトウキビは多年生作物ですが、トウモロコシと菜種は一年生作物です。砂糖とでんぷんを生産する作物はバイオエタノールを作るために使用され、石油を生産する作物はバイオディーゼルを作るために使用されます。米国はバイオエタノールの最大の生産国であり、EUはバイオディーゼルの最大の生産国です。[8]バイオエタノールとバイオディーゼルの世界的な生産におけるエネルギー含有量は、それぞれ年間2.2と1.5EJです。[9]エネルギーのために収穫された食用作物からのバイオ燃料は、「第1世代」または「従来の」バイオ燃料とも呼ばれ、排出量の節約は比較的少ない。

2010年、2020年、および2030年に、農業に適した土地、すでに使用された土地、およびバイオエナジーに利用可能な土地の合計量。[10]

多年生エネルギー作物は、高収量と一年生作物よりも(はるかに)優れた生態学的プロファイルのために、「[...]エネルギー生産に適した作物のカテゴリー[...]」と見なされています[.. 。] "。[11]しかしながら、これらの作物の商業生産は現在、世界規模で重要ではありません。[w]英国では、政府は2021年に、多年生のエネルギー作物と短期輪作林業のために確保された土地面積を10.000から704.000ヘクタールに増やすと宣言しました。[x] IRENAの2030年の世界的な推定値は33〜39 EJであり、これは保守的であると考えられています。[12]多年生エネルギー作物だけの技術的な世界のエネルギーポテンシャルは、年間300EJと推定されています。[y]

IRENAによると、現在15億ヘクタールの土地が食料生産に使用されており、「[...]約14億ヘクタールの追加の土地が適切ですが、現在は使用されていないため、将来的にバイオエネルギー供給に割り当てることができます。 「」[10]しかし、この土地面積の60%は13カ国しか所有していません。[z] IPCCは、世界にバイオエナジーに適した限界地が3億2千万から14億ヘクタールあると推定しています。[aa] EUプロジェクトMAGIC(成長する工芸作物の限界地)は、欧州連合の永年性作物であるススキ×ギガンテウスに適した利用可能な限界地が4500万ヘクタール(449 901 km2、スウェーデンに相当)あると推定しています( 12 EJ)[ab]また、一般にバイオエナジーに適した利用可能な限界地の6,200万ヘクタール(619 182 km2、ウクライナに匹敵するサイズ)。[13]

世界の40億ヘクタールの森林面積の3分の1は、木材生産やその他の商業目的に使用されています。[14]森林は、世界のエネルギーに使用されるすべてのバイオマスの85%を提供しています。[g]森林はまた、EUでエネルギーに使用されるすべてのバイオマスの60%を提供し[15]、最大の森林バイオマスエネルギー源は木材の残留物と廃棄物です。[16]

残留物や廃棄物の形でのバイオマス

残留物と廃棄物は、主に非エネルギー目的で収穫された生物学的物質からの副産物です。最も重要な副産物は、木材残留物、農業残留物、都市/産業廃棄物です。

木材残留物は、林業または木材加工産業からの副産物です。残留物が収集されてバイオマスに使用されなかったとしたら、それらは林床や埋め立て地で腐敗した(したがって排出物を生成した) [ac]か、森林や屋外の道路脇で燃やされた(そして排出物を生成した)でしょう。木材加工施設。[17]

おがくずは、木材加工産業からの残留物です。

林業活動からの副産物は、伐採残さまたは森林残さと呼ばれ、木のてっぺん、枝、切り株、損傷または枯れ木または枯れ木、不規則または曲がった幹部分、間伐(助けるために片付けられる小さな木)で構成されます大きな木は大きくなります)、そして野火のリスクを減らすために木は取り除かれます。[ad]伐採残留物の抽出レベルは地域ごとに異なりますが、[ae] [af]ですが、持続可能な可能性が大きいため[ag]、この原料の使用に対する関心が高まっています(年間15EJ)。[ah] EUの総森林バイオマスの68%は木の幹で構成され、32%は切り株、枝、頂上で構成されています。[18]

木材加工産業からの副産物は木材加工残渣と呼ばれ、切り抜き、削りくず、おがくず、樹皮、黒液で構成されています。[ai]木材加工残留物の総エネルギー含有量は、年間5.5EJです。[19]木質ペレットは、主に木材加工残渣[aj]から作られ、総エネルギー含有量は0.7EJです。[ak]木材チップは原料の組み合わせから作られ[20]、総エネルギー含有量は0.8EJです。[al]

エネルギーに使用される農業残渣のエネルギー含有量は約2EJです。[am]しかし、農業残留物には未開発の大きな可能性があります。農業残渣の世界的な生産におけるエネルギー含有量は、年間78 EJと推定されており、ストロー(51 EJ)が最大のシェアを占めています。[an]他の人は18から82EJの間を推定しました。[ao] IRENAは、持続可能で経済的に実現可能な[ap]農業残留物と廃棄物の使用が、2030年には37から66EJに増加すると予想しています。 [aq]

都市ごみは1.4EJ、産業廃棄物は1.1EJでした。[2]都市および産業からの木材廃棄物も1.1EJを生成しました。[19]木材廃棄物の持続可能な可能性は、2〜10EJと推定されています。[21] IEAは、廃棄物利用を2050年に毎年45EJに劇的に増やすことを推奨している。[3]

多年生のエネルギー作物、残留物、廃棄物からのバイオ燃料は、「第2世代」または「高度な」バイオ燃料(つまり、非食用バイオマス)と呼ばれることもあります。エネルギーのために収穫された藻類は、「第3世代」バイオ燃料と呼ばれることもあります。[ar] [22]コストが高いため、藻類からのバイオ燃料の商業生産はまだ実現していません。[23]

バイオマス変換

生のバイオマスは、圧縮するだけで(たとえば、木質ペレット)、または熱、化学、生物学に大まかに分類されるさまざまな変換によって、より優れたより実用的な燃料にアップグレードできます。[24]

熱変換

熱アップグレードは、熱を主要な変換ドライバーとして、固体、液体、または気体燃料を生成します。基本的な代替手段は、焙焼熱分解、およびガス化であり、これらは主に、関与する化学反応をどこまで進行させることができるかによって分離されます。化学反応の進行は、主に利用可能な酸素の量と変換温度によって制御されます。

スコットランドのバイオマスプラント。

トレファクションは穏やかな形の熱分解であり、有機物が無酸素から低酸素の環境で400〜600°F(200〜300°C)に加熱されます。[25] [26]加熱プロセスは、エネルギー含有量が最も低い部分を残しながら、エネルギー含有量が最も低い部分を(ガス化によって)除去します。つまり、バイオマスの約30%が焙焼プロセス中にガスに変換され、70%が残り、通常は圧縮されたペレットまたはブリケットの形になります。この固形製品は、耐水性、粉砕が容易、非腐食性であり、元のバイオマスエネルギーの約85%を含んでいます。[27]基本的に、質量部分はエネルギー部分よりも縮小しており、その結果、焙焼バイオマスの発熱量は、発電に使用される石炭(蒸気/一般炭)と競合できる範囲で大幅に増加します。今日最も一般的な一般炭のエネルギー密度は22〜26 GJ / tです。[28]アップグレード(「ウェット」トレファクションと呼ばれることもあります)など、利点を提供する可能性のある、あまり一般的ではない、より実験的または独自の熱プロセスが他にもあります。バイオマス、例えば水性スラリー。[29]

熱分解では、酸素がほぼ完全に存在しない状態で、有機物を800〜900°F(400〜500°C)に加熱する必要があります。バイオマス熱分解は、バイオオイル、木炭、メタン、水素などの燃料を生成します。水素化処理は、再生可能なディーゼル、再生可能なガソリン、および再生可能なジェット燃料を生成するために、触媒の存在下で高温高圧下で水素を使用してバイオオイル(高速熱分解によって生成)を処理するために使用されます。[30]

ガス化では、有機材料を1,400〜1700°F(800〜900°C)に加熱し、制御された量の酸素および/または蒸気を容器に注入して、合成ガスまたは合成ガスと呼ばれる一酸化炭素と水素に富むガスを生成します。合成ガスは、ディーゼルエンジンの燃料、暖房、およびガスタービンでの発電に使用できます。また、水素をガスから分離するために処理することもでき、水素を燃焼させたり、燃料電池で使用したりすることもできます。合成ガスは、フィッシャー・トロプシュ合成プロセスを使用して液体燃料を生成するためにさらに処理することができます。[24] [31]

化学変換

バイオマスを他の形態に変換するために、さまざまな化学プロセスを使用することができます。たとえば、貯蔵、輸送、使用するのにより実用的な燃料を製造したり、プロセス自体の特性を活用したりできます。これらのプロセスの多くは、フィッシャー・トロプシュ合成などの同様の石炭ベースのプロセスに大部分基づいています。[32]エステル交換として知られる化学的変換プロセスは、植物油、動物性脂肪、およびグリースを、バイオディーゼルの製造に使用される脂肪酸メチルエステル(FAME)に変換するために使用されます。[24]

生物学的変換

バイオマスは天然素材であるため、バイオマス分子を分解するために多くの生物学的プロセスが自然界で発達しており、これらの変換プロセスの多くを利用することができます。ほとんどの場合、微生物は、嫌気性消化発酵堆肥化などの変換プロセスを実行するために使用されます。発酵はバイオマスをバイオエタノールに変換し、嫌気性消化はバイオマスを再生可能な天然ガスに変換します。バイオエタノールは車両燃料として使用されます。再生可能な天然ガス(バイオガスまたはバイオメタンとも呼ばれます)は、下水処理施設や乳製品および畜産事業の嫌気性消化槽で生成されます。それはまた、固形廃棄物の埋め立て地で形成され、そこから捕獲される可能性があります。適切に処理された再生可能天然ガスは、化石燃料天然ガスと同じ用途があります。[24]

IRENAは、大規模な国際バイオエネルギー取引の成功には、高密度の商品を低コストで輸送するためにバイオマス変換が必要であると主張しています。[で]

気候への影響

以前は、バイオエナジーに木質バイオマスを使用することは、一般的にカーボンニュートラルと見なされていました。しかし、研究者が土地利用の変化[au]と原生林の伐採の影響を計算し始めたとき、状況は変わりました。[33]現在、林業を含む多くのバイオエナジー経路の実際の炭素強度について活発な議論が行われている。批評家は特に短期的または中期的な気候の影響を懸念しています。批評家は研究者[av]と環境活動家の両方の間で現れました。[aw] [ax]同時に、IPCC、IEA、EUの合同調査センターなどの影響力のある研究機関のバイオエナジーサポーターは、正しく行われた場合、バイオエナジーは気候にやさしいと主張しています(以下を参照)。以下では、この議論の主な科学的議論が提示されます。

炭素会計の原則

さまざまな炭素会計手法は、計算結果、したがって科学的議論に大きな影響を及ぼします。一般に、炭素会計の目的は、エネルギーシナリオの炭素強度、つまり、それがカーボンポジティブ、カーボンニュートラル、またはカーボンネガティブであるかどうかを判断することです。カーボンポジティブシナリオはCO2の正味排出者である可能性が高く、カーボンネガティブプロジェクトはCO 2正味吸収者であり、カーボンニュートラルプロジェクトは排出と吸収のバランスを完全に取っています。[ay]

自然の原因と人間の慣行の両方の結果として、炭素は炭素プール間を継続的に流れます。たとえば、大気中の炭素プール、森林の炭素プール、収穫された木材製品の炭素プール、化石燃料の炭素プールなどです。大気中の炭素プール以外のプールの炭素レベルが上昇すると、大気中の炭素レベルが低下し、地球温暖化の緩和に役立ちます。[az]研究者は、あるプールから別のプールに移動する炭素の量を数えると、洞察を得て、大気中の炭素プール以外の炭素プールに蓄積される炭素の量を最大化する方法を推奨できます。3つの概念、すなわち炭素債務、炭素回収時間、および炭素パリティ時間は特に重要です。

バイオマスが森林などの成長サイトから除去されると、炭素債務が発生します。UNFCCC(各国が排出量を報告している国連組織)が、燃焼イベントではなく、この時点で排出量をすでにカウントする必要があると決定したため、樹木が伐採されたときにカウントされます。[ba]

炭素回収時間は、森林に大気から同量の炭素を再吸収させることにより、この炭素が森林に「返済」されるまでにかかる時間です。

炭素パリティ時間は、あるエネルギーシナリオが別のシナリオと炭素パリティに達するのにかかる時間です(つまり、別のシナリオと同じ量の炭素を保存します)。[bb]これらのシナリオの1つは、たとえば、炭素をカウントしたバイオエネルギーシナリオです。収穫されなかった森林の部分に保管され、炭素は失わ森林量として数えられ収穫された(上記のUNFCCC規則を参照)。ただし、この収穫から作られた木質建設資材とバイオ燃料に存在する炭素の量は、これまでにかかる時間の間、バイオエネルギーシナリオの炭素プールに「カウントバック」できます。炭素は自然に崩壊するか、エネルギーのために燃やされます。代替シナリオは、たとえば、炭素が森林全体に貯蔵されていると見なされる森林保護シナリオです。これは、木がまったく収穫されておらず、さらに成長を続けているため、バイオエナジーシナリオよりも大きい森林です(待機中バイオエナジーシナリオで貯蔵された炭素がそれ自身の炭素レベルに追いつくために。)[bc]ただし、森林内の炭素の暗黙の「ロックイン」は、この炭素が木質建設資材やバイオ燃料の生産に利用できなくなったことも意味します。つまり、これらを他の供給源に置き換える必要があります。ほとんどの場合、最も現実的な発生源は化石発生源です。つまり、ここでの森林保護シナリオは、責任のある化石燃料排出量を炭素プールから差し引くことによって「罰せられる」ことを意味します。(この化石炭素は、技術的に言えば、バイオエナジー炭素プールに追加されたものとしてカウントされ(非バイオエナジー炭素プールから差し引かれるのではなく)、「置換」または「回避」化石炭素と呼ばれることが多いことに注意してください。)

バイオエナジーシナリオの正味炭素債務は、森林保護シナリオの炭素プールに貯蔵されている炭素の正味量が、バイオエナジーシナリオの炭素プールに貯蔵されている炭素の正味量よりも大きい場合に計算されます。バイオエナジーシナリオの正味炭素クレジットは、森林保護シナリオの炭素プールに貯蔵されている炭素の正味量が、バイオエナジーシナリオの炭素プールに貯蔵されている炭素の正味量よりも少ない場合に計算されます。[34]炭素パリティ時間は、バイオエネルギーシナリオが債務からクレジットに移行するのにかかる時間です。[bd]

要約すると、プロジェクトまたはシナリオは、それ自体のメリット、具体的には除去された炭素の回収にかかる時間(炭素回収時間)のみに基づいて評価できます。ただし、代替シナリオ(「参照シナリオ」または「参照シナリオ」とも呼ばれます)を含めるのが一般的です。比較のための反事実」)。[be]複数のシナリオがある場合、これらのシナリオ間の炭素パリティ時間を計算できます。代替シナリオは、既存のプロジェクトと比較してわずかな変更のみのシナリオから、根本的に異なるシナリオ(つまり、森林保護または「バイオエナジーなし」の反事実)にまで及びます。一般に、シナリオ間の違いは、実際の炭素削減の可能性と見なされます。シナリオの。[bf]言い換えると、見積もられた排出削減量は相対的な節約額です。研究者が提案するいくつかの代替シナリオと比較した節約。これにより、研究者は計算結果に大きな影響を与えることができます。

炭素会計システムの境界

炭素会計のシステム境界:オプション1(黒)は炭素計算をスタック排出量に制限し、オプション2(緑)は計算を森林炭素貯蔵量に制限し、オプション3(青)は計算を森林とスタック排出量の合計(供給)に制限しますチェーン)およびオプション4(赤)には、スタック排出量、森林および生物経済(木製品および置換化石燃料の炭素貯蔵)の両方が含まれます。[bg]

代替シナリオの選択に加えて、他の選択も行う必要があります。いわゆる「システム境界」は、実際の計算に含まれる炭素排出量/吸収量と除外される炭素排出量を決定します。システム境界には、時間的、空間的、効率関連、および経済的境界が含まれます。[bg]

時間的システム境界

時間的境界は、炭素カウントを開始および終了するタイミングを定義します。「初期の」イベントが計算に含まれる場合があります。たとえば、最初の収穫前に森林で起こっている炭素吸収などです。たとえば、工場の解体など、関連するインフラストラクチャの寿命末期の活動によって引き起こされる排出など、「遅い」イベントも含まれる場合があります。プロジェクトまたはシナリオに関連する炭素の排出と吸収は時間とともに変化するため、正味の炭素排出は時間に依存するもの(たとえば、時間軸に沿って移動する曲線)または静的な値として表すことができます。これは、定義された期間にわたって計算された 平均排出量を示しています。

時間依存正味排出量曲線は、通常、最初に高い排出量を示します(バイオマスが収穫されたときにカウントが開始された場合)。あるいは、開始点を植栽イベントに戻すこともできます。この場合、土地利用の変化による返済のための炭素債務がなく、さらにますます多くの炭素が植えられた木に吸収される場合、曲線は潜在的にゼロ未満(炭素の負の領域に)移動する可能性があります。その後、排出曲線は収穫時に上向きに急上昇します。収穫された炭素は他の炭素プールに分配され、曲線はこれらの新しいプールに移動される炭素の量(Y軸)と時間と連動して移動します。炭素がプールから出て、大気(X軸)を経由して森林に戻るのにかかります。上記のように、炭素回収時間は、収穫された炭素が森林に戻るのにかかる時間であり、炭素パリティ時間は、2つの競合するシナリオで貯蔵された炭素が同じレベルに達するのにかかる時間です。[bh]

静的炭素排出量の値は、特定の期間の平均年間純排出量を計算することによって生成されます。具体的な期間は、関係するインフラストラクチャの予想寿命(ライフサイクル評価に一般的、LCA)、パリ協定に触発されたポリシー関連の期間(たとえば、2030、2050、または2100までの残り時間)、[35]期間です。さまざまな地球温暖化係数(GWP、通常は20年または100年)、[bi]またはその他の期間に基づいています。EUでは、土地利用の変化による正味の炭素効果を定量化する際に20年の期間が使用されます。[bj]一般に、法律では、静的な数値アプローチが、動的な時間依存の曲線アプローチよりも優先されます。この数値は、いわゆる「排出係数」(生成されたエネルギー単位あたりの正味排出量、たとえばGJあたりのkg CO 2 e)として表されるか、特定のバイオエナジー経路の平均温室効果ガス節約率としてさらに単純に表されます。[bk]再生可能エネルギー指令(RED)およびその他の法的文書で使用される特定のバイオエナジー経路に関するEUの公表された温室効果ガス節約率は、ライフサイクルアセスメント(LCA)に基づいています。[bl] [bm]

空間システムの境界

空間境界は、炭素排出/吸収計算の「地理的」境界を定義します。森林におけるCO2の吸収と排出の2つの最も一般的な空間境界は、1。)特定の林分に沿ったものと2.)年齢が上がる多くの林分を含む森林景観全体の端に沿ったものです(森林林分は、林分がある限り何年にもわたって収穫され、次々に植え替えられます。)3番目のオプションは、いわゆる林分レベルの炭素計算方法です。

–林分レベルの炭素会計では、研究者は、林分が収穫されたときに大量の排出イベントをカウントし、その後、林分が成熟年齢に達して再び収穫されるまで続く蓄積フェーズ中の年間吸収量が少なくなる場合があります。

–同様に、スタンドレベルの会計処理を増やす場合、研究者はスタンドが収穫されたときに大量の排出イベントをカウントし、その後、蓄積期間中に毎年少量の炭素を吸収します。しかし、最初の収穫から1年後、新しい林分が収穫されます。研究者は、最初の隣接する林分が収穫された後にこの2番目の林分で吸収された炭素を数えず、2番目の林分の収穫イベントでの大量の排出のみを数えます。翌年、同じ手順が3番目のスタンドでも繰り返されます。1番目と2番目のスタンドの収穫後にこのスタンドによって吸収された炭素はカウントされませんが、3番目のスタンドの収穫時に大量の排出量がカウントされます。言い換えると、

–景観レベルの会計では、研究者は最初の林分が収穫されたときに大量の排出イベントをカウントし、その後、この特定の林分の蓄積期間中に毎年少量の炭素を吸収します。スタンドレベルの会計処理の増加と同様に、2年目と3年目などで新しいスタンドが収穫され、これらの排出イベントがすべてカウントされます。ただし、林分レベルの会計処理を増やす場合とは異なり、研究者は、森林景観の最初の林分を収穫した後にすべての林分で吸収される炭素もカウントします。言い換えれば、多くの異なる開始点からの炭素排出量を計算する代わりに、森林景観会計は、森林景観全体、つまり最初の林分が収穫された年に共通の開始点を1つだけ使用します。[36]

したがって、研究者は、個々の林分に焦点を合わせるか、林分の数を増やすか、それとも森林景観全体に焦点を合わせるかを決定する必要があります。

Lamers et al。によると、初期の炭素モデリングでは、林分レベルの空間境界の選択が一般的であり、鋸歯状の炭素循環につながります(収穫時の排出量が劇的に増加し、その後、林分が炭素を吸収するにつれてゆっくりと減少します)。スタンドレベル分析の主な利点はその単純さであり、これが今日の炭素分析の一部である主な理由です。ただし、単一の林分を調査すると、簡単に理解できる結果が得られますが(たとえば、さまざまな収穫方法の炭素効果について)、実際の木材/木質バイオマスの供給地域は、成熟度の異なるいくつかの林分、たとえば80で構成されます。それから80年の間に、すべての林分は連続的に収穫され、植え替えられます。[37] Cowie etal。景観レベルの会計は、林業部門が木材製品の継続的な供給を管理する方法をより代表していると主張し[bn] IPCCは、景観レベルの炭素会計も推奨しています(下記の短期的な緊急性を参照)。

さらに、研究者は、直接/間接の土地利用変化からの排出量を計算に含めるべきかどうかを決定する必要があります。ほとんどの研究者は、直接的な土地利用の変化からの排出を含みます。たとえば、代わりにそこで農業プロジェクトを開始するために森林を伐採することによって引き起こされる排出です。間接的な土地利用変化の影響を含めることは、正確に定量化することが難しいため、より議論の余地があります。[bo] [bp]他の選択肢には、将来の森林の可能性のある空間境界を定義することが含まれます。たとえば、林産物の需要が高い状況では、収穫量の増加、そしておそらく森林の拡大でさえ、森林保護よりも現実的ですか?あるいは、林産物の需要が低く、住宅や都市開発のための新しい土地や新しい地域の需要が高い状況では、小さな森林はおそらく森林保護よりも現実的ですか?Lamers&Jungingerは、自然保護と炭素戦略の評価の観点から、森林保護は有効な選択肢であると主張しています。ただし、森林プランテーションが保護される可能性は低いです。林産物(木材、パルプ、ペレットなど)の需要がない場合、「[...]農業への転換や都市開発などのオプションがより現実的な選択肢になる可能性があります[... ]。」[bq] Cowie etal。個人所有の森林は収入を生み出すためにしばしば使用され、したがって一般的に市場の発展に敏感であると主張します。森林保護は、森林所有者が収入の損失を補償できない限り、ほとんどの私有林にとっては現実主義的なシナリオです。[br] EUの合同調査センターによると、ヨーロッパの森林の60%は私有林です。[38]米国では、80%以上が東部で私有であり、80%以上が西部で公有である。[39]

効率関連のシステム境界

代替化石燃料のバイオエナジー変位係数。[40]
置換化石ベースの材料に対する木質材料の変位係数。[41]

効率に関連する境界は、さまざまなバイオマス燃焼経路の燃料代替効率の範囲を定義します。供給チェーンが異なれば、供給されるエネルギー単位ごとに排出される炭素の量も異なり、燃焼施設が異なれば、さまざまな燃料に蓄えられた化学エネルギーが、効率の異なる熱または電気エネルギーに変換されます。研究者はこれについて知っており、検討中のさまざまなバイオマス燃焼経路の現実的な効率範囲を選択する必要があります。選択された効率は、いわゆる「変位係数」を計算するために使用されます。これは、化石炭素が生体炭素にどれだけ効率的に置き換えられるかを示す単一の数値です。[bs]たとえば、10トンの炭素が現代の石炭火力発電所の半分の効率で燃焼される場合、実際には5トンの石炭だけが変位としてカウントされます(変位係数0.5)。Schlamadinger&Marlandは、バイオマスと石炭ベースの森林保護シナリオを比較した場合に、このような低効率がどのように高いパリティ時間をもたらすか、一方、石炭シナリオと同じ効率がどのように低いパリティ時間をもたらすかについて説明します。[42]一般に、非効率的な(古いまたは小さい)燃焼施設で燃焼された燃料は、効率的な(新しいまたは大きな)施設で燃焼された燃料よりも低い排気量係数が割り当てられます。同じ量のエネルギーを生成します。[bt]

同様に、木材ベースの建設資材の生産は、化石ベースの建設資材(セメントや鋼など)の生産よりも化石燃料の投入量が少ないため、セメントと鋼ベースの建設資材の代替が現実的である場合、木材ベースの建設資材には変位係数が割り当てられます、すなわち、それらが建設において同じ有用性を持っている場合。ユーティリティと同等の木材建設製品を使用することで回避される化石燃料の排出量が多いほど、割り当てられる変位係数は高くなります。[bu]さらに、製品の耐用年数中に木材製品に蓄積された炭素と、木材製品が耐用年数の終わりにエネルギーのために燃焼したときに置換される化石炭素の両方を変位係数の計算に含めることができます。ただし、これまでのところ、これは一般的な方法ではありません。[bv](EUで収穫された森林バイオマスの52%が材料に使用されています。)[43]

Sathre&O'Connorは、21の個別の研究を調査し、建設用木材製品の変位係数が-2.3〜15で、平均が2.1であることを発見しました。これは、生成される生体炭素1トンあたり、平均2.1トンの化石炭素が変位することを意味します。 。[44]木材ベースのバイオ燃料の場合、置換係数は約0.5から1の間で変動し、「[...]交換される化石燃料の種類と相対的な燃焼効率に大きく依存します。」[45]著者は、建設用木材製品が耐用年数の終わりにエネルギーのために燃焼されるとき、変位効果が計算に追加されることがあると書いています。「[...]材料代替と燃料代替の両方のGHGの利点として発生します。」[46]この追加の耐用年数を経た燃焼代替効果が除外された建設用木材製品に関する別のメタ研究では、著者はやや低い変位係数を発見しました。燃焼固有の変位係数は同様でしたが、範囲が広くなりました(右のグラフを参照)[47] 。

置換係数は、バイオマス燃料と置換された化石燃料の両方の炭素強度によって異なります。バイオエナジーが負の排出量を達成できる場合(たとえば、植林、エネルギー草のプランテーション、および/または炭素回収貯留を伴うバイオエナジー(BECCS)、[bw]、またはサプライチェーンで排出量の多い化石燃料エネルギー源がオンラインになり始めた場合(フラッキングやシェールガスの使用量の増加などにより、置換係数が上昇し始めます。一方、化石燃料よりも排出量が少ない新しいベースロードエネルギー源がオンラインになり始めると、置換係数は上昇し始めます。ドロップ。変位係数が変化するかどうかが計算に含まれるかどうかは、関連するシナリオの時間システム境界でカバーされる期間内に発生すると予想されるかどうかによって異なります。[bx]

経済システムの境界

経済的境界は、もしあれば、計算に含める市場効果を定義します。市況の変化は、サプライチェーンや森林からの炭素排出量と吸収量に小さな変化または大きな変化をもたらす可能性がありますたとえば、需要の変化への対応としての森林面積の変化。マイナー他 研究者が、市場への影響にも対処する、より広く統合されたフレームワークで森林バイオエナジーをどのように調査し始めたかを説明します。経験的データとモデリングの両方に基づいて、これらの研究は、需要の増加がしばしば森林面積を増加させ、森林管理の改善を奨励する林業への投資につながることを決定しました。状況に応じて、このダイナミクスは森林の炭素貯蔵量を増やす可能性があります。成長率が比較的高く、投資反応が強い場合、化石燃料の排出と投資反応のタイミングにもよりますが、エネルギーとしての樹木の使用を増やすことによる正味のGHG効果は10年か2年以内に実現できます。樹木の成長が遅く、投資反応が不足している場合、エネルギーにラウンドウッドを使用することによる正味の利益を確認するには、何十年もかかる可能性があります。投資対応は、米国南部のように、土地への経済的利益が森林地域の利益と損失に直接影響を与えることが示されている場所で特に重要であることがわかっています。[48] Abt etal。米国南部は世界最大の材木生産者であり、森林は私有であり、したがって市場主導であると主張します。[49]さらに、EUの合同調査センターは、マクロ経済の出来事/政策の変更が森林の炭素蓄積に影響を与える可能性があると主張している。[bz]間接的な土地利用の変化と同様に、経済的変化を定量化するのは難しい場合があるため、一部の研究者はそれらを計算から除外することを好みます。[ca]

システム境界の影響

選択したシステム境界は、計算結果にとって非常に重要です。[cb]化石炭素強度、森林成長率、バイオマス変換効率が増加した場合、または初期の森林炭素貯蔵量や収穫レベルが減少した場合、より短い回収/パリティ時間が計算されます。[50]研究者がスタンドレベルの炭素会計よりも景観レベルを選択した場合、より短い回収/パリティ時間も計算されます(炭素会計が植栽イベントではなく収穫時に開始される場合)。逆に、炭素強度の場合、より長い回収/パリティ時間が計算されます。 、成長率と変換効率が低下するか、初期の炭素貯蔵量および/または収穫量が増加すると、または研究者は、景観レベルの炭素会計よりもスタンドレベルを選択します。[cc]

批評家は、非現実的なシステム境界の選択が行われている、[cd]、または狭いシステム境界が誤解を招く結論につながると主張しています。[ce]他の人々は、結果の範囲が広いことは、利用できる余地が多すぎることを示しており、したがって、計算は政策立案には役に立たないと主張している。[cf] EUのJoinResearch Centerは、方法論が異なれば結果も異なることに同意しています。[cg]しかし、人間の自然との最適な関係に関する倫理的理想の結果として、さまざまな研究者が意識的または無意識にさまざまな代替シナリオ/方法論を選択するため、これは予想されることでもあると主張します。持続可能性の議論の倫理的核心は、隠されるのではなく、研究者によって明確にされるべきです。[ch]

時間とともに変化するものとして表される気候への影響

石炭および天然ガスの代替シナリオと比較した、森林バイオマス経路の時間依存の正味排出量の推定。プラス記号は正の気候効果を表し、マイナス記号は負の気候効果を表します。[16]

EUの合同調査センターによると、バイオエナジー専用に収穫された北方の幹材の使用は、長期的にのみ気候にプラスの影響を与えますが、木材残留物の使用は、短期から中期にも気候にプラスの影響を与えます。[ci]代替シナリオでの石炭や天然ガスからのエネルギー生成と比較した、幹材、残留物、新しいプランテーションなど、さまざまな森林バイオエナジー経路からの予想排出削減量の概要については、右のグラフを参照してください。短回転の雑木林または短回転の森林からの茎も、短中期的には気候にプラスの影響を及ぼします(以下を参照)。

森林残留物の短い炭素回収/パリティ時間

最も現実的な非バイオエナジーシナリオが、材木生産のために「良い」木材の茎を収穫し、残留物を燃やしたり、森林や埋め立て地に残したりする従来の林業シナリオである場合、短い炭素回収/パリティ時間が生成されます。そのような残留物の収集は、「[...]とにかく(バイオームの崩壊率によって定義される時間の経過とともに)その炭素を(崩壊または燃焼によって)大気に放出したであろう材料を提供します[...]」。[51]言い換えると、回収時間とパリティ時間は減衰速度に依存します。崩壊速度は、a。)場所(崩壊速度は「[...]気温と降雨量にほぼ比例する[...]」[52]であるため] 、およびb。)残留物の厚さに依存します。[cj]残留物は暖かく湿った場所でより速く腐敗し、薄い残留物は厚い残留物よりも速く腐敗します。したがって、暖かく湿った温帯林の薄い残留物は最も速く減衰し、寒くて乾燥した北方林の厚い残留物は最も遅い減衰を示します。代わりに、残留物がバイオエナジーのないシナリオで、たとえば工場の外や森林の道端で燃やされた場合、排出は瞬時に行われます。この場合、パリティ時間はゼロに近づきます。[ck]

Madsen&Bentsenは、同じ北欧のCHP(熱電併給)プラントで燃焼した森林残留物と石炭の両方からの排出量を調べ、炭素のパリティ期間が1年であることを発見しました。[cl]低いパリティ時間は、主に残留物の使用、通常の発電所と比較したCHPプラントの一般的に高い変換効率(この場合は85.9%)、および石炭のより長い輸送距離の結果でした。[cm]著者は、ほとんどのバイオエナジー排出量研究は実際のフィールドデータではなく仮想データを使用しており、EUの純粋な発電所よりも16倍多くのバイオマスがCHPプラントで燃焼していることに注目しています。[cn]言い換えれば、現在の状況に最も関連するのは、このような熱関連の回収/パリティ時間です。シンタスらを含む他の研究者は、同様のパリティ時間を発見しました。(0年、スウェーデン)、[co] Zetterberg&Chen(0年、スウェーデン)、[53] Repo etal。(0年、フィンランド)、[54]およびZanchi etal。(0年、オーストリア)。[cp]一般に、このような低いパリティ時間は、森林がバイオマス生産にまったく使用されないが、材木生産に引き続き使用される石炭使用の代替シナリオに依存します。材木生産は同じままであるが、代替シナリオで石炭が天然ガスに置き換えられた場合、ほとんどの研究者は、残留物の厚さと場所に応じて、約5〜20年のパリティ時間を見つけました。[cq] IRENAは、太陽熱、ヒートポンプ、地熱よりもCHPプラントを推奨しています。これは、CHPがプロセス熱をより安価に、必要な温度で生成できるためです。[cr]

Holmgrenは、40年間(スウェーデン1980〜 2019年)にわたって全国の実際の林業慣行による気候への影響を調査し、国の景観レベルでは、この期間中のどの時点でも炭素債務が発生していないことを発見しました。実際の林業慣行は、2つの代替的な森林保護シナリオと比較されました。実際の林業シナリオでの初期収穫によって引き起こされたカウントされた排出量は、炭素債務につながりませんでした。1。)初期収穫関連の炭素排出量は、森林の他の場所での成長によって引き起こされた炭素吸収によって上回っていました(なぜなら、国の森林保護政策は、化石燃料で機能するように変換されたときに、国の木材ベースの製品とエネルギーインフラストラクチャから大量の初期排出を引き起こすからです。[cs]変換は、「[...] 1回限りの変換であり、エネルギーシステム、インフラストラクチャ、産業処理、建築セクター、消費者製品の製造、および化石ベースの生産に向けたその他の経済活動に対する主要かつ必要な変更を表します。収穫なしのシナリオを実施する場合。」[55]もちろん、バイオエナジーシナリオの最初の収穫関連排出イベントが1.)他の場所での森林成長、および2.)インフラストラクチャ変換排出(森林保護シナリオで)よりも重要である場合、炭素債務はまったく発生しません。回収時間とパリティ時間はゼロに減少します。著者は、森林保護は生体炭素の代わりに化石炭素を放出する可能性が最も高いので、地下の化石炭素プールから、燃焼を介して大気中の炭素プールに移動し、次に光合成を介して森林の炭素プールに移動しますしかし、炭素が地下の化石貯留層ではなく森林に貯蔵されている場合、それはより不安定になります。つまり、自然の乱れのためにCO2に変換しやすくなります。[56]生産された生物起源の炭素1トンあたり0.78トンの化石炭素が置換された控えめな置換係数は、収穫された木材製品(HWP)とエネルギーの組み合わせの両方に使用されます。[ct]著者は、炭素会計を森林自体の炭素の流れに限定し、化石の移動効果を除外する研究を批判し、この狭いシステム境界は本質的に「[...]純利益のない他の場所での継続的な化石排出の正当化として機能する」と主張します地球の気候のために。」[57]スウェーデンでは、エネルギーに利用できるバイオマスは主に暖房設備で使用されています(暖房に7.85 Mtoe、電気に0.84 Mtoe)。[58]

米国では、ウォーカー等。ニューイングランドの森林残留物を使用して、通常の公益事業規模の発電所で石炭を置き換える場合、10年以下のパリティ時間が見つかりました。[59]同様に、マイナー等。米国の東部では、あらゆる種類の森林残留物が、石炭ベースの代替シナリオと比較して10年以内、および天然ガスベースの代替シナリオと比較して20年以内に、気候上の利益を伴うバイオマスに使用できると主張します。[cu]

さまざまな原料からの木質ペレット電気の炭素パリティ時間(Hanssen et al.2017)。[60]

ハンセン他 米国南東部での継続的なペレット生産を含むバイオエネルギーシナリオを、3つの代替化石燃料混合シナリオと比較しました。これらはすべて、森林保護よりも現実的なシナリオと見なされています。間伐の慣行をやめます。つまり、小さな木をそのままにしておくと、成長の可能性がより高くなります。3。)残留物をそのままにしておくと、発電所でほとんどすぐに燃やされるのではなく、時間の経過とともに自然に腐敗します。代替シナリオごとに、3つの異なるレベルの需要(低、平均、高)が含まれていました。パリティ時間は、すべての需要シナリオで0〜21年、平均需要シナリオで0〜6年の範囲でした(右のグラフを参照)。著者はランドスケープレベルの炭素会計を使用し、ローテーション時間は25年でした。[履歴書]

代替シナリオと比較した、さまざまな残留物ベースのエネルギーシステムの炭素パリティ時間。[cw]
森林残留物、穀物わらおよびバイオガススラリーの時間依存の地球温暖化緩和の可能性。[61]
切り株(30 cm)、間伐(10 cm)、枝(2 cm)など、さまざまな厚さの腐敗した森林残留物からの時間依存の排出レベル。点線=北フィンランド、実線=南フィンランド。[cx]

Lamers&Jungingerは、(サブ)北方林の残留物(場合によっては切り株を含む)に関する多くの研究を調査し、0〜16年の炭素パリティ時間を発見しました。バイオエナジーシナリオは、残留物が自然に腐敗するために森林に残されたか、道端で焼却された別の参照シナリオと比較されました。残留物が道路脇で燃やされ、代わりに石炭火力発電所によって電気が生成されるシナリオと比較して、パリティ時間は0年でした。しかし、路傍の燃焼が自然崩壊と交換され、石炭が石油と交換されたとき、パリティ時間は3〜24年に増加しました。石油が天然ガスに置き換えられたとき、パリティ時間はさらに4〜44年に増加しました。すべてのバイオマスシナリオは、景観レベルの炭素会計を使用しました。[62]

Zanchi etal。簡単に分解できる森林残留物をバイオエナジーに使用する場合、最初から気候上の利点があることに同意します。彼らはまた、「[...]限界農地など、初期のC [炭素]ストックが少ない土地にある新しいバイオエナジープランテーションは、排出削減の点で最も明確な利点がある」と書いています。[63]その理由は、新しく植えられた地域(現在、樹木や他の植物のストックが大量に成長している)が、以前よりもはるかに多くの炭素を吸収するためです。そのような地域は、炭素債務の代わりに炭素クレジットを構築し、クレジットは後で(収穫時に)「無債務」バイオマスを取得するために使用されます。一般に、このような「初期の」炭素会計は、収穫イベントではなく植栽イベントで始まります(cf.上記の時間的システム境界)は、植生が非常に少ない陸域の新しいバイオエナジープランテーションについては議論の余地がないものと見なされています。一方、すでに大量の植生が存在する地域では、「後期」の炭素計算がしばしば好まれます。この場合、炭素会計は収穫時に開始され、以前の炭素クレジットは蓄積されません。このタイプの炭素会計では、計算結果は、木がバイオマスエネルギーのためだけに伐採される場合(いわゆる「追加伐採」)、短期から中期の悪影響があることを示しています。林床に残留物が腐敗したままになると、状況はさらに悪化します。また、生産性の低い植林地を確保するために、森林などバイオマスの多い地域を皆伐すると、悪影響が出るリスクもあります。

最初の輪作が完了した後の「新しい」バイオマスプランテーションからのそのような「追加の伐採」の評価は、選択された炭素会計方法に依存します。「初期の」炭素会計が継続する場合、最初のローテーション後、つまり樹木が植え替えられた瞬間から、炭素クレジットが蓄積されます。その時点で研究者が「後期」炭素会計に変更した場合、炭素クレジットは計算されず、2回目のローテーションの終わり(収穫時)に代わりに大きな炭素債務が作成され、回収時間とパリティ時間が劇的に増加します。

森林残留物の長い炭素回収/パリティ時間

EUの共同研究センターは、EUの現在の電力構成に等しい排出量の非バイオエネルギーシナリオと比較して、残留物ベースの木質ペレット、穀物わら、およびスラリーからのバイオガスからの大規模な電力生産の時間依存排出量推定値を提供します。変換効率は、木質ペレット、わら、バイオガスでそれぞれ34%、29%、36%です。発電に使用しなかった場合、森林の残滓は林床に腐敗し、藁の残滓も畑に残され、生の肥料は有機肥料として使用されていたでしょう。結果は、これらのバイオマスタイプが代わりに電力を生産するために使用された場合、地球温暖化緩和効果は、木材、わら、バイオガスのそれぞれについて、約50年、10年、5年の使用後に始まることを示しています。木質ペレットのパリティ時間が長い主な原因は、EUの電力ミックス(石炭よりも排出量が少ない太陽光、風力、化石燃料からの電力を含む)からの電力との比較です。また、森林残留物のカテゴリーには切り株が含まれます。[cy]

EUの合同調査センターはまた、フィンランドでは、石炭ベースの代替シナリオと比較した場合、切り株を含むすべての種類の残留物のパリティ時間が0年であることを発見しました。ただし、天然ガスベースの代替シナリオと比較すると、切り株は緯度に応じて30〜50年のパリティ時間に達します(右のグラフを参照)。[cx]したがって、JRCは次のように書いています。 CRF [累積放射強制]削減[温度低下]が、長期的なCRF削減をもたらすにもかかわらず、石油と天然ガスを交換すると、最初の10〜25年間でCRFが増加します。」[65]

JRCはまた、他のいくつかの代替シナリオと比較した場合、収穫残さ(枝、間伐、切り株を含む)のパリティ[cz]時間が0年から35年の範囲であることを発見しました。フィンランドでは、切り株のパリティ時間は石油と比較して22年、天然ガスと比較して35年であり、林分レベルの炭素会計が使用されています。カナダでは、収穫されたバイオマスが木質ペレットの代わりにエタノールを生産するために使用され、石炭ベースの代替シナリオの代わりにガソリンベースの代替シナリオと比較された場合、パリティ時間は16年から74年に増加しました。[da]米国オレゴン州の原生林から除去された全樹木からのエタノール生産(山火事を防ぐために樹木が伐採されたため、残留物として分類)は、パリティ時間を劇的に増加させ、最悪のシナリオは459年でした。著者らは、収穫イベントから始まるスタンドレベルの炭素会計を使用し、25年ごとに追加の野焼きを想定し、これを、山火事防止伐採がなく、230年ごとに山火事が発生するシナリオと比較しました。[66]問題の樹木は、巨大なアメリカツガと海岸のダグラスモミの木であり、どちらも成熟するのに数百年かかり、非常に太い茎のために山火事に耐えることができます。エネルギー集約的なエタノール生産はわずか0.39の低い排気量を引き起こしたので、長いパリティ時間が計算されました。[67]一般に、JRCの報告されたパリティ時間は、変位係数、代替シナリオ、残留物のサイズ、および気候タイプの影響を受けました。上記のチャートを参照してください。

幹材の短い炭素回収/パリティ時間

植林のためのスペースを確保するために既存の自然林が皆伐されている場合、暗黙の炭素変化は、伐採された樹木に存在する炭素の量とほぼ等しい重要な炭素債務を生み出します(化石ベースの林業事業は、追加の小さな債務を生み出します) 。)しかし、農地や限界地のような「空の」土地にある新しいプランテーションでは、立木がなく、炭素は除去されません。この場合、カーボンクレジット代わりに、木が成熟するにつれてすぐに構築されます。後でそれらの木が伐採されると、樹木に存在する炭素の量が蓄積された炭素クレジットから差し引かれます(立っている樹木の炭素量ではありません)。したがって、この場合、炭素債務は発生しません。収穫時に炭素債務が発生しない場合、残留物と幹材の両方について、炭素の回収/パリティ時間はゼロまたは非常に低くなります。[db]

短い回転の森林はまた、低いパリティ時間を持っています。Lamers&Jungingerは、幹材に関する多くの個別の報告を研究しました[dc]米国南部のプランテーション森林におけるバイオエナジーの収穫。これらの木の輪作時間は20〜25年です(輪作時間は、新しい木が収穫された木と同じサイズに成長するのにかかる時間です)。バイオエネルギーのシナリオでは、木の茎は電力生産のためだけに収穫されました。代わりに森林が保護され、石炭火力発電所によって電力が生成されるさまざまな代替シナリオと比較した場合、バイオエネルギーシナリオの炭素パリティ時間は12〜46年でした。ローテーション時間が35年に増加し、代替シナリオで石炭が化石燃料混合物と交換されたとき、パリティ時間は35年から50年の間に増加しました。著者らはまた、ブリティッシュコロンビア(カナダ)の自然(管理されていない)北方林は、石炭ベースの代替シナリオで、樹木が昆虫によって殺され、その後バイオマスのために収穫されたときのパリティ時間が0年であることを発見しました。しかし、他の3つの成長の遅い北方林地域の生きている木が生物エネルギーのために収穫されたとき、石炭ベースの代替シナリオと比較して、パリティ時間は最大105年に達しました。しかし、著者は、「[...]のこぎり品質の幹材が体系的にバイオエナジー原料になる可能性は非常に低い」と述べています。また、石炭ベースの代替シナリオと比較しました。しかし、著者は、「[...]のこぎり品質の幹材が体系的にバイオエナジー原料になる可能性は非常に低い」と述べています。また、石炭ベースの代替シナリオと比較しました。しかし、著者は、「[...]のこぎり品質の幹材が体系的にバイオエナジー原料になる可能性は非常に低い」と述べています。[68]

Jonker etal。米国南東部の森林から収穫された20〜25年の輪作時間で、林分レベル、増加する林分レベル、および景観レベルの炭素会計の両方を使用して、幹材の炭素回収時間と炭素パリティ時間の両方を計算しました。スタンドレベルの炭素会計では、著者は、高、中、低収量のシナリオで、それぞれ5年、7年、11年の炭素回収期間を見つけました。スタンドレベルの会計処理が増えるにつれ、高利回り、中利回り、低利回りのシナリオでは、回収期間はそれぞれ12年、13年、18年でした。ランドスケープレベルの会計では、すべての利回りシナリオで回収期間は1年未満でした。[36]著者らはまた、平均的な石炭ベースの発電所での同時燃焼に、茎のみ(残留物の収集なし)からの木質ペレットを使用したシナリオのパリティ時間を計算しました。変換効率は41%でした。これは、効率的なサプライチェーンとともに、0.92という比較的高い排気量係数につながります。代替シナリオは、幹材が代わりに材木生産に使用された非バイオマスシナリオであったため、この場合はまったく同時燃焼はありません(石炭からの電力のみ)。増加するスタンドレベルの会計原則を使用する場合、著者はパリティ時間を計算しました高、中、低収量のシナリオでは、それぞれ17年、22年、39年です。ランドスケープレベルの会計原則を使用する場合、著者は、高、中、低利回りのシナリオで、それぞれ12年、27年、46年のパリティ時間を計算しました。別の代替シナリオは、バイオマスが森林からまったく抽出されなかった森林保護シナリオでした。材木用ではなく、バイオエナジー用でもありません。森はただ放置されていたので、ゆっくりと再生しました。このシナリオのランドスケープレベルのパリティ時間は、高、中、低収量のシナリオでそれぞれ3年、3年、30年でした(スタンドレベルまたはスタンドレベルのパリティ時間の増加は提供されていません)。[69]

著者らは、「炭素収支の結果は、炭素会計方法の選択が炭素回収と炭素オフセットパリティポイントの計算に大きな影響を与えることを明確に示している」と述べています。[70]彼らは、短いパリティ時間は、米国南東部の針葉樹植林地での速い成長率(1ヘクタールあたり年間10〜12トンの乾燥質量)によって引き起こされると主張しています。他の研究者は、自然の北方林の広葉樹に典型的な遅い成長率に基づいて計算を行うことがよくあります。これにより、はるかに高い投資回収とパリティ時間が生成されます。著者らはまた、確立された針葉樹植林地については、土地利用の変化によって引き起こされる炭素債務はないと主張している。また、小規模なバイオマス発電所ではなく通常の石炭火力発電所で木質ペレットを同時燃焼に使用すると、効率的なサプライチェーンと高い変換効率が達成されるため、変位係数は他のいくつかの研究よりも高くなります。後者は、他の研究ではしばしばそうであると想定されていました。事実上、これらの好ましいシステム境界により、パリティ時間は1回転または2回転に減少します。パリティポイントの前の炭素債務は少なく、パリティポイントを通過した後の後続の炭素クレジットは高くなります。「一時的な負の炭素収支の絶対サイズが制限されているのに対し、損益分岐後の正の炭素収支も明らかです。 -すぐに何倍ものレベルに到達します。」[71]著者らは、ここの森林は私有であり、大規模な木材加工産業がすでに実施されているため、バイオエナジーなしおよび森林保護のシナリオは調査地域では非現実的であると主張している。この状況(実行可能な代替シナリオなし)では、著者は、最も関連性のある時間的測定基準は、景観レベルの炭素会計原則に基づいて、すべての収量シナリオで1年未満の炭素回収期間であると主張します。[72] Abt etal。また、米国南東部では、森林は私有であるため、森林保護のシナリオは非現実的であると主張しています。[49]

さまざまな代替化石ベースのシナリオと比較した、バイオエナジー専用に収穫された幹材の炭素パリティ時間。[73]

EUの合同調査センターは多くの研究をレビューし、バイオマス木材製品の両方で幹材を収穫する場合、40年の期間を考えると、継続的な収穫は森林保護よりも気候に適していることを発見しました。[dd]その理由は、バイオエナジーと比較して木材製品の変位効果が大きいためです。木材製品が寿命に達したときにエネルギーとして使用される場合(いわゆる「カスケード」)、変位効果はさらに大きくなり、最適な条件下では、パリティ時間は数世紀からゼロに減少する可能性があります。したがって、JRCは、材料変位効果のために木材を含めなかった研究は、誤解を招く結論に達する可能性があると主張しています。[de]一方、森林が独占的に収穫された場合バイオエナジーの場合、木製品に変位の影響は発生しません。つまり、変位係数が低くなり、計算されたCO2排出量が正味増加します" [...]短期および中期(数十年)[...] 「化石燃料と比較した場合。ただし、限界地、農地、または放牧地の新しいプランテーションから収穫された場合を除きます。この場合、事前に樹木を伐採せずに植えると、そこでのバイオマスの量が増えるため、サイトでは炭素が即座に正味増加します。[df]繰り返しますが、炭素債務がない場合、回収時間とパリティ時間はゼロに減少します。[dg]

幹材の長い炭素回収/パリティ時間

Zanchi etal。オーストリアアルプスのトウヒの茎がバイオエナジー専用に収穫された場合、パリティ時間は石炭ベースの代替シナリオでは175年、天然ガスベースの代替シナリオでは300年に達する可能性があることがわかりました。主な理由は、これらの木の回転時間が長い(90年)ことです。一般に、北方林で樹木が成熟するまでには70〜120年かかります。[74]批評家は、品質要件を満たす茎は、木質ペレットなどの低価値製品ではなく、製材などの高価値製品やクロスラミネーテッド木材などの集成材製品の生産に使用されていると回答しています。[dh]このタイプの森林が皆伐され、バイオエナジーと無垢材製品に50/50が使用され、その後、短い輪作林に置き換えられる別のシナリオでは、石炭代替シナリオのパリティ時間は17年から114年の間で変化します。最短の輪作時間と最高の収量で森林によって達成される最短のパリティ時間(年間1ヘクタールあたり16トンの収量で10年の輪作時間)石油ベースの代替電力と比較した場合、パリティ時間は20年から145年に増加しましたケース、および天然ガスベースの電気代替ケースと比較した場合、25年から197年の間。植林と化石燃料の混合シナリオでは、0年のパリティ時間が報告されました。

著者は、これらのシナリオは「実例」であり、「結果は行われた仮定に強く影響される」と述べています。著者らは、残留物が林床に収集されずに残され、そこで腐敗して排出物を生成すると仮定しました。代わりにこれらの残留物が収集されてバイオエナジーに使用される場合、パリティ時間は100年減少します。木質燃料と比較して化石燃料の供給ルートが長いことによって生じる余分な排出量は、計算に含まれていません。[di]害虫、倒木、森林火災(通常、管理されていない森林が老朽化すると増加すると予想される)からの追加排出量も計算に含まれていません。市場への影響は含まれていません。一方、景観レベルの炭素会計が使用され、バイオマスと石炭の想定される変換効率は同じでした。[75]

他の科学者と同様に、JRCのスタッフは、炭素会計の結果のばらつきが大きいことに気づき、これをさまざまな方法論に帰しています。[dj]調査した研究では、JRCは、森林/バイオエネルギーシステムと代替化石の両方のさまざまな特性と仮定に応じて、バイオマス専用に収穫された幹材の炭素パリティ時間が0〜400年(右のグラフを参照)であることを発見しました。システムでは、置換された化石燃料の排出強度が最も重要な要素と見なされ、次に変換効率とバイオマス成長率/回転時間が続きます。炭素パリティ時間に関連する他の要因は、初期の炭素貯蔵量と既存の収穫レベルです。より高い初期炭素貯蔵量とより高い収穫レベルの両方は、より長いパリティ時間を意味します。[76]液体バイオ燃料は、バイオマスのエネルギー含有量の約半分が処理中に失われるため、パリティ時間が長くなります。[dk]

静的な数値として表される気候への影響

いくつかのバイオエナジー経路の静的排出量の推定

さまざまなバイオ燃料経路からの純排出量(熱生成)。点線は、EU石炭、軽油、最も関連性の高い化石燃料代替物、および天然ガスの純排出量を示しています。点線の領域は、最も関連性の高い化石燃料の代替燃料(白70〜80%、緑80〜85%、青85〜100%)と比較した排出削減率を示しています。[77]
さまざまなバイオ燃料経路(輸送)からの純排出量。点線は、最も関連性の高い化石燃料の代替燃料の純排出量を示しています。点線の領域は、最も関連性の高い化石燃料の代替燃料(白50〜60%、緑60〜70%、青70〜100%)と比較した場合の排出削減率も示しています。[77]
さまざまなバイオ燃料経路からの純排出量(発電)。点線は、EU石炭(黒)、最も関連性の高い化石燃料代替(緑)、電力ミックス(赤)、天然ガス(青)の純排出量を示しています。点線の領域は、最も関連性の高い化石燃料の代替燃料(白70〜80%、緑80〜85%、青85〜100%)と比較した排出削減率を示しています。[78]
米国からEUへの木質ペレットの生産と輸送からの温室効果ガス排出量(Hanssen et al.2017)。[dl]

EUの共同研究センターは、文献に見られる多くのバイオエナジー排出量の推定値を調査し、それらの研究に基づいて、熱生産、輸送燃料生産、および電力生産におけるバイオエナジー経路の温室効果ガス節約率を計算しました(右のグラフを参照)。計算は、帰属LCA会計原則に基づいています。これには、原材料の抽出から、エネルギーと材料の生産と製造、寿命末期の処理と最終処分に至るまでのすべてのサプライチェーン排出量が含まれます。また、サプライチェーンで使用される化石燃料の生産に関連する排出量も含まれます。システムの境界外で発生する放出/吸収効果、たとえば市場関連、生物地球物理学的(アルベドなど)、および時間依存の効果は除外されます。[79]また、バイオエナジー経路は典型的な小規模の変換効率を持っています。発電用の固体バイオ燃料の効率は、ほとんどの場合25%、場合によっては21〜34%です。発電用のバイオガスは32〜38%です。熱経路は76〜85%です。森林残留物のカテゴリーには丸太と切り株が含まれ、特に崩壊速度の遅い森林で炭素強度が増加します。[80]

チャートには、各バイオエナジー経路で見つかった排出範囲を表す垂直バーがあります(同じ経路の排出量は研究ごとに異なるため)。範囲の上限は、たとえば輸送距離が長く、短いと仮定した研究で見つかった排出レベルを表します。変換効率が高く、化石燃料の排出効果はありません。範囲の下限は、最適化されたロジスティクス、より高い変換効率、プロセス熱とプロセス電気を供給するための再生可能エネルギーの使用を想定した研究で見つかった排出レベルを表し、化石燃料の代替による置換効果を含みます。[dm]これらの基準は、EUで利用可能な複数の代替エネルギーシステムに関連する排出レベルと比較できます。点線の色付きの領域は、化石燃料の代替燃料と比較した場合の経路の排出削減率を表しています。[78]著者は、「[m]ほとんどのバイオベースの商品は、サプライチェーンに沿って化石製品よりも少ないGHGを放出しますが、GHG排出量の大きさは、ロジスティクス、原料の種類、土地と生態系の管理、資源効率、とテクノロジー。」[81]

さまざまなバイオ燃料経路の気候緩和の可能性が異なるため、政府や組織は、バイオマスの使用が持続可能であることを保証するためにさまざまな認証スキームを設定します。たとえば、EUのRED(再生可能エネルギー指令)や国際標準化機構によるISO規格13065などです。標準化。[82]米国では、RFS(Renewables Fuel Standard)は、従来のバイオ燃料の使用を制限し、許容可能な最小のライフサイクルGHG排出量を定義しています。バイオ燃料は、石油化学製品と比較して最大20%のGHG排出削減を達成する場合は従来型と見なされ、少なくとも50%を節約する場合は先進的であり、60%を超える場合はセルロース系燃料と見なされます。[dn]

木質ペレットの静的排出量の推定

チャートと一致して、EUの再生可能エネルギー指令(RED)は、化石燃料を熱生産のために森林残留物からの木質ペレットに置き換える場合の典型的な温室効果ガス排出削減量は、輸送距離に応じて69%から77%の間で変化すると述べています。は0〜2500 kmで、排出量の節約は77%です。排出量の節約は、距離が2500〜10000 kmの場合は75%に、距離が10000 kmを超える場合は69%に低下します。幹材を使用する場合、排出量の節約は輸送距離に応じて70%から77%の間で異なります。木材産業の残留物を使用すると、節約額は79%から87%の間で変動します。[する]

同様の方法論に基づいて、ハンセン等。米国南東部で生産され、EUに出荷された木質ペレットに基づく電力生産による温室効果ガス排出削減量は、EUの化石燃料ミックスと比較して65%から75%の間で変動することがわかりました。[dp]彼らは、米国から輸入され、EUで電気のために燃やされた木質ペレットからの平均正味GHG排出量は、kWhあたり約0.2 kg CO 2に相当すると推定していますが、現在電気のために燃やされている化石燃料の混合物からの平均排出量はEUでは、kWhあたり0.67 kg CO 2 -eqになります(右のグラフを参照)。海上輸送の排出量は、生産されたkWhあたりの化石燃料混合排出量の7%に相当します。[dq]

同様に、IEAバイオエナジーは、カナダの木質ペレットがヨーロッパの石炭火力発電所の石炭に完全に置き換わるシナリオでは、海上輸送関連の排出量(バンクーバーからロッテルダムまでの距離)は、発電所の石炭関連排出量の約2%に達すると推定しています。[83]ここでの割合が低いのは、EUの化石燃料の組み合わせではなく、特定の石炭火力発電所であるという代替シナリオが原因です。カウイら。実際のサプライチェーンからの計算は、大陸間バイオマス輸送からの排出量が少ないことを示していると主張しています。たとえば、米国南東部からヨーロッパへの最適化された木質ペレットサプライチェーンです。[dr]Lamers&Jungingerは、木質ペレットの将来のEU輸入は、「[...]北米、特に米国南東部からの[...]が引き続き支配的である可能性が高い」と主張しています。[84] 2015年には、輸入されたペレットの77%が米国からのものでした。[ds]

短回転エネルギー作物の静的排出量の推定

通常の林分は数十年にわたる輪作期間を持ちますが、短輪作林業(SRF)[u]林分は8〜20年、短輪作雑木林(SRC)[t]は2〜4年です。[85] EUの森林の12%は雑木林です。[dt]多年生草の輪作期間は、温帯地域では1年、熱帯地域では4〜12か月です。[86]小麦やトウモロコシなどの食用作物も、1年の輪作期間があります。

短回転エネルギー作物は、収穫される前に短時間だけ炭素を成長/蓄積することができたため、土地利用による追加の大きな炭素債務がなければ、収穫に関連する炭素債務を返済するのは比較的簡単です。対処するための変更(たとえば、この土地をエネルギー作物に使用するために自然林を皆伐することによって作成された)、および問題の地域のより良い気候関連の使用はありません。Schlamadinger&Marlandは、「[...]短回転エネルギー作物は、プランテーションのためのスペースを提供するために最初の森林を収穫する場合よりも、以前に森林に覆われていない土地に実装した場合、はるかに早く、より大きなC [炭素]緩和の利点を提供します」と書いています。[87]EUの合同調査センターは次のように述べています。「食品、飼料、繊維、または直接的または間接的な土地利用の変化による土地の炭素貯蔵量の変化など、他のセクターからの原材料の移動がない場合でも、カーボンニュートラルの仮定を考慮することができます。年間作物、農産物、短回転のコピス、および短い回転サイクルのエネルギーグラスに有効です。これは、原料の成長サイクルよりもはるかに長い時間範囲での分析にも有効です。」[88]他の研究者は、エネルギー作物の収穫に関連する小さな炭素債務は、炭素の回収とパリティの時間が短く、多くの場合1年未満であることを意味すると主張している。[du] IRENAは、短回転エネルギー作物と農業残渣は毎年収穫されるため、カーボンニュートラルであると主張しています。[dv]IEAは、2050年に正味ゼロ排出量に到達する方法に関する特別報告書で、「NZE [正味ゼロ排出シナリオ]におけるエネルギーセクターの変革により、AFLOU [農林業およびその他の土地]からのCO2排出量削減されると書いています。使用] 2050年には、従来の作物からの切り替えと、限界地および牧草地での短回転の高度なバイオエナジー作物の生産の増加を考慮して、約150 Mt CO2までに。[89]

一部の林業プロジェクトで計算された長い回収期間とパリティ時間は、エネルギー作物では問題とは見なされないため(上記の場合を除く)、研究者は代わりに、LCAベースの炭素会計手法を使用してこれらの作物の静的気候緩和の可能性を計算します。特定のエネルギー作物ベースのバイオエナジープロジェクトは、CO 2の総量に基づいて、カーボンポジティブ、カーボンニュートラル、またはカーボンネガティブと見なされます。生涯を通じて蓄積された同等の排出量と吸収量:農業、加工、輸送、燃焼中の排出量が、プロジェクトの存続期間中に地上と地下の両方で植物によって吸収(および貯蔵)される排出量よりも多い場合、プロジェクトは炭素陽性です。同様に、総吸収量が総排出量よりも多い場合、プロジェクトはカーボンネガティブです。言い換えれば、正味の炭素蓄積が正味のライフサイクル温室効果ガス排出量を補う以上の場合、炭素の負の可能性があります。

Miscanthus×giganteusは、多年生のエネルギーグラスです。

最も気候に優しいエネルギー作物は、エネルギー投入量が少なく、土壌に大量の炭素が蓄積されているため、多年生のエネルギー草であるように思われます。研究者は、永年性作物ススキの平均エネルギー入力/出力比は一年生作物の10倍優れており、温室効果ガス排出量は化石燃料の20〜30倍優れていると主張しています。[dw]英国では、暖房用のススキチップが1ヘクタールあたり年間22.3トンのCO 2排出量を節約し、暖房と電力用のトウモロコシは6.3を節約しました。バイオディーゼル用菜種は3.2を節約しました。[dx]他の研究者も同様の結論を出している。[dy]

通常、多年生作物は一年生作物よりも多くの炭素を隔離します。これは、根の蓄積が何年にもわたって妨げられることなく継続できるためです。また、永年性作物は、一年生作物の栽培に関連する毎年の耕作手順(耕作、掘削)を回避します。耕うんは、土壌微生物集団が利用可能な炭素を分解し、CO2を生成するのに役立ちます。[dz] [ea]土壌有機炭素は、特に30 cm(12インチ)未満の深さで、耕作地よりもスイッチグラス作物の下で大きいことが観察されています。[90]Harris et al。が行った138の個別研究のメタ研究では、耕作地に植えられた多年生の草ススキとスイッチグラスは、平均して、短回転雑木林または短回転林業プランテーション(ポプラと柳)。[eb] McCalmont etal。ジャイアントミスカンス×ギガンテウス炭素隔離に関するヨーロッパの個々の報告の数を比較し、蓄積率が1ヘクタールあたり年間0.42〜3.8トンの範囲であり、[ec]平均蓄積率が1.84トン、[ed]または総収穫量の25%であることを発見しました。年間炭素。[ee]

基本的に、地下の炭素蓄積は、地上の炭素循環(植物から大気への循環、そして新しい植物への循環)から炭素を除去するため、温室効果ガス緩和ツールとして機能します。循環は、光合成と燃焼によって駆動されます。 、植物はCO 2を吸収し、地上と地下の両方の組織で炭素として同化します。地上の炭素を回収して燃焼させると、CO 2分子が再び形成され、大気中に放出されます。その後、次のシーズンの成長によって同量のCO 2が吸収され、このサイクルが繰り返されます。

カーボンネガティブ(ススキ)およびカーボンポジティブ(ポプラ)の生産経路。[ef]

この地上循環はカーボンニュートラルになる可能性がありますが、もちろん、それを操作および誘導する人間の関与は、化石源から来ることが多い追加のエネルギー入力を意味します。操業に費やされる化石エネルギーが生成されるエネルギー量と比較して高い場合、総CO 2フットプリントは、化石燃料のみの燃焼に起因するCO 2フットプリントに近づくか、一致するか、さらには超える可能性があります。いくつかの第一世代のバイオ燃料プロジェクト。[eg] [eh] [ei]この点で、輸送用燃料は固体燃料よりも悪いかもしれません。[ej]

この問題は、地下に貯蔵される炭素の量を増やすという観点からも、地上での操業への化石燃料の投入を減らすという観点からも対処することができます。十分な量の炭素が地下に貯蔵されている場合、特定のバイオ燃料のライフサイクル全体の排出量を補うことができます。同様に、地上の排出量が減少した場合、バイオ燃料がカーボンニュートラルまたはマイナスになるために必要な地下の炭素貯蔵量は少なくなります。

地上収量(対角線)、土壌有機炭素(X軸)、および土壌の炭素隔離の成功/失敗の可能性(Y軸)の関係。基本的に、収量が多いほど、GHG緩和ツールとして使用できる土地が多くなります(比較的炭素が豊富な土地を含む)。[91]

Whitaker etal。年間1ヘクタールあたり10トンの収量のススキ作物は、農業、加工、輸送関連の排出量の両方を補うのに十分な炭素を貯蔵していると主張します。右のグラフは、2つの炭素陰性ススキ生産経路と2つの炭素陽性ススキ生産経路を示しており、メガジュールあたりのCO2換算グラムで表されています。大気中のCO2が増減すると推定されるため、バーは連続して上下に移動します。灰色/青色のバーは農業、加工、輸送に関連する排出量を表し、緑色のバーは土壌の炭素変化を表し、黄色のひし形は最終的な総排出量を表します。[ef]2番目のグラフは、既存の炭素の量が異なる土壌で長期的な炭素陰性を達成するために必要な平均収量を示しています。収率が高いほど、炭素陰性になる可能性が高くなります。他の研究者は、ドイツのススキの炭素陰性について同じ主張をしており、1ヘクタールあたり年間15乾燥トンの収量、1ヘクタールあたり年間1.1トンの炭素貯蔵を行っています。[ek]

最良の土壌は現在炭素が少ない土壌であるため、貯蔵の成功は植栽地に依存します。[el]英国の場合、イングランドとウェールズの大部分の耕作可能な土地での貯蔵の成功が期待され、スコットランドの一部では、すでに炭素が豊富な土壌(既存の森林)のために貯蔵の失敗が予想されます。また、スコットランドの場合、この寒い気候での比較的低い収量は、炭素陰性を達成するのを難しくします。すでに炭素が豊富な土壌には、泥炭地や成熟した森林が含まれます。英国で最も成功した炭素貯蔵は、改良された草地の下で行われます。[em]しかし、草地の炭素含有量はかなり変化するため、土地利用の成功率も草地から多年生植物に変化します。[en]ススキやススキなどの多年生エネルギー作物の下の正味炭素貯蔵量は、通常の草地、森林、耕作作物の下の正味炭素貯蔵量を大幅に上回っていますが、炭素投入量が少なすぎるため、初期の確立段階での既存の土壌炭素の損失を補うことができません。 。[92]しかしながら、時間の経過とともに、草地についても土壌炭素が増加する可能性がある。[93]

研究者たちは、いくつかの最初の議論の後、「[...]多年生のバイオエナジー作物栽培のGHG [温室効果ガス]バランスはしばしば好ましい[...]」という科学界のコンセンサスが現在(2018)あると主張しています。暗黙の直接的および間接的な土地利用の変化を考慮する場合。[eo]

アルベドと蒸発散による気候への影響

1750年から2005年までの排出量とアルベドによる地球の気温の影響。[ep]

植物は地表の色を変え、これが表面の反射率に影響を及ぼします(いわゆる「アルベド」効果)。明るい色は熱を反射する傾向があり、暗い色は熱を吸収する傾向があります。たとえば、ある領域の色が土の茶色から緑色に変わると、吸収される熱が少なくなります。逆に、雪の多い場所が白から緑に変わると、より多くの熱が吸収されます。研究によると、樹木の色は雪の色よりも暗いため、植林は雪の多い北方の地域で正味の温暖化効果をもたらします(植林による炭素吸収も考慮された後)。言い換えれば、アルベド効果は、そのような領域でのロギングによって引き起こされる長い回収時間とパリティ時間を補うのに役立ちます。森林アルベドは世界的にわずかな冷却効果があります。[ep]

植物はより多くの蒸発散を引き起こし、したがって局所湿度を増加させます。湿度が高くなると、入ってくる太陽エネルギーの多くが地面を加熱するのではなく、水を蒸発させるために費やされ、それによって冷却効果が生まれます。熱帯林では、蒸発散によって太陽光を反射する垂れ下がった雲ができ、アルベド効果が高まります。森林は、燃焼を介して、また生きている木から直接、有機炭素と呼ばれる小さな粒子を放出します。粒子は太陽光を反射するため、それ自体で冷却効果がありますが、水蒸気が粒子の周りに凝縮するため、雲の作成にも役立ちます。どちらの場合も、反射によって冷却効果が生まれます。[eq]

米国中部の一年生作物が多年生草に置き換えられた場合、それは主に蒸発散効果からだけでなくアルベドからも、重大な地球寒冷化を引き起こすでしょう。アルベド効果だけでも、草の化石燃料置換効果の6倍でした。この場合のアルベド効果の理由は、多年生草が一年生作物と比較して、一年中より長い期間表面を緑に保つためでした。[er] [94]

環境への影響

地表発電密度

バイオマスまたはその他の再生可能エネルギー生産によって引き起こされる環境への影響は、その土地利用要件にある程度依存します。土地利用要件を計算するには、関連する地表発電密度(たとえば、平方メートルあたりの発電量)を知ることが不可欠です。Vaclav Smilは、現代のバイオ燃料、風力、水力、太陽光発電の平均ライフサイクル表面電力密度は、それぞれ0.3 W / m 2、1 W / m 2、3 W / m 2、5 W / m 2であると推定しています(電力バイオ燃料の場合は熱の形態、風力、水力、太陽光の場合は電気の形態)。[95]ライフサイクルの表面電力密度には、すべてのサポートインフラストラクチャ、製造、採掘/収穫、および廃止措置によって使用される土地が含​​まれます。Van Zalk etal。バイオ燃料の場合は0.08W / m 2、水力の場合は0.14 W / m 2、風力の場合は1.84 W / m 2、太陽光の場合は6.63 W / m 2と推定されます中央再生可能エネルギー源はいずれも10 W / m 2を超えません) 。 化石ガスは482W / m 2最も高い表面密度を持っていますが、240 W / m2の原子力発電は唯一の高密度で低炭素のエネルギー源です。[96]氷のない土地での平均的な人的消費電力は0.125W / m 2(熱と電気の合計)ですが[97]、都市部と工業地帯では20 W / m2に上昇します。[98]

一部のバイオ燃料の電力密度が低い理由は、低収量と植物の部分的な利用のみの組み合わせです(たとえば、エタノールは通常、サトウキビの糖含有量またはトウモロコシのデンプン含有量から作られますが、バイオディーゼルは多くの場合、油から作られます菜種または大豆の含有量)。

アメリカの麦畑。

エタノール生産に使用される場合、1ヘクタールあたり年間15トンの収量を持つススキのプランテーションは0.40 W / m2を生成します[99]トウモロコシ畑は0.26W / m 2(収量10 t / ha)を生成します。[100]ブラジルでは、サトウキビ畑は通常0.41 W / m2を生成します[100]冬小麦(米国)は0.08 W / m 2を生成し、ドイツ小麦は0.30 W / m2を生成します[101]ジェット燃料用に栽培した場合、大豆は0.06 W / m 2を生成し、パーム油は0.65 W / m2を生成します[102]辺境の土地で育ったジャスロパは、0.20 W / m2を生成します[102]バイオディーゼル用に栽培した場合、菜種は0.12 W / m 2(EU平均)を生成します。[103]液体バイオ燃料の生産は、固体バイオ燃料の生産と比較して、大量のエネルギー投入を必要とします。[es]これらの入力が補償されると(つまり、使用エネルギーが生成エネルギーから差し引かれると)、電力密度はさらに低下します。オランダのラペシードベースのバイオディーゼル生産は、調整された電力密度0.08WでEUで最も高いエネルギー効率を示します。 / m 2、スペインで生産されたサトウキビベースのバイオエタノールは最も低く、わずか0.02 W / m2です[104]

インドのユーカリ農園。

植物全体を利用できるため、エネルギー目的で固体バイオマスを使用する方が、液体を使用するよりも効率的です。たとえば、燃焼用の固体バイオマスを生産するトウモロコシ農園は、収量が同じ場合、エタノール用に生産するトウモロコシ農園と比較して1平方メートルあたり2倍以上の電力を生成します。10t/ haは0.60W / m2と0.26W /を生成します。エネルギー入力を補償せずに、それぞれm2[105]温帯地域にマツ、アカシア、ポプラ、ヤナギが生息する大規模なプランテーションでは、1ヘクタールあたり年間5〜15乾燥トンの収量が達成されると推定されています。これは、0.30〜0.90 W / mの地表発電密度を意味します。2[106]熱帯および亜熱帯地域にユーカリ、アカシア、ギンネム、マツ、ツルサイカチが生息する同様に大規模なプランテーションの場合、収量は通常20〜25 t / haであり、これは1.20〜1.50 W / m2の地表発電密度を意味しますこの収量により、これらのプランテーションの電力密度は、風力と水力の密度の中間になります。[106]ブラジルでは、ユーカリの平均収量は21 t / haですが、アフリカ、インド、東南アジアでは、典型的なユーカリの収量は10 t / ha未満です。[107]

木材、ススキ[108]、ネピア[109]草を含む一般的なオーブン乾燥バイオマスのカロリー含有量は、約18 GJ / tです。[110]平方メートルあたりの発電量を計算する場合、乾燥バイオマス収量のt / haごとに、プランテーションの発電量が0.06 W / m2増加します[et]前述のように、風力、水力、太陽光発電の世界平均は1 W / m 2、3 W / m 2、5 W / m2ですそれぞれ。これらの表面電力密度を一致させるために、プランテーションの収量は、風力、水力、太陽光でそれぞれ17 t / ha、50 t / ha、83 t / haに達する必要があります。これは、上記の熱帯農園(収量20〜25 t / ha)や、ススキ(10〜40 t / ha)やネピア(15〜80 t / ha)などの象の草では達成できるようですが、森林や他の多くの種類のバイオマス作物。バイオ燃料の世界平均(0.3 W / m 2)に合わせるには、プランテーションで1ヘクタールあたり年間5トンの乾燥質量を生産する必要があります。代わりに、水力、風力、太陽光のVan Zalk推定値を使用する場合(0.14、1.84、および6.63 W / m 2それぞれ)、プランテーションの収量は、競争するために2 t / ha、31 t / ha、111 t / haに達する必要があります。ただし、これらの歩留まりのうち最初の2つだけが達成可能と思われます。

古い燃焼設備の場合、バイオマス中の水分量を補うために収量を調整する必要があることに注意してください(生成された蒸気をエネルギーに利用できない限り、発火点に到達するために水分を蒸発させることは無駄なエネルギーです)。[eu]バイオマスわらまたは俵の水分は、周囲の空気の湿度と最終的な予備乾燥対策によって異なりますが、ペレットの標準化された(ISO定義の)含水率は10%未満(木質ペレット)[ev]および15%未満です。 (他のペレット)。[ew]同様に、風力、水力、太陽光の場合、電力線の送電損失は世界全体で約8%に達するため、考慮する必要があります。[元]バイオマスを熱生産ではなく電力生産に利用する場合、現在の熱から電気への変換効率はわずか30〜40%であるため、風力、水力、太陽光に対抗するには、収量を約3倍にする必要があります。[111]バイオ燃料、風力、水力、太陽光の地表電力生産密度を、コストを考慮せずに単純に比較すると、電力密度の観点から、水力と太陽光の両方が最も高収量のプランテーションの手の届かないところに効果的に押しやられます。[ey]

生物多様性

Gasparatos etal。あらゆる種類の再生可能エネルギー生産の副作用に関する現在の研究をレビューし、一般に「[...]サイト/地域固有の保全目標と国のエネルギー政策/気候変動緩和の優先順位[.. 。]。」著者らは、例えば生物多様性は、同様に「GHG排出を抑制することとしてのグリーン経済の正当な目標」と見なされるべきであると主張している。[112]アブラヤシとサトウキビは、生物多様性の減少に関連している作物の例です。[113]他の問題は、肥料/農薬の使用による土壌と水の汚染[114]と、主に残留物の野外燃焼による周囲の大気汚染物質の排出です。[115]

EUでの追加のバイオエナジー経路によって引き起こされる、双方にメリットのある(緑)、トレードオフ(オレンジ)、および敗北(赤)のシナリオの分類スキーム。[ez]
EUの3つの代替バイオエナジー経路(森林残留物、植林および森林プランテーションへの転換)に対する短期的な気候および生物多様性の影響。ここでは、短期は0〜20年、中期は30〜50年、および長期と定義されます。 50年以上。[116]

著者らは、環境への影響の程度は「[...]バイオマスエネルギーの選択肢によって大きく異なる」と述べています。[113]影響を緩和するために、彼らは「[...]環境に優しいバイオエナジー生産慣行を採用することを推奨します。たとえば、単一栽培プランテーションの拡大を制限し、野生生物に優しい生産慣行を採用し、汚染防止メカニズムを設置し、継続的な景観モニタリングを実施します。 「」[117]彼らはまた、「[...]多機能バイオエナジー景観」を推奨している。[117]他の対策には、「[...]原料の慎重な選択が含まれます。原料が異なれば、環境のトレードオフも根本的に異なる可能性があるためです。たとえば、米国の研究では、未受精地で栽培された第2世代の原料は、単文化の一年生植物と比較して生物多様性に利益をもたらす可能性があることが示されています。農薬を多用するトウモロコシや大豆などの作物。」[117] ススキススキは、そのような作物の例です。[118]

生物多様性はEUによって重要な政策目標として定義されているため、EUの合同調査センターは、バイオエネルギーの使用の増加がヨーロッパの森林の生物多様性に悪影響を及ぼさないようにする方法を検討しました。[fa]既存の林業慣行と比較して追加のバイオエナジー資源を提供するバイオエナジー経路のみが考慮されました。すなわち、1。)伐採残さの使用の増加、2。)未使用の土地の植林、3。)自然林のより生産的な森林への転換プランテーション。[fb]著者は、気候と生物多様性の緩和の可能性に応じて、結果を4つのカテゴリに分類しました。1。)Win-Winシナリオ(右のグラフの緑色の象限)は、気候と生物多様性の両方にプラスの結果をもたらします。2。)勝ち負けのシナリオ(黄色の象限)は、気候にプラスの結果をもたらすが生物多様性にマイナスの結果をもたらすトレードオフシナリオです。3。)負け勝ちのシナリオ(黄色の象限)は、気候にマイナスの結果をもたらすがプラスの結果をもたらすトレードオフシナリオです。生物多様性の場合、および4.)喪失シナリオ(赤い象限)は、気候と生物多様性の両方に悪影響を及ぼします(右のグラフを参照)。

「[...]気候変動自体が生物多様性喪失の主な要因である」ため、長期的には、バイオエネルギーの増加は生物多様性にプラスの影響を与える可能性があります。ただし、これを定量化するのは難しいため、控えめな方法として、著者は、短期的にはポジティブと見なされる生物多様性への影響を伴うバイオエナジー経路のみを推奨することを選択しました。[fc]同じことが気候の影響にも当てはまります。短期的にプラスの結果をもたらすバイオエナジー経路のみが推奨されました(短期は0〜20年、中期は30〜50年、長期は50年以上と定義されます)。すべてのバイオエナジーシナリオの代替シナリオ化石燃料ミックス(「化石源」)、つまり石炭だけではありませんでした。[119]市場への影響は考慮されていないため、結果は小規模なバイオエナジーの展開にのみ有効であると見なされます。[fd]

Win-Winのシナリオには、雑木林からの樹木全体の使用の増加、減衰速度が遅い北方林からの薄い森林残留物の使用の増加、および減衰速度が速い温帯林からのあらゆる種類の残留物の使用の増加が含まれます。Win-Winのシナリオには、混合または自然に再生する森林によるかつての農地の植林も含まれます。[fe]勝ち負けのシナリオ(気候に良い、生物多様性に悪い)には、決して森林ではなかった古代の生物多様性に富んだ草地生態系への植林、および単一栽培プランテーションによるかつての農地の植林が含まれます。[ff]負け勝ちのシナリオ(気候に悪い、生物多様性に良い)には、かつての農地での自然林の拡大が含まれます。[fg]負け負けのシナリオには、崩壊速度が遅い一部の北方林からの切り株のような厚い森林残留物の使用の増加、および自然林の植林地への転換が含まれます。[fh]トレードオフシナリオ(黄色の象限)での悪影響のいくつかは、RED IIの持続可能性基準を実装することで最小限に抑えることができます。たとえば、バイオマス収穫のための立ち入り禁止区域などです。[fi]しかし、ヨーロッパの森林が老化するにつれて、著者は「森林年齢のダイナミクス」のために、そして森林火災、害虫および暴風によって引き起こされる排出を避けるために、適度な収穫レベルの増加を期待しています。[J F]一般に、科学者は状況を見て、政策オプションを提供することができますが、この優先順位付けは倫理的価値の選択に基づいているため、トレードオフシナリオで気候と生物多様性の緩和の間で優先順位を付けるのは最終的には政治家次第です。理科。[fk]

汚染

調理用ストーブや直火での木材の伝統的な使用は汚染物質を生成し、それは深刻な健康と環境への影響につながる可能性があります。しかし、現代のバイオエナジーへの移行は、生活の向上に貢献し、土地の劣化と生態系サービスへの影響を減らすことができます。[fl] IPCCによると、現代のバイオエナジーが大気の質に「大きなプラスの影響」を及ぼしているという強力な証拠があります。[120]同様に、IEAは、従来のバイオエナジーは非効率的であり、このエネルギー源の段階的廃止には大きな健康上の利益と大きな経済的利益の両方があると主張している。[fm]産業施設で燃焼すると、木質バイオマスに由来する汚染物質のほとんどは、野焼きと比較して97〜99%減少します。[121]南アジアの広い地域を定期的にカバーする巨大な茶色のもやの研究では、その3分の2が主に家庭料理と農業の燃焼によって生成され、3分の1が化石燃料の燃焼によって生成されたことがわかりました。[122]

地元の抗議

バイオエナジーは地球規模で温室効果ガスの排出を軽減することで一般的に合意されていますが、環境活動家は、バイオマス需要の増加はバイオマスが生産される場所に重大な社会的および環境的圧力を生み出す可能性があると主張しています。[123]影響は、主にバイオマスの低表面電力密度に関連しています。低い表面電力密度は、たとえば化石燃料と比較して、同じ量のエネルギーを生成するためにはるかに広い土地面積が必要になるという効果があります。

ドイツの発電所の石炭を、3000万ヘクタール以上の茂みの侵入を経験しているナミビアで収穫された茂みのバイオマスに置き換えるための実現可能性評価は、環境団体からの抗議を引き起こしました。組織は、木や茂みが炭素を貯蔵し、それらを燃やすと、石炭を燃やすよりも多くのCO2を前もって放出すると主張しています。[124]ナミビアの研究者は、茂みの侵入は農民の収入の低下、生物多様性の低下、地下水位の低下、野生生物の移動を引き起こすと主張している。[125]バイオマスの長距離輸送は無駄で持続不可能であると批判されており[126]、スウェーデンでは森林バイオマスの輸出に反対する抗議があった[127]。とカナダ。[128]

ミシシッピ州では、英国の発電所向けの木質ペレットを製造している会社が、揮発性有機化合物の汚染を何年にもわたって超えたとして、250万ドルの罰金を科されました。[129]場合によっては、自然林の大部分が違法に伐採されており(例えば、ルーマニア[130]やシベリア[131]、残りの森林は違法な作戦を隠蔽するために火がつけられている。[132]

森林バイオマス討論

石炭と比較した森林バイオマスからの煙突排出量

生成されたエネルギー単位あたりの煙突の排出量は、燃料の含水量、燃料間の化学的差異、および変換効率に依存します。ISO規格17225-2:2014で定義されているように、木質ペレットの含水率は通常10%未満です。[133]石炭タイプの無煙炭は通常、15%未満の水分を含み、瀝青炭は2〜15%、亜瀝青炭は10〜45%、亜炭は30〜60%を含みます。[134]ヨーロッパで最も一般的な石炭の種類は亜炭です。[135]

ロシアの石炭港。

同じ熱から電気への変換効率で燃焼施設で燃焼した場合、オーブン乾燥木材は、オーブン乾燥石炭と比較して、生成される熱の単位あたりわずかに少ないCO2を排出します。[fn]しかし、多くのバイオマスのみの燃焼施設は、一般的にはるかに大きな石炭火力発電所と比較して、比較的小さく非効率的です。さらに、生のバイオマス(たとえば木材チップ)は、石炭よりも水分含有量が高くなる可能性があります(特に石炭が乾燥している場合)。この場合、乾燥した石炭と比較して、木材の固有のエネルギーの多くを水分の蒸発にのみ費やす必要があります。つまり、単位生成熱あたりに排出される CO2の量が多くなります。

したがって、一部の研究者(研究グループのチャタムハウスなど)は、「[...]エネルギーに木質バイオマスを使用すると、石炭よりも高レベルの排出物が放出される[...]」と主張しています。[136]同様に、マノメット保全科学センターは、石炭の変換効率が32%、バイオマスの変換効率が20〜25%の小規模な公益事業の場合、石炭の排出量は木材チップからの排出量より31%少ないと主張しています。木材チップの想定含水率は45%です。石炭の推定含水率は提供されていません。[137]

Hektor etal。湿気の問題は、最新の燃焼設備によって効率的に軽減されると主張します。[eu] Cowie etal。バイオマスと石炭のスタック排出量は、バイオマスが大規模発電所で石炭と同時燃焼される場合と同じであり、焙焼されたバイオマスは低品位炭よりも高い変換効率を持っていると主張します。[fo]英国のドラックス(世界最大のバイオマス発電所)で燃焼した木質ペレットの水分は7%であり、燃焼した場合の変換効率は、英国の石炭火力発電所の平均よりも高くなります(38.6対35.9%)。 )。スタック排出量は、2015年の英国の石炭平均より2%高かった。[fp]木質ペレットのサプライチェーンからの排出量を含めると(ペレットは米国から英国に出荷されます)、ドラックスは、排出量が石炭と比較して80%以上削減されると主張しています。[fq]

ドイツの木質ペレットミル。

バイオエナジーコンサルタントグループFutureMetricsは、両方の燃料が同じ変換の施設で燃焼される場合、水分含有量が6%の木材ペレットは、水分が15%の亜瀝青炭と比較して、同じ量の生成熱に対して22%少ないCO2排出すると主張しています。効率(ここでは37%)。[fr]同様に、彼らは「[...] MCの[含水率]が20%未満の乾燥木材は、MMBTU [百万英熱量]あたりのCO2排出量がほとんどの石炭と同じかそれ以下であると述べています。10未満の木材ペレット%MCは、他の点では同等の状況下で、どの石炭よりもCO2排出量が少なくなります。[138]ただし、代わりに生の木材チップを使用すると(含水率45%)、この木質バイオマスは、同じ量の熱を生成するために、一般に石炭よりも9 %多くのCO2を排出します。[138]

既存の小規模バイオマス燃焼施設を考慮に入れると、IEAバイオエナジーは森林バイオマスが平均して石炭よりも10%多いCO 2を生成すると推定し[139]、IPCCは16%と推定しています。[fs]しかしながら、両方の研究グループは、総排出量に焦点を当てることは要点を見逃していると主張し、重要なのは排出量吸収による正味の気候効果を合わせたものです。[ft] [fu] IEAバイオエナジーは、バイオマスからの追加のCO 2は、「バイオマスが持続可能な方法で管理された森林に由来する場合、[...]は無関係である」と結論付けています。[139]

持続可能な林業と森林保護

CO 2緩和の文脈では、森林の持続可能性に関する重要な指標は、森林の炭素貯蔵量の大きさです。「生産林におけるすべての持続可能な管理プログラムの主な目的は、収穫と再成長の間の長期的なバランスを達成することです。[。 ..] [T]収穫と再成長のバランスを維持することの実際的な効果は、管理された森林で長期的な炭素貯蔵を安定に保つことです。」[140] IPCCは、生態学的、経済的、社会的基準を含めながら、同様の方法で持続可能な林業を定義しています。[F V]

FAOによると、世界的に、森林の炭素蓄積量は0.9%減少し、樹木被覆率は1990年から2020年の間に4.2%減少しました。[141] IPCCは、世界の森林が縮小しているかどうかについて意見の相違があると述べており、1982年から2016年の間に樹木被覆が7.1%増加したことを示す研究を引用しています。熱帯地方では減少していると推定されていますが、温暖な北方林の資源が増加しているため、世界的に増加しています[...]。」[142]

一部の研究者は、「ただ」持続可能な方法で管理された森林以上のものを望んでいるようです。彼らは森林の完全な炭素貯蔵の可能性を実現したいと考えています。たとえば、EASACは次のように書いています。「現在の政策では、炭素貯蔵のための森林ストックを増やすのではなく、エネルギー生産における森林の使用を過度に強調しているという本当の危険があります。」[143]さらに、彼らは、「[...]最も高い炭素貯蔵量を示すのは、より古く、より長い回転の森林と保護された原生林である」と主張している。[144]チャタムハウスは、古い木は非常に高い炭素吸収率を持っており、古い木を伐採することは、将来の炭素吸収のこの大きな可能性が失われることを意味すると主張している。さらに、彼らは収穫作業のために土壌炭素の損失があると主張します。

ヨーロッパでは、すべての森林の25%が保護されており[146]、原生林/原生林の89%が含まれています。[147] 2021年に導入された再生可能エネルギー指令(RED II)の新しいバージョンは、その持続可能性基準を液体バイオ燃料生産から、森林バイオマスから生産される可能性が高い固体(および気体バイオ燃料)も含むように拡張しました。[fx]

フランスの原生林。

スティーブンソン等。完全に成長した木の葉面積が大きいため、古い木は若い木よりも多くのCO2を吸収することに同意します。[148]しかし、枯れ木からのCO 2排出が残りの生きている木のCO2吸収を相殺するため、古い森林(全体として)は最終的にCO2の吸収を停止します[fy]古い森林(または林分)は、CO2を生成する自然の乱れに対しても脆弱ですIPCCは次のように書いています。「植生が成熟したとき、または植生と土壌の炭素貯留層が飽和状態に達したとき、CO2の毎年の除去大気からの炭素貯蔵量を維持しながら、ゼロに向かって低下します(高い信頼性)。しかし、植生や土壌に蓄積された炭素は、洪水、干ばつ、火災、害虫の発生などの障害によって引き起こされる将来の損失(またはシンクの逆転)、または将来の不十分な管理(高い信頼性)のリスクにさらされています。 IPCCは、次のように述べています。 ]。 " [150]

EUの共同研究センターは、土壌炭素に対する収穫と再植林の測定された効果は「[...]短期的にはわずかであり、炭素の減少は林床と土壌表面の近くに集中し、炭素の増加は深部鉱物で発生すると書いています。土壌層。」[151] JRCはまた、「バイオマス生産のための[w]全樹木収穫は、有機物(O地平線)を含む表層土壌層が現場に残され、栄養素が管理され、現場にある場合、土壌炭素貯蔵量にほとんど長期的な影響を及ぼさないと主張している。再生が許可されています[...]。」[151] IPCCは、現在の科学的根拠は土壌炭素排出係数を提供するのに十分ではないと述べている。[fz]

ハワイのプランテーションフォレスト。

IPCCは、管理されていない森林から管理された森林への転換による正味の気候への影響は、状況に応じてプラスまたはマイナスになる可能性があると主張しています。炭素貯蔵量は減少しますが、管理された森林は管理されていない森林よりも速く成長するため、より多くの炭素が吸収されます。収穫されたバイオマスが効率的に使用される場合、プラスの気候効果が生み出されます。[ga]森林の炭素貯蔵量を最大化し、それ以上炭素を吸収しないことの利点と、その炭素貯蔵量の一部を「ロック解除」し、代わりに再生可能な化石燃料の代替ツールとして機能することの利点との間にはトレードオフがあります。たとえば、脱炭素化が困難または高価なセクターで。[gb] [gc]稼働すると、この炭素は森林の炭素プールから林産物やエネルギー担体に移動し、次に燃焼によって大気中に移動し、次に光合成によって森林に戻ります。往復ごとに、熱生産、産業生産、電力生産で通常使用される化石燃料炭素をますます置き換えます。いくつかのラウンドトリップの後、置き換えられた炭素の量は、閉じ込められた炭素の量をはるかに上回ります。森林炭素貯蔵削減のGHGコストを超えるGHG節約[...]。」[152]別の言い方をすれば、「森林が成長し続けることが許されれば、バイオマスエネルギーは化石燃料に置き換えられ、木製品は代替材料に置き換えられるでしょう。」[153]マイナーは、「長期的には、持続可能な方法で生産された森林バイオマスを炭素集約型製品や化石燃料の代わりに使用することで、保全よりも大気中のCO2を恒久的に大幅に削減できる」と主張しています[154]

上記を要約すると、IEAバイオエナジーは次のように書いています3つの理由から、保全のためだけに管理されている森林よりも。まず、保全林が成熟に近づくにつれて、シンクの強度が低下します。第二に、木製品はGHGを大量に消費する材料や化石燃料に取って代わります。第三に、オーストラリアやカリフォルニアを含む世界の多くの地域で最近見られるように、森林中の炭素は、昆虫の蔓延や山火事などの自然災害による損失に対して脆弱です。森林を管理することは、森林および木材製品の炭素プールに隔離される炭素の総量を増やし、隔離された炭素の損失のリスクを減らし、化石燃料の使用を減らすのに役立ちます。」[155]

EU1990-2020年の森林面積の増加。[156]

IPCCは、木材、繊維、バイオマス、および非木材資源を提供することを目的とした持続可能な森林管理は、コミュニティに長期的な生計を提供し、森林を非森林用途(定住、作物)に転換するリスクを減らすことができると主張しています。など)、土地の生産性を維持し、土地劣化のリスクを軽減します[...]。」[150]林業における経済的機会と森林サイズの拡大との関係は、他の研究者によっても強調されています。[gd] [ge]ただし、Cowie etal。森林の生産性が非常に低い高緯度などの状況では、特にバイオエナジーによるGHGの節約の場合、バイオエナジーを含む木材製品のために森林を収穫するよりも、森林の炭素貯蔵を維持および強化することで、より大きな削減がもたらされる可能性があると主張します。使用量は少ないです[...]。」[152]彼らはまた、私有林の所有者に収入をもたらす森林は保護される可能性が低いと主張している。林産物の需要があるときしたがって、森林は木材生産のために管理されます。最も現実的な非バイオエナジーシナリオは、森林保護ではなく、残留物の収集と利用を伴わない継続的な木材生産です。この場合、残留物は代わりにそれ自体で崩壊するか、焼却されます。どちらの場合も、化石燃料の置換効果なしに排出物を生成します。林産物の需要が低い場合の最も現実的な非バイオエナジーシナリオは、自然林への土地利用の変更(山火事のリスクが高まる)、または農業や都市化に備えるための皆伐です。[gf]

おそらく上記の議論を強化するために、FAOからのデータは、ほとんどの木質ペレットが持続可能な方法で管理された森林によって支配されている地域で生産されていることを示しています。ヨーロッパ(ロシアを含む)は2019年に世界の木質ペレットの54%を生産し、この地域の森林炭素蓄積量は1990年から2020年の間に158.7Gtから172.4Gtに増加しました。EUでは、地上の森林バイオマスは年間1.3%増加します。しかし、平均して、森林が成熟しているため、増加は鈍化しています。[157] 2020年には、森林面積はEUの総面積の39.8%を占めていた。[156]同様に、北米は2019年に世界のペレットの29%を生産しましたが、森林の炭素貯蔵量は同期間に136.6から140Gtに増加しました。炭素蓄積量は、アフリカで94.3から80.9 Gt、南アジアと東南アジアを合わせて45.8から41.5 Gt、オセアニアで33.4から33.1 Gt 、中央アメリカで5から4.1 Gt、南アメリカで161.8から144.8Gtに減少しましたこれらの地域を合わせた木質ペレットの生産量は、2019年には13.2%でした。[gh]しかし、チャタムハウスは、「エネルギーの使用とはまったく関係のない理由で、[f]炭素貯蔵量は同じままか、増加する可能性がある」と主張しています。[158]

短期的な緊急性

一部の研究グループは、ヨーロッパと北米の森林炭素貯蔵量が増加している場合でも、収穫された木が元に戻るには時間がかかりすぎると主張しています。たとえば、EASACは、世界はすでに10年ほどで1.5度の温度上昇という合意された目標を通過する軌道に乗っているため、高い回収率とパリティ時間を持つ供給源からのバイオエナジーはその目標を達成するのを難しくすると主張します。したがって、EUは持続可能性の基準を調整して、炭素回収期間が10年未満の再生可能エネルギーのみが持続可能なものとして定義されるようにする必要があることを示唆しています。比較的速く燃焼または分解し、短回転コピー(SRC)からのバイオマス。[159]

カウイら。「[...]適切な緩和オプションを特定するための基準としての10年の回収期間は、パリ協定の長期的な気温目標と矛盾している。今世紀の半分[...]。」[gj]彼らはまた、前者は円形で後者は線形であるため、バイオエナジーからの排出は化石燃料からの排出とは根本的に異なると主張している。[gk]バイオマスは現在のエネルギーインフラストラクチャと互換性があるため、現在は機能しますが、排出量の少ない提案された代替案は、「未成熟な開発、高コスト、または新しいインフラストラクチャへの依存によって制限される可能性があります」。[gl]

チャタムハウスは、温暖化が加速する温度尺度に沿って転換点がある可能性があると主張しています。[gm] Cowie etal。転換点は不確実であると主張しますが、地球規模の転換点は「[...]温暖化が2°Cを超えない場合[...]」とは考えにくいようです。[gn] IPCCは、「[...]地域の転換点の存在について、特に北極圏で[...]」という議論がある一方で、「[...]グローバルな証拠はない」と主張している。 21世紀の気候進化の研究でこれまでに評価された最も包括的なモデルのいずれかにおけるスケールの転換点。」[160]

「樹木の再成長が遅すぎる」という議論の重要な前提は、特定の収穫された林分からの樹木が燃焼したときに炭素会計を開始する必要があり、それらの林分にある樹木が成長し始めたときではないという見解です(上記の時間システム境界を参照) 。)[go]この考え方の範囲内で、燃焼イベントが、収穫された林分の再成長を通じて返済されなければならない炭素債務を生み出すと主張することが可能になります。[gp]

代わりに、樹木が成長し始めたときに炭素会計を開始する必要があると仮定すると、排出された炭素が債務であると主張することは不可能になります。たとえば、FutureMetricsは、収穫された炭素は債務ではなく、「[...] 30年間の管理と成長によって得られた利益[...]」であると主張しています。[161]同様に、Lamers&Jungingerは、既存の集中的に管理された、同じ年齢の森林の所有者は、おそらくプランテーションの設立年を炭素会計の論理的な開始年と見なし、収穫は新しい債務を作成するのではなく、炭素クレジットを償還すると主張します。しかし、政策立案者の観点からは、[...]主な問題は、むしろ彼/彼女がバイオエナジーのために収穫を奨励すべきかどうかです。」[162]言い換えれば、「[...]気候政策にとって重要なのは、木質バイオマスエネルギーへの切り替えがある場合とない場合の将来の大気GHGレベルの違いを理解することです。森林の事前の成長は政策の質問とは無関係です[... ]。」[163]後でこの推論の線が「空の」土地(例えば、農地や辺境の土地)に植えられた新しい森林プランテーションに適用される場合、炭素会計の開始は、植林イベントから収穫イベントにシフトします。 2回目の回転後のインスタンス。

上記の空間システムの境界で述べたように、一部の研究者は、森林の残りの部分で発生する炭素吸収を無視して、特定の林分に炭素の計算を制限しています。[gq]他の研究者は、炭素会計を行う際に森林全体の風景を含めています。たとえば、FutureMetricsは、森林全体が継続的にCO 2を吸収するため、バイオマスプラントで日々燃焼される比較的少量のバイオマスを即座に補償すると主張しています。[gr]同様に、IEAバイオエナジーは、森林景観で起こっている炭素吸収を無視しているとしてEASACを批判し、年間収穫量が森林の年間成長よりも少ない場合、炭素の純損失はないことを指摘しています。[gs]

IPCCは同様の方針に沿って、「森林内の個々の林分はソースまたはシンクのいずれかである可能性がありますが、森林の炭素収支はすべての林分の正味収支の合計によって決定されます」と主張しています。[164] IPCCまた、炭素会計への唯一の普遍的に適用可能なアプローチは、管理された土地(例えば森林景観)の炭素排出と炭素除去(吸収)の両方を会計処理するアプローチであると述べている。火事や昆虫の蔓延のように差し引かれ、残っているのは人間の影響です。[gu]

ラウンドウッドと残留物

研究者はまた、丸太と伐採残さの使用についても議論しています。ラウンドウッドは、EUの合同調査センターによって、森林から除去されたすべての木質材料として定義されており、伐採残さは、バイオエナジーからの需要がない場合に森林に残る可能性が最も高い部分です。伐採されたバイオマスの20%は、現在、伐採残さとして森林に残されています。[gv]残留物には、木のてっぺん、枝、切り株だけでなく、商業化前の間伐(林分全体の生産性を高めるために伐採された小さくて細い若い樹木)、サルベージ伐採、火災の危険を制御するために伐採された樹木が含まれます。[広告]ステムウッドはラウンドウッドの一種です。JRCの定義によれば、木の幹は地上15 cmの高さで切断され、幹の直径が9cm以上になるまでまっすぐに伸びます。丸太、幹材、薪、サルベージ伐採、パルプ材、製材の完全な定義については脚注を参照してください。[gw]一般に、残留物とカスケード木材(耐用年数の終わりにエネルギーのために燃焼される木材製品)は、「バイオエナジーの気候へのプラスの影響」を最大化すると見なされています。[gx]ヨーロッパでは、約20%の幹材がバイオエナジーに使用され、残りは伐採残渣、加工残渣、消費後の木材から使用されています。幹材の少なくとも半分は、回収/パリティ時間が短く、生態系サービスを提供する短い輪作の雑木林から供給されています。[gy]

スウェーデンの森林から木製品、紙、エネルギーへのバイオマスの流れを示すサンキーダイアグラム。[165]

チャタムハウスは、丸太として定義されているバイオマスの一部(特に茎)を収穫して木質ペレットに使用しない方がよいと主張しています。これにより、森林での炭素貯蔵量が増加するからです。[166]彼らはまた、「[...]高品質の製材とはみなされない樹木は、それでもパルプ、パネル、または積層製品に使用できる」と主張している。[167]つまり、前者の場合、炭素の貯蔵期間が長くなるため、この低価値バイオマスを木質ペレット以外の原料として利用したほうがよいのです。チャタムハウスはまた、利用可能なすべての製材所の残留物がすでにペレット製造に使用されているため、拡張の余地はないと主張しています。バイオエナジーセクターが将来大幅に拡大するためには、収穫されたパルプ材のより多くがペレット工場に行かなければなりません。[166]

カウイら。米国では、約20%の「[...]ラウンドウッド(幹材とも呼ばれる)、たとえば間伐による小さな茎[...]」が木質ペレットに使用されていると主張しています。ただし、低回転林からの幹材の使用はパリティ時間が短く、長回転林では、木質ペレットに使用される幹材は通常、製材生産からの副産物で構成されます(間伐または不規則/曲がった/損傷した幹部木。)ソーンウッドの生産は、森林管理者の収入の90%以上を提供し、林業が存在する主な理由です。[dh] [gz]低品質の茎部分や間伐材の市場がなければ、それらは腐敗するために森に残されるか、道端で焼却されたでしょう。カウイら。また、間伐の実践はより多くの製材を生産するのに役立つため、バイオエナジーに間伐を使用すると、収穫された木材製品の炭素置換効果が強化されると主張しています。[ha]

同様に、FutureMetricsは、製材所から木のこの部分により多くのお金を得るので、林業家が製材所品質のラウンドウッドをペレット工場に販売することは意味がないと主張します。林業家は収入の80〜90%を製材品質の丸太で、パルプ材で10〜15%しか稼ぎません。これは、次のように定義されます。 、およびb。)間伐。この低価値バイオマスは、主に製紙用のパルプ工場に販売されていますが、場合によってはペレット製造用のペレット工場にも販売されています。[168]ペレットは通常、製材所がある地域の製材所の残留物から作られていますが、製材所のない地域のパルプ材からも作られています。[hb]Lamers&Jungingerは、「[...]木材とセルロース[パルプ]製品の経済的価値が高いため、繊維をめぐる地域的な競争がある場合はどこでも、エネルギー目的で樹木全体を大規模に使用する可能性は非常に低い」と主張しています。[hc] EUの合同調査センターによると、バイオエナジーセクター、ウッドパネルセクター、パルプセクターの両方が「[...]すべて製材の需要に依存しており、同じ原料をめぐって競争している」とのことです。[hd]

短期対長期の気候上の利点

Cowie et al。によると、「[...]特定の森林バイオエナジーオプションの知覚される魅力は、短期的な気候目標と長期的な気候目標の優先順位に影響されます。」[169]たとえば、IPCCは、森林炭素排出回避戦略は常に短期的な緩和効果をもたらすと述べているが、持続可能な林業活動からの長期的な利益がより重要であると主張している。

ベースラインと比較して、最大の短期的利益は、排出回避を目的とした緩和活動を通じて常に達成されます[...]。しかし、排出が回避されると、その森林の炭素貯蔵量は維持されるか、わずかに増加するだけです。[...]長期的には、森林から木材、繊維、またはエネルギーの年間収量を生み出しながら、森林の炭素貯蔵量を維持または増加させることを目的とした持続可能な森林管理戦略は、最大の持続的な緩和効果を生み出します。[164]

同様に、一般的な現代のバイオエナジーの気候への影響の問題に対処するために、IPCCは次のように述べています。[170]その結果、IPCCのGHG緩和経路のほとんどには、バイオエナジー技術の実質的な展開が含まれています。[4]バイオエナジー経路が制限されているか、まったくない場合、気候変動が増加したり、バイオエナジーの緩和負荷が他のセクターにシフトしたりします。[o]さらに、緩和コストが増加します。[彼]

IEAバイオエナジーは、短期に専念することで長期的に効率的な炭素削減を達成することが難しくなると主張し、新しいバイオエナジー技術への投資を、2030年以降にのみ排出削減を提供する他の再生可能エネルギー技術への投資と比較します。バッテリー製造のスケールアップまたは鉄道インフラの開発。[hf]全米大学森林資源プログラム協会は、累積排出量の現実的な評価を行うために、100年の期間を推奨しています。[hg]

参考文献

参考文献

引用とコメント

  1. ^ Eurostat defines biomass as "[...] organic, non-fossil material of biological origin that can be used for heat production or electricity generation. It includes: wood and wood waste; agricultural crops; biogas; municipal solid waste; biofuels." See European Commission 2018b. Conversely, the UNFCCC defines biofuels as "[a] fuel produced from dry organic matter or combustible oils produced by plants. These fuels are considered renewable as long as the vegetation from which they derive is maintained or replanted. These include firewood, alcohol obtained from sugar fermentation and combustible oils extracted from oilseeds." See European Commission 2018a.
  2. ^ "Biofuels are transportation fuels such as ethanol and biodiesel that are made from biomass materials." EIA 2021b.
  3. ^ In EU legislation, biofuel is defined as: "Liquid or gaseous fuel for transport produced from biomass." See European Commission 2018a.
  4. ^ "Solid biofuels cover organic, non-fossil material of biological origin which may be used as fuel for heat and electricity production. [...] Primary solid biofuels are defined as any plant matter used directly as fuel or converted into other forms before combustion. This covers a multitude of woody materials generated by industrial process or provided directly by forestry and agriculture (firewood, wood chips, bark, sawdust, shavings, chips, sulphite lye also known as black liquor, animal materials/wastes and other solid biofuels). This category excludes charcoal. Wood pellets are agglomerates produced either directly by compression or by the addition of a binder in a proportion not exceeding 3% by weight. Such pellets are cylindrical, with a diameter not exceeding 25 mm and a length not exceeding 100 mm. The term ‘other agglomerates' is the term used for agglomerates that are not pellets, such as briquettes or log agglomerates. Wood pellets and other agglomerates are often reported jointly, with other agglomerates being usually a minor part. Black liquor is a by-product from chemical and semi-chemical wood pulp industry." Camia et al. 2021, pp. 20–21.
  5. ^ In 2020, the world produced a total of 24.6 EJ of electrical energy from all renewables except bioenergy. The individual contributions consists of 15.5 EJ from hydro, 5.8 EJ from wind, 3 EJ from solar and 0.3 EJ from geothermal (all values converted from TWh with IEA's unit converter.)
  6. ^ In 2020, 9.5 EJ of heat energy for industrial applications was consumed, and 5 EJ of heat for buildings. 3.7 EJ of liquid fuels for transportation was produced (ethanol 2.2 EJ, biodiesel 1.5 EJ), and 2.2 EJ in the form of electricity.
  7. ^ a b "The forestry sector is the largest contributor to the bioenergy mix globally. Forestry products including charcoal, fuelwood, pellets and wood chips account for more than 85% of all the biomass used for energy purposes. One of the primary products from forests that are used for bioenergy production is woodfuel. Most of the woodfuel is used for traditional cooking and heating in developing countries in Asia and Africa. Globally, 1.9 billion m3 of woodfuel was used for energy purposes." WBA 2019, p. 3. In the EU, 60% of all renewable energy comes from biomass. 75% of all biomass is used in the heating and cooling sector. See JRC 2019, p. 1.
  8. ^ "Biomass-based electricity can provide balancing power needed to maintain power stability and quality as the contribution from solar and wind power increases (Arasto et al., 2017; Lenzen et al., 2016; Li et al., 2020), complementing other balancing options such as battery storage, reservoir hydropower, grid extensions and demand-side management (Göransson & Johnsson, 2018). Beyond its value as a dispatchable resource for electricity generation, biomass is an important option for renewable heating in buildings and industrial processes. In 2019, bioenergy contributed almost 90% of renewable industrial heat consumption and two-thirds of the total modern renewable heating and cooling in buildings and industrial processes (IEA, 2020; IRENA/IEA/REN21, 2020). It is one of the options available to reduce emissions from heavy industries such as iron and steel production (Mandova et al., 2018, 2019) and cement production (IEA, 2018). Furthermore, carbon-based transportation fuels will remain important in the coming decades, as electrification of the transport sector will take time (IEA-AMF/IEA Bioenergy, 2020). Biofuels can contribute to reducing fossil fuel use and associated GHG emissions while there remain vehicles that use carbon-based fuels. In the longer term, biofuels will likely be used in sectors where the substitution of carbon-based fuels is difficult, such as long-distance aviation and marine transportation." Cowie et al. 2021, p. 1212.
  9. ^ "The recent discussions on renewable energy are mostly focused on the rapid growth of wind and solar deployment and their impressive drop in cost. While these developments are remarkable, they also overshadow what remains the most important source of renewable energy today – bioenergy." IEA 2017a.
  10. ^ "Bioenergy is the main source of renewable energy today. IEA modelling also indicates that modern bioenergy is an essential component of the future low carbon global energy system if global climate change commitments are to be met, playing a particularly important role in helping to decarbonise sectors such as aviation, shipping and long haul road transport. However, the current rate of bioenergy deployment is well below the levels required in low carbon scenarios. Accelerated deployment is urgently needed to ramp up the contribution of sustainable bioenergy across all sectors, notably in the transport sector where consumption is required to triple by 2030." IEA 2017b.
  11. ^ "Bioenergy has an essential and major role to play in a low-carbon energy system. For instance, modern bioenergy in final global energy consumption should increase four-fold by 2060 in the IEA's 2°C scenario (2DS), which seeks to limit global average temperatures from rising more than 2°C by 2100 to avoid some of the worst effects of climate change. It plays a particularly important role in the transport sector where it helps to decarbonize long-haul transport (aviation, marine and long-haul road freight), with a ten-fold increase in final energy demand from today's 3 EJ to nearly 30 EJ. Bioenergy is responsible for nearly 20% of the additional carbon savings needed in the 2DS compared to an emissions trajectory based on meeting existing and announced policies. But the current rate of bioenergy deployment is well below these 2DS levels. In the transport sector, biofuel consumption must triple by 2030, with two-thirds of that coming from advanced biofuels. That means scaling up current advanced biofuels production by at least 50 times to keep pace with the 2DS requirements by 2030. In scenarios with more ambitious carbon reduction objectives, such as the IEA's Beyond 2 Degree Scenario (B2DS), bioenergy linked to carbon capture and storage also becomes necessary. [...] The roadmap also points out the need for a five-fold increase in sustainable bioenergy feedstock supply, much of which can be obtained from mobilising the potential of wastes and residues." IEA 2017a.
  12. ^ "The International Energy Agency (IEA, 2012) defines traditional use of biomass as: '…the use of wood, charcoal, agricultural residues and animal dung for cooking and heating in the residential sector' and notes that 'it tends to have very low conversion efficiency (10% to 20%) and often relies on unsustainable biomass supply.'" IRENA 2014, p. 7.
  13. ^ "The trend towards modern and industrial uses of biomass is growing rapidly. However, the demand often occurs in locations geographically distant from the supply source. This results in increasingly complex production systems (e.g., feedstock supply and conversion combinations) (Searcy et al., 2013). REmap 2030 shows that biomass use worldwide could grow by 3.7% per year from 2010 to 2030 – twice as fast as it did from 1990 to 2010 (IEA, 2013a) – if costeffective applications are put in place. Global biomass demand would then double from 53 exajoules (EJ) in 2010 to 108 EJ by 2030 (IRENA, 2014a). [...] Unlike the increasing demand for primary solid biomass in modern renewable energy applications, traditional biomass demand for space heating and cooking is expected to decrease from 21 EJ in the Reference Case to 6 EJ in REmap 2030, marking an important transition towards the more efficient use of biomass in households. [...] " IRENA 2014, pp. 1, 24.
  14. ^ "Bioenergy has a significant greenhouse gas (GHG) mitigation potential, provided that the resources are developed sustainably and that efficient bioenergy systems are used. Certain current systems and key future options including perennial cropping systems, use of biomass residues and wastes and advanced conversion systems are able to deliver 80 to 90% emission reductions compared to the fossil energy baseline. However, land use conversion and forest management that lead to a loss of carbon stocks (direct) in addition to indirect land use change (d+iLUC) effects can lessen, and in some cases more than neutralize, the net positive GHG mitigation impacts." IPCC 2012, p. 214.
  15. ^ a b "For example, limiting deployment of a mitigation response option will either result in increased climate change or additional mitigation in other sectors. A number of studies have examined limiting bioenergy and BECCS. Some such studies show increased emissions (Reilly et al. 2012). Other studies meet the same climate goal, but reduce emissions elsewhere via reduced energy demand (Grubler et al. 2018; Van Vuuren et al. 2018), increased fossil carbon capture and storage (CCS), nuclear energy, energy efficiency and/or renewable energy (Van Vuuren et al. 2018; Rose et al. 2014; Calvin et al. 2014; Van Vuuren et al. 2017b), dietary change (Van Vuuren et al. 2018), reduced non-CO2 emissions (Van Vuuren et al. 2018), or lower population (Van Vuuren et al. 2018)." IPCC 2019e, p. 637.
  16. ^ "Bioenergy is a versatile renewable energy source that can be used in all sectors, and it can often make use of existing transmission and distribution systems and end-user equipment. But there are constraints on expanding the supply of bioenergy, and possible trade-offs with sustainable development goals, including avoiding conflicts at local level with other uses of land, notably for food production and biodiversity protection. To navigate these risks, our Roadmap to Net Zero by 2050 combined for the first time the IEA's global energy system modelling with the International Institute for Applied Systems Analysis (IIASA)'s Global Biosphere Management Model to provide insights on bioenergy's supply, land use and net emissions. We aimed to ensure that the peak level of total primary bioenergy demand – including losses from the conversion of biomass into useful fuels – falls within the lowest estimates of global sustainable bioenergy potential in 2050, namely around 100 exajoules (EJ). Bioenergy demand in our global net zero pathway – the Net-Zero Emissions by 2050 (NZE) Scenario – is lower than all comparable scenarios from the Intergovernmental Panel on Climate Change (IPCC) that are aligned with 1.5 °C. Those IPCC scenarios use a median of 200 EJ of bioenergy in 2050." IEA 2021a.
  17. ^ IEA estimates high levels of sustainable bioenergy in 2050, but set their NZE target to only 100 EJ for conservative reasons: "The level of bioenergy use in the NZE [Net Zero Emissions scenario] [...] in 2050 is around 100 EJ. The global sustainable bioenergy potential in 2050 has been assessed to be at least 100 EJ (Creutzig, 2015) and recent assessments estimate a potential between 150‐170 EJ when integrating relevant UN Sustainable Development Goals (Frank, 2021; IPCC, 2019; IPCC, 2014; Wu, 2019). However, there is a high degree of uncertainty over the precise levels of this potential. Using modelling developed in co‐operation with IIASA, here we examine the implications for achieving net‐zero CO2 emissions by 2050 if the available levels of sustainable bioenergy were to be lower." IEA 2021b, p. 90.
  18. ^ According to IRENA, "[...] biomass energy comes from two different sources. One is primary bioenergy, which uses farmland or forests to produce biomass, the other is biomass residue, which is generated as a by-product of food or wood products throughout their supply-consumption chain." IRENA 2014, p. 5.
  19. ^ "There are two broad categories for woody biofuels: primary sources, such as logging residues, stumps, and low-quality logs, and secondary sources, i.e., by-products from the forest industries such as bark, saw dust, and black liqueur." Eggers et al. 2020, p. 2.
  20. ^ a b "Some fast growing tree species can be cut down to a low stump (or stool) when they are dormant in winter and go on to produce many new stems in the following growing season. This practice is well established in the UK and Europe, having been a traditional method of woodland management over several hundred years for a variety of purposes including charcoal, fencing and shipbuilding." Forest Research 2022c.
  21. ^ a b "While short rotation coppicing (SRC) cuts the tree back to a stool to promote the growth of multiple stems, on a regular cycle of roughly 2-4 years, it is also possible to practice something more closely akin to conventional forestry, though on a shorter timescale. Short rotation forestry (SRF) consists of planting a site and then felling the trees when they have reached a size of typically 10-20 cm diameter at breast height. Depending on tree species this usually takes between 8 and 20 years, and is therefore intermediate in timescale between SRC and conventional forestry. This has the effect of retaining the high productivity of a young plantation, but increasing the wood to bark ratio." Forest Research 2022a.
  22. ^ "Woody energy crops: Short‐rotation plantings of woody biomass for bioenergy production, such as coppiced willow and miscanthus." IEA 2021b, p. 212.
  23. ^ For instance is the promising crop Miscanthus × giganteus only grown on 30.000 hectares in the EU. See ETIP Bioenergy 2021. 30.000 hectares produces approximately 0.01 EJ annually, given the EU average peak yield of 22 tonnes dry matter per hectare per year (approximately 15 tonnes during spring harvest). See Anderson et al. 2014, p. 79. The energy content in miscanthus biomass is 18 GJ/t. Ghose 2011, p. 263.
  24. ^ "We will establish the amount of land that could be used in the UK for perennial energy crop production and for short rotation forestry (SRF). Existing biomass support schemes (Renewables Obligation, Contracts for Difference, RHI & RTFO) already support the use of perennial energy crops such as short rotation coppice and Miscanthus grown specifically for bioenergy purposes and as a material. However, only a small land area (~10,000 hectares) is cultivated with perennial energy crops in the UK at present, and this is mainly used for heat and electricity generation. Currently, there is little to no use of perennial energy crops for low carbon fuels supported under the RTFO due to a lack of commercial-scale processing capacities to convert these resources cost-efficiently into fuel. [...] The CCC's 6th Carbon Budget report highlighted the significant potential for perennial energy crops and SRF to contribute towards our carbon budget targets by increasing soil and biomass carbon stocks while also delivering other ecosystem benefits. In their balanced pathway, the CCC suggests that up to 708,000 hectares of land could be dedicated to energy crop production, which has led to an increased interest in the role of perennial energy crops and SRF as biomass feedstocks to deliver GHG savings in the land use and energy sectors. The Defra land use net zero programme, which is currently building a spatial understanding of the land use trade-offs across a number of policy areas, will help determine the potential scale of future availability of domestically grown biomass and their potential for delivering GHG savings in a landscape where land use change will need to be optimised for multiple benefits. This programme will inform our understanding and evidence on the availability and mix of biomass feedstocks for uses across sectors." Department for Business, Energy & Industrial Strategy 2021, pp. 15–16.
  25. ^ Brauch et al. write that in theory "[...] energy farming on current agricultural (arable and pasture) land could, with projected technological progress, contribute over 800 EJ, without jeopardizing the future world's food supply." The authors also write that "[...] a significant part of the technical potential (around 200 EJ in 2050) for biomass production may be developed at low production costs in the range of US$2/GJ [...] assuming this land is used for perennial crops. Another 100 EJ of biomass could be produced with lower productivity and higher costs at marginal and degraded lands." Brauch et al. 2009, p. 384.
  26. ^ "According to FAO, the issue is not the volume of available land, which is enough to supply growing demand, but securing the substantial financial investments to actually deploy these potential areas, plus the disparate distribution of land resource by country. For example, 60% of the world's unexploited prime land is held by only thirteen countries. [...] These thirteen countries are Madagascar, Mozambique, Canada, Angola, Kazakhstan, the Democratic Republic of the Congo, China, the Sudan, Australia, Argentina, Russia, the US and Brazil (in ascending order)." IRENA 2014, p. 40.
  27. ^ "Estimates of marginal/degraded lands currently considered available for bioenergy range from 3.2–14.0 Mkm2, depending on the adopted sustainability criteria, land class definitions, soil conditions, land mapping method and environmental and economic considerations (Campbell et al. 2008; Cai et al. 2011; Lewis and Kelly 2014)." IPCC 2019c, p. 193.
  28. ^ Given the EU average peak yield of 22 tonnes dry matter per hectare per year (approximately 15 tonnes during spring harvest). See Anderson et al. 2014, p. 79. The energy content in miscanthus biomass is 18 GJ/t, see Ghose 2011, p. 263. The calculation goes like this: 44990100 hectares times 15 tonnes per hectare times 18 GJ per tonne is 12147327000 GJ, or approximately 12 EJ.
  29. ^ "Plants convert CO2 from the atmosphere into biomass. Carbon stored in biomass is called biogenic carbon. Some of this carbon stays above ground and some in the ground. When plants die, decomposition starts. As plant material decays, the stored carbon is released as CO2 back into the atmosphere." IRENA 2014, p. 45.
  30. ^ a b "Wood from thinnings may, to some extent, be assimilated to harvest residues (especially pre-commercial thinnings). If not collected for bioenergy it would be left in the forest to decay, or combusted at roadside. On the other hand, depending on the wood quality, the use of thinnings wood for bioenergy may compete with other uses, such as pulp and paper or engineered wood. Salvage loggings can also be assimilated to harvest residues. Damaged, dying or dead trees affected by injurious agents, such as wind or ice storms or the spread of invasive epidemic forest pathogens, insects and diseases would remain in the forest and decay or combusted at roadside. Wood removed for prescribed fire hazard control as well can be considered residual wood." JRC 2014, pp. 42–43, table 3.
  31. ^ "This study estimated quantities of logging residues that can physically be recovered from harvest sites and utilized for electricity production in the US South. [...] Although almost all physically available logging residues could be recovered with a relatively short hauling distance, a mail survey indicated that only 4 percent of mills utilized this feedstock." Pokharel et al. 2019, p. 543.
  32. ^ "Currently, logging residue extraction, i.e., the harvest of tops and branches left during final felling, occurs on less than 20% of the harvested area in northern Sweden, and about 60% in southern Sweden. Stump harvest occurs to a limited extent today, but is expected to increase to about 5%–10% of the annual clear-felled area in the coming years. Similarly, logging residues constitute the main primary source of woody biofuels in most countries, but in the near future stumps and roundwood may play a more prominent role. Biofuel harvest from early thinnings in dense young forests are currently done to insignificant levels, but will increase, as for stumps, if prize levels rise. Therefore, there is considerable potential for increased extraction rates of primary woody biofuels, especially in northern Sweden, where current extraction rates are relatively low due to longer transport distances and lower harvestable volume per hectare compared to southern Sweden. The situation is similar in other European countries, with large un-used potentials for woody biomass for energy use." Eggers et al. 2020, p. 2.
  33. ^ "Logging residues are increasingly being extracted for bioenergy purposes." Dahlberg et al. 2011, p. 1220
  34. ^ van den Born et al. distinguish between logging residues in general and dead wood, with the logging residues potential at 14 EJ, and the dead wood potential at 1 EJ annually. For the logging residues potential, see van den Born et al. 2014, p. 20, table 4.2. Regarding the dead wood potential, the authors write: "A biomass pool is dead wood that remains in the forest, either standing or lying, and is transferred to the soil. It is often too costly to harvest dead wood. Besides, it is useful in increasing biodiversity (the proportion of dead wood is a sustainability criteria, (EEA, 2012). The global quantity of dead wood is estimated roughly at 67 Gt of biomass, which is about 11% of the total biomass (FAO, 2010), and about 20 times the annual wood harvest. [...] Dead wood: the global stock of dead wood is estimated at about 1200 EJ of biomass (FAO, 2010). This large pool has build up over a long period of time and in the entire forest area. Assuming an average rotation of 50 to 100 years, this implies a biomass pool of 10 to 20 EJ yr-1 [EJ per year]. When primary forests are excluded because they have not been used (based on FAO, 2010), about 7 to 14 EJ yr-1 of dead biomass remains. Forests with large quantities of dead wood are located in Russia and in parts of Africa. A limitation to the use of salvaged wood is the high costs of access and transport (Niquidet et al., 2012). A conservative estimate of accessible planted forests reduces the pool of available dead wood to about 2 EJ yr-1 biomass (Table 4.2). When an additional assumption is made that half of the dead wood needs to remain in forests to maintain biodiversity (Verkerk et al, 2012), the estimate is about 1 EJ yr-1 biomass available annually for energy production." (p. 15, 19-20)
  35. ^ "Biomass for bioenergy is usually a by-product of sawlog and pulpwood production for material applications (Dale et al., 2017; Ghaffariyan et al., 2017; Spinelli et al., 2019; Figure 1). Logs that meet quality requirements are used to produce high-value products such as sawnwood and engineered wood products such as cross laminated timber, which can substitute for more carbon-intensive building materials such as concrete, steel and aluminium (Leskinen et al., 2018). Residues from forestry operations (tops, branches, irregular and damaged stem sections, thinnings) and wood processing residues (e.g. sawdust, bark, black liquor) are used for bioenergy (Kittler et al., 2020), including to provide process heat in the forest industry (Hassan et al., 2019). These biomass sources have high likelihood of reducing net GHG emissions when substituting fossil fuels (Hanssen et al., 2017; Matthews et al., 2018), and their use for bioenergy enhances the climate change mitigation value of forests managed for wood production (Cintas, Berndes, Hansson, et al., 2017; Gustavsson et al., 2015, 2021; Schulze et al., 2020; Ximenes et al., 2012). Part of the forest biomass used for bioenergy consists roundwood (also referred to as stemwood), such as small stems from forest thinning. For example, roundwood was estimated to contribute around 20% of the feedstock used for densified wood pellets in the United States in 2018 (US EIA, 2019)." Cowie et al. 2021, pp. 1215–1216.
  36. ^ "The most crucial feedstock for the wood pellet sector is currently sawmill residues (85% of the mix), roundwood (13%), and recovered wood (2%). This mix is likely to change in the coming years with the forecasted expansion of the wood pellet industry. [...] Experience from North America shows that it is possible to use more forest residues as fiber furnish. Although it yields pellets with higher ash content, it is often a lower-cost raw material than, for example, roundwood and wood chips. This practice is increasingly common in both the US South (mainly for pellets exported to Europe) and Canada (mainly exported to Europe and Asia). In Western Canada, the sawmill residue share of the total feedstock has fallen from 97% in 2010 to 72% in 2020, with the balance being forest residues and roundwood." Wood Resources International 2022.
  37. ^ Recalculated from a total production of 43678925 tonnes wood pellets (FAO 2020), with 17 GJ/t energy content.
  38. ^ Recalculated from a total production of 265212933 m3 wood chips (FAO 2020), with 3.1 GJ/m3 energy content.
  39. ^ "In 2017, 55.6 EJ of biomass was utilized for energy purposes [...]. One of the most promising sectors for growth in bioenergy production is in the form of residues from agriculture sector. Currently, the sector contributes less than 3% to the total bioenergy production." WBA 2019, p. 3.
  40. ^ The Netherlands Environmental Assessment Agency estimated in 2014 that the total amount of agricultural residues amounts to 78 EJ, with 51 EJ from straw alone (pp. 12-13, table 3.4). "The large production of rice and the relatively low residue flow to the soil makes rice residues the residue with the highest potential for bioenergy, followed by residues from oilcrops, cereals, corn and sugarcane."(p. 19) Because a certain amount should be left in the fields for soil quality purposes, the total amount of agricultural residues that can be sustainably harvested amounts to 24 EJ. van den Born et al. 2014, pp. 2–21.
  41. ^ "One of the most promising sectors for growth in bioenergy production is in the form of residues from agriculture sector. Currently, the sector contributes less than 3% to the total bioenergy production. Data shows that utilizing the residues from all major crops for energy can generate approx. 4.3 billion tonnes (low estimate) to 9.4 billion tonnes (high estimate) annually around the world. Utilizing standard energy conversion factors, the theoretical energy potential from residues can be in the range of 17.8 EJ to 82.3 EJ. The major contribution would be from cereals – mainly maize, rice and wheat." WBA 2019, p. 3.
  42. ^ "In reality, most residues are not utilised for energy because they are difficult to collect or used for specific purposes, such as land conservation, manure and straw incorporation in the field to maintain soil organic matter. This is accounted for in the residue recovery rates. The historical and projected annual crop production growth by region and the residue coefficients are provided in Annex A. About a quarter of the residue generated for each crop is assumed to be recoverable, reflecting an assessment that half the residue could be collected sustainably and half of that amount could be collected economically. After the recoverable fraction of residues is estimated, the amount of residue used for animal feed is calculated separately. This is deducted from the total residue volume." IRENA 2014, p. 9.
  43. ^ "At present, traditional methods of space heating and cooking, such as burning firewood, account for 35 EJ, or two-thirds of total biomass use. By 2030, this would give way to modern biomass consumption, including substantially larger shares for power and transport applications. Power and district heating would reach 36 EJ (one-third of total biomass use in 2030) and transport 31EJ (almost 29%), while heat for industry and buildings would reach up to 41 EJ, of which only 6 EJ would be from less sustainable traditional uses. While global biomass potential is sufficient to meet growing demand, different types of biomass resources are distributed unevenly. Global biomass supply potential in 2030 is estimated to range from 97 EJ to 147 EJ per year. Approximately 40% of this total would originate from agricultural residues and waste (37-66 EJ). The remaining supply potential is shared between energy crops (33-39 EJ) and forest products, including forest residues (24-43 EJ). In geographic terms, the largest supply potential — estimated at 43-77 EJ per year — exists in Asia and Europe. North and South America together account for another 45-55 EJ per year." IRENA 2021.
  44. ^ "Advanced (second and third generation) biofuels are biofuels produced from feedstock that do not compete directly with food and feed crops, such as wastes and agricultural residues (i.e. wheat straw, municipal waste), non-food crops (i.e. Miscanthus and short rotation coppice) and algae." European Commission 2018.
  45. ^ "Recent studies by Reza et al. and Smith et al. have reported of the fate of inorganics and heteroatoms during HTC [hydrothermal carbonisation] of Miscanthus and indicate significant removal of the alkali metals, potassium and sodium, along with chlorine. [...] Analysis of ash melting behaviour in Smith et al., showed a significant reduction in the slagging propensity of the resulting fuel, along with the fouling and corrosion risk combined. [...] Consequently HTC offers the potential to upgrade Miscanthus from a reasonably low value fuel into a high grade fuel, with a high calorific value, improved handling properties and favourable ash chemistry. [...] HTC at 250 °C can overcome slagging issues and increase the ash deformation temperature from 1040 °C to 1320 °C for early harvested Miscanthus. The chemistry also suggests a reduction in fouling and corrosion propensity for both 250 °C treated fuels." Smith et al. 2018, pp. 547, 556.
  46. ^ "The success of large-scale international bioenergy trade will require the transport of high density commodities at low costs. Transport costs can be decreased by introducing pre-treatment into the supply chain. Pre-treatment, including torrefaction, pelletisation and pyrolysis, increases energy density from 2-8 MJ/m3 of raw biomass up to 11-20 MJ/m3 for pre-treated biomass. By optimising the supply chain through incorporating pretreatment, logistics costs could be significantly reduced compared with the raw materials-based supply chain." IRENA 2014, p. 53.
  47. ^ "It may not always be the case that energy crops will be grown on existing agricultural land. Other nonagricultural land such as forest or pasture land could be converted to grow energy crops as well. This is called land use change (LUC). LUC, like most other effects of bioenergy use, can be distinguished as direct (dLUC) and indirect (iLUC) land use change. dLUC occurs when bioenergy crops are grown on land not previously used for cropland or farming (e.g., forests), but this could also be land that is degraded or agriculturally unmanaged. iLUC is among the different indirect effects of bioenergy, such as increase in agricultural commodity prices or food security (Dehue, Cornelissen and Peters, 2011). iLUC may occur when biofuels are produced on existing agricultural land, but the demand for food and feed crops still remains and be met elsewhere. This can imply land use change by changing, for example, forests into agricultural land in another country or region. For example, converting land with high carbon stock into agricultural land would imply that substantial amounts of CO2 emissions would be released into the atmosphere (European Commission, 2012)." IRENA 2014, p. 46.
  48. ^ "A critical factor in the use of forest biomass in energy provision is the ‘payback time', during which atmospheric concentrations of carbon dioxide (CO2) will be increased as a result of using biomass. EASAC concludes that the European Commission should consider the extent to which large-scale forest biomass energy use is compatible with UNFCCC targets (of limiting warming to 1.5 °C above pre-industrial levels), and whether a maximum allowable payback period should be set in its sustainability criteria." EASAC 2017, p. 2.
  49. ^ "The UK's plan to burn more trees to generate “renewable” electricity has come under fire from green groups and sustainable investment campaigners over the controversial claim that biomass energy is carbon-neutral. A letter to the government signed by more than a dozen green groups including Greenpeace and Friends of the Earth warns ministers against relying too heavily on plans to capture carbon emissions to help tackle the climate crisis. The plans are being pioneered by Drax Group, which claims that burning wood pellets is carbon-neutral because trees absorb as much carbon dioxide when they grow as they emit when they are burnt. Capturing the carbon emissions from biomass power plants would then effectively create “negative carbon emissions”, according to Drax. The green groups have disputed these claims and warned that the plans “will be costly” and “will not deliver negative emissions” after accounting for the full carbon footprint of biomass in the power sector." Ambrose 2021.
  50. ^ "By definition, clear-cutting trees and combusting their carbon emits greenhouse gases that heat up the earth. But policymakers in the U.S. Congress and governments around the world have declared that no, burning wood for power isn't a climate threat—it's actually a green climate solution. [...] [T]he [...] basic argument is that the carbon released while trees are burning shouldn't count because it's eventually offset by the carbon absorbed while other trees are growing. That is also currently the official position of the U.S. government, along with many other governments around the world. In documentaries, lawsuits and the teenage activist Greta Thunberg's spirited Twitter feed, critics of the industry have suggested an alternative climate strategy: Let trees grow and absorb carbon, then don't burn them. [...] Cutting down a tree and burning it clearly releases more carbon than leaving the tree alone; replanting the tree can only pay back the carbon debt in the long run, and an even longer run if the replanted tree is eventually reharvested. But biomass defenders say that focusing on one tree or even one clear-cut is far too narrow a way to think about forest carbon, because as long as the carbon absorbed by forests equals the carbon released from forests, the climate doesn't care. [...] The industry's position is that wood pellets actually help expand forests, by making it more lucrative for the private landowners who control most U.S. forest land to stay in the forestry business. The opponents argue that what wood pellets make more lucrative is deforestation. [...] “We can't say, ‘Oh, we can sacrifice forest over here, because it's growing over there. We need to stop sacrificing forest.” Grunwald 2021.
  51. ^ The IEA defines carbon neutrality and carbon negativity like so: "Carbon neutrality, or 'net zero,' means that any CO2 released into the atmosphere from human activity is balanced by an equivalent amount being removed. Becoming carbon negative requires a company, sector or country to remove more CO2 from the atmosphere than it emits."IEA 2020.
  52. ^ "Schlamadinger & Marland describe how the atmospheric carbon pool changes depending on what is happening in other carbon pools (living biomass, soils and forest litter, wood and wood products, fossil fuels displaced by biomass fuels, fossil fuels used for forest management activities and for biomass conversion processes, and fossil fuels required to manufacture wood products or their substitutes.)" Schlamadinger & Marland 1996, p. 275. See also Sathre & O'Connor 2010, p. 104
  53. ^ Some researchers would like to move the counting to the combustion event, but Cowie et al. and others argue against this: "The UNFCCC reporting requirements specify that CO2 emissions associated with biomass combustion are counted in the land use sector, that is, where the harvest takes place; they are therefore reported as zero in the energy sector to avoid double-counting (Goodwin et al., 2019). This reporting approach is accurate, has no gaps and does not assume that bioenergy is carbon neutral (Haberl at al., 2012; Marland, 2010), although it has sometimes been described as such (e.g. Norton et al., 2019; Searchinger et al., 2009). [...] While the UNFCCC reporting approach is theoretically sound, incomplete coverage of the Kyoto Protocol created a gap in accounting: if an Annex I party (i.e. country with a Kyoto Protocol commitment) imported forest biomass from a country with no Kyoto Protocol commitment, any associated stock change in the forest of the exporting country was not accounted. [...] Several authors (Brack, 2017; Hudiburg et al., 2019; Norton et al., 2019) propose changing the UNFCCC accounting rules by which biomass is treated as having zero emissions at the point of combustion. However, accounting for CO2 emissions from bioenergy within the energy sector would require revision of the established GHG accounting framework to adjust the land sector values to remove the component related to biomass used for energy, to avoid double-counting of emissions, which would be very difficult to achieve, as explained by Camia et al. (2021). It would create a disincentive for countries to utilize biomass to displace fossil fuels, adversely affecting all types of bioenergy systems irrespective of their potential to provide climate benefits (Pingoud et al., 2010). Rather than changing the accounting convention solely for bioenergy, a flux-based ‘atmospheric flow approach' (Rüter et al., 2019) could potentially be applied to all wood products. However, if carbon fluxes from all wood products were to be reported at the time and place of emission, emissions due to forest harvest for export would not be reported by the country where the harvest takes place, thereby removing incentives for maintaining forest carbon stocks and potentially leading to deforestation because the country where the harvest takes place would report no emissions. Furthermore, reporting only at the time and place of emission would create a disincentive for use and trade in all sustainable wood products, including use for construction and bioenergy (Apps et al., 1997; Cowie et al., 2006; UNFCCC, 2003). [...] With respect to the treatment of bioenergy in UNFCCC reporting and accounting, we disagree with proposals to count emissions at the point of combustion, which could have adverse climate impacts. We recommend that complete and transparent reporting and accounting be applied consistently across the whole land sector, to ensure recognition of the interactions between terrestrial carbon stocks and biomass use for energy and other purposes, and to incentivize land use and management systems that deliver climate benefits." Cowie et al. 2021, pp. 1220–1222.
  54. ^ A graphical explanation of carbon payback and parity times, with carbon debt shown as a curve that moves along a time axis, is available here: EASAC 2017, p. 23.
  55. ^ "The potential carbon debt caused by harvest and the resulting time spans needed to reach pre-harvest carbon levels (payback) or those of a reference case (parity) have become important parameters for climate and bioenergy policy developments." Lamers & Junginger 2013, p. 373.
  56. ^ Lamers & Junginger state that the carbon debt "[...] can be indicated to the site itself (absolute) or against a baseline (relative)." The absolute carbon balance approach (payback time) is chosen to define the time until a site reaches its own pre-harvest carbon level, and the relative carbon balance approach (parity time) is chosen to define the time until an alternative land or biomass use scenario "[...] reaches the same carbon volume as its counterfactual (reference case)." The reference or alternative scenarios can be for example "[...] material use of biomass (e.g. pulp and paper), land protection (no harvest) or conversion to agriculture." According to the authors, "[t]his provides insight whether it is more beneficial from a net carbon perspective to keep biogenic carbon sequestered in plants (subjected to natural disturbances such as insects or wildfire) or use it for energy purposes." Lamers & Junginger 2013, p. 375.
  57. ^ EU's Joint Research Centre defines "counterfactual" like so: "The impacts of each bioenergy pathway are evaluated against a counterfactual, i.e. a reference use of the biomass or of the land (thus the results should be interpreted as conditional to the chosen reference)." Camia et al. 2021, p. 83.
  58. ^ "It is important to notice that the definition of the reference system (both the energy system and the counterfactual biomass use) is as important as the definition of the bioenergy systems since the stated goal of the study is to assess the mitigation potential of the new systems as compared to the reference one." Camia et al. 2018, p. 100.
  59. ^ a b "Critical methodology decisions include the definition of spatial and temporal system boundaries [...] and reference (counterfactual) scenarios [...]. Focus on stack emissions (Option 1) neglects the key differences between fossil and biogenic carbon [...]. Focus on the forest only (Option 2) captures the effects of biomass harvest on forest carbon stocks [...] but omits the climate benefits of displacing fossil fuels. Option 3, the biomass supply chain, overlooks the interactions between biomass and other forest products [...]. Option 4 covers the whole bioeconomy, that is, the forest, the biomass supply chain and all bio-based products from managed forests, and thus provides a more complete assessment of the climate effects of forest bioenergy. In order to quantify the net climate effect of forest bioenergy, assessments should take a whole systems perspective. While this increases the complexity and uncertainty of the assessments, it provides a sound basis for robust decision-making. Biomass for bioenergy should be considered as one component of the bioeconomy (Option 4 [...]). Studies should therefore assess the effects of increasing biomass demand for bioenergy on carbon stocks of the whole forest, and also include the broader indirect impacts on emissions (potentially positive or negative) due to policy- and market-driven influences on land use, use of wood products and GHG-intensive construction materials, and fossil fuel use, outside the bioenergy supply chain. The bioenergy system should be compared with a realistic counterfactual(s) that includes the reference land use and energy systems [...]. This approach is consistent with consequential LCA [...]. The temporal boundary should recognize: forest carbon dynamics, for example, modelling over several rotations; the trajectory for energy system transition; and short- and long-term climate objectives. Matthews et al. (2018) suggest criteria that could be used to identify woody biomass with greater climate benefits when assessed from a full life cycle, whole system perspective." Cowie et al. 2021, pp. 1213, 1219–1220.
  60. ^ A simplified curve, complete with carbon payback and parity times, is available here: EASAC 2017, p. 23.
  61. ^ "The GWP is a measure of the effect of the pulse emission of a unit (mass) of a certain gas over its lifetime on the radiative properties of the atmosphere for a certain period of time. In the methodology designed by the IPCC [IPCC 2006], the GWP of CO2- is taken as the reference value and assigned the value of 1. The reasoning of the authors is that biogenic CO2- has indeed the same radiative effect of fossil CO2 on the atmosphere but, while fossil CO2- can only be reabsorbed by oceans and biosphere (according to the formulation using Bern CC equation, as given by [IPCC 2006]), biogenic-CO2- has an additional factor which is the reabsorption of the CO2- via re-growth of vegetation on the same piece of land. By this mathematical formulation, they have been able to assign various values of a so-called GWPbio- over the typical time horizons of 20, 100 and 500 years and depending on the timing of biomass re-growth. Technically, this factor can then be simply used in a classical LCA and applied as correction factor to the amount of the biogenic-CO2 emitted by the combustion of biomass." JRC 2014, p. 45.
  62. ^ "Annualised emissions from carbon stock changes caused by land-use change, el, shall be calculated by dividing total emissions equally over 20 years." European Parliament, Council of the European Union 2018, p. Annex VI.
  63. ^ See for instance the European Union's official emission savings percentages for different fuels here: European Parliament, Council of the European Union 2018, p. ANNEX VI. Note that these estimates do not include the average net emissions which results from an eventual land use change prior to planting.
  64. ^ "The Renewable Energy Directive (RED), as well as the Fuel Quality Directive (FQD) and the proposal for a RED-Recast (EP 2009, EP 2009b and EC 2016) apply a simplified attributional LCA methodology to assess GHG emissions savings for a series of liquid biofuels pathways used in the transport sector. A similar methodology is also extended to biomass used for power, heat and cooling generation (EC 2016). The RED evaluates the supply-chains GHG emissions of various bioenergy pathways and compares them to each other on a common basis (GHG emission savings with respect to a fossil fuel comparator) to promote the pathways that perform best on this relative scale and to exclude the pathways with the worst technologies and GHG performances." Camia et al. 2018, p. 89.
  65. ^ "Two main modelling principles are in use in LCA practice: Attributional (A-LCA) and Consequential (C-LCA) modelling, with the former being more widely used for historical and practical reasons. [...] Attributional modelling makes use of historical, fact-based, average, measureable data of known (or at least knowable) uncertainty, and includes all the processes that are identified to relevantly contribute to the system being studied. In attributional modelling, the system is hence modelled “as it is” or “as it was” (or as it is forecasted to be) (EC, 2010). Attributional modelling is also referred to as “accounting”, “book-keeping”, “retrospective”, or “descriptive”. [...] [P]urely attributional LCA studies of bioenergy systems are unable to capture properly all of the complexities linking bioenergy, climate, bioenergy and ecosystem services (e.g. market-mediated effects, biogeophysical, time-dependent effects). [...] The results of these types of assessment are static in time and do not account for biogenic-C flows. It has become established practice in A-LCA to assume that any emission of biogenic CO2 (release to the atmosphere of the carbon contained in biological resources) is compensated by photosynthesis during the re-growth of the biomass feedstock. This assumption originates from an interpretation of the rules for reporting national GHG inventories to the United Nations Framework Convention on Climate Change (UNFCCC). Biogenic-C flow are accounted for in the land use, land-use change, and forestry (LULUCF) chapter at the time the biomass commodity is harvested and are therefore not accounted for in the energy sector at the time the biomass is burnt (JRC, 2013). It remains valid for system-level analysis, when the changes in biomass carbon stocks are accounted in the land-use sector rather than in the energy sector (EC, 2016c)." Camia et al. 2018, pp. 89–91.
  66. ^ "Some studies of forest bioenergy consider carbon dynamics at the individual stand level [...]. Stand-level assessments represent the forest system as a strict sequence of events (e.g. site preparation, planting or natural regeneration, thinning and other silvicultural operations, final felling). Results are strongly influenced by the starting point: commencing the assessment at harvest shows upfront emissions, followed by a CO2 removal phase, giving a delay before forest bioenergy contributes to net reductions in atmospheric CO2, particularly in long-rotation forests. This delay has been interpreted as diminishing the climate benefit of forest bioenergy [...]. In contrast, commencing at the time of replanting shows the opposite trend: a period of CO2 removal during forest growth, followed by a pulse emission returning the CO2 to the atmosphere. Thus, stand-level assessments give inconsistent results and can be misleading as a basis to assess climate impacts of forest systems [...]. Furthermore, when considering only the stand level, it is difficult to identify whether the forest is sustainably managed or subject to unsustainable practices that cause declining productive capacity and decreasing carbon stocks. [...] The alternative to stand level is landscape-scale assessment, that considers the total area of managed forests. Stand- and landscape-level assessments respond to different questions. Stand-level assessment provides detailed information about plant community dynamics, growth patterns and interactions between carbon pools in the forest. But the stand-level perspective overlooks that forests managed for wood production are generally a series of stands of different ages, harvested at different times to produce a continuous supply of wood products. Across the whole forest landscape, that is, at the scale that forests are generally managed, temporal fluctuations observed at stand level are evened out and the forest carbon stock fluctuates around a trend line that can be increasing or decreasing, or roughly stable, depending on the age class distribution and weather patterns (Cowie et al., 2013). Landscape-level assessment provides a more complete representation of the dynamics of forest systems, as it can integrate the effects of all changes in forest management and harvesting taking place in response to—experienced or anticipated—bioenergy demand, and it also incorporates the effects of landscape-scale processes such as fire [...]. In a forest managed such that annual carbon losses due to harvest plus other disturbances and natural turnover equal the annual growth in the forest, there is no change in forest carbon stock when considered at landscape level [...]. To conclude, impacts of bioenergy policy should be assessed at the landscape scale because it is the change in forest carbon stocks at this scale, due to change in management to provide bioenergy along with other forest products, that determines the climate impact. Understanding of stand-level dynamics is critical to forest management and is useful to inform assessments at the landscape scale." Cowie et al. 2021, pp. 1217–1218.
  67. ^ "Bioenergy from dedicated crops are in some cases held responsible for GHG emissions resulting from indirect land use change (iLUC), that is the bioenergy activity may lead to displacement of agricultural or forest activities into other locations, driven by market-mediated effects. Other mitigation options may also cause iLUC. At a global level of analysis, indirect effects are not relevant because all land-use emissions are direct. iLUC emissions are potentially more significant for crop-based feedstocks such as corn, wheat and soybean, than for advanced biofuels from lignocellulosic materials (Chum et al. 2011; Wicke et al. 2012; Valin et al. 2015; Ahlgren and Di Lucia 2014). Estimates of emissions from iLUC are inherently uncertain, widely debated in the scientific community and are highly dependent on modelling assumptions, such as supply/demand elasticities, productivity estimates, incorporation or exclusion of emission credits for coproducts and scale of biofuel deployment (Rajagopal and Plevin 2013; Finkbeiner 2014; Kim et al. 2014; Zilberman 2017). In some cases, iLUC effects are estimated to result in emission reductions. For example, market-mediated effects of bioenergy in North America showed potential for increased carbon stocks by inducing conversion of pasture or marginal land to forestland (Cintas et al. 2017; Duden et al. 2017; Dale et al. 2017; Baker et al. 2019). There is a wide range of variability in iLUC values for different types of biofuels, from –75–55 gCO2 MJ–1 (Ahlgren and Di Lucia 2014; Valin et al. 2015; Plevin et al. 2015; Taheripour and Tyner 2013; Bento and Klotz 2014). There is low confidence in attribution of emissions from iLUC to bioenergy." IPCC 2019i, p. 194.
  68. ^ One often cited example of indirect land use change is the land use change from forest to agriculture that happened in Brazil after the US started to use some of its harvested corn for ethanol production rather than animal feed. The resulting lower supply of animal feed on the global market was seen as an opportunity by Brazilian farmers, who subsequently cut down forests in order to plant soya beans destined for the animal feed market. See Bird et al. 2010, p. 5, and also Searchinger et al. 2008, pp. 1238–1240 for the original research article.
  69. ^ The authors also note that depending on the biome, forest protection implies exposure to natural disturbances, such as wildfires, droughts, or insect infestations. While wildfires have been studied and are often included in the carbon calculations, droughts, insect outbreaks, and other related climate change impact factors on forest are much harder to predict. These natural disturbances "[...] may have severe carbon implications" however. The authors conclude that "[...] forest protection assumptions postulate that the carbon and thus the land will not be used for human economic activities for centuries; an assumption generally questionable in our land-constrained world." Lamers & Junginger 2013, pp. 378–379.
  70. ^ "Assuming the forest would remain unharvested in the no-bioenergy scenario is not a realistic reference in situations where landholders use the land to generate income, unless landholders can obtain equivalent income from payments for carbon sequestration or other ecosystem services (Srinivasan, 2015). In cases where a no-harvest scenario is a valid reference case, there are challenges in quantifying future carbon stocks: carbon sequestration rate in unharvested forests, especially in the longer term, is uncertain in many cases due to a paucity of relevant data (e.g. Derderian et al., 2016) and uncertain effects of climate change. Furthermore, accumulated carbon is vulnerable to future loss through disturbances such as storm, drought, fire or pest outbreaks. Where more than one alternative is plausible, it is informative to analyse several alternative reference land-use scenarios (Koponen et al., 2018)." Cowie et al. 2021, p. 1218.
  71. ^ According to Nabuurs et al., displacement factors takes into consideration the difference in CO2 emissions per unit of primary energy produced, differences in efficiency of energy conversion (e.g. conversion from primary energy to electricity) and in some cases also the emission differences in the supply chains. See Nabuurs, Arets & Schelhaas 2017, p. 4. See also Cowie et al. 2021, p. 1214.
  72. ^ "Wood and coal have similar CO2 emission factors, as the ratio of heating values between the two fuels is similar to the ratio of carbon content [...]. Where biomass is co-fired with coal in large power plants, the conversion efficiency may decrease a few percent, although there is usually no significant efficiency penalty when the co-firing ratio is below 10% [...]. Conversion efficiencies depend on fuel properties including moisture content and grindability in addition to heating value [...]. For low rank coal, biomass co-firing (especially torrefied biomass) can increase the boiler efficiency and net power plant efficiency [...]. Smaller biomass-fired plants can have lower electric conversion efficiency than large coal-fired plants, but as they are typically combined heat and power plants, they also displace heat production from other sources, that could otherwise have generated fossil fuel emissions [...]. Large dedicated biomass units (converted from coal) can operate with roughly the same level of thermal efficiency as delivered historically from coal [...]. Cowie et al. 2021, p. 1214.
  73. ^ Sathre & O'Connor found that in general, wood products require less production energy and less use of fossil fuels than what is needed to produce a functionally equivalent amount of metals, concrete, or bricks. They write that a displacement factor of wood product substitution is a measure of the amount of GHG emissions that is avoided when wood is used instead of some other material. In other words, a displacement factor shows the efficiency with which the use of biomass reduces net GHG emissions. The authors also write that a higher displacement factor indicates that more GHG emissions are avoided per unit of wood used. Likewise, a negative displacement factor means that emissions are greater when using the wood product. Sathre & O'Connor 2010, pp. 104–111.
  74. ^ Myllyviita et al. regrets that most researchers do not include wood storage in their calculations: "If the aim of DFs [displacement factors] is to describe the overall climate effects of wood use, DFs should include all the relevant GHG flows, including changes in forest and HWP [harvested wood products] carbon stock and post-use of HWPs, however, based on this literature review this is not a common practice." Myllyviita et al. 2021, p. 1.
  75. ^ "Bioenergy with carbon capture and storage (BECCS) plays a critical role in the NZE Scenario by offsetting emissions from sectors where full decarbonisation is extremely difficult to achieve. In 2050, around 10% of total bioenergy is used in facilities equipped with carbon capture, utilisation and storage, and around 1.3 billion tonnes of CO2 is captured using BECCS. Around 45% of this CO2 is captured in biofuels production, 40% in the electricity sector, and the rest in heavy industry, notably cement production." IEA 2021a.
  76. ^ "In case that there is no raw material displacement from other sectors such as food, feed, fibers or changes in land carbon stocks due to direct or indirect land use change, the assumption of carbon neutrality can still be considered valid for annual crops, agriresidues, short-rotation coppices and energy grasses with short rotation cycles. This can also be valid for analysis with time horizons much longer than the feedstock growth cycles. [...] The timeframe of the comparison too plays a relevant role in the performances of the reference system. If the timeframe chosen is short, the current emissions from the reference system can be considered appropriate and constant. In the case of a long-term analysis, though, also the changes in the fossil reference system have to be accounted for. For instance, practically in all of the studies analyzed the reference system (coal or NG) is kept constant and unchanged for the whole duration of the analysis (even centuries), while, according to EU policies, by 2050 the EU should be decarbonized, implying that future savings might be much smaller than current ones. In this case [...] it may happen that the payback time is never reached. [...] On the other hand, if the reference fossil system gets ‘dirtier', as in the case of most of the unconventional fossil energy (shale gas, bituminous coal etc.) the fossil fuel parity may be reached sooner than with a constant reference fossil fuel." JRC 2014, pp. 23, 51–52. Note that the JRC use the term "payback time" in the sense of "parity time" as defined in Carbon accounting principles above. See JRC 2014, p. 16.
  77. ^ "Studies of real forest landscapes show that the net GHG effects of bioenergy incentives are more variable than suggested by studies that do not consider economic factors and varying conditions in the forest and wood products sector." Cowie et al. 2021, p. 1218.
  78. ^ EU's Joint Research Centre describes how the economic boundaries can expand to reach macro-economic size: "Large scale techno-economic modeling: This type of analysis includes a macroeconomic model that estimates the developments of the wood market in terms of imports, quantity of wood used for wood products and for bioenergy etc. as response to a given decision. The market model is coupled with a forest model that can model changes in carbon stocks in all the pools of forests (including living and dead wood, soil-C etc.) and eventually the carbon stocked in wood products. These two models can then be combined with several scenarios for the substitution of wood products in which a typical LCA (biogenic-CO2 emissions are set to zero) is applied to calculate the GHG savings due to the use of biomass compared to the alternative materials / feedstocks. The combination of these calculations would provide a clear and quantitative forecast of possible carbon savings or emissions due to different policy scenarios and over different time horizons." JRC 2014, p. 69.
  79. ^ See for instance Camia et al. 2021, pp. 86, 100.
  80. ^ "Wide variation in published estimates of payback time for forest bioenergy systems reflects both inherent differences between these systems and different methodology choices [...]. Critical methodology decisions include the definition of spatial and temporal system boundaries [...] and reference (counterfactual) scenarios [...]. Misleading conclusions on the climate effects of forest bioenergy can be produced by studies that focus on emissions at the point of combustion, or consider only carbon balances of individual forest stands, or emphasize short-term mitigation contributions over long-term benefits, or disregard system-level interactions that influence the climate effects of forest bioenergy." Cowie et al. 2021, pp. 1213, 1221.
  81. ^ Jonker et al. examined the carbon intensity for southeastern forests in the US, and concluded that due to the large number of possible methodological choices and reference systems, the calculations produce a wide range of payback and parity times, from below 1 year payback time with landscape level carbon accounting to 27 years with stand level accounting, and parity times of 2 –106 years depending on system boundaries and the choice of alternative scenarios. The authors consider landscape-level carbon accounting more appropriate for the examined situation. Under this precondition, the issue of carbon payback time is basically nonexistent. If comparison against a protection scenario is deemed realistic and policy relevant, and assuming that wood pellets directly replace coal in an average coal power plant, the carbon parity time is 12–46 years; i.e. one or two rotations. Switching to intensively managed plantations yields the most drastic reduction in parity time (below 18 years in 9 of 12 cases). The authors conclude that the choice of carbon accounting method has a significant impact on the carbon payback and parity times. Jonker, Junginger & Faaij 2013, pp. 371–387.
  82. ^ "Studies reporting long carbon debt payback times in general assume that the biomass is utilized for electricity production with low conversion efficiencies and that the woody biomass originates from the dedicated harvest of trees for energy from long rotation forestry. Looking at the current use of bioenergy in the EU, there is little evidence that such supply chains dominate." Madsen & Bentsen 2018, p. 1.
  83. ^ "Misleading conclusions on the climate effects of forest bioenergy can be produced by studies that focus on emissions at the point of combustion, or consider only carbon balances of individual forest stands, or emphasize short-term mitigation contributions over long-term benefits, or disregard system-level interactions that influence the climate effects of forest bioenergy. Payback time calculations are influenced by subjective methodology choices and do not reflect the contribution of bioenergy within a portfolio of mitigation measures, so it is neither possible nor appropriate to declare a generic value for the maximum acceptable payback time for specific forest bioenergy options. To answer the key question ‘what are the climate implications of policies that promote bioenergy?' assessment should be made at the landscape level, and use a full life cycle approach that includes supply chain emissions, changes in land carbon stocks and other variables influenced by the policies studied. Effects on land cover, land management and the wood products and energy sectors need to be considered, including indirect impacts at international level. The bioenergy system should be compared with reference scenarios (counterfactuals) that describe the most likely alternative land use(s) and energy sources that would be displaced by the bioenergy system, and the probable alternative fates for the biomass being utilized. A no-harvest counterfactual is not realistic in most current circumstances, but markets that pay for carbon sequestration and other ecosystem services could change incentives for harvest in the future."Cowie et al. 2021, pp. 1221–1222.
  84. ^ Bentsen examined 245 individual studies and found that the carbon payback time of apparently comparable forest bioenergy supply scenarios vary by up to 200 years, which provides ample room for confusion and dispute about the climate benefits of forest bioenergy. He concludes that the outcome of carbon debt studies lie in the assumptions, and that methodological rather than ecosystem and management related assumptions determine the findings. The findings are therefore seen as inadequate for informing and guiding policy development. Bentsen 2017, p. 1211.
  85. ^ "There is a large variability in the literature results for fossil fuel parity times. This is due to differences in the characteristics of the forest system considered (growth rate, management), in the carbon pools included, in the system boundaries definition and in the reference baseline used in the analysis." JRC 2014, p. 75.
  86. ^ EU's Joint Research Centre recommend that "[...] policymakers and scientists alike recognize that diverging values, worldviews, and ethical perceptions of natural resources and their management are a core part of the debate. These will not be solved by more scientific research, because science is a social endeavour where value-choices and judgements are inevitable. Transparency is key and cooperation with policymakers and co-creation of useful results should be welcomed." Camia et al. 2021, p. 93. In a presentation of this report for IEA Bioenergy, the JRC staff expand on this conclusion. They write that the question “Does forest bioenergy mitigate climate change?” really has no answer, as it is depends on "modelling approaches and the assumptions about hypothetical futures", and that researchers "come to equally valid, but opposite answers depending on assumptions chosen." They also write that "the assumptions chosen will align (consciously or unconsciously) with the worldviews and ethical values of the authors." According to the JRC, supporters of bioenergy usually have a more anthropocentric view of the human-nature relationship, while opposers of bioenergy are more aligned with nature conservation values. These norms lead to different concerns and definitions of what sustainability really is. See Mubareka, Giuntoli & Grassi 2021, pp. 8–9.
  87. ^ "Most of the forest feedstocks used for bioenergy, as of today, are industrial residues, waste wood, residual wood (thinnings, harvest residues, salvage loggings, landscape care wood etc.) for which, in the short to medium term, GHG savings may be achieved. On the other hand, in the case of stemwood harvested for bioenergy purposes only, if all the carbon pools and their development with time are considered in both the bioenergy and the reference fossil scenario, there is an actual increase in CO2 emissions compared to fossil fuels in the short-term (few decades). In the longer term (centuries) also stemwood may reach the fossil fuel parity points and then generate GHG savings if the productivity of the forest is not reduced because of bioenergy production. [...] The results attained are strongly correlated with the following parameters: the fossil fuel replaced, efficiency of the biomass utilization, the future growth rate of the forest, the frequency and intensity of biomass harvests and the initial landscape carbon stock." JRC 2014, p. 75.
  88. ^ "Increased removal of FWD [fine woody debris], low stumps, CWD (course woody debris): It depends strongly on the decay rates considered. For instance, (Giuntoli et al., 2015) and (Giuntoli et al., 2016) found that residues with decay rates of 11.5%/year would mitigate climate change compared to natural gas heating and natural gas electricity after about 20 years, but residues with decay rate lower than 2.7%/year would take more than 86 years to payback compared to natural gas heating, or more than a century compared to the current EU power mix. FWD are thus likely to achieve carbon mitigation in a short term. However, decay rates for low stumps have been reported to range between 0.7%/year up to even 11%/year (Persson and Egnell, 2018), depending on climatic conditions and species. Considering a representative decay rate for temperate/boreal forests of between 3 and 6%/year would mean stumps would be unlikely to achieve climate mitigation before 50 years. This is substantiated also by the work of (Laganière et al., 2017). However, we indicate a range of uncertainty across other climate change levels. CWD are very likely to exhibit low decay rates and to have very long payback times." Camia et al. 2021, p. 143. See also JRC 2014, pp. 16–17, 43–44.
  89. ^ Lamers & Junginger examined a number of studies and argue that parity times for residues "[...] mostly vary depending on the respective fossil fuel used in the reference scenario [...]." However, the second most important influencing factor "[...] is the size/diameter of the residue and the forest biome, i.e. conditions affecting the decay rate." The shortest parity times were found for forest residues which would otherwise be burned at the factory or roadside. This immediate carbon release in the alternative scenario causes an immediate carbon benefit and a net zero parity time for the bioenergy scenario. The longest parity times were for stump harvest in the cold boreal forests of northern Finland, when compared to a natural decay scenario for the stumps, and instead production of electricity from natural gas. For stemwood, parity times vary to some degree by forest biome with significantly shorter periods for highly productive regions, such as the temperate moist forests of the South-Eastern USA. In the boreal or sub-boreal forests, parity times against a forest protection scenario are about twice as large, but there are variations between studies. Under specific conditions, for instance where insect infestation has killed a large amount of merchantable timber stock, "[...] bioenergy harvest can reach parity times as low a zero." The high share of fast decaying tree biomass in the protection scenario shortens parity times. Parity times against regular timber harvest (buisness as usual) vary greatly with the fossil fuel alternative scenario, the shortest being coal and oil compared to natural gas. Afforestation on the other hand has a parity time of zero years if the land area in question would not be sequestering large amounts of carbon otherwise. Lamers & Junginger 2013, p. 379.
  90. ^ "Here, we analyze carbon debt and payback time of substituting coal with forest residues for combined heat and power generation (CHP). The analysis is, in contrast to most other studies, based on empirical data from a retrofit of a CHP plant in northern Europe. The results corroborate findings of a carbon debt, here 4.4 kg CO2eq GJ−1. The carbon debt has a payback time of one year after conversion, and furthermore, the results show that GHG emissions are reduced to 50% relative to continued coal combustion after about 12 years. The findings support the use of residue biomass for energy as an effective means for climate change mitigation. [...] Dehue points out that there is no universally applied definition of ‘carbon debt' and ‘carbon debt payback time', leading authors to apply different definitions in an inconsistent manner. A definition often referred to is by Mitchell et al., where the terms ‘carbon debt', ‘carbon debt repayment', and ‘carbon offset parity point' are introduced. However, this definition only applies to bioenergy scenarios where the source of woody biomass comes from dedicated harvest and forest regrowth is included in the modelling. In contrast, bioenergy sources from wood waste and forest residues are resources that are generated independently of a bioenergy demand. The method that is used here is in line with the typical approach to carbon debt and payback time analyses, allowing for a comparison with other studies." Madsen & Bentsen 2018, pp. 1–2.
  91. ^ "The study covers the direct emissions from the extraction and processing, transportation and the combustion of the fuels. It therefore excludes the embodied emissions in the used fuels or materials, e.g., the emissions related to produce diesel used for transportation of biomass or coal. The system boundary also exclude emissions related to distribution and use of the produced heat and electricity together with emissions that are related to the end of life of the CHP plant. Furthermore, GHG emission related to indirect effects, e.g., indirect land use change or indirect wood use change, of biomass consumption are not considered. The carbon debt concept is adopted from Mitchell et al., but applied to waste and residue resources, as e.g., demonstrated by Sathre et al. (Equation (1)). NE [equals] Ebio − (Efossil + Edecay) where NE is the annual net GHG emission to the atmosphere, Ebio is the direct GHG emissions from the bioenergy supply chain including emissions from biomass combustion, Efossil the direct GHG emissions from the counterfactual fossil supply chain, including emissions from fossil fuel combustion, and Edecay the GHG emissions from the counterfactual decay of forest residues. The payback time is determined as the time, where the time integrated NE [equals] 0. (Figure 2). The conceptual carbon emission profile corresponds to modelled profiles for the use of stumps or branches for energy. The payback time is understood as the point in time, where the bioenergy scenario starts to reduce the atmospheric GHG emissions relative to the counterfactual reference scenario. [...] In order to set up a reference scenario, the realistic alternative use of the biomass must be determined. Based on a literature review and interview with some of the biomass suppliers to the plant, the most likely alternative is decomposition on the forest floor, either as logs or as branches. [...] The total emissions per produced GJ are almost identical for both scenarios. Emissions from the biomass scenario are slightly higher by 4.4 kg CO2eq GJ−1, which represents the carbon debt, equaling 3.2% of the total emissions. [...] Emissions from processing are roughly identical for both scenarios; however, transport emissions are approximately three times higher in the reference scenario than the biomass scenario. This is in line with earlier research and is mainly attributable to longer transport distances for coal. The carbon debt incurred in the transition from coal to biomass is primarily related to the higher carbon intensity of biomass when compared to coal due to a lower carbon to oxygen ratio in biomass. Lower supply chain emissions in the biomass scenario, on the other hand, reduces the carbon debt." Madsen & Bentsen 2018, pp. 2–3, 5, 7. In simpler terms, the calculation starts with the total bioenergy-related emissions, then the coal-related emissions are subtracted (including the emissions from decaying forest residues).
  92. ^ "Buchholz et al. conducted a meta-analysis of 59 carbon debt studies, and showed that the majority (47 studies) was based on hypothetical data and only a dozen were based on field data. [...] Data from EUROSTAT show that less than 1% of electricity production in the EU comes from solid biomass fired power plants. Solid biomass is more prevalent in combined heat and power (CHP) and heat production that are plants feeding into district heating systems. 16.3% of heat production to district heating in the EU comes from solid biomass, while the majority comes from natural gas and coal. [...] Contrary to most other studies, which are based on hypothetical scenarios, this analysis benefits from the use of data from an existing power plant retrofit in northern Europe, which is considered to be representative for the use of biomass for CHP in the EU." Madsen & Bentsen 2018, pp. 1–2.
  93. ^ "The biomass that is used for energy is assumed to displace either a combination of coal-based heat boilers (efficiency 0.8946) and condensing power plants (efficiency 0.3847) or natural gas (NG)-based CHP plants [overall efficiency of 85% (LHV basis) and power-to-heat ratio of 0.6739]. The former can be said to represent a situation where existing nonintegrated coal-based heat and power generation is shut down and replaced with new biomass-based CHP, and the latter represents a situation where new biomass-based CHP is built instead of new gas-based CHP, either to replace old generation or to meet increasing energy demand. [...] As is shown in Figure 5 below, when biomass is extracted from the forest landscape to displace coal, the C emissions reduction can be immediate. As explained in section scenarios, coal was assumed to be used in a heat boiler and a condensing power plant, which together had a lower combined efficiency than the corresponding biomass CHP plant. In contrast, the fossil C displacement factor was much lower in the NG case as this fuel is less C intensive than coal and the associated technologies were assumed to have higher conversion efficiencies. [...] When coal is displaced, the net C savings are practically instantaneous for all scenarios, while they appear later when NG is displaced. NG displacement with slash (BIO1) results in net C savings earlier than when stumps (BIO2) are also used, but in the longer term harvesting stumps in addition to slash brings larger C savings thanks to the larger total biomass output for fossil fuel displacement. [...] As can be seen, when NG is chosen as reference fuel, these specific forest bioenergy cases are associated with a small initial warming before the effect of avoided fossil C emissions starts to dominate (note the differences in scales in the magnified diagrams). When coal is chosen as the reference fuel instead, these forest bioenergy scenarios are associated with a net cooling from the start." Cintas et al. 2015, pp. 356–362.
  94. ^ When the reference scenario is oil or natural gas, carbon parity time increases to 7 and 16 years, respectively. Zanchi, Pena & Bird 2011, p. 767, figure 5.
  95. ^ Zetterberg & Chen found that "it takes 3–7 years before branches and tops and 17–18 years before stumps have lower total emissions than fossil gas." See Zetterberg & Chen 2014, p. 791. Cintas et al. found parity times of approximately 20 years for slash and 40 years when including stumps, see Cintas et al. 2015, p. 359, figure 5. Repo et al. found that the bioenergy practice "[...] had to be carried out for 22 (stumps) or four (branches) years until the total emissions dropped below the emissions of natural gas." See Repo, Tuomi & Liski 2010, p. 107. Zanchi et al. found that "in the cases where bioenergy substitutes for oil and natural gas", parity time takes "7 and 16 years respectively." See Zanchi, Pena & Bird 2011, p. 767.
  96. ^ "[...] CHP is an alternative for a wide range of production processes as the temperature and pressure of delivered steam can be adjusted to the specific requirements of industrial processes. There are other renewable alternatives for process heat generation (e.g., solar thermal, heat pumps or geothermal technologies). These are, however, either more costly or their deployment is constrained by the maximum temperature of the steam they can deliver. Therefore, biomass CHP plays a critical role for the manufacturing industry to raise its renewable energy share." IRENA 2014, p. 24.
  97. ^ See Holmgren 2021, pp. 10–26. The climate mitigation effect of the established forestry practice was determined by counting the specific annual changes over 10 and 40 years in this scenario's aggregated carbon pools. First, the net annual carbon increase in the national forest carbon pool was calculated: Annual total forest growth minus natural losses minus harvest removals (harvest removals includes both stemwood and residues). Subsequently, carbon used for harvested wood products, and the residues that is left in the forest but not yet decayed, are added to their respective pools (the HWP pool and the dead biomass pool). Then the carbon emitted from the decaying residues (including stumps, roots and branches) is subtracted. Finally, the displaced fossil carbon is added to the displaced fossil carbon pool (the fossil carbon is seen as "held back" in the fossil carbon reservoirs underground since forest biogenic carbon, which is already counted as emissions at harvest, has been used in its place.) As mentioned, and unlike in other studies, the study boundaries here included fossil fuel displacment effects, including from "[...] solid wood products and fibre products, representing normal wood utilization in Sweden where different parts of the tree is used for either of these product categories [...]." A displacement factor of 0.78 tonne fossil carbon displaced per 1 tonne biogenic carbon produced (which "[...] corresponds to displacement effects for the integrated mix of solid wood products, fiber products and bioenergy applied in several studies [...]") (p. 12) is used for both harvested wood products and bioenergy combined, and the forest residues half-life decay rate is set to 10 years (p. 13). In the two forest protection scenarios, the forest increases by 64% and 91% over 40 years respectively, while the actual forestry practice only achieve an increase of 44% (p. 17). However, since the forest in the forest protection scenarios is left to itself, the natural carbon losses (pests, fires etc.) increases by 4% and 6% for the two scenarios, respectively (p. 14). As mentioned above, substantial emissions are caused when the national forest carbon products and energy infrastructure is converted to fossil carbon products and energy infrastructure. The difference compared to the actual forestry practice over these 40 years was calculated by: 1.) Adding the extra amount of carbon that would have been absorbed from the atmospheric carbon pool and stored in the protected forest pool, compared to the amount of carbon stored in the actually managed forest. 2.) Subtracting the projected loss of carbon in the harvested wood products pool during the same time period (since each year some harvested wood products would be cycled out of this carbon pool and into the atmospheric carbon pool because of combustion or rotting when reaching end-of-life, while no new harvested wood products would have entered this pool. 3.) Subtracting the substantial amount of fossil carbon that would have to be moved from the underground fossil reservoirs and into fossil carbon products and energy carriers, in order to a.) replace the forest carbon products and energy carriers, and b.) convert the national forest carbon products and energy infrastructure into a fossil carbon products and energy infrastructure. These subtractions are highest at the beginning of the 40-year period, and (together with the carbon absorption going on elsewhere in the forest) more than compensate for the carbon debt caused by harvest-related carbon emissions (p. 14-17).
  98. ^ Recalculated from Holmgren's 0.5 tonne CO2e per m3 (Holmgren 2021, p. 12), 40% spruce and 40% pine in Swedish forests (Swedish Wood, p. Fig. 5), and 320 vs. 390 kg dry mass per m3 for spruce and pine, respectively. Here, an average value of 350 kg/m3 was assumed, together with 50% carbon content, and 3.67 kg CO2e per kg carbon. The actual forestry practice mitigated in total 3.54 Gt CO2e, with the displacement-specific mitigation effects estimated at 1.84 Gt CO2e. If the displacement effects were left out of the calculation, one of the forest protection scenarios (the one with only a 4% increase in natural losses (e.g. wildfires and diseases), had more carbon stored in the forest after 10 and 40 years compared to the actual forestry practice (0.74 vs. 0.55 and 2.41 vs. 1.84 Gt CO2e, respectively.) The other forest protection scenario (the one with a 6% increase in natural losses) had less carbon absorbed in the forest compared to the actual forestry practice after 40 years (1.56 vs. 1.84 Gt CO2e) but more after 10 years (0.64 vs. 0.55 Gt CO2e.) In addition to the forest protection scenarios, the author also included a 10% reduced harvest scenario, which performed similar to the actual forestry scenario.
  99. ^ Miner et al. writes that in the eastern parts of the USA, bioenergy from forest residues that otherwise would have been left to decay naturally, typically accomplishes net GHG benefits within a decade when displacing coal-based electricity, and within two decades when displacing natural gas-based electricity. Miner et al. 2014, p. 599.
  100. ^ See Hanssen et al. 2017, pp. 1407–1410, and table S1 in the supporting information document, link available at the bottom of the article.
  101. ^ "The studies analyzed report payback times in the range of 0 – 74 years for harvest residues. The main factors affecting these values are mostly similar to the ones described for stemwood. The ratio of fossil carbon displacement is the main parameter. If the residues are used with high efficiency to displace coal (such as in co-firing), the payback times are rather short, if any. In case the residues are heavily processed to produce liquid biofuel the payback time increases dramatically. Also the size of the residue plays a relevant role, as well as the geographic and local conditions that influence the bacterial decomposition rates. Wood from thinnings may, to some extent, be assimilated to harvest residues (especially pre-commercial thinnings). If not collected for bioenergy it would be left in the forest to decay, or combusted at roadside. On the other hand, depending on the wood quality, the use of thinnings wood for bioenergy may compete with other uses, such as pulp and paper or engineered wood. Salvage loggings can also be assimilated to harvest residues. Damaged, dying or dead trees affected by injurious agents, such as wind or ice storms or the spread of invasive epidemic forest pathogens, insects and diseases would remain in the forest and decay or combusted at roadside. Wood removed for prescribed fire hazard control as well can be considered residual wood." JRC 2014, pp. 42–43, table 3. Note that the JRC use the term "payback time" in the sense of "parity time" as defined in Carbon accounting principles above. See JRC 2014, p. 16.
  102. ^ a b "Total GHG emission per energy content from the production of energy from harvest residues. Norway spruce stumps (diameter 30 cm), young stand delimbed thinning wood (diameter 10 cm) and branches (diameter 2 cm). Emissions over a 100 year period after start of the practice in Northern Finland (dotted line) and Southern Finland (solid line) and the entire fuel cycle emissions of some fossil fuels. The total emission estimates of forest bioenergy include emissions resulting from the changes in carbon stocks and the emissions from production chain including collecting, transporting, chipping and combusting the forest residues." JRC 2014, p. 42.
  103. ^ "Three systems were designed to represent three different power production scales (see Figure 7.15): i) large-scale power plant of 80 MWel. fuelled with wood pellets from forest logging residues (FRel); ii) medium-scale power plant of 15 MWel. fuelled with cereal straw bales (STel); iii) small-scale internal combustion engine of 300 kWel. fuelled with biogas produced from anaerobic digestion of cattle slurry, employing an open or gas-tight tank for digestate storage (Biogas OD/CD). [...] The results are explicit in time, Near-Term Climate Forcers (i.e. ozone precursors and aerosols) are included, an instantaneous, absolute climate metric is used and biogenic-C flows are explicitly accounted for (see Table 7.1 for all methodological details). These results reveal additional details compared to the analysis in section 7.3.1. For instance, they indicate with clarity that power generation from cereal straws and cattle slurry can provide, by 2100, global warming mitigation compared to the current European electricity mix in all of the systems and scenarios considered. Power generation from forest logging residues is an effective mitigation solution only in situations in which the decay rates of the residues on the forest floor were above 5.2% /yr. Even with faster-decomposing feedstocks, bioenergy temporarily causes a climate change worsening compared to the fossil system. Strategies for bioenergy deployment should thus take into account the potential increase in global warming rate and temporary increase in temperature anomaly. Further details on the methodology and on the results of the case studies can be found in Giuntoli et al. (2016)." Camia et al. 2018, pp. 100–104. The supporting documentation show that the "residues" category includes not only small-diameter residues like branches, but also logs and stumps. See JRC 2018 and JRC 2015, p. 92.
  104. ^ The JRC here actually use the term "payback time", but define this term in the same way the term "parity time" is defined above: "[...] [A]t the payback time the fossil fuel parity is reached (i.e. the bioenergy system and the fossil counterfactual have emitted the same amount of CO2 in the atmosphere). After the fossil fuel parity time, the bioenergy system starts to provide CO2 savings." See JRC 2014, p. 16. Normally, the time it takes for a bioenergy scenario to store as much carbon as a no-bioenergy scenario (i.e. when their net emission level is the same) is known as the carbon parity time: "Eventually carbon levels in the forest return to the level at which they would have been if they had been left unharvested. (Some of the literature employs the term ‘carbon payback period' to describe this longer period, but it is more commonly used to mean the time to parity with fossil fuels; this meaning is used in this paper.)" Chatham House 2017, p. 27.
  105. ^ In the JRC's chart above, landscape level carbon accounting is assumed for this scenario. However, the original research article does not actually say which accounting method is used, only that biomass is sourced "[...] from 5.25 million hectares within the GLSL forest region in Ontario." McKechnie et al. 2010, p. 791.
  106. ^ Lamers & Junginger argue that payback times are mainly determined by plant growth rates, i.e. the forest biome (e.g. climate zone), tree species, site productivity and management. Parity times are primarily influenced by the choice and construction of the reference scenario and fossil carbon displacement efficiencies. The authors write that using "[...] small residual biomass (harvesting/processing), deadwood from highly insect-infected sites, or new plantations on highly productive or marginal land offers (almost) immediate net carbon benefits." The actual climate mitigation potential however is determined by the effectiveness of the fossil fuel displacement. Lamers & Junginger 2013, p. 373.
  107. ^ Stemwood definition: "Wood from the main part of a tree; not from the branches, stump, or root. Salvage logging wood, thinnings, landscape care wood and other similar sources of wood that can be considered as by-products/residues are not included in this category of wood." See JRC 2014, p. 10.
  108. ^ The JRC's example here is from a UK coniferous forest study: "In the case wood is used for bioenergy only the total emissions of the bioenergy system would be −5.5 tCO2/ha*y (5.1 tCO2/ha*y from displacement of fossil fuel and 0.4 tCO2/ha*y due to the sink of the forest system), that, compared to the missed growth of the forest (14 tCO2/ha*y) [14 tonnes CO2 per hectare per year] results in net emissions of 8.5 tCO2/ha*y. This result shows that, in a 40 years timeframe, CO2 emissions are lower for the suspended management forest than for the forest managed for bioenergy only. The second case is if the wood is used for materials as well as bioenergy (bioenergy from residues). In this case the total emissions of the material and bioenergy system would be −22.8 tCO2/ha*y, (-6 tCO2/ha*y in carbon stock of the forest and products and −16.8 tCO2/ha*y from displacement of products) to which the missed growth of the forest has to be subtracted (14 tCO2/ha*y) resulting in net GHG savings of 8.8 tCO2/ha*y. Therefore managing the forest for products determines higher GHG savings than suspending the management." JRC 2014, p. 26.
  109. ^ "In fact, wood products have multiple climate mitigation benefits: they increase the anthropogenic carbon pools, they are often much less GHG and energy intensive than similar materials of fossil origin (e.g. concrete, metals etc.) and, finally, bioenergy can be obtained from these products at the end of life to replace fossil fuels and guarantee additional substitution. [...] [W]hen wood is used in a cascade utilization, then climate mitigation can be achieved in much shorter times than when wood is used purely for energy. Moreover, with the proper measures (longer storage, substitution of C-intensive materials and fossil fuels), the payback time can be even shortened to zero, as compared to centuries indicated for energy-only use. Studies that fail to consider the wood for material displacement may come to misleading conclusions." JRC 2014, pp. 59, 61. Note that the JRC use the term "payback time" in the sense of "parity time" as defined in Carbon accounting principles above. See JRC 2014, p. 16.
  110. ^ "The reviewed studies indicate that the use of stemwood from dedicated harvest for bioenergy would cause an actual increase in GHG emissions compared to those from fossil fuels in the short-and medium term (decades), while it may start to generate GHG savings only in the long-term (several decades to centuries), provided that the initial assumptions remain valid. The harvest of stemwood for bioenergy purposes is not common today, however, it is becoming a more common practice that is expected to expand in the future. [...] The GHG saving can be immediate if in the counterfactual scenario the wood would be burnt at roadside. This feedstock is expected to provide most of the additional increment of biomass for bioenergy by 2020. Also in the case of new plantations on agricultural or grazing land the GHG savings can be immediate (in absence of iLUC)." JRC 2014, pp. 16–17.
  111. ^ "The initial landscape conditions and land-use history are also fundamental in determining the amount of time required for forests to recover the initial additional emissions of the bioenergy system over the fossil one. While Recently Disturbed and Old-Growth landscapes required very long payback times, Post- Agricultural and Rotation Harvest landscapes were capable of recovering the additional emission in relatively short time periods, often within 1 year [Mitchell 2012]. This is a conclusion also of Zanchi et al. [Zanchi 2011]. The reason is that planting a short-rotation forest on unused agricultural land does not start with high carbon stocks so causes an increase in average carbon stocks." JRC 2014, pp. 40–41. Note that the JRC use the term "payback time" in the sense of "parity time" as defined in Carbon accounting principles above. See JRC 2014, p. 16.
  112. ^ a b "The source of forest biomass is a key determinant of climate change effects of bioenergy (Matthews et al., 2018). Concerns have been raised that bioenergy demand could lead to widespread harvest of forests solely for bioenergy, causing large GHG emissions and forgone carbon sequestration (Brack, 2017; Norton et al., 2019; Searchinger et al., 2018). However, long-rotation forests are generally not harvested for bioenergy products alone: Biomass for bioenergy is usually a by-product of sawlog and pulpwood production for material applications (Dale et al., 2017; Ghaffariyan et al., 2017; Spinelli et al., 2019; Figure 1). Logs that meet quality requirements are used to produce high-value products such as sawnwood and engineered wood products such as cross laminated timber, which can substitute for more carbon-intensive building materials such as concrete, steel and aluminium (Leskinen et al., 2018). Residues from forestry operations (tops, branches, irregular and damaged stem sections, thinnings) and wood processing residues (e.g. sawdust, bark, black liquor) are used for bioenergy (Kittler et al., 2020), including to provide process heat in the forest industry (Hassan et al., 2019). These biomass sources have high likelihood of reducing net GHG emissions when substituting fossil fuels (Hanssen et al., 2017; Matthews et al., 2018), and their use for bioenergy enhances the climate change mitigation value of forests managed for wood production (Cintas, Berndes, Hansson, et al., 2017; Gustavsson et al., 2015, 2021; Schulze et al., 2020; Ximenes et al., 2012). Part of the forest biomass used for bioenergy consists of roundwood (also referred to as stemwood), such as small stems from forest thinning. For example, roundwood was estimated to contribute around 20% of the feedstock used for densified wood pellets in the United States in 2018 (US EIA, 2019)." Cowie et al. 2021, pp. 1215–1216.
  113. ^ Hektor write that supply chain emissions for biomass are "[...] in most cases less than half of the corresponding emissions from fossil fuels." Hektor, Backéus & Andersson 2016, p. 4.
  114. ^ "There is a large variability in the results of forest bioenergy fossil fuel parity times calculations. This large variability depends on the many different characteristics of the systems compared and non-consistent modeling assumptions and approaches. The first, most important assumption is on the fossil fuel displaced. Then, concerning both the bioenergy system and the reference fossil system the following characteristics heavily impact the results: efficiency in the final use, future growth rate of the forest, the frequency and intensity of biomass harvests, the initial forest carbon stock, the forest management practices assumed." JRC 2014, p. 17.
  115. ^ "The reviewed studies show payback times ranging from 0 to almost 500 years. This large variability depends on the many different characteristics and assumptions on both the forest/bioenergy system and the reference fossil system. The most straight forward relation is with the fossil fuel used as a reference in the fossil scenario. Obviously, the more carbon intensive the fossil fuel replaced is, the shorter is the payback time. [...] A further correlation exists with the efficiency of the biomass utilization. The less efficient the bioenergy system is, the longer are the payback times. In case of electricity production, in biomass only plants, the electrical efficiency of biomass conversion is lower than the fossil, while thermal conversion energetic efficiency is similar for biomass and fossil fuels. In co-firing plants, biomass generally achieves the same efficiency as coal. An intensive processing, such as for liquid biofuel substitution via lignocellulosic ethanol, causes much longer payback times because of the loss of energy in the biofuels production (about half of the energy content of the biomass is lost in the processing [...]. The slower the forest growth rate is, the longer is the payback time. The forest growth rate depends on the latitude (boreal, temperate, tropical), but also on specific characteristics of the trees species, the microclimate and the soil fertility." JRC 2014, p. 34. Note that the JRC use the term "payback time" in the sense of "parity time" as defined in Carbon accounting principles above. See JRC 2014, p. 16.
  116. ^ See Hanssen et al. 2017: Figure S3 at page 3 in the Supporting Information document, link to document available at the bottom of the article.)
  117. ^ "The modeller assigns independent inputs to specific parameters, called here decision variables, thus producing a range of results deriving from different configurations of the same supply-chains associated to a single commodity. For instance, the distance at which biomass resources are transported influences significantly the overall impact of bio-based commodities. Conversion efficiencies can be both a source of variability (e.g. range of possible efficiencies for a single engine) and important decision variables (e.g. modelling different conversion technologies).[...] Another source of variation is linked to methodological choices in each assessment (e.g. allocation basis, background processes, etc.); for the benefit of the users, critical methodological choices are reported explicitly in the database. [...] The range of results associated with each pathway is dependent on several factors of variability:1. Transport distances of the feedstock or of the final product, 2. End-use conversion efficiencies, 3. Utilities, 4. Process characteristics, 5. Background data, 6. LCA Methodology. The GHG emissions reported in this work, therefore, should not be interpreted as a universal property associated to the product/commodity, since the changes in methodological choices and background data can largely influence the absolute value of GHG emission. However, the relative benchmarking among similar products and commodities can provide important information. The results [...] show that, most bioenergy pathways emit less GHG along their supply chain than fossil fuel pathways. However, the various pathways can achieve very different GHG emission levels. For instance, using dairy cattle slurry to produce biogas or biomethane can guarantee the highest GHG emissions mitigation due to the emission credits assigned for the avoided methane emissions associated to the use of raw manure as organic fertilizer (Giuntoli et al., 2017). In order for commodities to achieve the highest ambitions in terms of GHG emission savings (>85% savings), generally, high resource efficiency along the supply chain is required, and in particular: 1. Optimized logistics with short or efficient transport options (e.g. biomass feedstock is traded within EU neighbouring countries), 2. High efficiency of final conversion, 3. Use of renewable energy sources to supply process-heat and process-electricity, 4. Optimal process design (e.g. digestate residue from anaerobic digestion is stored in gas-tight tanks), 5. Use of wastes, residual or low-input feedstocks, 6. Assignment of credits to co-products (substitution method). Nonetheless, the results show that even with current technologies, significant optimizations are available to reduce the impacts of each supply chain (lower boundary of floating columns)." Camia et al. 2018, pp. 95, 98.
  118. ^ "In addition to the EU, the US has also amended its Renewables Fuel Standard 1 (RFS1) to include minimum life-cycle GHG emissions in the RFS2. RFS2 distinguishes between the production of conventional and advanced biofuels, which are defined based on their GHG abatement potential. All biofuels which can save up to 20% GHG in their life cycle compared to the petroleumbased equivalents are categorised as conventional. Conventional biofuel production is limited to 15 billion gallons to 2022. Advanced biofuels production accounts for the remainder 21 billion gallons. A biofuel can be considered advanced if it saves at least 50% GHG. Cellulosic biofuels require a 60% GHG emission reduction compared to the petrochemical equivalent (EPA, 2012). These emissions include ILUC GHG emissions." IRENA 2014, p. 47.
  119. ^ The estimates are for the "medium case" considered (case 2a); a pellet mill that uses wood for processing heat, but sources electricity from the grid. Estimates (for forest residue based pellets) reduce to 50–58% when fossil fuels is used for processing heat (case 1), but increase to 84-92% when electricity is sourced from a CHP biomass power plant (case 3a). See European Parliament, Council of the European Union 2018, p. Annex VI.
  120. ^ "[...] GHG emission reductions of wood-pellet electricity compared to fossil EU grid electricity are 71% (for small roundwood and harvest residues), 69% (for commercial thinnings) or 65% (for mill residues), as shown in more detail in Fig. S3. The GHG reduction percentage of wood-pellet electricity from mill residues was [...] 75% [...]." Hanssen et al. 2017, pp. 1415–1416.
  121. ^ See Hanssen et al. 2017: Figure S3 and Table S1 at pages 3–4 in the Supporting Information document, link to document available at the bottom of the article.)
  122. ^ "It is commonly perceived that bioenergy supply chain emissions are substantial, particularly when biomass is transported internationally, and could negate the climate benefits of fossil fuel substitution. However, fossil energy use along domestic forest biomass supply chains, from harvest, processing and transport, is generally small compared to the energy content of the bioenergy product and, with efficient handling and shipping, even when traded internationally [...]. The European Commission's Joint Research Centre determined that shipping pellets between North America and Europe increases supply chain emissions by 3–6 g CO2/MJ, from around 3–15 g CO2/MJ for wood chips or pellets dried using bioenergy and transported 500 km by truck (Giuntoli et al., 2017). For context, the EU average emission factors for hard coal are 96 and 16 g CO2/MJ for combustion and supply respectively (Giuntoli et al., 2017). This underscores the importance of assessing actual supply chains. For example, the international pellet supply chain between the southeast United States and Europe has been intentionally designed to minimize trucking and associated handling costs, with pellet mills and large end users such as power plants located near rail lines, waterways and ports, thereby minimizing transport emissions and increasing net climate benefits (Dwivedi et al., 2014; Favero et al., 2020; Kline et al., 2021)."Cowie et al. 2021, p. 1219.
  123. ^ "In 2015 the net imports (i.e. imports minus exports) of wood pellets amounted to 3% of the total wood for energy mix (around 16 Mm3). The UK accounted for 97% of EU net imports of wood pellets (JFSQ). The United States was by far the most important source of EU wood pellets imports, with a 77% share (United Nations, 2020)." Camia et al. 2021, pp. 7, 42.
  124. ^ "Following the findings of the COST Action EuroCoppice (FP1301)17, coppice forests cover more than 19 Mha in the EU, corresponding to about 12% of the total forest area in 2015. The large majority (17 Mha) are in the EU Mediterranean countries, where about 32% of the forest area is reported as coppice (Unrau et al. 2018)." Camia et al. 2021, p. 33.
  125. ^ "The initial landscape conditions and land-use history are also fundamental in determining the amount of time required for forests to recover the initial additional emissions of the bioenergy system over the fossil one. While Recently Disturbed and Old-Growth landscapes required very long payback times, Post- Agricultural and Rotation Harvest landscapes were capable of recovering the additional emission in relatively short time periods, often within 1 year [Mitchell 2012]. This is a conclusion also of Zanchi et al. [Zanchi 2011]. The reason is that planting a short-rotation forest on unused agricultural land does not start with high carbon stocks so causes an increase in average carbon stocks." JRC 2014, pp. 40–41. Note that the JRC use the term "payback time" in the sense of "parity time" as defined in Carbon accounting principles above. See JRC 2014, p. 16. Likewise, Liu et al. found an average carbon payback time of 0.97 years for miscanthus planted on marginal, eroded soils in the Loess Plateau in China. Liu et al. 2016, p. 1.
  126. ^ "If the total biogenic carbon released during biomass decay and/or combustion is sequestered, the system continues to be in balance. As a result, the amount of CO2 in the atmosphere does not increase. [...] When short-rotation energy crops or agricultural residues are used as fuel, they result in a balanced carbon cycle because they grow/renew themselves annually. In comparison, the rapid expansion of palm oil plantations in Indonesia and Malaysia, for example, has led to major problems associated with bioenergy. Logging rain forests or peat bogs for palm oil plantations has a negative effect. Plantations which were partly built on carbon-rich peat soils in the region resulted in drainage. The subsequent oxidation of peat and natural or anthropogenic fires results in substantial CO2 emissions. Peat digging also has a negative effect, which results in an increase in CO2 emissions in the atmosphere." IRENA 2014, p. 45.
  127. ^ "Perennial Miscanthus has energy output/input ratios 10 times higher (47.3 ± 2.2) than annual crops used for energy (4.7 ± 0.2 to 5.5 ± 0.2), and the total carbon cost of energy production (1.12 g CO2-C eq. MJ−1) is 20–30 times lower than fossil fuels." McCalmont et al. 2017, p. 489.
  128. ^ "The results in Fig. 3c show most of the land in the UK could produce Miscanthus biomass with a carbon index that is substantially lower, at 1.12 g CO2-C equivalent per MJ energy in the furnace, than coal (33), oil (22), LNG (21), Russian gas (20), and North Sea gas (16) (Bond et al., 2014), thus offering large potential GHG savings over comparable fuels even after accounting for variations in their specific energy contents. Felten et al. (2013) found Miscanthus energy production (from propagation to final conversion) to offer far higher potential GHG savings per unit land area when compared to other bioenergy systems. They found Miscanthus (chips for domestic heating) saved 22.3 ± 0.13 Mg [tonnes] CO2-eq ha−1 yr−1 [CO2 equivalents per hectare per year] compared to rapeseed (biodiesel) at 3.2 ± 0.38 and maize (biomass, electricity, and thermal) at 6.3 ± 0.56." McCalmont et al. 2017, p. 500.
  129. ^ "The costs and life-cycle assessment of seven miscanthus-based value chains, including small- and large-scale heat and power, ethanol, biogas, and insulation material production, revealed GHG-emission- and fossil-energy-saving potentials of up to 30.6 t CO2eq C ha−1 y−1 and 429 GJ ha−1 y−1, respectively. Transport distance was identified as an important cost factor. Negative carbon mitigation costs of –78€ t−1 CO2eq C were recorded for local biomass use. The OPTIMISC results demonstrate the potential of miscanthus as a crop for marginal sites and provide information and technologies for the commercial implementation of miscanthus-based value chains. [...] The overall biomass transport distance was assumed to be 400 km when bales were transported to the bioethanol plant or to the plant producing insulation material as well as in the value chain 'Combined heat and power (CHP) bales.' For the value chains 'CHP pellets' and 'Heat pellets' the bales were transported 100 km to a pelleting plant and from there the pellets were transported 400 km to the power plants. The average farm-to-field distance was assumed to be 2 km. This transport distance is also assumed for the value chain 'heat chips' in which a utilization of the chips as a biomass fuel on the producing farm was assumed. Because of the higher biomass requirements of the biogas plant an average transport distance of 15 km from field to plant was assumed." Lewandowski et al. 2016, pp. 2, 7.
  130. ^ "Any soil disturbance, such as ploughing and cultivation, is likely to result in short-term respiration losses of soil organic carbon, decomposed by stimulated soil microbe populations (Cheng, 2009; Kuzyakov, 2010). Annual disturbance under arable cropping repeats this year after year resulting in reduced SOC levels. Perennial agricultural systems, such as grassland, have time to replace their infrequent disturbance losses which can result in higher steady-state soil carbon contents (Gelfand et al., 2011; Zenone et al., 2013)." McCalmont et al. 2017, p. 493.
  131. ^ "Tillage breaks apart soil aggregates which, among other functions, are thought to inhibit soil bacteria, fungi and other microbes from consuming and decomposing SOM (Grandy and Neff 2008). Aggregates reduce microbial access to organic matter by restricting physical access to mineral-stabilised organic compounds as well as reducing oxygen availability (Cotrufo et al. 2015; Lehmann and Kleber 2015). When soil aggregates are broken open with tillage in the conversion of native ecosystems to agriculture, microbial consumption of SOC and subsequent respiration of CO2 increase dramatically, reducing soil carbon stocks (Grandy and Robertson 2006; Grandy and Neff 2008)." IPCC 2019a, p. 393.
  132. ^ "A systematic review and meta-analysis were used to assess the current state of knowledge and quantify the effects of land use change (LUC) to second generation (2G), non-food bioenergy crops on soil organic carbon (SOC) and greenhouse gas (GHG) emissions of relevance to temperate zone agriculture. Following analysis from 138 original studies, transitions from arable to short rotation coppice (SRC, poplar or willow) or perennial grasses (mostly Miscanthus or switchgrass) resulted in increased SOC (+5.0 ± 7.8% and +25.7 ± 6.7% respectively)." Harris, Spake & Taylor 2015, p. 27.
  133. ^ "[...] it seems likely that arable land converted to Miscanthus will sequester soil carbon; of the 14 comparisons, 11 showed overall increases in SOC [soil organic carbon] over their total sample depths with suggested accumulation rates ranging from 0.42 to 3.8 Mg C ha−1 yr−1. Only three arable comparisons showed lower SOC stocks under Miscanthus, and these suggested insignificant losses between 0.1 and 0.26 Mg ha−1 yr−1." McCalmont et al. 2017, p. 493.
  134. ^ "The correlation between plantation age and SOC can be seen in Fig. 6, [...] the trendline suggests a net accumulation rate of 1.84 Mg C ha−1 yr−1 with similar levels to grassland at equilibrium." McCalmont et al. 2017, p. 496.
  135. ^ Given the EU average peak yield of 22 tonnes dry matter per hectare per year (approximately 15 tonnes during spring harvest). See Anderson et al. 2014, p. 79. 15 tonnes also explicitly quoted as the mean spring yield in Germany, see Felten & Emmerling 2012, p. 662. 48% carbon content; see Kahle et al. 2001, table 3, page 176.
  136. ^ a b See Whitaker et al. 2018, p. 156, Fig. 3, or Fig. 3 in Appendix S1 (Supplementary Materials)
  137. ^ "The environmental costs and benefits of bioenergy have been the subject of significant debate, particularly for first‐generation biofuels produced from food (e.g. grain and oil seed). Studies have reported life‐cycle GHG savings ranging from an 86% reduction to a 93% increase in GHG emissions compared with fossil fuels (Searchinger et al., 2008; Davis et al., 2009; Liska et al., 2009; Whitaker et al., 2010). In addition, concerns have been raised that N2O emissions from biofuel feedstock cultivation could have been underestimated (Crutzen et al., 2008; Smith & Searchinger, 2012) and that expansion of feedstock cultivation on agricultural land might displace food production onto land with high carbon stocks or high conservation value (i.e. iLUC) creating a carbon debt which could take decades to repay (Fargione et al., 2008). Other studies have shown that direct nitrogen‐related emissions from annual crop feedstocks can be mitigated through optimized management practices (Davis et al., 2013) or that payback times are less significant than proposed (Mello et al., 2014). However, there are still significant concerns over the impacts of iLUC, despite policy developments aimed at reducing the risk of iLUC occurring (Ahlgren & Di Lucia, 2014; Del Grosso et al., 2014)." Whitaker et al. 2018, p. 151.
  138. ^ "The impact of growing bioenergy and biofuel feedstock crops has been of particular concern, with some suggesting the greenhouse gas (GHG) balance of food crops used for ethanol and biodiesel may be no better or worse than fossil fuels (Fargione et al., 2008; Searchinger et al., 2008). This is controversial, as the allocation of GHG emissions to the management and the use of coproducts can have a large effect on the total carbon footprint of resulting bioenergy products (Whitaker et al., 2010; Davis et al., 2013). The potential consequences of land use change (LUC) to bioenergy on GHG balance through food crop displacement or 'indirect' land use change (iLUC) are also an important consideration (Searchinger et al., 2008)." Milner et al. 2016, pp. 317–318.
  139. ^ "While the initial premise regarding bioenergy was that carbon recently captured from the atmosphere into plants would deliver an immediate reduction in GHG emission from fossil fuel use, the reality proved less straightforward. Studies suggested that GHG emission from energy crop production and land-use change might outweigh any CO2 mitigation (Searchinger et al., 2008; Lange, 2011). Nitrous oxide (N2O) production, with its powerful global warming potential (GWP), could be a significant factor in offsetting CO2 gains (Crutzen et al., 2008) as well as possible acidification and eutrophication of the surrounding environment (Kim & Dale, 2005). However, not all biomass feedstocks are equal, and most studies critical of bioenergy production are concerned with biofuels produced from annual food crops at high fertilizer cost, sometimes using land cleared from natural ecosystems or in direct competition with food production (Naik et al., 2010). Dedicated perennial energy crops, produced on existing, lower grade, agricultural land, offer a sustainable alternative with significant savings in greenhouse gas emissions and soil carbon sequestration when produced with appropriate management (Crutzen et al., 2008; Hastings et al., 2008, 2012; Cherubini et al., 2009; Dondini et al., 2009a; Don et al., 2012; Zatta et al., 2014; Richter et al., 2015)." McCalmont et al. 2017, p. 490.
  140. ^ "Significant reductions in GHG emissions have been demonstrated in many LCA studies across a range of bioenergy technologies and scales (Thornley et al., 2009, 2015). The most significant reductions have been noted for heat and power cases. However, some other studies (particularly on transport fuels) have indicated the opposite, that is that bioenergy systems can increase GHG emissions (Smith & Searchinger, 2012) or fail to achieve increasingly stringent GHG savings thresholds. A number of factors drive this variability in calculated savings, but we know that where significant reductions are not achieved or wide variability is reported there is often associated data uncertainty or variations in the LCA methodology applied (Rowe et al., 2011). For example, data uncertainty in soil carbon stock change following LUC has been shown to significantly influence the GHG intensity of biofuel production pathways (Fig. 3), whilst the shorter term radiative forcing impact of black carbon particles from the combustion of biomass and biofuels also represents significant data uncertainty (Bond et al., 2013)." Whitaker et al. 2018, pp. 156–157.
  141. ^ "Miscanthus is one of the very few crops worldwide that reaches true CO2 neutrality and may function as a CO2 sink. [...] Related to the combustion of fuel oil, the direct and indirect greenhouse gas emissions can be reduced by a minimum of 96% through the combustion of Miscanthus straw [...]. Due to the C‐sequestration [carbon storage] during Miscanthus growth, this results in a CO2‐eq mitigation potential of 117%". Emmerling & Pude 2017, pp. 275–276. Emmerling & Pude paraphrase Felten et al. 2013. For yield, carbon sequestration and GHG calculations, see Felten et al. 2013, pp. 160, 166, 168.
  142. ^ "Whilst these values represent the extremes, they demonstrate that site selection for bioenergy crop cultivation can make the difference between large GHG [greenhouse gas] savings or losses, shifting life‐cycle GHG emissions above or below mandated thresholds. Reducing uncertainties in ∆C [carbon increase or decrease] following LUC [land use change] is therefore more important than refining N2O [nitrous oxide] emission estimates (Berhongaray et al., 2017). Knowledge on initial soil carbon stocks could improve GHG savings achieved through targeted deployment of perennial bioenergy crops on low carbon soils (see section 2). [...] The assumption that annual cropland provides greater potential for soil carbon sequestration than grassland appears to be over‐simplistic, but there is an opportunity to improve predictions of soil carbon sequestration potential using information on the initial soil carbon stock as a stronger predictor of ∆C [change in carbon amount] than prior land use." Whitaker et al. 2018, pp. 156, 160.
  143. ^ "Fig. 3 confirmed either no change or a gain of SOC [soil organic carbon] (positive) through planting Miscanthus on arable land across England and Wales and only a loss of SOC (negative) in parts of Scotland. The total annual SOC change across GB in the transition from arable to Miscanthus if all nonconstrained land was planted with would be 3.3 Tg C yr−1 [3.3 million tonnes carbon per year]. The mean changes for SOC for the different land uses were all positive when histosols were excluded, with improved grasslands yielding the highest Mg C ha−1 yr−1 [tonnes carbon per hectare per year] at 1.49, followed by arable lands at 1.28 and forest at 1. Separating this SOC change by original land use (Fig. 4) reveals that there are large regions of improved grasslands which, if planted with bioenergy crops, are predicted to result in an increase in SOC. A similar result was found when considering the transition from arable land; however for central eastern England, there was a predicted neutral effect on SOC. Scotland, however, is predicted to have a decrease for all land uses, particularly for woodland due mainly to higher SOC and lower Miscanthus yields and hence less input." Milner et al. 2016, p. 123.
  144. ^ "In summary, we have quantified the impacts of LUC [land use change] to bioenergy cropping on SOC [soil organic carbon] and GHG balance. This has identified LUC from arable, in general to lead to increased SOC, with LUC from forests to be associated with reduced SOC and enhanced GHG emissions. Grasslands are highly variable and uncertain in their response to LUC to bioenergy and given their widespread occurrence across the temperate landscape, they remain a cause for concern and one of the main areas where future research efforts should be focussed." Harris, Spake & Taylor 2015, pp. 33, 37 The authors note however that "[t]he average time since transition across all studies was 5.5 years (Xmax 16, Xmin 1) for SOC" and that "[...] the majority of studies considered SOC at the 0–30 cm profile only [...]." Harris, Spake & Taylor 2015, pp. 29–30. Low carbon accumulation rates for young plantations are to be expected, because of accelerated carbon decay at the time of planting (due to soil aeration), and relatively low mean carbon input to the soil during the establishment phase (2-3 years).
  145. ^ "In 2015, a workshop was convened with researchers, policymakers and industry/business representatives from the UK, EU and internationally. Outcomes from global research on bioenergy land‐use change were compared to identify areas of consensus, key uncertainties, and research priorities. [...] Our analysis suggests that the direct impacts of dedicated perennial bioenergy crops on soil carbon and nitrous oxide are increasingly well understood and are often consistent with significant life cycle GHG mitigation from bioenergy relative to conventional energy sources. We conclude that the GHG balance of perennial bioenergy crop cultivation will often be favourable, with maximum GHG savings achieved where crops are grown on soils with low carbon stocks and conservative nutrient application, accruing additional environmental benefits such as improved water quality. The analysis reported here demonstrates there is a mature and increasingly comprehensive evidence base on the environmental benefits and risks of bioenergy cultivation which can support the development of a sustainable bioenergy industry." Whitaker et al. 2018, p. 150.
  146. ^ a b "In tropical regions, afforestation may be beneficial since beside sequestering carbon it can lead to cloud formation resulting in a net cooling. In boreal regions, however, low surface albedo of afforested areas might have a warming climatic forcing that 'may exceed the cooling forcing from sequestration' [Thompson 2009]. Bright et al. have defined a possible way of integrating the impact on albedo in the LCA of a forest biofuel [Bright 2012]. [...] In their paper an example for the clear-cut of a boreal forest is reported. In that specific case the increase in albedo that follows the clear-cut harvest may offset about half of the total CO2 emissions (that include also the biogenic emissions due to carbon stock changes) in a 100 years timeframe. Also Schwaiger and Bird [Schwaiger 2010] have attempted to integrate albedo effects into the bioenergy GHG calculations. They have considered an afforestation project in a south European mountainous area and used average yearly meteorological data. They have concluded that afforestation in the case study area accumulates up to 624 t CO2 eq./ha, while the change in albedo due to crown cover is equivalent to emissions of roughly 401 t CO2 eq./ha by the end of the first rotation period (90 years). The net effect, thus, varies around a neutral level with the cumulative result of a slight cooling in the long term. [...] With a similar approach Bright et al. [Bright 2011] have come to the conclusion that for a boreal forest, the albedo effect of the forest management in addition to the fossil fuel replacement leads to a near-neutral climate system. At a global level Bala et al. [Bala 2007] have simulated the climate impacts of deforestation, including the climate forcing of the CO2 emitted and the albedo changes. They found that global-scale deforestation has a net cooling influence on Earth's climate because the warming carbon-cycle effects of deforestation are overwhelmed by the net cooling associated with changes in albedo and evapotranspiration. Latitude-specific deforestation experiments indicate that afforestation projects in the tropics would be clearly beneficial in mitigating global-scale warming, but would be counterproductive if implemented at high latitudes and would offer only marginal benefits in temperate regions [Betts 2000]." JRC 2014, pp. 57–58.
  147. ^ "Black carbon, like other aerosol particles, interacts with clouds, changing their reflectivity and lifetime, with effects on local and global climate. In addition, when calculating the climate effect of BC, it is important to realize that it is often mixed with organic carbon (OC) which is also produced during combustion and which reflects sunlight much more strongly than it absorbs it. A low OC-to-BC ratio means a predominantly absorbing aerosol that will contribute to warming. A high OC-to-BC ratio means a predominantly reflecting (or scattering) aerosol that will contribute to cooling. The ratio depends on the emission source: it can be lower than 1 in the case of emissions from diesel engines, but will be much higher in the case of, for example, smoldering wood (Table 9). [...] In other studies [Kulmala 2004] the analysis has been further expanded to include the emissions of organic carbon (mainly terpenes) from boreal forests, that, besides having an intrinsic cooling effect, act as condensation nuclei for cloud formation, thus enhancing the cloud albedo effect and resulting in additional climate cooling to that of the carbon sink. Spraklen et al. [Spraklen 2008] have quantified the relevance of the cooling effect of organic aerosols emissions and compared it to the warming effect of land surface albedo changes. Using a global atmospheric model they have shown that changes in cloud albedo cause a radiative forcing sufficiently large to result in boreal forests having an overall cooling impact on climate. This is the result of emissions of organic vapours and increased cloud formation due to the increased amount of condensation nuclei (doubled). They conclude that the combination of climate forcings related to boreal forests may result in an important global homeostasis [optimization, stableization]. In cold climatic conditions, the snow–vegetation albedo effect dominates and boreal forests warm the climate, whereas in warmer climates they may emit sufficiently large amounts of organic vapour modifying cloud albedo and acting to cool climate." JRC 2014, pp. 56–58.
  148. ^ "Georgescu et al. [Georgescu 2011] have shown that the bio-geo-physical effects that result from hypothetical conversion of annual to perennial bioenergy crops across the central United States would have a significant global climate cooling effect, beside the local cooling related mainly to local increases in transpiration, due to higher albedo. They concluded that the reduction in radiative forcing from albedo alone is equivalent to a carbon emission reduction of 78 t C/ha, which is six times larger than the annual biogeochemical effects that arise from offsetting fossil fuel use." JRC 2014, pp. 58.
  149. ^ "An intensive processing, such as for liquid biofuel substitution via lignocellulosic ethanol, causes much longer payback times because of the loss of energy in the biofuels production (about half of the energy content of the biomass is lost in the processing [...]." JRC 2014, p. 34. Note that the JRC use the term "payback time" in the sense of "parity time" as defined in Carbon accounting principles above. See JRC 2014, p. 16.
  150. ^ See for instance the estimate of 0.60 W/m2 for the 10 t/ha yield above. The calculation is: Yield (t/ha) multiplied with energy content (GJ/t) divided by seconds in a year (31 556 926) multiplied with the number of square metres in one hectare (10 000).
  151. ^ a b Hektor et al. argue that flue gas condensation devices combined with natural drying of biomass makes it possible to achieve similar or better combustion efficiency than coal: "When burning moist biomass, energy is 'lost' in the evaporation of water. However, modern technology makes it possible to recover a large portion of that energy by flue gas condensation devices." The author also recommends "[...] simpler measures, such as natural drying [...]", and argue that "[...] state-of-the art technologies are nowadays generally included in new applications of biomass energy [...]" and that "[...] taking these factors into consideration, biomass would have about the same gross CO2 emissions per generated amount of energy as coal [...]." Hektor, Backéus & Andersson 2016, p. 4. See also OECD/IEA 2004, p. 20.
  152. ^ "The raw material for wood pellets is woody biomass in accordance with Table 1 of ISO 17225‑1. Pellets are usually manufactured in a die, with total moisture content usually less than 10 % of their mass on wet basis." ISO 2014a.
  153. ^ "The raw material for non-woody pellets can be herbaceous biomass, fruit biomass, aquatic biomass or biomass blends and mixtures. These blends and mixtures can also include woody biomass. They are usually manufactured in a die with total moisture content usually less than 15 % of their mass." ISO 2014b.
  154. ^ Transmission loss data from the World Bank, sourced from IEA. The World Bank 2010.
  155. ^ Additionally, Smil estimates that newly installed photovoltaic solar parks reaches 7–11 W/m2 in sunny regions of the world. Smil 2015, p. 191.
  156. ^ "Pathways in the first and fourth quadrants are relatively clear situations in which trade-offs are not evident, and should thus clearly be a target for governance measures; in the sense that pathways in quadrant 1 should be incentivised, while pathways in quadrant 4 should be discouraged. Forest bioenergy pathways which fit within the first quadrant are the ones that are very likely to contribute to climate change mitigation in a short-medium term, and at the same time are likely to improve the condition of local ecosystems and biodiversity (or at least do not affect paths of ecosystem restoration). Pathways in the fourth quadrant are the ones that are unlikely to contribute to climate change mitigation in the short-medium term and at the same time are likely to further degrade ecosystems' condition. Conversely, pathways in quadrants 2 and 3 are the ones for which trade-offs between climate mitigation and biodiversity can be identified or assumed. Pathways in quadrant 2 are the ones that even though they are likely to mitigate climate change, they are also likely to negatively impact local biodiversity. For these pathways, safeguards or mitigation strategies should be investigated, and if available, should be considered mandated as contingent to the promotion of bioenergy. This case is also the only case in which the trade-off mentioned above (global climate change mitigation vs. local degradation) could influence the final evaluation of the pathway. Pathways in the third quadrant are likely to improve local ecosystem condition, but might not mitigate climate change in the short term. In these cases, bioenergy production might be seen as a by-product of restoration operations. In both cases in quadrants 2 & 3, trade-offs that cannot be resolved will need to be weighted and discussed during the decision-making process." Camia et al. 2021, p. 107.
  157. ^ "In May 2020, the EU Biodiversity Strategy for 2030 (COM/2020/380) was adopted. In the communication, under section 2.2.5 (“Win-win solutions for energy generation”), the Commission committed to publishing this report on the use of forest biomass for energy production in order to inform the EU climate and energy policies that govern the sustainable use of forest biomass for energy production and the accounting of associated carbon impacts, namely the Renewable Energy Directive, the Emissions Trading Scheme (ETS), and the Regulation on land use, land use change and forestry (LULUCF). [...] [T]he study would take stock of the available data related to the use of woody biomass for bioenergy; assess the uses of woody biomass in the EU with a focus on bioenergy; provide suggestions on how to improve the knowledge base on forests in a harmonised way; and expand the evidence basis by highlighting pathways that minimise trade-offs between climate mitigation and biodiversity conservation." Camia et al. 2021, p. 5.
  158. ^ "In this study, we assess three categories of interventions and their potential impacts: removal of logging residues, afforestation and conversion of natural forests to plantations. These three interventions were chosen because they are considered as practices that aim to supply ‘additional' biomass, i.e. growing biomass that would not be produced in the absence of bioenergy demand, or using biomass, such as residues and wastes, which would otherwise decompose or be burned on site. We acknowledge that, until now, many of these responses have not been triggered as a direct consequence of bioenergy expansion, but they are high on the agenda of potential climate mitigation strategies and could occur, in the EU or outside, as a direct or indirect effect of increased EU demand for forest biomass for wood products and bioenergy." Camia et al. 2021, pp. 6–7.
  159. ^ "Assessing the impact of forest bioenergy on ecosystems' condition in general, and in particular on biodiversity, is complicated because bioenergy pathways can exert multiple pressures on ecosystems and biodiversity and at the same time alleviate others. This creates an intricate matrix of trade-offs and synergies between forest bioenergy production and biodiversity and the condition of forests. [...] At the local level, intensified forest management to produce additional biomass can increase pressures on forest ecosystems. Similarly, land use change associated to afforestation can drive positive or negative impacts on local biodiversity. Additionally, the supply chain to produce bioenergy commodities is associated to the emission of pollutants which may contribute to acidification, eutrophication, and further climate change. Nevertheless, at the global level, climate change in itself is a major driver of biodiversity loss, therefore the overall benefit to the ecosystems and biodiversity might still be higher from global climate change mitigation if compared with the local level effects mentioned above. The trade-off between potential long-term advantages from climate change mitigation and short term, local ecosystems' degradation is very difficult to quantify. Therefore, under the precautionary principle, we exclude it from this analysis, assuming that we should not evaluate hypothetical long-term benefits versus short-term effects on ecosystems. Instead, we focus our analysis on potential pressures on local biodiversity and ecosystems from land use changes and forest management intensification in order to highlight potential pathways causing negative environmental trade-offs, or “bio-perversities” (Lindenmayer et al., 2012)." Camia et al. 2021, pp. 102–103.
  160. ^ "Secondly, concerning the assessment of carbon emissions: the impacts reported here are based on a ‘ceteris paribus' perspective, which is apt to capture only small-scale changes and not suitable to capture the overall impact of large-scale deployment of bioenergy, since it excludes market-mediated effects on other sectors." Camia et al. 2021, p. 148.
  161. ^ "Win-win management practices that benefit climate change mitigation and have either a neutral or positive effect on biodiversity include removal of slash (fine, woody debris) below thresholds defined according to local conditions, and afforestation of former arable land with mixed forest or naturally regenerating forests. [...] [C]oppice forests are particularly important in Mediterranean countries, they provide many ecosystem services, have relevant socio-economic functions in many rural areas and are mainly utilised for bioenergy. However, in large areas coppices are no longer managed or completely abandoned, resulting in old or overgrown declining stands. In these cases, it is suggested to encourage active forest management, that would enhance the capacity of these ecosystems to store carbon and supply services. Depending on local considerations the preferred option could be active conversion to high forest, or coppice restoration (see Section 5.9.2). [...] [W]e find that collecting slash within the limits of locally recommended thresholds could generate energy without damaging forest ecosystems and at the same time likely contributing to reducing GHG emissions. Similarly, afforesting former agricultural land with mixed species plantations or with naturally regenerating forests would enhance the terrestrial sink even before producing biomass for energy and thus would contribute to climate change mitigation, while at the same time improving ecosystems' conditions. [...] Collecting slash within the limits of locally recommended thresholds could be used to generate energy without damaging forest ecosystems while likely contributing to reducing GHG emissions. Afforesting former agricultural land with mixed species plantations or with naturally regenerating forests would enhance the terrestrial sink even before producing biomass for material and energy uses and thus would contribute to climate change mitigation, while at the same time improving ecosystems' conditions. [...] [C]ollection and use of low stumps within locally established thresholds in climate areas with high decay rates could potentially provide carbon emissions mitigation without damaging local biodiversity; local conditions should be evaluated in these cases." Camia et al. 2021, pp. 8–149.
  162. ^ "Although not extensively captured in the case studies, there is clear consensus in the literature that afforestation of primary, ancient grassland ecosystems which were never forests, may have very detrimental effects on local biodiversity; some authors compare these effects to the destructive effects of deforestation (Abreu et al., 2017; Bond, 2016; Bond et al., 2019; Feurdean et al., 2018; Veldman et al., 2015a, 2015b). Semi-natural grasslands and anthropogenic heathlands are ecosystems where closed canopy forest did not historically develop because of natural processes such as fire or mega fauna, or because of extensive management by local people. Local biodiversity adapted to open spaces has evolved in those ecosystems, and afforestation or tree planting of closed canopy forests is considered as a significant threat for local biodiversity, as highlighted by IPBES (2018a, b). Bubová et al. (2015) reviewed how abandonment of traditional grassland management followed by natural forest succession or active afforestation, is the main driver for the decline of butterfly diversity in Europe.[...] [P]athways in quadrant 2 may provide a significant contribution to climate change that would benefit global ecosystems and biodiversity even if local ecosystems are damaged in the process. However, this is a very uncertain trade-off and would be contrary to the precautionary principle, as explained in section 5.7. In this quadrant, for instance, we can find afforestation of former agricultural land with monoculture plantations: this intervention is likely to lead to carbon benefits in the short-term, but the impacts on local ecosystem should be evaluated carefully, for instance in the framework of landscape mosaic management and climate change resilience. Afforestation of natural grasslands or anthropogenic heathlands could also produce carbon benefits in the medium term, but the cost for local biodiversity, especially for species adapted to open spaces, could be devastating. Indeed, these practices are already discouraged within the Pan-European Guidelines for Afforestation and Reforestation, but they are still popular around the world (Veldman et al., 2015b, 2015a). Further in this quadrant, operations which should be already discouraged by sustainable management guidelines are classified: removing slash in very high quantities could be detrimental for local biodiversity." Camia et al. 2021, pp. 125–147.
  163. ^ "The overall carbon impact of afforestation operations needs to be properly calculated including changes in biogenic C-stocks and sinks, the substitution benefits of the newly produced wood, and eventual market-mediated indirect land use change effects. Generally, the overall carbon impact of afforestation is found to be positive, albeit the time scale required might be long (Agostini et al., 2014; Giuntoli et al., 2020b). Nonetheless, not always newly planted forests show a higher C-stock [carbon stock] than existing ecosystems, especially when considering the carbon in soil organic matter. Several studies in our review have tried to provide insights. Bárcena et al. (2014) found increased SOC [soil organic carbon] with afforestation on former cropland and heathland in Northern Europe, however afforestation on former grassland actually decreased SOC levels even for mature forests (>30 years). Laganière et al. (2010) found very similar results from their global meta-analysis, with afforestation on former cropland leading to a significant increase in SOC, but no significant changes in SOC for former pastures and natural grasslands. Furthermore, they also found that the tree species (and thus plantation features) influence the final result, with broadleaves forests generating the highest SOC increase and coniferous forests having the same SOC as the former land use. Li et al. (2012), similarly, found increased SOC for new forests on former cropland and pastureland, but a stable or slightly decreased SOC in former grassland. [...] Pathways in quadrant 3 are probably unlikely to be driven by bioenergy demand, however, they might be definitely valuable for conservation interventions and produce biomass for bioenergy." Camia et al. 2021, pp. 125–147.
  164. ^ "Lose-lose pathways include removal of coarse woody debris, removal of low stumps, and conversion of primary or natural forests into plantations. [...] Bubová et al. (2015) reviewed how abandonment of traditional grassland management followed by natural forest succession or active afforestation, is the main driver for the decline of butterfly diversity in Europe. [...] Generally, the overall carbon impact of afforestation is found to be positive, albeit the time scale required might be long (Agostini et al., 2014; Giuntoli et al., 2020b). Nonetheless, not always newly planted forests show a higher C-stock than existing ecosystems, especially when considering the carbon in soil organic matter. Several studies in our review have tried to provide insights. Bárcena et al. (2014) found increased SOC with afforestation on former cropland and heathland in Northern Europe, however afforestation on former grassland actually decreased SOC [soil organic carbon] levels even for mature forests (>30 years). Laganière et al. (2010) found very similar results from their global meta-analysis, with afforestation on former cropland leading to a significant increase in SOC, but no significant changes in SOC for former pastures and natural grasslands. Furthermore, they also found that the tree species (and thus plantation features) influence the final result, with broadleaves forests generating the highest SOC increase and coniferous forests having the same SOC as the former land use. Li et al. (2012), similarly, found increased SOC for new forests on former cropland and pastureland, but a stable or slightly decreased SOC in former grassland. [...] [S]everal pathways are categorized in the lose-lose quadrant and should be discouraged. For instance, the removal of CWD [course woody debris] and low stumps can be detrimental to forest ecosystems while at the same time likely not contributing to reducing carbon emissions in the short or even medium term compared to fossil sources. [...] Further, as expected, the conversion of natural and old growth forests to plantations aiming to provide wood for bioenergy would be extremely negative for local biodiversity, and at the same time it would provide no carbon mitigation in the short-medium term and should be thus discouraged. Similar considerations are valid also for the conversion of naturally regenerating forests to high-intensity management plantations: the impact on local biodiversity is highly negative while, even though wood production might increase, the benefits in terms of carbon mitigation are only accrued in the medium to long term. [...] Depending on local conditions, determining the decay rates on the forest floor, the removal of Coarse Woody Debris and low stumps can be detrimental to forest ecosystems while at the same time likely not contribute to reducing carbon emissions in the short or even medium term compared to fossil sources." Camia et al. 2021, pp. 8–147.
  165. ^ "[W]e are of the opinion that several negative impacts associated with the pathways reviewed in this study could be effectively minimised through swift and robust implementation of the RED II sustainability criteria related to forest biomass, which will be further operationalised through the upcoming EU operational guidance on the evidence for demonstrating compliance with the forest biomass criteria. [...] More specifically, RED II indicates specific no-go areas for agricultural biomass, meaning that biomass for bioenergy cannot be directly produced from land that was, at any time after 2008, classified as highly biodiverse grasslands, primary forest, highly biodiverse forest, or protected areas. However, these criteria do not apply to forest biomass (except for the protected areas criterion). Expanding such land criteria to forest biomass would introduce additional safeguards to ensure that forest biomass for energy is not associated with the afforestation pathways that have the most negative impacts, i.e. those on high-nature value grasslands or anthropogenic heathlands, and it would also forbid the sourcing of wood from plantations established on converted old-growth, primary forest for energy feedstock." Camia et al. 2021, pp. 10–11.
  166. ^ "Irrespective from market drivers, a moderate future increase in the production of harvested wood products at EU level may be expected because of forest age dynamics (Grassi et al. 2018 and Korosuo et al. 2020) and, in some circumstance, to reduce risks (or as consequence) of forest fires, pests and windstorms. The residues and the industrial by-products associated with these harvested wood products – along with wood from silvicultural operations specifically aimed at enhancing the quality of trees and the growth of the forest stands - may be meaningfully used for energy production, also contributing to the economic viability of forestry which is an integral element of Sustainable Forest Management." Camia et al. 2021, p. 93.
  167. ^ "[...] [A]s scientists, we need to clearly understand our role in this debate: we can gather and synthesise evidence highlighting problems and possible solutions as honest brokers of policy options, but we cannot identify the ‘right' policy tool or the ‘right' policy principle to follow because those issues are within the realm of the political arena and no amount of scientific research will appease ethical disputes. [...] If the question is ‘Is forest bioenergy sustainable?' the answer might be positive or negative depending on who attempts to answer it, and how. [...] [T]o a large extent there are no right or wrong answers, and the definition of ‘good enough' solutions is the role of policymaking, not science. [...] As illustrated schematically in Figure 28, the various tools within the EU legal framework provide incentives towards different management goals for European forests, from incentivising forest bioeconomy to protecting the carbon sink and forest ecosystems. The resulting balance of these different pulling drivers will eventually define both the contribution of forests wood-based products to EU climate mitigation, as well as the resulting state of forests' health (Wolfslehner et al., 2020). As mentioned also in Section 5.2.1, it is natural that different stakeholders with different worldviews, including within the scientific community, have a preference for one driver or another. At the same time, many different equilibrium points are possible and acceptable within the socio-economic context of each Member State. [...] Differences in ethical values on the interaction between humans and nature clearly play a role in defining what ‘sustainable management' means. We think that if we want to de-toxify the debate surrounding the sustainability of forest bioenergy, these divergences in values should be acknowledged and discussed explicitly also within the scientific community." Camia et al. 2021, pp. 6, 83, 91, 166.
  168. ^ "Traditional biomass (fuelwood, charcoal, agricultural residues, animal dung) used for cooking and heating by some 2.8 billion people (38% of global population) in non-OECD countries accounts for more than half of all bioenergy used worldwide (IEA 2017; REN21 2018) (Cross-Chapter Box 7 in Chapter 6). Cooking with traditional biomass has multiple negative impacts on human health, particularly for women, children and youth (Machisa et al. 2013; Sinha and Ray 2015; Price 2017; Mendum and Njenga 2018; Adefuye et al. 2007) and on household productivity, including high workloads for women and youth (Mendum and Njenga 2018; Brunner et al. 2018; Hou et al. 2018; Njenga et al. 2019). Traditional biomass is land-intensive due to reliance on open fires, inefficient stoves and overharvesting of woodfuel, contributing to land degradation, losses in biodiversity and reduced ecosystem services (IEA 2017; Bailis et al. 2015; Masera et al. 2015; Specht et al. 2015; Fritsche et al. 2017; Fuso Nerini et al. 2017). Traditional woodfuels account for 1.9–2.3% of global GHG emissions, particularly in ‘hotspots' of land degradation and fuelwood depletion in eastern Africa and South Asia, such that one-third of traditional woodfuels globally are harvested unsustainably (Bailis et al. 2015). Scenarios to significantly reduce reliance on traditional biomass in developing countries present multiple co-benefits (high evidence, high agreement), including reduced emissions of black carbon, a short-lived climate forcer that also causes respiratory disease (Shindell et al. 2012). A shift from traditional to modern bioenergy, especially in the African context, contributes to improved livelihoods and can reduce land degradation and impacts on ecosystem services (Smeets et al. 2012; Gasparatos et al. 2018; Mudombi et al. 2018)." IPCC 2019a, p. 375.
  169. ^ "In the NZE Scenario, bioenergy rapidly shifts to 100% sustainable sources of supply, and sustainable use. There is a complete phase-out of the traditional use of solid biomass for cooking, which is inefficient, often linked to deforestation, and whose pollution was responsible for 2.5 million premature deaths in 2020. The traditional use of solid biomass – estimated at around 40% of total bioenergy supply, or around 25 EJ, today – falls to zero by 2030 in the NZE Scenario, in line with achieving UN Sustainable Development Goal 7 on universal access to affordable, reliable, sustainable and modern energy for all. [...] Sustainable use of bioenergy in the NZE Scenario not only avoids negative impacts such as increased deforestation and competition with food production – it also delivers benefits beyond the energy sector. Shifting from traditional use of biomass to modern bioenergy can avoid undue burdens on women often tasked with collecting wood for fuel, bring health benefits from reduced air pollution and proper waste management, and reduce methane emissions from inefficient combustion and waste decomposition. More generally, sustainable bioenergy can provide a valuable source of employment and income for rural communities in emerging economies." IEA 2021a.
  170. ^ See EPA 2020, p. 1. The emission factors are based on the higher heating value (HHV) of the different fuels. The HHV value reflects the actual chemical energy stored in the fuel (mainly carbon and hydrogen molecules), without taking into account 1.) the energy that is lost by producing steam (when the fuel's hydrogen content reacts with oxygen at combustion), and 2.) the energy that is lost in combustion by evaporating the fuel's moisture content. The fuel's lower heating value (LHV) is the energy that remains after the necessary amount of energy has been spent to vaporize all this water. See OECD/IEA 2004, p. 20.
  171. ^ "Some scientific papers state that burning biomass for energy produces higher emissions of CO2 per kWh of electricity at the smoke-stack compared with burning coal due to lower energy density of wood and/or less efficient conversion to electricity (e.g. Brack, 2017; Norton et al., 2019; Searchinger et al., 2018; Sterman et al., 2018; Walker et al., 2013), leading to the assertion that ‘biomass is worse for the climate than coal' (Johnston & van Kooten, 2015; McClure, 2014; PFPI, 2011; RSBP, 2012; Tsanova, 2018; Yassa, 2017). However, this interpretation neglects several significant factors. First, stack emissions will not necessarily increase when there is a shift to biomass fuels. The CO2 emission factor (g CO2 per GJ of fuel) is solely dependent on the chemical composition of the fuel. Wood and coal have similar CO2 emission factors, as the ratio of heating values between the two fuels is similar to the ratio of carbon content (ECN, undated; Edwards et al., 2014; US EPA, 2018; van Loo & Koppejan, 2008). Where biomass is co-fired with coal in large power plants, the conversion efficiency may decrease a few percent, although there is usually no significant efficiency penalty when the co-firing ratio is below 10% (van Loo & Koppejan, 2008). Conversion efficiencies depend on fuel properties including moisture content and grindability in addition to heating value (Mun et al., 2016; Shi et al., 2019; Zuwała & Lasek, 2017). For low rank coal, biomass co-firing (especially torrefied biomass) can increase the boiler efficiency and net power plant efficiency (Liu et al., 2019; Thrän et al., 2016). Smaller biomass-fired plants can have lower electric conversion efficiency than large coal-fired plants, but as they are typically combined heat and power plants, they also displace heat production from other sources, that could otherwise have generated fossil fuel emissions (e.g. Madsen & Bentsen, 2018). Large dedicated biomass units (converted from coal) can operate with roughly the same level of thermal efficiency as delivered historically from coal (Koss, 2019)." Cowie et al. 2021, p. 1214.
  172. ^ Total stack emissions for wood pellets were 0.897 Mt CO2/MWhel vs. 0.877 Mt CO2/MWhel for coal. Buchholz & Gunn 2017, pp. 4, 6, 9.
  173. ^ "Drax's biomass delivers carbon savings of more than 80% compared to coal – this includes emissions from our supply chain." Drax 2020.
  174. ^ See FutureMetrics 2015a, pp. 1–2. Chatham House notes that modern CHP plants (Combined Heat and Power) achieve much higher efficiencies, above 80%, for both fossil fuels and biomass. Chatham House 2017, p. 16.
  175. ^ The individual emission rates are: Wood 112 000 kg CO2eq per TJ, anthracite 98 300, coking coal 94 600, other bituminous 94 600, sub-bituminous 96 100, lignite 101 000. IPCC 2006a, pp. 2.16–2.17.
  176. ^ "Estimating gross emissions only, creates a distorted representation of human impacts on the land sector carbon cycle. While forest harvest for timber and fuelwood and land-use change (deforestation) contribute to gross emissions, to quantify impacts on the atmosphere, it is necessary to estimate net emissions, that is, the balance of gross emissions and gross removals of carbon from the atmosphere through forest regrowth [...]." IPCC 2019a, p. 368.
  177. ^ "It is incorrect to determine the climate change effect of using biomass for energy by comparing GHG emissions at the point of combustion [...] the misplaced focus on emissions at the point of combustion blurs the distinction between fossil and biogenic carbon, and it prevents proper evaluation of how displacement of fossil fuels with biomass affects the development of atmospheric GHG concentrations." IEA Bioenergy 2019, pp. 3–4.
  178. ^ "Sustainable Forest Management (SFM) is defined as ‘the stewardship and use of forests and forest lands in a way, and at a rate, that maintains their biodiversity, productivity, regeneration capacity, vitality and their potential to fulfill, now and in the future, relevant ecological, economic and social functions, at local, national, and global levels, and that does not cause damage to other ecosystems' [...]. This SFM definition was developed by the Ministerial Conference on the Protection of Forests in Europe and has since been adopted by the Food and Agriculture Organization [of the United Nations (FAO)]." IPCC 2019a, p. 351. Further, IPCC writes: "Sustainable forest management can prevent deforestation, maintain and enhance carbon sinks and can contribute towards GHG emissions-reduction goals. Sustainable forest management generates socio-economic benefits, and provides fibre, timber and biomass to meet society's growing needs. IPCC 2019a, p. 348.
  179. ^ "The trends of productivity shown by several remote-sensing studies (see previous section) are largely consistent with mapping of forest cover and change using a 34-year time series of coarse resolution satellite data (NOAA AVHRR) (Song et al. 2018). This study, based on a thematic classification of satellite data, suggests that (i) global tree canopy cover increased by 2.24 million km2 between 1982 and 2016 (corresponding to +7.1%) but with regional differences that contribute a net loss in the tropics and a net gain at higher latitudes, and (ii) the fraction of bare ground decreased by 1.16 million km2 (corresponding to –3.1%), mainly in agricultural regions of Asia (Song et al. 2018), see Figure 4.5. Other tree or land cover datasets show opposite global net trends (Li et al. 2018b), but high agreement in terms of net losses in the tropics and large net gains in the temperate and boreal zones (Li et al. 2018b; Song et al. 2018; Hansen et al. 2013)." IPCC 2019a, p. 367.
  180. ^ "In the previous version of the Renewable Energy Directive (EU, 2009) in force until 2020, sustainability criteria were defined only for biomass used for the production of biofuels and bioliquids. With the REDII, to be transposed by countries by June 2021, new criteria are defined also cover solid and gaseous biomass fuels used in large installations for the production of power and heating or cooling." Camia et al. 2021, p. 78.
  181. ^ "Second, our findings are similarly compatible with the well-known age-related decline in productivity at the scale of even-aged forest stands. [...] We highlight the fact that increasing individual tree growth rate does not automatically result in increasing stand productivity because tree mortality can drive orders-of-magnitude reductions in population density. That is, even though the large trees in older, even-aged stands may be growing more rapidly, such stands have fewer trees. Tree population dynamics, especially mortality, can thus be a significant contributor to declining productivity at the scale of the forest stand." Stephenson et al. 2014, p. 3.
  182. ^ "Recent studies indicate, that effects of forest management actions on soil C [carbon] stocks can be difficult to quantify and reported effects have been variable and even contradictory (see Box 4.3a)." Because the "current scientific basis is not sufficient", the IPCC will not currently provide soil carbon emission factors for forest management.IPCC 2019f, p. 4.6.
  183. ^ "SFM [sustainable forest management] applied at the landscape scale to existing unmanaged forests can first reduce average forest carbon stocks and subsequently increase the rate at which CO2 is removed from the atmosphere, because net ecosystem production of forest stands is highest in intermediate stand ages (Kurz et al. 2013; Volkova et al. 2018; Tang et al. 2014). The net impact on the atmosphere depends on the magnitude of the reduction in carbon stocks, the fate of the harvested biomass (i.e. use in short – or long-lived products and for bioenergy, and therefore displacement of emissions associated with GHG-intensive building materials and fossil fuels), and the rate of regrowth. Thus, the impacts of SFM on one indicator (e.g., past reduction in carbon stocks in the forested landscape) can be negative, while those on another indicator (e.g., current forest productivity and rate of CO2 removal from the atmosphere, avoided fossil fuel emissions) can be positive. Sustainably managed forest landscapes can have a lower biomass carbon density than unmanaged forest, but the younger forests can have a higher growth rate, and therefore contribute stronger carbon sinks than older forests (Trofymow et al. 2008; Volkova et al. 2018; Poorter et al. 2016)." IPCC 2019a, p. 351.
  184. ^ "Bioenergy provides only 5% of total electricity generation in 2050, but it is an important source of low-emissions flexibility to complement variable generation from solar PV and wind. In the industry sector, where solid bioenergy demand reaches 20 EJ in 2050, it is used to meet high temperature heat needs that cannot be easily electrified such as paper and cement production. In 2050, bioenergy meets 60% of energy demand in the paper sector and 30% of energy demand for cement production." IEA 2021a.
  185. ^ The IEA estimates that replacing short rotation coppice forests with hydrogen production (for heat processing purposes) would cost 4.5 trillion USD: "The additional wind, solar, battery and electrolyser capacity, together with the electricity networks and storage needed to support this higher level of deployment would cost more than USD 5 trillion by 2050. This is USD 4.5 trillion more than would be needed if the use of bioenergy were to be expanded as envisaged in the NZE [Net Zero Emissions scenario], and would increase the total investment needed in the NZE by 3%. While it might therefore be possible still to achieve net‐zero emissions in 2050 without expanding land use for bioenergy, this would make the energy transition significantly more expensive. " IEA 2021b, p. 94.
  186. ^ "Research demonstrates that demand for wood helps keep land in forest and incentivizes investments in new and more productive forests, all of which have significant carbon benefits. [...] Failing to consider the effects of markets and investment on carbon impacts can distort the characterization of carbon impacts from forest biomass energy." NAUFRP 2019, p. 2.
  187. ^ Favero et al. focus on a potential future increase in demand and argues: "Increased bioenergy demand increases forest carbon stocks thanks to afforestation activities and more intensive management relative to a no-bioenergy case [...] higher biomass demand will increase the value of timberland, incentivize additional investment in forest management and afforestation, and result in greater forest carbon stocks over time". Favero, Daigneault & Sohngen 2020, p. 6.
  188. ^ "Some studies assess unharvested forest as one (and sometimes the only) reference scenario [...] and attribute extra GHG emissions to the bioenergy system based on forgone sequestration in comparison with natural regeneration. Others use a historical baseline reference point, without considering the dynamic nature of carbon stocks under a no-bioenergy scenario [...]. For biomass obtained as a co-product from forests managed for timber production, the relevant reference is commonly management for timber only, with thinning and harvest residues decomposing (or burned) on-site [...]. In some situations, the most likely reference land use could involve land use change. For example, markets for wood products can be an important incentive for private landowners to retain land as managed forest rather than converting to other uses [...]; the reference scenario in this situation may involve: regeneration of natural forest, possibly subject to higher incidence of wildfire; replacement of forest stands with agriculture; or urbanization, each with different impacts on the land carbon stock [...]. Assuming the forest would remain unharvested in the no-bioenergy scenario is not a realistic reference in situations where landholders use the land to generate income, unless landholders can obtain equivalent income from payments for carbon sequestration or other ecosystem services [...]." Cowie et al. 2021, p. 1218.
  189. ^ According to FAO, tree cover in Australia is increasing, but carbon stock is only provided for Oceania as a whole. FAO 2020, p. 136.
  190. ^ Wood chips, mainly used in the paper industry, have similar data; Europe (including Russia) produced 33% and North America 22%, while forest carbon stock increased in both areas. West, Central and East Asia combined produced 18%, and the forest carbon stock in this areas increased from 31.3 to 43.3 Gt. Wood chips production in the areas of the world were carbon stock is decreasing, was 26.9% in 2019. For wood pellet and wood chips production data, see FAOSTAT 2020. For carbon stock data, see FAO 2020, p. 52, table 43.
  191. ^ "The potentially very long payback periods for forest biomass raise important issues given the UNFCCC's aspiration of limiting warming to 1.5 °C above preindustrial levels to ‘significantly reduce the risks and impacts of climate change'. On current trends, this may be exceeded in around a decade. Relying on forest biomass for the EU's renewable energy, with its associated initial increase in atmospheric carbon dioxide levels, increases the risk of overshooting the 1.5°C target if payback periods are longer than this. The European Commission should consider the extent to which large-scale forest biomass energy use is compatible with UNFCCC targets and whether a maximum allowable payback period should be set in its sustainability criteria." EASAC 2017, p. 34.
  192. ^ "Some authors (e.g. Booth, 2018; Brack, 2017; Norton et al., 2019) propose that forest bioenergy should only receive support under renewable energy policies if it delivers net reduction in atmospheric CO2 within about a decade, due to the urgent need to reduce GHG emissions. However, besides the subjectivity of payback time analysis raised above, applying a 10-year payback time as a criterion for identifying suitable mitigation options is inconsistent with the long-term temperature goal of the Paris Agreement, which requires that a balance between emission and removals is reached in the second half of this century (Tanaka et al., 2019). Furthermore, it reflects a view on the relationship between net emissions, global warming and climate stabilization that contrasts with the scenarios presented in the SR1.5: The report shows many alternative trajectories towards stabilization temperatures of 1.5 and 2°C warming that reach net zero at different times and require different amounts of CDR (IPCC, 2018). The IPCC report did not determine that individual mitigation measures must meet specific payback times, but rather that a portfolio of mitigation measures is required that together limits the total cumulative global anthropogenic emissions of CO2." Cowie et al. 2021, p. 1213.
  193. ^ "Furthermore, applying a payback time criterion when evaluating forest bioenergy, and determining the contribution of bioenergy to meeting the Paris Agreement temperature goal, is complicated by the fact that bioenergy systems operate within the biogenic carbon cycle (see Section 3), which implies a fundamentally different influence on atmospheric CO2 concentrations over time compared to fossil fuel emissions (Cherubini et al., 2014). [...] [C]omparing GHG emissions from biomass and fossil fuels at the point of combustion ignores the fundamental difference between fossil fuels and biomass fuels. Burning fossil fuels releases carbon that has been locked up in the ground for millions of years. Fossil fuel emissions transfer carbon from the lithosphere to the biosphere–atmosphere system, causing temperature increases that are irreversible on timescales relevant for humans (Archer et al., 2009; Solomon et al., 2009; Ter-Mikaelian, Colombo, & Chen, 2015). In contrast, bioenergy operates within the biosphere–atmosphere system, and burning biomass emits carbon that is part of the continuous exchange of carbon between the biosphere and the atmosphere (Smith et al., 2016)." Cowie et al. 2021, pp. 1213–1215.
  194. ^ "The IPCC emphasizes the need for transformation of all sectors of society to achieve the ‘well below 2°C' goal of the Paris Agreement (IPCC, 2018). This will entail technology and infrastructure development to generate a portfolio of emissions reduction and CDR strategies. Such investments may include, for example, scaling-up battery manufacturing to support electrification of car fleets, building rail infrastructure and district heating networks and changing the management and harvesting of forests and other lands to provide biomass for biobased products. The mobilization of mitigation options such as these can initially increase net GHG emissions while providing products and services with low, neutral or net negative emissions in the longer term (Cuenot & Hernández, 2016; Hausfather, 2019). The contribution of specific options to mitigation will depend on technology readiness level, costs, resource availability and inertia of existing technologies and systems. Options assessed as having low net GHG emissions per unit energy provided may be restricted by immature development, high cost or dependence on new infrastructure. Other options, including bioenergy, have greater near-term mitigation potential due to being compatible with existing infrastructure and cost competitive in many applications. Strategy development needs to recognize the complementarity of many mitigation options, and balance trade-offs between short- and long-term emissions reduction objectives. Critically, strategies based on assessments of individual technologies in isolation from their broader context, and that apply a strong focus on emissions reduction in the short term, can make long-term climate goals more difficult to achieve (e.g. Berndes at al., 2018; Smyth et al., 2014). Mitigation options available in the near term need to be evaluated beyond the direct effect on GHG emissions, considering also their influence on systems transition and implementation of other mitigation options (see Section 2)." Cowie et al. 2021, p. 1214.
  195. ^ "Some have argued that the length of the carbon payback period does not matter as long as all emissions are eventually absorbed. This ignores the potential impact in the short term on climate tipping points (a concept for which there is some evidence) and on the world's ability to meet the target set in the 2015 Paris Agreement to limit temperature increase to 1.5°C above pre-industrial levels, which requires greenhouse gas emissions to peak in the near term. This suggests that only biomass energy with the shortest carbon payback periods should be eligible for financial and regulatory support." EASAC 2017, p. 4.
  196. ^ "Risks related to climate tipping points are sometimes raised in relation to the timing of GHG savings: crossing thresholds, for example, associated with forest dieback or thaw of permafrost, could lead to large, irreversible changes in the global climate system (e.g. Grimm et al., 2013). A recent study found a low probability of crossing a tipping point in the global climate system if warming does not exceed 2°C (Fischer et al., 2018). Also, critical threshold values and irreversibility of specific tipping points are uncertain (Collins et al., 2013), and the universal application of critical threshold values is questioned in relation to ecosystem function (Hillebrand et al., 2020). Nevertheless, uncertainties and risks associated with climate tipping points are additional considerations in evaluations of different trajectories towards temperature stabilization. Rather than connecting the timing of GHG savings to specific but uncertain climate tipping points, evaluation of bioenergy options is preferably based on a holistic assessment that considers how bioenergy can contribute to resilience and adaptation to changes in climate along with other environmental stressors." Cowie et al. 2021, p. 1214.
  197. ^ "Harvesting immediately reduces the standing forest carbon stock compared with less (or no) harvesting (Bellassen and Luyssaert, 2014; Sievänen et al., 2014) and it may take from decades to centuries until regrowth restores carbon stocks to their former level—especially if oldgrowth forests are harvested." EASAC 2017, p. 21.
  198. ^ "Following this argument, the carbon dioxide (and other greenhouse gases) released by the burning of woody biomass for energy, along with their associated life-cycle emissions, create what is termed a ‘carbon debt' – i.e. the additional emissions caused by burning biomass instead of the fossil fuels it replaces, plus the emissions absorption foregone from the harvesting of the forests. Over time, regrowth of the harvested forest removes this carbon from the atmosphere, reducing the carbon debt. The period until carbon parity is achieved (i.e. the point at which the net cumulative emissions from biomass use are equivalent to those from a fossil fuel plant generating the same amount of energy) is usually termed the ‘carbon payback period'. After this point, as regrowth continues biomass may begin to yield ‘carbon dividends' in the form of atmospheric greenhouse gas levels lower than would have occurred if fossil fuels had been used. Eventually carbon levels in the forest return to the level at which they would have been if they had been left unharvested. (Some of the literature employs the term ‘carbon payback period' to describe this longer period, but it is more commonly used to mean the time to parity with fossil fuels; this meaning is used in this paper.)" Chatham House 2017, p. 27.
  199. ^ "It has been argued that carbon balances should not be assessed at the stand level since at landscape level depletion of carbon in one stand may be compensated by growth in a stand elsewhere. For scientific analysis of the impact on climate forcing, however, it is necessary to compare the effects of various bioenergy harvest options against a baseline of no bioenergy harvest (or other credible counterfactual scenarios) for the same area of forest. Such studies provide information on the impacts of changes at the stand level, which can then be integrated with other factors (economic, regulatory and social) that may influence effects at landscape level." EASAC 2017, p. 23.
  200. ^ "It is important to realize that our 3650 ton per year CHP plant does not receive 3650 tons in one delivery and does not release 3650 tons of wood's worth of carbon in one lump either. In fact, the forest products industry can be characterized as a just-in-time manufacturing system. For our CHP plant, 10 tons per day are sustainably harvested and delivered off of our 3650 acre FSC or SFI certified forest. So the carbon released into the atmosphere that day is from 10 tons of wood. The atmosphere “sees” new carbon. But during that same day on our 3650 acre plot, 10 new tons of wood grow and sequester the amount of carbon that was just released." FutureMetrics 2011b, p. 2.
  201. ^ "Forests are generally managed as a series of stands of different ages, harvested at different times, to produce a constant supply of wood products. When considered at plot level, long-rotation forests take many years to regrow after harvest, and the EASAC statement indicates this as a time gap between releasing forest carbon and its reabsorption from the atmosphere. However, across the whole forest estate or landscape, the temporal fluctuations are evened out since other stands continue to grow and sequester carbon, making the time gap as indicated by EASAC less relevant. If annual harvest does not exceed the annual growth in the forest, there is no net reduction in forest carbon." IEA Bioenergy 2019: "The use of forest biomass for climate change mitigation: response to statements of EASAC" IEA Bioenergy 2019, p. 2.
  202. ^ The forest landscape works as a proxy for calculating specifically human GHG emissions: "In the AFOLU [Agriculture, Forestry and Other Land Use] sector, the management of land is used as the best approximation of human influence and thus, estimates of emissions and removals on managed land are used as a proxy for anthropogenic emissions and removals on the basis that the preponderance of anthropogenic effects occurs on managed lands (see Vol. 4 Chapter 1). This allows for consistency, comparability, and transparency in estimation. Referred to as the Managed Land Proxy (MLP), this approach is currently recognised by the IPCC as the only universally applicable approach to estimating anthropogenic emissions and removals in the AFOLU sector (IPCC 2006, IPCC 2010)." IPCC 2019j, p. 2.67.
  203. ^ "The natural disturbance component is subtracted from the total estimate of [...] emissions and removals, yielding an estimate of the emissions and removals associated with human activity on managed land." See IPCC 2019j, p. 2.72. "The 2006 IPCC Guidelines are designed to assist in estimating and reporting national inventories of anthropogenic greenhouse gas emissions and removals. For the AFOLU Sector, anthropogenic greenhouse gas emissions and removals by sinks are defined as all those occurring on ‘managed land'. Managed land is land where human interventions and practices have been applied to perform production, ecological or social functions. [...] This approach, i.e., the use of managed land as a proxy for anthropogenic effects, was adopted in the GPG–LULUCF and that use is maintained in the present guidelines. The key rationale for this approach is that the preponderance of anthropogenic effects occurs on managed lands. By definition, all direct human-induced effects on greenhouse gas emissions and removals occur on managed lands only. While it is recognized that no area of the Earth's surface is entirely free of human influence (e.g., CO2 fertilization), many indirect human influences on greenhouse gases (e.g., increased N deposition, accidental fire) will be manifested predominately on managed lands, where human activities are concentrated. Finally, while local and short-term variability in emissions and removals due to natural causes can be substantial (e.g., emissions from fire, see footnote 1), the natural ‘background' of greenhouse gas emissions and removals by sinks tends to average out over time and space. This leaves the greenhouse gas emissions and removals from managed lands as the dominant result of human activity. Guidance and methods for estimating greenhouse gas emissions and removals for the AFOLU Sector now include: • CO2 emissions and removals resulting from C stock changes in biomass, dead organic matter and mineral soils, for all managed lands; • CO2 and non-CO2 emissions from fire on all managed land; • N2O emissions from all managed soils; • CO2 emissions associated with liming and urea application to managed soils; • CH4 emissions from rice cultivation; • CO2 and N2O emissions from cultivated organic soils; • CO2 and N2O emissions from managed wetlands (with a basis for methodological development for CH4 emissions from flooded land in an Appendix 3); • CH4 emission from livestock (enteric fermentation); • CH4 and N2O emissions from manure management systems; and • C stock change associated with harvested wood products." See IPCC 2006b, p. 1.5.
  204. ^ "Only part of the biomass from felled trees is removed from forests during harvest operations, on average around 80 percent for the EU as a whole during the period 2004 to 2013 (estimate also based on Pilli et al. 2017). The remainder is left as logging (primary) residues." Camia et al. 2021, p. 34.
  205. ^ "Salvage loggings are any harvesting activity consisting of recovering timber that can still be used, at least in part, from lands affected by natural disturbances (source: EU 2013.); with natural disturbances denominating damages caused by any factor (biotic or abiotic) that adversely affects the vigour and productivity of the forest and that is not a direct result of human activities (FAO 2018). Salvage logging is part of the removals. It includes both the removal of dead trees (belonging to what is reported as natural losses) and living trees (part of the growing stock) to prevent the spread of diseases or pests. Roundwood includes all wood removed with or without bark, including wood removed in its round form, or split, roughly squared or in other form (e.g. branches, roots, stumps and burls (where these are harvested)) and wood that is roughly shaped or pointed. It is a general term referring to wood fuel, including wood for charcoal and industrial roundwood. All roundwood is also referred to as primary wood or primary woody biomass. Fuelwood is roundwood that will be used as fuel for energy purposes such as cooking, heating, or power production. It includes wood harvested from main stems, branches and other parts of trees (where these are harvested for fuel), round or split, and wood that will be used for the production of charcoal (e.g. in pit kilns and portable ovens), wood pellets and other agglomerates. It also includes wood chips to be used for fuel that are made directly (i.e. in the forest) from roundwood. It excludes wood charcoal, pellets, and other agglomerates. Industrial roundwood corresponds to all roundwood except fuelwood. It includes sawlogs and veneer logs; pulpwood, round and split; and other industrial roundwood. As described in Chapter 3, industrial roundwood, although normally intended to be used for manufacturing of woodbased products, can sometimes end up as fuel." Pulpwood is defined like so: "Roundwood that is primarily intended for the production of pulp, particleboard or fibreboard. It includes: roundwood (with or without bark) in its round form or as splitwood or wood chips made directly (i.e. in the forest) from roundwood." Stemwood is defined like so: The wood of the stem(s) of a tree, i.e. the above ground main growing shoot(s). Stemwood includes wood in main axes and in major branches where there is at least X m of ‘straight' length to Y cm top diameter. (Source: Camia et al. 2018). Stemwood, within the context of this study, is the over bark biomass of the stem from 15 cm height (thus excluding the stump) up to a minimum top diameter of 9 cm." Sawnwood is defined like so: "Wood that has been produced from roundwood, either by sawing lengthways or by a profile-chipping process and that exceeds 6 mm in thickness. It includes planks, beams, joists, boards, rafters, scantlings, laths, boxboards and 'lumber', etc., in the following forms: un-planed, planed, end jointed, etc." Camia et al. 2021, pp. 21, 68.
  206. ^ "In general, prioritizing residues and a cascade use of wood remains a key overarching principle for maximizing the positive climate impact of bioenergy [...]." Camia et al. 2021, p. 92.
  207. ^ "Further characterising the primary woody biomass used, we estimate that roughly 20% of the total wood used for energy production is made up of stemwood, while 17% is made up of other wood components (treetops, branches, etc.). Based on available knowledge, at least half of the stemwood used for energy is assumed to be derived from coppice forests, which are particularly important in Mediterranean countries. Coppice forests, for the most part, provide many ecosystem services, and this management system has relevant socio-economic functions in many rural areas. However, in large areas coppices are no longer managed, resulting in old or overgrown declining stands; it is suggested to encourage active coppice restoration or conversion into high forest, depending on local conditions, to enhance the capacity of these ecosystems to store carbon and supply wood and other services. [...] Following what illustrated in section 3.4, for the year 2015 about 20% of this biomass can be broadly estimated as stemwood from primary wood (of which at least half is likely from coppice forests), while a larger part would come from either primary other wood components (tree tops, branches, that would have anyway emitted CO2 in their decaying processes if left in the forest as residues, about 17%) or from secondary sources (by-products of wood processing industries, bark, post-consumer wood, about 49%); the remaining 14%, being reported as uncategorized, cannot be attributed (see Figure 8). Based on this analysis, it could be preliminary concluded that the large majority of forest bioenergy currently used in the EU is based on residues and the widely recommended “cascade” approach (EU 2015). However, the increase in woody biomass used for energy production from 2005 to 2018 (about 34%, dashed blue line) seems mainly associated to an increase in fuelwood (see Figure 10). More importantly, the large uncertainty in the bioenergy input mix highlighted in chapter 3 prevents to assign a high confidence to the conclusion above." Camia et al. 2021, pp. 7, 88.
  208. ^ Sathre & O'Connor cite research on woody construction materials and write that "[...] over 90% of revenue is gained from the main wood product, with less than 10% gained from other biomass co-products." They also write that "[...] the average economic value added per hectare of forestland is over 40 times greater for main products made from sawlogs than for harvest residues." In other words, "[...] it is unlikely that trees will be harvested solely to produce these low-value products; instead, trees are harvested to produce high-value main products, and by-products are generated simultaneously." Sathre & O'Connor 2010, p. 111.
  209. ^ The existence of a bioenergy market can improve the financial viability of forest thinning (Cintas et al., 2016), which stimulates production of high-quality timber with the aforementioned climate benefits from product substitution. In addition, extracting (otherwise unutilized) lower quality biomass (e.g. resulting from pest and disease impacts or overstocking) can reduce the frequency and severity of wildfires and associated loss of forest carbon and release of non-CO2 GHGs, further enhancing the climate benefit (Agee & Skinner, 2005; Evans & Finkral, 2009; Mansuy et al., 2018; Regos et al., 2016; Sun et al., 2018; Verkerk et al., 2018). On the other hand, the mitigation value of forest bioenergy could be diminished if policies supporting bioenergy reduce timber availability for material applications (Favero et al., 2020), thereby reducing the wood products pool and increasing use of GHG-intensive materials; if excessive removal of residues reduces forest productivity (Achat et al., 2015; Helmisaari et al., 2011); or if reforestation displaces food production and results in deforestation elsewhere to provide new cropland. Cowie et al. 2021, pp. 1216–1217.
  210. ^ "In many locations sawmill residuals from structural lumber production are abundant and they supply much of the raw material needed to produce wood pellets. In other locations, there are insufficient sawmill residuals. In those locations, the pellet mills, just like the pulp mills, use the non-sawlog portions of the tree." FutureMetrics 2017, p. 8.
  211. ^ Lamers & Junginger write that the vast majority of wood pellets imported to Europe are based on processing and harvesting residues "[...] with an increasing though still minor share from low-grade roundwood." They state that generally, "[...] the higher economic value for timber and cellulose products makes large-scale use of whole-trees for energy purposes highly unlikely wherever there is regional competition for the fiber." The technical potential for additional use of harvest residues is high in areas with large forests and harvest residues is therefore "[...] more likely to be used as feedstock when process-based wood waste streams become scarce." Lamers & Junginger 2013, p. 382.
  212. ^ "Synergies as well as competition within the wood-based economy are evident. Similar to the energy sector, the wood-based panel and pulp industries are likewise largely based on forest industry by-products. Therefore, the energy sector, wood-based panel, and pulp industries are all dependant on the demand for sawnwood, and they compete for the same feedstocks." Camia et al. 2021, pp. 57–58. In Germany, "[...] two thirds of the distributed sawmill by-products are delivered to panel and pulp industry; only 12% are distributed directly to energy producers (11% pellets, 1% directly to power plants)." Hoefnagels et al. 2017, p. 50.
  213. ^ "Limitations on bioenergy and BECCS can result in increases in the cost of mitigation (Kriegler et al. 2014; Edmonds et al. 2013). Studies have also examined limiting CDR, including reforestation, afforestation, and bioenergy and BECCS (Kriegler et al. 2018a,b). These studies find that limiting CDR can increase mitigation costs, increase food prices, and even preclude limiting warming to less than 1.5°C above pre-industrial levels (Kriegler et al. 2018a,b; Muratori et al. 2016)." IPCC 2019e, p. 638.
  214. ^ "Concern about near-term emissions is not a strong argument for stopping investments that contribute to net emissions reduction beyond 2030, be it the scaling-up of battery manufacturing to support electrification of car fleets, the development of rail infrastructure, or the development of biomass supply systems and innovation to provide biobased products displacing fossil fuels, cement and other GHG-intensive products. We assert that it is critical to focus on the global emissions trajectory required to achieve climate stabilization, acknowledging possible trade-offs between short- and long-term emissions reduction objectives. A strong focus on short-term carbon balances may result in decisions that make long-term climate objectives more difficult to meet."IEA Bioenergy 2019, p. 4.
  215. ^ "Comparisons between forest biomass emissions and fossil fuel emissions at the time of combustion and for short periods thereafter do not account for long term carbon accumulation in the atmosphere and can significantly distort or ignore comparative carbon impacts over time. [...] The most common timeframe for measuring the impacts of greenhouse gases is 100 years, as illustrated by the widespread use of 100-year global warming potentials. This timeframe provides a more accurate accounting of cumulative emissions than shorter intervals." NAUFRP 2019, pp. 1–2.

Shortened footnotes

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  2. ^ a b IEA 2019.
  3. ^ a b IEA 2021a.
  4. ^ a b IPCC 2019b, p. B 7.4.
  5. ^ Norton et al. 2019, pp. 1256–1263.
  6. ^ a b c IEA 2021d.
  7. ^ ETIP Bioenergy 2022.
  8. ^ IRENA 2014, p. 20-21.
  9. ^ IEA 2021c.
  10. ^ a b IRENA 2014, p. 8.
  11. ^ Brauch et al. 2009, p. 384.
  12. ^ IRENA 2014, pp. 1, 5.
  13. ^ MAGIC 2021.
  14. ^ WBA 2016, p. 4.
  15. ^ JRC 2019, p. 3.
  16. ^ a b JRC 2014, p. 75.
  17. ^ Camia et al. 2021, p. 7.
  18. ^ Camia et al. 2018, p. 6.
  19. ^ a b van den Born et al. 2014, p. 20, table 4.2.
  20. ^ ETIP Bioenergy 2020.
  21. ^ van den Born et al. 2014, p. 2, 21.
  22. ^ IRENA 2014, p. 21.
  23. ^ IEA Bioenergy 2017, pp. 1, 22.
  24. ^ a b c d EIA 2022.
  25. ^ Basu et al. 2013, pp. 171–176.
  26. ^ Koukoulas 2016, p. 12.
  27. ^ Wild 2015, p. 72.
  28. ^ Smil 2015, p. 13.
  29. ^ Renewable Energy 2021, pp. 473–483.
  30. ^ EIA 2021.
  31. ^ Akhtar, Krepl & Ivanova 2018.
  32. ^ Liu et al. 2011.
  33. ^ Nabuurs, Arets & Schelhaas 2017, p. 120.
  34. ^ Zetterberg & Chen 2014, p. 785.
  35. ^ C2ES 2021.
  36. ^ a b Jonker, Junginger & Faaij 2013, pp. 378–381.
  37. ^ Lamers & Junginger 2013, p. 375.
  38. ^ Camia et al. 2018, p. 29.
  39. ^ Nelson, Liknes & Butler, pp. 1–2.
  40. ^ Myllyviita et al. 2021, p. 7-8.
  41. ^ Myllyviita et al. 2021, p. 9-11.
  42. ^ Schlamadinger & Marland 1996, pp. 283–285.
  43. ^ Camia et al. 2018, p. 34, 45.
  44. ^ Sathre & O'Connor 2010, p. 104.
  45. ^ Sathre & O'Connor 2010, p. 109.
  46. ^ Sathre & O'Connor 2010, p. 110.
  47. ^ Myllyviita et al. 2021, p. 5-11.
  48. ^ Miner et al. 2014, p. 602.
  49. ^ a b Abt et al. 2021, p. 28.
  50. ^ JRC 2014, p. 41, table 2.
  51. ^ Lamers & Junginger 2013, p. 380.
  52. ^ Bird et al. 2010, p. 26.
  53. ^ Zetterberg & Chen 2014, p. 792, figure 3a.
  54. ^ Repo, Tuomi & Liski 2010, p. 111, figure 3.
  55. ^ Holmgren 2021, p. 13.
  56. ^ Holmgren 2021, pp. 16, 24, 26.
  57. ^ Holmgren 2021, p. 25.
  58. ^ Chatham House 2020, p. 1, table 12.
  59. ^ Walker et al. 2013, p. 153.
  60. ^ Hanssen et al. 2017, p. 1416.
  61. ^ Camia et al. 2018, p. 104.
  62. ^ Lamers & Junginger 2013, p. 379-380.
  63. ^ Zanchi, Pena & Bird 2011, p. 768.
  64. ^ Zanchi, Pena & Bird 2011, pp. 761, 768.
  65. ^ JRC 2014, p. 42.
  66. ^ Mitchell, Harmon & O'Connell 2009, pp. 648, 651.
  67. ^ Mitchell, Harmon & O'Connell 2016.
  68. ^ Lamers & Junginger 2013, pp. 379–380, table 2.
  69. ^ Jonker, Junginger & Faaij 2013, pp. 381–387, table 5.
  70. ^ Jonker, Junginger & Faaij 2013, p. 386.
  71. ^ Jonker, Junginger & Faaij 2013, p. 381.
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