The use of biomass for energy can increase atmospheric concentrations of CO₂ for years or even decades. Yet many countries grant it financial and regulatory support, ignoring the emissions from its combustion.
This chapter reviews the types of woody biomass feedstock that are burnt for power and heat, and the impact their emissions have on the global climate, in particular, the carbon payback period – the length of time taken before forest regrowth absorbs the emissions from combustion. It looks at the way in which biomass emissions are reported and accounted for and the problems this may cause for countries’ policy frameworks and accounting of emissions against national targets. (All of these issues are discussed further in Woody Biomass for Power and Heat: Impacts on the Global Climate, published by Chatham House in 2017.)
2.1 Biomass feedstocks
Wood, along with other forms of biomass, has always been burnt for energy in traditional uses such as open fires or simple cooking stoves. These uses are still important in rural areas of many developing and even industrialized countries. Wastes and residues from timber harvesting operations have long been used to generate energy on-site in sawmills and pulp mills. In recent years, however, the creation of incentives to use biomass for power and heat production has seen a much greater uptake of wood feedstocks for those purposes.
In fact, almost any organic material can be used to generate biomass energy, but the practicalities of harvesting and collection, and the degree of contamination of some categories (e.g. municipal waste) in practice limit the types of feedstocks that are of commercial utility. The main categories used for energy in the EU, UK and elsewhere are various types of forest biomass:
- Wood fuel (also referred to as firewood): logs, branches and twigs burnt in that form. (The term ‘roundwood’ is also often used: while in production statistics, roundwood is an aggregate of wood fuel and industrial roundwood for other uses, terms for different types of wood are not always used consistently.)
- Forest residues from logging operations for other wood products or forest management: stumps, tops, small branches and pieces either too short or irregular to be used for other commercial purposes. Trees cut but not removed from the forest and unmerchantable trees may also be defined as forest residues after a timber harvest. Typically, about one-third of the wood in a harvested tree is contained in roots and small branches. Leaving these in the forest to decompose contributes positively to forest ecosystem health and vitality, and excessive extraction is harmful.
- Sawmill residues: bark, shavings, sawdust, trim ends and offcuts produced in sawmills. Recently these have mostly been used for panelboard manufacture and in pulp mills. They can also be burnt on-site to provide energy for the mill itself.
- Black liquor: a waste product from the kraft pulping process used in many pulp and paper mills to produce high-quality paper. Black liquor is generally burnt in recovery boilers on-site to generate energy for the mill, and also sometimes for export to the local electricity grid.
For ease of transport, logs or forest residues may be converted to wood chips, but are now commonly transformed into pellets, produced by drying and compressing wood material and extruding it through a small cylinder-shaped die. Roughly two tonnes of green – i.e. recently cut, not dried – wood are needed to produce one tonne of pellets. Sawmill and agricultural residues can also be used. Wood pellets are increasingly favoured for long-distance transport and storage, as they are denser and contain lower moisture content than other products. Pellets are now widely used in the EU and UK for both heating and power generation.
Available statistics do not always distinguish between different types of solid biomass. The organic fraction of municipal solid waste is sometimes included, alongside forest and agricultural sources. Black liquor, which is generally categorized as solid biomass despite being a liquid, forms a substantial share of the wood-based fuel consumed in those EU member states with a large pulp and paper industry, such as Finland and Sweden. Estimates suggest that in 2018 various types of wood (including wood fuel, wood residues and by-products and wood pellets) accounted for 77 per cent of the solid biomass burnt for energy in the EU. Black liquor accounted for a further 14 per cent. The remaining 9 per cent was agricultural crop and animal residues and wastes.
Estimates suggest that in 2018 various types of wood accounted for 77 per cent of the solid biomass burnt for energy in the EU. Black liquor accounted for a further 14 per cent.
The term ‘residue’ is often used very loosely, whether in the context of forestry or sawmill residues. It can sometimes include any kind of roundwood not suitable for wood products – i.e. not the straight, unblemished and appropriately sized logs that sawmills generally demand. This can include, for example, ‘low-value’ or ‘unmerchantable’ wood, or diseased and storm-damaged trees. Regulators’ definitions, both in the EU and UK, are not always clearly drawn and often permit whole trees to be classified as ‘residues’. Company reports sometimes include ‘low-value wood’ in the same category as residues. ‘Thinnings’ – the selective removal of trees, primarily undertaken to improve the growth rate or health of the remaining trees – can be identified separately, but are also sometimes grouped together with genuine residues.
A 2021 report from the EU’s Joint Research Centre (JRC) concluded that almost half (49 per cent) of wood-based bioenergy production in the EU during 2009–15 could be classified as ‘secondary woody biomass’: forest-based industry by-products and recovered post-consumer wood. ‘Primary woody biomass’ harvested from forests made up at least 37 per cent of the input mix of wood for energy: about 20 per cent was stemwood (the main part of the tree, including larger branches) and 17 per cent forest residues. The remaining 14 per cent of the mix was uncategorized in the reported statistics, but the report’s authors believed it was likely to be primary wood. This category showed faster growth than the others over the study period, causing some concern over the ability of the data to reflect the real impact on the climate of using wood biomass for energy. Since 2015 the rate of extraction has increased significantly. As another JRC analysis concluded, the total area of forests clear-cut in the EU during 2016–18 was 49 per cent higher than in 2011–15. This may mean that the proportion of primary woody biomass burnt for energy has grown in recent years.
Looking more narrowly at US-sourced wood pellets burnt for energy, supply reports from Drax from 2015–19 indicate that on average almost one-half (48 per cent) of the wood was sourced from sawmill residues (25 per cent) and forest residues (23 per cent). Just over one-half (51 per cent) was from whole trees: 21 per cent from ‘low-grade roundwood’ and 30 per cent from thinnings. This is discussed further in the Annex.
2.2 Impacts on the climate
This discussion of feedstocks matters because the impact on the climate of burning wood for energy varies substantially depending on the type of feedstock used. As discussed in Woody Biomass for Power and Heat: Impacts on the Global Climate (Brack, 2017), burning any kind of wood for electricity or heat will produce more CO₂ than if fossil fuels are used to generate the same amount of energy (with a few exceptions for certain types of coal). For the same energy output, burning wood releases about 10–15 per cent more CO₂ than anthracite and about 100 per cent more than gas (under laboratory conditions, with the complete combustion of the fuel in the presence of oxygen). Biomass stations tend to have lower thermal and electrical efficiencies than coal or gas plants, so the real world differences will be larger.
Assuming that the harvested trees are replaced by new planting, these carbon emissions will be absorbed over time by forest regrowth, so the net impact on the climate depends on the balance between the level of emissions produced during harvesting, collecting, processing, transporting and burning the biomass and regrowth, and, crucially, what would have happened to the forest or the feedstock in the absence of demand for wood for energy – the counterfactual.
Carbon payback periods
Many attempts have been made to measure the net impact on the atmosphere of using different biomass feedstocks compared to using fossil fuels. The initial combustion, along with the associated life cycle emissions of the biomass feedstock, create what can be termed a ‘carbon debt’ – i.e. the additional emissions caused by burning biomass instead of the coal or gas it replaces, plus the emissions absorption forgone from the harvesting of the forest. Regrowth of the harvested forest removes this carbon from the atmosphere over time, reducing the carbon debt. The period until carbon parity is achieved – 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 the trees had been left unharvested.
The attempts made to estimate carbon payback periods suggest that they vary substantially, ranging from less than 20 years to many decades, and in some cases centuries, depending on the feedstock used and the efficiency of combustion. As would be expected, the shortest payback periods derive from the use of residues and wastes from forest harvesting or forest industries that imply no additional harvesting and, if otherwise burnt as waste or left to decompose, would release carbon to the atmosphere in any case. This includes, in particular, sawmill wastes (unless they are diverted from use for wood products), and black liquor that would otherwise require disposal. In many cases, burning these types of woody biomass for energy will be economic without the need for subsidy, particularly if burnt on site or if replacing high-carbon fossil fuels such as coal and oil.
If forest residues are used that would otherwise have been left to decompose in the forest, the impact is complex, as decay rates vary significantly depending on local climatic conditions. Burning slowly-decaying forest residues may mean that CO₂ levels stay higher in the atmosphere for decades longer than if fossil fuels had been used. In addition, excessive removal can reduce levels of soil carbon and rates of tree growth, increasing the period needed for the residual trees or new trees to compensate for the lost carbon.
The most negative impacts on carbon concentrations in the atmosphere derive from increasing harvest volumes or frequencies in already managed forests, harvesting natural forests or converting natural forests into plantations, or displacing wood from other uses. Where whole trees are harvested and used for energy, not only is the stored carbon in the tree released to the atmosphere immediately, but the tree’s future carbon sequestration capacity is lost.
On the other hand, in the absence of forest management, the rate of net carbon absorption by most forests falls as the incidence of dead and diseased trees increases, and over time the forest may also become more vulnerable to wildfire or other disturbances. There can, therefore, be long-term benefits from some level of harvesting. However, due to the urgency of the need to reduce greenhouse gas emissions, immediate benefits are more desirable.
The EU JRC’s recent report summarized a range of studies to suggest that only the use of fine woody residues from forest operations (tops, branches and needles) had short carbon payback periods (10–20 years) compared to the use of coal or gas. The use of coarse residues (snags, standing dead trees and high stumps), with generally slower decay rates, extended the carbon payback periods to more than 50 years.
Plantation forests have higher growth rates than natural forests and are typically harvested at a relatively young age. Naturally regenerated forests tend to be older and have larger trees when harvested. Therefore, more stored carbon is lost when natural forests are harvested, and it takes longer to replace that stored carbon emitted to the atmosphere. The conversion of natural forests to fast-growing plantations will therefore lead to a large release of carbon at the time of conversion, plus a lower stock of carbon when trees are harvested. While this may be somewhat offset by faster tree growth rates in the plantation, the net impact on forest carbon storage will be negative. A study looking at this scenario in the southern US found that the carbon payback period would be 60–70 years compared to using coal and 120 years compared to gas. Regular harvesting and clearing of plantations releases stored CO₂ back into the atmosphere every 10–20 years.
Limiting the types of feedstocks that may be burnt for energy can help to minimize negative impacts on the climate. This is why the 2017 Chatham House paper concluded that only sawmill residues and post-consumer wood waste should be eligible for subsidy. (While fast-decaying forest residues could also be acceptable, the practical challenges of identifying and verifying them are substantial.) The JRC paper similarly recommended that the use of coarse woody residues should be strictly constrained and that biomass produced from plantations established on recently cleared natural forest should not receive support.
Two further points about carbon payback periods are worth noting. First, the use of coal is being phased out steadily in the EU and rapidly in the UK, while the deployment of other renewables, particularly wind and solar, is increasing in both. Carbon payback periods measured comparatively to coal or gas are therefore not representative of current fuel mixes. The real payback periods compared to the average EU or UK fuel mix, with falling amounts of coal and rising amounts of renewables, are much longer.
Second, even if the carbon payback period is relatively short, there is still an impact on the climate during the years when CO₂ emissions are higher than they would otherwise have been. Some have argued that the length of the carbon payback period does not matter, as long as all emissions are eventually absorbed. A recent paper in GCB Bioenergy, for example, drew attention to the Paris Agreement’s aim of achieving ‘a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century’, which would therefore allow the use of feedstocks with carbon payback periods potentially up to 75–80 years. Yet the Paris Agreement also calls for parties to ‘aim to reach global peaking of greenhouse gas emissions as soon as possible’, a reference which is curiously omitted from the GCB Bioenergy paper.
As well as the provisions of the Paris Agreement, there is increasing concern over the possible existence of ‘climate tipping points’, when a small rise in global temperature prompts a large and potentially irreversible change in the global climate. Examples include boreal forest dieback, Amazon rainforest dieback, the loss of Arctic and Antarctic sea ice and the melting of the Greenland and Antarctic ice sheets. Although in 2013 the Intergovernmental Panel on Climate Change (IPCC) concluded that there was as yet no evidence for global tipping points, more recent studies have concluded that the probability is much higher than previously thought. The GCB Bioenergy paper cited a 2018 study that found a low probability of crossing a tipping point in the global climate system if warming does not exceed 2°C. Since the world is not currently on track to restrict warming to 2°C, this is not particularly reassuring.
All these arguments reinforce our conclusion that only biomass energy with the shortest carbon payback periods should be eligible for financial and regulatory support.
Attempts have been made in current policy frameworks to constrain the feedstock that is to be eligible for financial and regulatory support through the use of sustainability criteria. (The term ‘sustainability’ is somewhat misleading in this context. It is borrowed from the concept of sustainable forest management, which focuses on maintaining the extent of forest cover, not carbon stocks.) In the EU, the sustainability criteria for solid biomass introduced in the 2018 Renewable Energy Directive include requirements to ensure that the country of origin has either laws or forest management systems in place to ensure that forest biomass is legally harvested and sustainably sourced. These requirements include ensuring that the harvested forest is regenerated, that protected areas remain protected, that the impacts of harvesting on soil quality and biodiversity are minimized and that harvesting is limited to the long-term production capacity of the forest.
The country from which the forest biomass is sourced is required to be a party to the Paris Agreement which has submitted an NDC covering emissions and removals from agriculture, forestry and land use. The NDC must ensure either that changes in carbon stock associated with biomass harvests are accounted towards the country’s climate commitments or that there are laws in place to conserve and enhance carbon stocks and sinks. If evidence for these requirements is not available, forest management systems must be in place to ensure that forest carbon stock levels are maintained or strengthened.
There are also requirements for minimum greenhouse gas savings compared to fossil fuels: 70 per cent for installations starting operation after 2020 and 80 per cent for installations starting after 2025. (This relates only to supply-chain emissions, not to combustion emissions or changes in forest carbon stocks.) Finally, new biomass stations – i.e. those starting operation from 2022 – producing electricity with above 100 MW total rated thermal input (equating to about 30 MW electricity output capacity) must either use CHP technology or achieve a net electrical efficiency of at least 36 per cent or be a bioenergy with carbon capture and storage (BECCS) plant. (Stations between 50 and 100 MW have more relaxed efficiency rules and those below 50 MW no rules at all, though individual member states can decide to apply them.)
None of the above criteria apply at all to stations below 20 MW thermal rated input (about 7 MW electricity output capacity), though member states may choose to apply them, and, more broadly, may also choose to apply their own additional criteria.
In July 2021 the European Commission published a proposal for a revision of the criteria, as part of the ‘Fit for 55’ package of measures aimed at ensuring the EU meets its new target of a 55 per cent reduction in greenhouse gas emissions by 2030. The proposed changes include:
- The extension to forest biomass of the provision that feedstock must not be produced from land that was, at any time after 2008, classified as highly biodiverse grasslands, primary forest, highly biodiverse forest, protected areas, or be from wetlands or (with some exceptions) peatlands. This currently applies only to agricultural biomass.
- No support to be given to the use of saw logs, veneer logs, stumps or roots for feedstock.
- National legislation (or, where this is not available, forest management systems) should avoid harvesting of stumps or roots, the degradation of primary forests or their conversion into plantation forests and harvesting on vulnerable soils.
- The extension of the minimum greenhouse gas saving figure of 70 per cent to stations starting operation before 2021.
- The ending of support for the use of forest biomass in electricity-only installations after 2026, unless they are BECCS plants or are situated in a ‘region identified in a territorial just transition plan […] due to its reliance on solid fossil fuels’ (i.e. a coal-dependent region).
- The extension of the sustainability criteria to stations equal to or above 5 MW total rated thermal input.
The proposal must be agreed by the European Parliament and the Council of the European Union before it becomes law. Amendments can be expected.
The UK currently operates a simpler set of criteria, including similar requirements for legal and sustainable sourcing and targets for greenhouse gas savings per unit of electricity. These targets become stronger over time and, for existing contracts, currently average over the year at 200 kg CO₂eq/MWh, falling to 180 kg CO₂eq/MWh from April 2025 (with a higher ceiling for individual consignments of biomass). In August 2018, however, the UK government decided to lower the threshold for future contracts to 29 kg CO₂eq/MWh, which represented the median value of emissions from solid and gaseous biomass plants then operating in the UK. (As with the EU, the calculation includes only supply-chain emissions. It excludes emissions from combustion, changes in forest carbon stocks and emissions from indirect land-use change.)
For comparison, Drax’s annual supply-chain emissions from 2014 to 2019 came to an average of 124 kg CO₂eq/MWh, comfortably under the old threshold (and representing about a 70 per cent emissions saving compared to the life cycle emissions of hard coal of 414 kg CO₂eq/MWh), but well above the new one. About one-half of these emissions derived from the pelletizing process and 20 per cent from shipping (see Annex, section A2). The former figure could be reduced by using renewable sources of power, but it will be difficult to reduce the contribution of emissions from shipping. The new limit will therefore place severe constraints on the types and sources of biomass feedstock that can be used in future biomass stations, encouraging more local sourcing and possibly ruling out future imports of wood pellets entirely. In addition, new biomass plants will be required to have a minimum overall conversion efficiency of 70 per cent, which would require them to be CHP plants. Electricity-only stations generally have efficiencies below 40 per cent. These requirements do not apply to the contracts currently in place in the UK.
The proposed changes to EU sustainability criteria published in July 2021 seem unlikely to do much in practice to constrain the use of feedstocks, making them only slightly more effective in practice. None of the criteria currently apply to the smallest stations – i.e. those below 20 MW thermal rated input, which represents the majority of biomass plants in the EU and perhaps about 25 per cent of total feedstock consumption. The proposed lowering of the threshold to 5 MW would capture many of these. The efficiency criteria apply only to larger new plants, thus excluding the older and smaller plants that are more likely to have low efficiencies. The greenhouse gas saving criteria currently apply only to new plants, though the new proposals will extend them to existing plants too; however, they are not particularly stringent, particularly in comparison with the new UK criteria, which are far stricter. The proposal to extend support after 2026 for the use of forest biomass in electricity-only installations in coal-dependent regions is an open invitation to coal-to-biomass conversions.
The proposal to extend support after 2026 for the use of forest biomass in electricity-only installations in coal-dependent regions is an open invitation to coal-to-biomass conversions.
The sourcing criteria relate mainly to the existence of regulatory frameworks, rather than their implementation or effectiveness. Many of the conditions, such as the limitation of extraction to the ‘long-term production capacity of the forest’, are fairly loose. The European Commission’s July 2021 proposals help to tighten them somewhat, through banning sourcing from primary forests or plantations converted from primary forests, but there is very little primary forest left in the areas of the US (or EU) from which biomass is sourced, and the requirements are only retrospective to 2008. Sourcing from plantations that were converted from primary forest before 2008 would still be permitted.
Most importantly, the current criteria do not deal with the variability of carbon payback periods discussed above. The proposed ban on feedstock from saw logs, veneer logs, stumps or roots is welcome in so far as it introduces to the criteria the principle of limiting feedstock by category. In reality, though, specifying those categories will have very little effect. Saw logs and veneer logs are generally too valuable to use for energy, while stumps and roots are difficult and costly to extract. There is therefore still a strong argument for limiting support to the categories of feedstock with the shortest carbon payback periods. In January 2018 members of the European Parliament attempted to amend the draft directive to that effect but were defeated.
The impact of harvesting for biomass on forest and carbon growth rates
Another key element of the discussion is the question of whether the use of biomass for energy is likely to result in increased harvesting levels and a reduction in the overall volume of carbon stored in the forest. Claims are sometimes made that demand for wood for energy provides additional income to landowners, thereby encouraging them to maintain and possibly expand their forests, rather than allowing clearance. These claims are based on economic theory and are not consistent with the empirical evidence, which suggests the opposite. Demand for wood for energy leads to a reduction in the forest carbon store because the total area and volume harvested increases to meet this demand.
In 2014 the USDA Forest Service reported that, while forest hardwood inventories were expected to continue increasing to 2020, the rate of growth of forest carbon stocks would be lower as a result of demand for biomass for energy. It concluded: ‘Even assuming full utilization of mill residues and increased utilization of logging residues, harvest of pine and hardwood non-sawtimber feedstock increases […] hardwood inventories continue to increase although these end at lower levels’ than without new bioenergy demand. Subsequent projections by the USDA Forest Service indicated that increased demand for forest products (including bioenergy) would increase the area harvested, and a recent independent study used a similar harvest response scenario based on macroeconomic modelling. In 2018 a survey of forest professionals in the area of the three pellet mills in the southern US that supply the Drax power station in the UK concluded that demand for pellets led to additional harvesting in privately-owned pine plantations, mainly through thinning (although it was not leading to the overall expansion of plantations). A further study of the same area in 2021 confirmed that forest management practices on the non-industrial private forest pine plantations included thinning harvest treatments in the presence of pellet demand, and that thinnings were largely forgone in the absence of demand for wood pellets.
An average of 30 per cent of the feedstock for US-sourced wood pellets burnt by Drax during 2015–19 derived from thinnings. It is sometimes claimed that the practice of thinning can increase forest carbon storage, but almost all the studies on which this claim rests focus on volume growth of the remaining trees, conclude that this does not lead to an increase in total stand volume compared with an uncut stand, and have not reported statistics about carbon uptake by the ecosystem. A literature review in 1985 summarized how thinning affects growth and yield as measured by changes in volume, the metric reflecting the usual purpose of thinning – i.e. to increase merchantable volume. Most of the studies reviewed indicated that thinning would have no influence on total cubic volume yield or would reduce the total yield, unless the thinning were applied to extremely dense young stands in order to prevent stagnation of growth. In most cases, thinning increases the size of individual trees by redistributing the site’s growth potential to fewer stems through removals of suppressed or dying trees.
Until recently, almost all studies on thinning reported effects on volume, but not tree or ecosystem carbon. In 2010, however, results from three study sites where carbon fluxes were measured before and after thinning showed that it either had no effect on net ecosystem production or resulted in a reduction that rebounded after one or more years. Further studies have shown that the use of thinnings for energy does not reduce net greenhouse gas emissions for years at best, and can, under some circumstances, increase them. In general, intact forests with high tree species diversity largely free from human intervention have been shown to be the most carbon-rich ecosystems, with higher rates of biological carbon sequestration.
2.3 Reporting, accounting and incentives
Reporting greenhouse gas emissions
Parties to the UNFCCC are required to submit regular national inventory reports of their greenhouse gas emissions according to guidelines drawn up by the IPCC. While clearly recognizing that the harvesting of woody biomass and its burning for energy results in atmospheric emissions, the IPCC also acknowledged that reporting them in both the land-use sector – at the point of harvesting and removal from the forest – and in the energy sector – at the point of combustion – would result in double-counting. It was therefore determined that biomass emissions should only be included in the land-use sector. As mentioned in Chapter One, this categorization of emissions has contributed to many policymakers perceiving biomass as a carbon-neutral energy source, although this was not the IPCC’s intention.
This issue was addressed in the 2017 Chatham House paper, where it was suggested that reporting of biomass energy emissions should be moved to the energy sector, while at the same time additional rules should be implemented to avoid double-counting in the land use sector. This would shift the incentives to control emissions from producing to consuming countries – where the two are not the same, i.e. where biomass is traded internationally – and could thereby reduce incentives for the latter to use biomass for energy. However, this proposal could also lead to the inverse problem, of giving biomass-producing and exporting countries no incentive to control their use of forest biomass for energy. There would be no reason for them to limit production, since the associated reduction in their forest carbon stores would be transferred to the consuming countries’ energy sector reports (though demand from consuming countries would, presumably, fall in such circumstances). It would also complicate the reporting of the harvesting of wood for other uses, such as wood products, as some of this may end up being used for energy as post-consumer waste.
Accounting against national targets
In any case, however, it is not the global reporting of emissions under IPCC guidelines – which simply ensures that the global carbon budget balances – that causes the problem, but the impact on accounting against national targets for reducing greenhouse gas emissions, especially (though not only) where the countries producing and consuming the biomass are not the same. When importing countries replace fossil fuels with biomass for heat and power, they see an immediate fall in their emissions totals, since biomass combustion emissions are not included in their national figures. This enables them to make faster progress towards their targets than would otherwise be the case. Unless this is countered by the exporting countries recording a corresponding increase in their emissions totals and, as a consequence, adopting measures to reduce their other emissions accordingly, the system will not work to ensure that both producer and consumer countries achieve their respective climate goals.
This problem has been recognized by the IPCC itself. Its 2019 Special Report on Climate Change and Land observed: ‘One of the complications in assessing the total GHG [greenhouse gas] flux associated with bioenergy under UNFCCC reporting protocols is that fluxes from different aspects of bioenergy lifecycle are reported in different sectors and are not linked. […]Thus, the whole lifecycle GHG effects of bioenergy systems are not readily observed in national GHG inventories or modelled emissions estimates.’ Similarly, the 2021 EU JRC report drew attention to the same problem existing within countries, as well as between them, given the mismatch between policy signals for the energy and land-use sectors and the need for national policies to be guided by a full awareness of bioenergy-land-use links and trade-offs.
Resolving this problem can pose significant challenges. The weaknesses of the framework created under the 1997 Kyoto Protocol to the UNFCCC – the first international attempt to agree national targets for greenhouse gas emissions reductions – were explored in detail in the 2017 Chatham House paper. It identified the problem of ‘missing’ emissions – i.e. emissions unaccounted for against national targets – which could arise for two main reasons.
First, when a country using biomass for energy imported biomass from a country outside the accounting framework – e.g. the US, Canada and Russia, all significant exporters of woody biomass, that were either not parties to the Protocol or did not account for greenhouse gas emissions under its second commitment period.
Second, when a country using biomass for energy accounted for its biomass emissions either using a historical forest management reference level – its baseline – that included higher levels of biomass emissions than in the present or using a business-as-usual forest management reference level that included anticipated emissions from biomass energy. These problems arose from the complexity of establishing forest management reference levels (mainly because of the desire to allow for natural, as well as anthropogenic, changes in forest cover) and the decision to give parties to the Kyoto Protocol a choice of baselines against which they would measure changes in emissions. Most of them chose business-as-usual baselines that included – sometimes implicitly rather than explicitly – assumptions of increased growth in the use of forest biomass for energy. Emissions from harvesting forests for biomass in line with these projections would therefore count as zero for Kyoto Protocol accounting purposes, but would also count as zero in the energy sector. They were therefore ‘missing’ – unaccounted-for but nevertheless real – emissions.
The Kyoto Protocol’s second commitment period closed at the end of 2020, and in effect, its greenhouse gas reduction targets have now been replaced by the NDCs of the Paris Agreement. This helps to deal with the problem of importing biomass from countries outside the international framework, since almost every country is a party to the agreement, but it does not solve the double counting problem. Indeed, since the Paris Agreement does not establish any overall global framework for accounting for emissions, or any common means of setting forest management reference levels, the problem of ‘missing emissions’ is likely to be worse.
This problem may never be resolved within the Paris Agreement framework, since signatories are not required to include the land-use sector in their NDCs, or to include it in a consistent manner. The treatment of the land-use sector in the agreement was the subject of intense negotiations in the run-up to the Paris Conference in 2015. The agreement itself contains only limited references to it. While the decision of the Conference that accompanied the Agreement encouraged parties to ‘strive to include all categories of anthropogenic emissions or removals in their nationally determined contributions and, once a source, sink or activity is included, continue to include it’, they may choose not to do so. They may also choose to include land use or forests in broader economy-wide targets or to adopt separate quantitative targets expressed in non-emission metrics, such as a reduction of deforestation or an increase in forest cover.
A 2019 analysis of 167 NDCs submitted by January of that year found that 39 did not include any targets for the land use, land-use change and forestry (LULUCF) sector, 46 contained no separate targets, but integrated them into broader economy-wide targets, and only 27 contained separate LULUCF targets. Only 13 of those NDCs anticipated the use of any kind of accounting rules for their integrated targets and only 18 set out measures and policies for LULUCF mitigation. Where accounting for LULUCF emissions and removals was mentioned, the submitting countries chose a variety of accounting methods. Some proposed essentially the same system as all other emissions and removals (known as ‘net-net’ accounting). Some opted to use a variant of the Kyoto Protocol accounting rules and others intended to set accounting rules at a later date. Overall, the paper concluded that the combination of these ambiguities could cause an uncertainty in overall emission levels of about 3 gigatonnes of CO₂ (GtCO₂) per year in 2030, larger than the estimated total human-made land-use sink (-2 GtCO₂/year).
The EU has taken steps to improve its own LULUCF sector accounting. Under the LULUCF Regulation (2018/841), it will measure the climate impact of forest management using the ‘Forest Reference Level’ (FRL) concept: the projected level of forest emissions and removals for the period 2021–25, against which future emissions and removals will be compared. Whereas in the past these projections could include policy assumptions (for example, support for the use of wood for energy), with the risk of inflating the real impact of mitigation actions, the FRLs described in the regulation are exclusively based on the continuation of forest management practice and wood use during the period 2000–09. This should ensure that the kind of policy assumptions that could influence reference levels in accounting under the Kyoto Protocol are excluded and the carbon impact of any changes in management or wood use relative to a historical period is fully counted towards national climate targets. The 2021 JRC study suggested that this, combined with other measures, could allow the LULUCF sector to be treated, at least from 2030, like any other sector, which would: ‘introduce an important simplification of the LULUCF jargon, facilitate communication (i.e. it would be more evident that all the carbon impact of bioenergy is accounted for) and thus bring more transparency also in the accounting of forest bioenergy emissions’.
In January 2021 the US rejoined the Paris Agreement, having left it less than two years before. We do not know yet what targets it will set, or how it will treat the LULUCF sector and biomass for energy.
In January 2021 the US rejoined the Paris Agreement, having left it less than two years before. We do not know yet what targets it will set, or how it will treat the LULUCF sector and biomass for energy. In 2015, during negotiations prior to the Paris Agreement, the US indicated that it intended to track its greenhouse gas mitigation, including in the land-use sector, against a 2005 baseline. In 2005 US emissions from ‘forest land remaining forest land’ plus ‘land converted to forest land’ were -788.8 million tonnes of carbon dioxide equivalent (MtCO₂e) (a net carbon sink, represented as negative emissions). By 2018 this had fallen slightly to -773.8 MtCO₂e, with the reduction coming entirely from within the ‘forest land remaining forest land’ category.
Whether this reduction in the size of the forest carbon sink can be attributed to the extraction of wood for energy is impossible to determine from the US’s national inventory reports. The latest report included the comment that: ‘If timber is harvested to produce energy, combustion releases C immediately, and these emissions are reported for information purposes in the Energy sector while the harvest (i.e. the associated reduction in forest C stocks) and subsequent combustion are implicitly estimated in the LULUCF sector (i.e. the portion of harvested timber combusted to produce energy does not enter the HWP pools).’ [Authors’ own emphasis – HWP stands for harvested wood products.]
In other words, while emissions from the combustion of US-sourced biomass are definitely not accounted for against the national greenhouse gas targets of the EU or the UK (or of other countries importing biomass from the US), there is currently no way of knowing whether they are accounted for – at least to the same extent – against the US’s own targets. It should be possible to disaggregate this data, but if US data is as uncertain as EU data on the source of the wood used for energy (see above), the figures will not give an accurate picture of emissions from the extraction of wood for energy.
In any case, even if the figures could be accurately estimated and the accounting challenges overcome, the point remains that by treating biomass emissions as zero at the point of combustion, the system creates a significant incentive for consuming countries to burn wood for energy, despite CO₂ emissions to the atmosphere increasing (relative to fossil fuels) for a period of up to centuries as a result.
The incentives are even stronger at industry level. In the UK and most EU member states, energy companies are paid to burn biomass and face no responsibility to ensure that their emissions are compensated for elsewhere. Even if the country of origin reports higher land-use emissions as a result, that has no bearing on the activities of the company burning the biomass. And, as discussed above, it is not clear whether the country of origin will in reality come under pressure to reduce emissions elsewhere to compensate for higher land-use emissions. That depends on its own system of targets and incentives. Finally, as discussed above, even if the accounting rules and incentives can be adjusted to deal with these challenges, the policy framework will still lead to higher CO₂ levels in the atmosphere for the duration of the carbon payback period than would have occurred in the absence of support for burning biomass.