Recommendations for policy
Biomass energy feedstocks and impacts on the climate
Along with the total level of consumption of biomass for energy, the type of feedstock used plays a critical role in the impact of biomass use on the global climate. As discussed in the Chatham House paper, Woody Biomass for Power and Heat: Impacts on the Global Climate, any increase in forest harvesting rates caused by demand for energy will in almost all circumstances increase net carbon emissions very substantially compared to using fossil fuels, because of the combustion of stored carbon in the wood, the loss of future carbon sequestration from growing trees and the release of soil carbon consequent upon the disturbance.
Some types of biomass feedstock can be carbon-neutral, at least over a period of a few years: wastes from forest harvesting or forest industries that imply no additional harvesting, and if otherwise burnt as waste or left to rot would release carbon to the atmosphere in any case. This includes in particular sawmill wastes such as sawdust, and black liquor from the pulp and paper industry that would otherwise have to be disposed of. It can make sense to burn these types of woody biomass for energy (particularly on-site, with no need for processing or transport, but also if they replace high-carbon fossil fuels such as coal or oil), and in many instances this will be economic without the need for subsidy. Fast-decaying (small-diameter) forest residues, however, may not always be usable by biomass plants, and burning slowly decaying forest residues for energy may mean that carbon levels stay higher in the atmosphere for decades longer than if fossil fuels had been used, which is a matter of considerable concern given the current rate of global warming. If mill residues are diverted from use as wood products to use as energy (for which there is relatively little evidence to date), net carbon emissions will be higher as a result.
The carbon payback approach argues that while carbon emissions from burning woody biomass are higher than using fossil fuels, they can be absorbed by forest regrowth. The length of time this takes – the carbon payback period before which carbon emissions return to the level they would have been at if fossil fuels had been used – is of crucial importance. The many attempts that have been made to estimate carbon payback periods suggest that they vary substantially, from less than 20 years to many decades, and in some cases even centuries. As would be expected, the most positive outcomes for the climate, with short payback periods, derive from the use of mill residues (unless diverted from use for wood products). If forest residues are used that would otherwise have been left to rot in the forest, the impact is complex, as their removal may reduce levels of soil carbon and rates of tree growth. The most negative impacts involve increasing harvest volumes or frequencies in already managed forests, converting natural forests into plantations or displacing wood from other uses.244
Detailed data on biomass energy feedstocks are not always available, but a 2015 study for the European Commission estimated that, across the EU, wood fuel not suitable for industrial use accounted for 33 per cent of feedstock, black liquor for 27 per cent, industrial residues (e.g. from sawmills) for 24 per cent, and forest residues for 16 per cent.245 ‘Dedicated harvest of stemwood (for example pulpwood) for bioenergy plays a marginal role in EU produced feedstocks’ – but of course this has the potential to change with continued expansion of biomass energy use. (These figures differ from the 2015 study summarized in Table 3 in Chapter 2, which included equivalent figures of 27 per cent for wood fuel, 16 per cent for black liquor, 18 per cent for industrial residues and 14 per cent for forest residues.246 Another 23 per cent, however, was accounted for by post-consumer waste wood and wood pellets, some of which were imported, so the calculation has been carried out on a different basis.)
The feedstock for imports, particularly of wood pellets from North America and Russia, is a contentious subject. While pellet and biomass energy companies generally claim their original source as mill and forest residues, the evidence suggests that, particularly in the southeast of the US (the main source of pellet exports to Europe) roundwood is used extensively. In 2015, two studies concluded that only about a quarter of the feedstock used to produce pellets in the southern US was mill residues and forest residues, and three-quarters was pulpwood.247 (This topic is explored in more detail in the Chatham House paper, Woody Biomass for Power and Heat: Impacts on the Global Climate.) A further increase in EU imports of pellets from these sources – which seems likely – will, all else being equal, therefore have increasingly negative impacts on the climate, as well as on local ecosystems in the forests of origin. However, if EU or US forest industries expand – for example if climate policies encourage a greater use of wood in construction – the supply of mill and forest residues may increase, somewhat ameliorating this.
Recommendations
It is therefore important for policymakers in the EU to control the types of biomass feedstock used – and supported by EU and member states’ policy frameworks – in order to limit negative impacts on the climate. The burning of forest or mill residues that otherwise have no use, or would be burnt as waste; combustion for heat rather than electricity, or through combined heat and power; minimal transport distances (as in black liquor); and higher energy efficiencies of the technology in use; all contribute to reducing the carbon payback period. It is also, of course, vital that the forest carbon stock is replaced as fast as possible, not just through replanting – which, in replacing mature trees with much smaller young trees, leads to an overall reduction in carbon stocks for a period of years or decades – but in planting more trees and expanding forest area overall (note that this is not the same as ‘sustainable forest management’, which implies simply replanting to maintain forest area).
It is important for policymakers in the EU to control the types of biomass feedstock used – and supported by EU and member states’ policy frameworks – in order to limit negative impacts on the climate.
In principle, sustainability criteria can be used to distinguish between these different variables. None of the national sets of criteria currently in use achieve this, most notably in their failure to take account of changes in the forest carbon stock – though in limiting eligible feedstocks for support to wastes and residues, the Italian criteria do go some way to addressing this (see Chapter 7). The criteria proposed in the draft new Renewable Energy Directive (see Chapter 2) are similarly inadequate, partly because of the weaknesses in the system of accounting for biomass emissions from the land-use sector (see Chapter 12) to which they refer.248
Therefore, as argued in the 2017 Chatham House paper:
- In assessing the climate impact of the use of woody biomass for energy, changes in the forest carbon stock must be fully accounted for. It is not valid to claim that because trees absorb carbon as they grow, the emissions from burning them can be ignored. (From an accounting perspective, this is because absorption of carbon by forests prior to the setting of climate policies occurs in both the climate policies scenario and the fossil fuel counterfactual. Therefore, it cannot be treated as a credit in one scenario without treating it as a credit in the other.)
- Along with changes in forest carbon stock, a full analysis of the impact on the climate of using woody biomass for energy needs to take into account the emissions from combustion (which are generally higher than those for fossil fuels) and the supply-chain emissions from harvesting, collection, processing and transport. There is still some uncertainty over some of these factors, and they can vary considerably with the origin of the wood; further research would be helpful.
- The provision of financial or regulatory support to biomass energy on the grounds of its contribution to mitigating climate change should be limited to those feedstocks that reduce carbon emissions over the short term.
- In practice, this means that support should be restricted to sawmill residues, together with post-consumer waste. Fast-decaying forest residues could also fit into this category, but in practice this is small-diameter material that is likely to contain too much moisture and dirt to render it easily usable by biomass plants; and it would be difficult for policy to distinguish easily between fast and slow-decaying residues. Burning slow-decaying forest residues or whole trees means that carbon emissions stay higher than if fossil fuels had been used for decades, which is a matter of considerable concern given the current rate of global warming.
This is not to argue, of course, that fossil fuels should not be replaced by renewable energy for power and heat: this is essential if the world is to escape the most catastrophic impacts of climate change. It is to argue, rather, that public support and subsidy should be used for renewable technologies that reduce carbon levels in the atmosphere in the near term as well as the long term: some forms of biomass, as argued above, but primarily genuinely zero-carbon renewables such as solar or wind.
244 See Brack, D. (2017), Woody Biomass for Power and Heat: Impacts on the Global Climate, pp. 27–31.
245 European Commission (2016), Commission Staff Working Document – Impact Assessment: Sustainability of Bioenergy, Annex 5.
246 Indufor (2017), Outlook for Wood Energy for Biomass in the EU-28.
247 Strange Olesen et al. (2015), Environmental Implications of Increased Reliance of the EU on Biomass from the South East US, pp. 95–96; RISI (2015), An Analysis of UK Biomass Power Policy, US South Pellet Production and Impacts on Wood Fiber Markets, p. 20, http://docplayer.net/25281897-An-analysis-of-uk-biomass-power-policy-us-south-pellet-production-and-impacts-on-wood-fiber-markets-prepared-for-the-american-forest-paper.html (accessed 2 Feb. 2018).
248 For a longer discussion, see Brack, D. (2017), Woody Biomass for Power and Heat: Impacts on the Global Climate, p. 66.