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By Jocelyn Timperley

Excerpted from the Carbon Brief


Subsidies should end for many types of biomass, a new Chatham House report argues, because they are failing to help cut greenhouse gas emissions.

The report adds that policymakers should tighten up accounting rules to ensure the full extent of biomass emissions are included.

The analysis outlines how policies intended to boost the use of biomass are in many cases “not fit for purpose” because they are inadvertently increasing emissions by often ignoring emissions from burning wood in power stations and failing to account for changes in forest carbon stocks.

It argues that UK and recently revised EU rules for bioenergy are inadequate for managing and monitoring the emissions from burning biomass.

Carbon Brief examines the main arguments of the report, which cut through the long-running debate about the climate impacts of burning biomass.

Contentious issue

The rising demand for renewable power around the world has led to a large increase in the production and burning of wood pellets. Advocates, such as power firm Drax – the UK’s largest biomass user – argue they are more reliable for providing baseload power than other renewables, such as wind or solar.

Worldwide production hit a record 28 million tonnes (Mt) in 2015, according to the UN Food and Agriculture Organisation (FAO), up from under 20Mt just three years earlier. Meanwhile, the UK has become the world’s largest importer of wood pellets, burning 42% of the 15.5Mt of total global imports in 2015.

The chart below shows how global electricity generation from biomass, which includes wood pellets, more than doubled between 2005 and 2015.

As the chart shows, the EU is now the world’s biggest user of biomass for electricity generation. Bioenergy is expected to contribute 57% of the EU’s total renewable energy by 2020.

Following calls for the EU to introduce better safeguards for biofuels, a revised legislation proposal in the latest EU energy package in December introduced new sustainability criteria for bioenergy production.

These included new rules aimed at ensuring forests are harvested sustainably and conservation areas are protected. It also established new thresholds for how much greenhouse gas emissions need to be saved by switching to biofuels.

However, the Chatham House report argues that even countries who have already begun to apply these new criteria largely fail to include changes in the levels of forest carbon stock in their calculation of greenhouse gas savings.

The report attacks two underlying assumptions which are used to classify biomass as “carbon neutral”. It argues financial and regulatory support should only be given to biomass feedstocks which cut carbon emissions in the short term – which it says is not the case for most of the woody feedstocks used for biomass energy.

Wood for trees

The first assumption is that since trees absorb carbon as they grow, forest growth will balance the carbon emitted by burning wood for energy. For example, the methodology specified in the 2009 EU Renewable Energy Directive for calculating emissions from biomass only considers supply-chain emissions and counts combustion emissions as zero. Several national frameworks including the UK’s also make this assumption.

However, the reality of the situation is more complicated, the report argues. (See this Carbon Brief investigation for more.) The overall emissions from burning trees will depend on a variety of factors, including the type of woody biomass used, what would have happened to it if it had not been burnt for energy, and what happens to the forest from which it was sourced.

For instance, the report argues harvesting whole trees to burn as wood pellets will nearly always results in more emissions than using fossil fuels instead, since the trees will no longer sequester carbon as they grow and soil carbon can be lost during the harvesting. This is particularly the case for older trees, which sequester more carbon than younger trees.

The so-called “carbon payback period” – the time it takes for regrowth of the forest to reabsorb the emissions from biomass – also becomes important here. In a context where climate tipping points could be crossed in the short term, as some evidence suggests, increasing the amount of carbon in the atmosphere, even for a few decades, becomes relevant.

The report suggests only biomass energy with the shortest carbon payback periods should be eligible for financial and regulatory support. The feedstocks which are most likely to reduce net carbon emissions would be primarily mill residues and post-consumer waste.

In addition, since woody biomass is less dense and contains more moisture than fossil fuels, burning wood for energy usually emits more greenhouse gases per unit of energy produced than fossil fuels.

Meanwhile, supply-chain emissions from harvesting, collecting, processing and transport all play a role in the total climate impact of biomass feedstocks. The report says:

“Overall, while some instances of biomass energy use may result in lower life-cycle emissions than fossil fuels, in most circumstances, comparing technologies of similar ages, the use of woody biomass for energy will release higher levels of emissions than coal and considerably higher levels than gas.”

Some types of biomass feedstock which do not require extra harvesting – such as sawmill residues or black liquor – can be carbon-neutral at least over a period of a few years, the report adds. This is especially likely if these are burnt on-site as this will reduce emissions from transport and processing.

However, even for waste feedstocks, it is still important to consider whether they could have been used for other, lower carbon purposes. For instance, mill residues can also be used for wood products, which would keep the carbon trapped in materials, such as particleboard, for several decades more than if it is released into the atmosphere through burning it.

The concerns highlighted in the report are also relevant to bioenergy with carbon capture and storage (BECCS). This is the leading candidate to provide the negative emissions which are heavily relied on in many pathways to global climate goals, including those for the UK.

If the assumption that biomass is effectively emission free at the point of burning is flawed, then this puts a serious dent in the potential of BECCS providing negative emissions. The report reads:

“The reliance on BECCS of so many of the climate mitigation scenarios reviewed by the IPCC [International Panel on Climate Change] is of major concern, potentially distracting attention from other mitigation options and encouraging decision makers to lock themselves into high-carbon options in the short term on the assumption that the emissions thus generated can be compensated for in the long term.”