Is biomass really ‘zero carbon’?

So far it has only managed to do so with two of them, partly as a result of the British government’s crackdown on green energy subsidies in 2015. However, the criticism of the company hasn’t gone away, with the focus now having moved from coal to biomass, in tune with the company’s own attempts to become more sustainable.

This debate is rather complex, to say the least. Predictably perhaps, both Drax and its supplier, Enviva, deny charges of incorrect calculation of emissions and unsustainable harvesting. The overall impression, at first sight, is that one side says one thing while the other side says another. Who to believe?

The various criticisms against Drax have led to a complaint being delivered to the US financial regulator, the Securities and Exchange Commission (SEC), signed by the managers of 34 US pensions and investment funds. This alleges that Enviva has exploited a loophole in EU and UK law classing wood pellets as ‘zero carbon’ in order to falsely claim that its wood pellet fuel emits far less carbon dioxide than coal. It also maintains that Drax’s own data shows that although burning coal produces emissions of 1,901 pounds of carbon dioxide per megawatt hour (MWh), the figure for wood is significantly higher at 2,128 pounder per MWh.

Another allegation, based largely on on-the-ground investigations by the American environmental group Dogwood Alliance, claims that Enviva is sourcing its wood pellets from whole tree trunks that are clearcut from southern US forests. The group obtained photographs of 40-foot high hardwood trunks being transported to the Enviva pellet plant at Ahoskie, North Carolina, as well as areas of forest land that had been cleared for wood pellet production.

The EU rules classify wood pellets as zero-carbon on the basis that the trees used to supply them are replaced or will grow back, thereby reabsorbing the carbon dioxide emitted from burning biomass. This argument is based around a method of emissions calculation devised by former Department of Energy and Climate Change (DECC) chief scientist Professor David MacKay. This system is known as the Biomass Emissions and Counterfactual Model (BEAC). A study by the Spatial Informatics Group (SIG) questions the effectiveness of BEAC, but Drax and Enviva have both countered that the study, led by Dr Thomas Buchholz, used “a mountain of assumptions” and had applied BEAC incorrectly.

The standard thinking about biomass, for example noted by Carbon Brief, states that when trees are cut down and burned they release the carbon dioxide absorbed by them back into the atmosphere. However, the amount of carbon dioxide released can’t be more than was absorbed in the first place, thus trees are effectively carbon neutral. Nevertheless there are a range of other factors that must be taking into account, including the type of wood being burnt, be it whole logs, branches, twigs or sawdust and the location from where the trees were sourced. Research by the EC Joint Research Centre and also by Princeton University has found that the length of time taken by trees to regrow can mean that burning of whole trees leads to more carbon emissions than coal. This conclusion was apparently shared by BEAC and the news about this was leaked by environmental NGOs, something that in turn led to protests by its designer David MacKay and the Renewable Energy Association (REA) ‘Back Biomass’ campaign on the basis that at the time the system was still in development.

The REA ‘Back Biomass’ campaign rejects this notion that regrowth time (known as the ‘carbon debt’) can lead to higher emissions, because it’s based on the notion of harvesting a single tree. Standard forestry practice operates by harvesting and regrowing different sections, known as ‘stands’ or ‘plots’, at different stages. This in turn ensures a regular income for foresters and keeps the whole operation economically viable. The argument of the Back Biomass campaign is that demand from the biomass industry underpins that viability and that therefore the carbon debt argument is actually a myth. Consequently, the REA has come out strongly against the criticism of biomass by NGOs, branding their allegations as ‘scaremongering’ and ‘misinformation’ and REA chief executive Gaynor Hartnell commenting that their views on the matter are not “worthy of your stature”.

The US Natural Resources Defence Council (NRDC) claims that southern US forests are now at risk from the pellet industry. However, overall evidence shows that US forests are in fact growing, not receding. For example, the Abundant Forests Alliance noted in 2007 that the volume of American hardwood and softwood trees have grown by 49 percent between 1953 and 2006.

Nevertheless, the UK has taken the Buchholz study seriously and an EU delegation recently visited the states on a fact-finding mission to assess the impact of EU biomass policies. All of which means this argument has a while to run yet.