Scientists react to Chatham House biomass rebuttal

Materials World magazine
,
31 Mar 2017

Chatham House has published a paper arguing that energy policies for woody biomass are not fit for purpose. Simon Frost reports.

Burning woody biomass for power and heat is more likely to increase than reduce carbon emissions, according to a study published in February by prominent think tank Chatham House, UK. It concludes that current biomass policy frameworks equating it with renewables are not fit for purpose.   

Its author, environmental policy analyst Duncan Brack, notes that biomass is classified as a renewable energy source in national policy frameworks, which has led to similar regulatory and financial supports as those for solar, wind and tidal energy. However, the study claims, combustion of woody biomass typically emits carbon dioxide and methane at higher levels than coal and considerably more than gas. 

Supporters of biomass argue that sustainable management of forests offsets the CO2 that is released during combustion. Dr William Strauss, President of wood pellet consultancy FutureMetrics, USA, said that the study ‘does not understand how the forest products industry operates’. In his counter article, ‘Alternative Facts’ in the Recent Chatham House Paper, he writes that ‘the inherent sustainability of the resource that accrues from good forest management practices means that the aggregate carbon stock held in private forests are not being depleted’.

Brack’s report, however, disputes the industry’s assurances that carbon emissions from burning biomass can be absorbed by forest regrowth, highlighting the difficulty of calculating the carbon payback period. ‘The many attempts that have been made to estimate carbon payback periods suggest that these vary substantially, from less than 20 years to many decades and in some cases even centuries,’ he writes. Brack believes that a short-term net increase in emissions would preclude greenhouse emissions peaking in the near term – a condition of targets set in the 2015 Paris Agreement. 

Dr Glen Li, Department of Wood Science and Engineering at Oregon State University, USA, told Materials World, ‘Comprehensive life-cycle analyses of supply chain emissions specific to different feedstocks are challenging, particularly at this moment when appropriate methodologies are still under development. Not until the analyses are completed can the identification of feedstocks with low carbon payback periods be conducted on a quantitative basis.’ 

These feedstocks range from the remainder of harvested whole trees (after the high-value sawlogs have been sold for lumber), to sawdust and other waste from sawmills – already widely used for power at the mills themselves – and black liquor, a waste product of the pulp industry. Brack holds the latter to be the most appropriate feedstock for biomass energy, as it has no other use, unlike other wood waste products that can be made into products like MDF, keeping carbon stored.

While Li concurs with Brack’s argument that changes in forest carbon stock should be accounted for when assessing the life-cycle of woody biomass, he maintains reservations about reviewing energy policies while life-cycle analyses remain contentious. Instead, Li proposed that technology combining bioenergy with carbon capture and storage should be encouraged by policy incentives. 

One staunch opponent of biomass energy is the climate scientist Professor Mark Z Jacobson, Director of the Atmosphere and Energy Program at Stanford University, USA, and a leading advocate for a swift, global shift to a 100% renewable energy mix. 

Jacobson supports Brack’s paper, but noted that it does not account for black and brown carbon, and so ‘underestimates the global warming and health effects of biomass burning,’ he told Materials World. ‘It is physically impossible for woody biomass to be carbon neutral, even if there were no energy involved in cutting and transporting it, because the timelag between burning and regrowth mathematically requires an accumulation of CO2 in the atmosphere,’ he said. 

Asked whether biomass has any part in the energy mix of the future, his answer was direct. ‘No, particularly due to the air pollution impacts, regardless of the climate impact. The best use of woody biomass is to let it accumulate and soak up more carbon rather than burning it, causing hundreds of thousands of premature mortalities each year.’ 

Health concerns were also voiced by François-Marie Bréon, Senior Scientist for the Alternative Energies and Atomic Energy Commission, France. ‘Biomass burning is often incomplete, so it generates gases other than CO2, such as carbon monoxide, ozone and aerosol particles. These gases and aerosols contribute significantly to the degradation of air quality,’ he told Materials World. ‘In France, it is the primary contribution to pollution in some valleys of the French Alps, despite heavy traffic. Even in the Paris urban area, it has been shown that biomass burning contributes around a third of pollution particles.’ 

As we went to press, the IEA Bioenergy programme claimed that the report ‘does not present an objective overview of the current state of scientific understanding with respect to the climate effects of bioenergy.‘ Until supporters and sceptics agree on a definitive model for carbon accounting, it appears that biomass will remain a subject with few areas of consensus. 

To read Woody Biomass for Power and Heat: Impacts on the Global Climate, visit bit.ly/2mnKMnL