A new report from Chatham House has reignited debate over biomass as a carbon-neutral form of energy
The report, Woody biomass for power and heat: impacts on the global climate, argues that biomass emits more carbon per unit of energy than most fossil fuels because wood is less energy-dense.
Biomass’s claim to carbon neutrality rests on the planting of trees to absorb and store released carbon from burning biomass. However the report, written by former US government advisor Duncan Brack, argues that replacement trees absorb and store less CO2 because of their young age, and the losses of soil carbon from disturbance of the forest can delay a forest’s capacity to act as a carbon sink for 10-20 years.
“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,” the report says.
The report says even the use of forest residues instead of whole trees can result in net carbon emissions, particularly if slow-decaying residues are burnt. “In addition, removing residues from the forest can adversely affect soil carbon and nutrient levels as well as tree growth rates.”
The UK is the biggest importer of wood pellets for heat and power in the EU. It shipped in 7.5m tonnes in 2015, mostly from the US and Canada, and biomass now accounts for 9% of electricity generation. This is mostly to supply giant coal-power producer Drax, which is in the process of converting its coal-power plants to biomass, and received £450m in government subsidies in 2015.
In Channel 4 debate last week, Brack faced off against his former boss, Chris Huhne, who was energy secretary in 2010-12 and is now European chairman of Zilkha Biomass, a US supplier of wood pellets. Drack argued that the UK should not be subsidising biomass as a source of renewable energy. “We should instead be putting our money into zero-carbon technologies such as solar, wind, tidal or energy efficiency. We are taking stored carbon out of forests and burning it and we are subsidising that, which isn’t a good use of public money.”
Huhne countered that if farmers were not able to get an income from selling wood for wood pellets, they would sell their forests off for agriculture, removing a valuable carbon sink. “There’s been an increase in the amount of carbon stored in [US] forests.” He also argued that biomass was an important source of renewable energy because, unlike solar and wind, it is not intermittent in nature.
After the Channel 4 programme, Drax defended its use of biomass in a statement: “The biomass we use is sustainably sourced from working forests where biodiversity is protected, productivity is maintained and growth exceeds what is harvested. We take the low-grade material to make the compressed wood pellets used to generate electricity ... There is a widespread scientific consensus that this low-value wood is precisely the material which delivers the biggest carbon reductions.”