Wood is increasingly being used to replace coal as a source of electricity generation in many regions such as the European Union, where policymakers have declared it “carbon neutral.” However, new research from researchers at MIT, Climate Interactive, and UMass Lowell reveals that displacing coal with wood for power generation can make climate change worse for many decades or more.
In the new study, Does replacing coal with wood lower CO2emissions? Dynamic lifecycle analysis of wood bioenergy, the researchers—John Sterman, the Jay W. Forrester Professor of Management at MIT Sloan School of Management;Juliette Rooney-Varga, Director of the UMass Lowell Climate Change Initiative; and Lori Siegel, PhD, Senior Modeler for Climate Interactive—examine the climate impact of replacing coal power generation in the EU and UK with wood pellets sourced from forests in the Southern United States. The research is slated for publication on Friday, January 19, 2018 in the academic journal, Environmental Research Letters. The paper can be accessed online at http://iopscience.iop.org/article/10.1088/1748-9326/aaa512/pdf
The researchers found that wood pellets burned in European and UK power plants, such as the Drax facility in North Yorkshire—which has transitioned some of its coal power generation capacity to wood pellets with the support of UK government subsidies—actually emit more CO2 per kilowatt hour than that generated by coal. This is because wood is both less efficient at the point of combustion and has larger processing and supply chain emissions than coal. Their research shows that using wood instead of coal in power generation increases the amount of CO2 in the atmosphere, worsening climate change until—and only if—the harvested forests regrow.
US forests are a main source for EU wood pellet imports, which have been rising as demand has grown. These forests grow back slowly, so it takes a long time to repay the initial “carbon debt” incurred by burning wood instead of coal. For forests in the central and eastern US, which supply much of the wood used in UK power plants, the payback time for this carbon debt ranges from 44 to 104 years, depending on forest type—and assuming the land remains forest. If the land is developed, or converted to agricultural use, then the carbon debt is never repaid and grows over time as the harvested land emits additional carbon from soils.