While small-scale biomass heating and cogeneration plants may be a legitimate advance toward a renewable energy economy, large-scale biomass electricity presents the Faustian choice of burning the forest to keep the lights on.

Electricity from biomass is increasingly promoted as a “green” alternative to fossil fuels. As in a coal– or natural gas–burning power plant, biomass fuels are burned to make steam, which drives a turbine to generate electricity. Although biomass can refer to many different potential fuels including crop residue, construction waste, and garbage, the majority of existing biomass-fueled power plants burn wood. As of 2012, hundreds of new biomass-fueled facilities are proposed or under construction around the United States.

The U.S. Energy Information Agency’s 2009 electricity generation data shows about 1 percent coming from biomass. Wood has a much lower energy density than fossil fuels, which means that the mass of raw material input per electrical energy output is much higher for biomass than for either coal or natural gas. To meet even a modest percentage of current U.S. electricity demand with biomass would require dramatically increased logging of the nation’s forests, and increased removal of woody debris, which is vital for wildlife and healthy forest soils. Industrial biomass energy production, particularly whole-tree harvesting for wood chip–burning power plants, is a growing threat to forest ecosystems.

Biomass burning also produces dangerous air pollution, which is why many physician and medical groups are opposing biomass energy projects. Although biomass energy in theory has no net contribution to global greenhouse gas emissions because the carbon dioxide released during combustion will be recaptured by future forest growth (some question this assumption because climate change may reduce overall forest cover), there is a timing issue that is often overlooked by biomass proponents. The important time horizon for greenhouse gas reductions is the next fifty years. While CO2 emitted by burning wood will eventually be sequestered, full recovery can be on the order of several centuries. Thus burning wood today may exacerbate global warming in the near term, especially since more wood must be burned compared to other fuels to get the same amount of energy.