Biomass is considered a
renewable energy source because its inherent energy comes from the sun and because it can regrow in a relatively short time. Trees take in carbon dioxide from the atmosphere and convert it into biomass and when they die, it is released back into the atmosphere. Whether trees are burned or whether they decompose naturally, they release the same amount of carbon dioxide into the atmosphere. The idea is that if trees harvested as biomass are replanted as fast as the wood is burned, new trees take up the carbon produced by the combustion, the carbon cycle theoretically remains in balance, and no extra carbon is added to the atmospheric balance sheet—so biomass is arguably considered “carbon neutral.” Since nothing offsets the CO2 that fossil fuel burning produces, replacing fossil fuels with biomass theoretically results in reduced carbon emissions.
In fact, the reality is a lot more complicated. In 2014, the U.S. Environmental Protection Agency (EPA) found that “carbon neutrality cannot be assumed for all biomass energy a priori.” Whether or not biomass is truly carbon neutral depends on the time frame being studied, what type of biomass is used, the combustion technology, which fossil fuel is being replaced (since the combustion of both fossil fuels and biomass produces carbon dioxide), and what forest management techniques are employed in the areas where the biomass is harvested.
In 2010, a group of prominent scientists wrote to Congress explaining that the notion that all biomass results in a 100 percent reduction of carbon emissions is
wrong. Biomass can reduce carbon dioxide if fast growing crops are grown on otherwise unproductive land; in this case, the regrowth of the plants offsets the carbon produced by the combustion of the crops. But cutting or clearing forests for energy, either to burn trees or to plant energy crops, releases carbon into the atmosphere that would have been sequestered had the trees remained untouched, and the regrowing and thus recapture of carbon can take decades or even a century. Moreover, carbon is emitted in the combustion process, resulting in a net increase of CO2.
