The bioenergy carbon accounting debate is back. Leading scientists from around the US recently sent a letter to congressional leaders and Obama officials urging accurate accounting for CO2 emissions in laws and regulations designed to reduce GHG emissions.
With the passage of the American Power Act, bioenergy carbon accounting is back in the purview.
Most recently, a group of leading scientists from across the country sent a letter last week to congressional leaders and Obama officials urging them to accurately account for CO2 emissions from bioenergy in laws and regulations designed to reduce greenhouse gas (GHG) emissions.
Proper accounting can enable bioenergy to contribute to greenhouse gas reductions; improper accounting can lead to increases in greenhouse gas emissions both domestically and internationally.
The theory behind bioenergy carbon accounting errors, which is linked to land use change, was first postulated by a paper published in Science by Timothy D. Searchinger and other leading scientists (summarized here). Nathanael Greene offers a video explanation of the theory on NRDC’s blog, Switchboard.
The theory is best articulated by the authors of the letter:
Replacement of fossil fuels with bioenergy does not directly stop carbon dioxide emissions from tailpipes or smokestacks. Although fossil fuel emissions are reduced or eliminated, the combustion of biomass replaces fossil emissions with its own emissions (which may even be higher per unit of energy because of the lower energy to carbon ratio of biomass). Bioenergy can reduce atmospheric carbon dioxide if land and plants are managed to take up additional carbon dioxide beyond what they would absorb without bioenergy. Alternatively, bioenergy can use some vegetative residues that would otherwise decompose and release carbon to the atmosphere rapidly. Whether land and plants sequester additional carbon to offset emissions from burning the biomass depends on changes both in the rates of plant growth and in the carbon storage in plants and soils. For example, planting fast-growing energy crops on otherwise unproductive land leads to additional carbon absorption by plants that offsets emissions from their use for energy without displacing carbon storage in plants and soils. On the other hand, clearing or cutting forests for energy, either to burn trees directly in power plants or to replace forests with bioenergy crops, has the net effect of releasing otherwise sequestered carbon into the atmosphere, just like the extraction and burning of fossil fuels. That creates a carbon debt, may reduce ongoing carbon uptake by the forest, and as a result may increase net greenhouse gas emissions for an extended time period and thereby undercut greenhouse gas reductions needed over the next several decades.
Carbon legislation has a long way to go in the US, which suggests this issue will surface fairly frequently.
More on carbon accounting from Biomass Intel: