When biomass is used to produce energy, it is considered “carbon-neutral” by most standards. The rational here is that the emissions released through the burning of biomass do not add any new greenhouse gases to the atmosphere because the trees absorbed CO2 as they grew, and the gases produced during combustion end up being reabsorbed by new trees planted to replace the burned ones. However, this carbon-neutral claim has recently faced increased scrutiny, as the treatment of biomass in cap-and-trade accounting is called into question.
A recent paper, “Fixing a Critical Climate Accounting Error,” published in Science (Vol. 326, October 23, 2009) raises serious concerns about this manner of carbon accounting. The study, led by Princeton’s Tim Searchinger, assessed the impact of bioenergy in climate change mitigation efforts. The authors explain that the way we account for carbon emissions from biofuels is a “far-reaching but fixable flaw that will severely undermine the green house gas reduction goals.” Presently, the calculation methods for carbon emissions from biofuels does not include CO2 emitted from tailpipes and smokestacks when biofuels are used. Furthermore, current methodology does not count changes in carbon emissions from land use when biomass raised for energy use is harvested or grown.
Ignoring emissions associated with land-use, Searchinger and his co-authors write, “erroneously treats all bioenergy as carbon neutral,” which is a problem because the accounting method can lead to large differences in net emissions. In addition, cap-and-trade programs can exacerbate this problem, as the Wall Street Journal explains, because developed countries get credit for fossil fuel use reductions from ethanol (which is considered carbon neutral), yet these biofuels are grown on land in developing countries where the land-use emissions are not counted. In a similar study, a team of researchers led by Jerry Melillo of the Marine Biological Laboratory in Woods Hole, Massachusetts concluded that the effects of major biofuels expansion could end up increasing global greenhouse-gas emissions instead of reducing them. Time Magazine reports that Melillo found that if biofuels were linked to a global policy to stabilize carbon concentrations in the atmosphere at 550 parts per million (a modest goal) we would need more land for biofuel production by the end of the 21st century than we currently use for all food crops.
The solution?
Fix the accounting of bioenergy. The study’s authors explain “that means tracing the actual flows of carbon and counting emissions from tailpipes and smokestacks whether from fossil energy or bioenergy.” In other words, the use of biomass should receive renewable energy credit when its use actually results in the reduction of greenhouse gas emissions. A perfect example of this is the use of biowastes, such as the wood debris from construction and demolition activities, crop residues or animal manure, as a fuel in advanced clean technologies, to displace fossil fuel use.
