Science article on GHG accounting misses the mark on biofuels

Posted October 22, 2009, at 3:30 p.m. CST

Biofuels produced from biomass feedstocks (i.e. plant matter) are, by definition, carbon neutral because carbon dioxide tailpipe emissions from the combustion of biofuels are readily absorbed by growing plants. As such, the tailpipe emissions resulting from the use of a gallon of ethanol produced from corn grown on U.S. farmland are negated by the growing of the corn itself.

Yet, in a newly published article in Science, frequent biofuel critics Tim Searchinger, Dan Kammen, and others argue that this widely held scientific convention is erroneous. They argue that biofuels and other biobased energies should be accountable for the biogenic tailpipe and "smokestack" CO2 emissions that are absorbed by growing feedstocks and carbon emissions that could result from land clearing. The authors argue that existing and proposed regulations, such as the so-called U.S. cap and trade bill, create an accounting loophole that will lead to increased deforestation. They conceptually propose an unnecessary and impossible system that would trace actual flows of carbon.

However, the release of CO2 from recently living organisms has no overall effect on atmospheric CO2 levels and is therefore carbon neutral because atmospheric CO2 decreases when a plant photosynthesizes, then increases back to its initial level when that carbon (in the form of a biofuel) is burned and returned to the atmosphere. In this way, biofuels "recycle" organic carbon.

Conversely, accepted carbon accounting for fossil fuels such as petroleum does include tailpipe emissions from combustion. This is because the carbon in fossil fuels has been sequestered underground for millions of years rather than recently sequestered by growing organisms and cannot be naturally offset by feedstock uptake.

The United Nations Framework Convention on Climate Change (UNFCCC) consciously made the decision to treat biogenic emissions as carbon neutral when it established its carbon accounting guidelines. The scientific and regulatory communities, for their part, have always used this convention when analyzing the carbon impacts of bioenergy. For instance, the emissions from combustion of fossil fuels are appropriately placed under the cap in the House-passed cap-and-trade program while biogenic tailpipe or "stack" emissions from biomass are exempted.

After analyzing the article from the standpoint of U.S. biofuel production, the Renewable Fuels Association released the following statement:

"There is undeniable evidence that the climate concerns we face have been caused in large measure by the reckless use of finite fossil fuel resources. Developing a host of renewable alternatives, including from biomass feedstocks, should be a central goal. While recognizing that all carbon-based energy has associated carbon emissions, we must look for the least carbon-intensive alternatives and favor approaches that ‘recycle' above-ground carbon. Based on a fair apples-to-apples comparison with petroleum, biofuels clearly offer society a lower-carbon path forward.

"The real issue is not accounting tactics, but whether biofuels reduce GHG emissions compared to continued petroleum use. There is clear and substantial evidence that they do.

"The biogenic emissions resulting from the use of biofuels are recycled during the plant's growth via the photosynthesis process. This stands in stark contrast to petroleum, which when combusted releases carbon that has been stored underground for millions of years.

"RFA strongly agrees with the authors that natural ecosystems with high carbon storage-such as rainforest, peat soils, and other native lands-absolutely should not be converted to produce biofuel feedstocks. Those who directly convert these land types for biofuel crop production or any other purpose should be severely penalized and every effort should be taken locally to prevent this type of direct action.

"However, there is no credible evidence that positively links U.S. biofuels expansion to the conversion of these land types. There are ample supplies of agricultural land available, together with improvements in agricultural technology, to meet the energy and food demands of a growing population."