Biofuels made using corn waste could release 7 percent more greenhouse gases in the early years compared to conventional gasoline. As a result, this type of cellulosic ethanol could be inelligible to meet quotas under the 2007 Energy Independence and Security Act (EISA).

According to a new study published yesterday in Nature Climate Change, this type of cellulosic biofuel could result in a 7% net increase in emissions. The government-funded research states that the main cause of this increase comes down to absolute changes in soil carbon content.

The carbon content of soil is broadly a function of new inputs (plant and animal material) and losses (predominately via erosion and respiration). Conventionally, corn crop residue is left on the field after harvest in order to reduce soil erosion and maintain the carbon stocks and soil fertility.

By removing corn waste from fields, models indicate that soil carbon content will decrease over time. In turn, corn-waste ethanol will effectively produce 7% more carbon dioxide equivalent than conventional gasoline in the short-term. While the results vary according to the amount of carn residue that is removed, any removal resulted in a net increase in emissions in the model.

In the longer-term, the study says that these types of biofuels will result in a net emissions decrease. However, the short term increase is enough to keep this type of biofuel from complying with regulations in the 2007 Energy Independence and Security Act (EISA). This Act requires that biofuels produce 60% less pollution than conventional gasoline. This level is shown in relation to the study's results below:

David Tilman, a professor at the University of Minnesota who has done research on lifecycle emissions from biofuels has stated that "The study says it will be very hard to make a biofuel that has a better greenhouse gas impact than gasoline using corn residue." According to TIlman, this new study is the best that he has seen so far related to the corn-residue debate.

However, the study has already received significant criticism from the biofuels industry and Obama Administration officials. As a result, the sigificance of this study has been called into question, resulting in lingering uncertainty regarding the question "is corn-based ethanol (residue or otherwise) an advisable means of reducing energy-related greenhouse gas emissions?"

According to Jan Koninckx, global business director for biorefineries at DuPont "the core analysis [in this study] depicts an extreme scenario that no responsible farmer or business would ever employ because it would ruin both the land and the long-term supply of feedstock. It makes no agronomic or business sense." Furthermore, EPA spokeswoman Liz Purchia has stated that this study "does not provide useful information relevant to the life cycle greenhouse gas emissions from corn stover ethanol."

According to a 2012 peer-reviewed study performed at the Energy Department's Argonne National Laboratory, biofuels made with corn residue were 95% better than gasoline in greenhouse gas emissions. However, this study assumed some of the residue harvested would be used to replace coal-based electricity production (and their greenhouse gas emissions), which is not a certain outcome in ethanol biorefineries.

Photo Credit:

1. Photo of roasted corn on the cob in a bowl © stevendepoloby and used under this Creative Commons License.

2. Graph from Liska, et al. Biofuels from crop residue can reduce soil carbon and increase CO2 emissions. Nature Climate Change (2014) doi:10.1038/nclimate2187 Received 13 August 2013. Accepted 05 March 2014. Published online 20 April 2014