Study: Biofuel production may affect climate

By Ryan C. Christiansen
Web exclusive posted July 11, 2008 at 11:20 a.m. CST

According to a paper published in the July-September 2008 issue of the journal Environmental Research Letters, the "carbon payback time" for biofuels mandates will be decades to centuries before biofuels are produced from feedstocks grown on agricultural land that has expanded into productive tropical ecosystems.

However, producing biofuels from feedstocks grown on agricultural land that has expanded into degraded or already cultivated land provides an almost immediate carbon savings, according to the paper. The paper is entitled "Carbon payback times for crop-based biofuel expansion in the tropics: the effects of changing yield and technology" and was written by researchers from the University of Wisconsin in Madison, Wisc., Arizona State University in Tempe, Ariz., and McGill University in Montreal.

The report's authors calculated the carbon payback estimates using data about crop locations and yields, as well as vegetation and soil biomass estimates. The researchers determined that biofuel crop expansion into natural landscapes could release 17 to 420 times more carbon dioxide than the annual greenhouse gas reductions the biofuels will provide by displacing fossil fuels. For example, the production of annual crops such as corn or soybeans on deforested land will require 300 to 1,500 years before carbon savings will be realized. On the other hand, carbon savings can be realized within less than 100 years on grasslands.

The report said that even if producers could double the ethanol yield per unit from sugarcane, the payback time will be more than 30 years to replace lost rainforest carbon.

The entire report can be found at the journal's web site,