Biofuels Studies Summary

The following is an ENE summary of recent biofuels studies published in Science magazine .

Recent scientific studies have cast doubt on the ability of biofuels to reduce greenhouse gas emissions when compared to fossil fuels.  In fact, large-scale cultivation of biofuels could lead to increases in emissions.  Devoting large areas of land to biofuel production will displace crop and meat production.  This will either lead to new forest and grassland being cleared for crops, or increased cultivation of marginal agricultural lands that would otherwise have been allowed to revert back to forest.  Clearing forests for crops causes large releases of greenhouse gases.

Older models that calculate the life-cycle emissions of fossil fuels and biofuels have not been able to account for this indirect impact on land use.  However, two studies recently published in the online edition of Science magazine look at this issue in detail.

The first study (1), done in cooperation with The Nature Conservancy and The University of Minnesota, found that the negative emissions impact of converting rainforests, peatlands, or grasslands to produce biofuels in tropics and in the United States was 17 to 420 times larger than than the greenhouse gas reductions these biofuels could provide by displacing fossil fuel use. In contrast, biofuels made from waste biomass or from abandoned agricultural lands planted with perennial crops offer immediate and sustained greenhouse gas benefits.

The second study (2)  found that using corn ethanol in place of fossil fuels doubles greenhouse gas emissions over 30 years.  Upfront emissions from land conversion are large, and the study showed it would take 167 years for the emissions benefits of corn ethanol to balance out the upfront losses. Using switchgrass to make ethanol also increases emissions by 50%.  However, Brazilian sugarcane has the potential to reduce emissions after 4 years in certain cases, and the study found that waste products (municipal waste, crop wasted and grass harvests) could also provide immediate benefits. 
 

(1) J. Fargione, J. Hill, D. Tilman, S. Polasky, and P. Hawethorne. 7 February 2008.  Land clearing and the biofuel carbon debt. Science. (10.1126/science.1152747).

(2) T. Searchinger, R. Heimlich, R.A. Houghton, F. Dong, A. Elobeid, J. Fabiosa, S. Tokgoz, D. Hawes and T. Yu.  7 February 2008.  Use of U.S. croplands for biofuels increases greenhouse gases through emissions from land use change.  Science.  (10.1126/science.1151861).