A new analysis by Michigan State University (MSU) researchers suggests that other studies that have concluded that land use changes resulting from biofuel production are significant contributors to greenhouse gas emissions are based on a set of assumptions that may not be correct.

In a paper published in the journal Science in February 2008, Timothy Searchinger from Princeton and colleagues at Woods Hole Research Center and Iowa State University concluded that, for example, when emissions from land-use change are considered, corn-based ethanol, instead of producing a net 20% savings in greenhouse gases, nearly doubles greenhouse emissions over 30 years and increases greenhouse gases for 167 years. Biofuels from switchgrass, if grown on US corn lands under the same analysis, increase emissions by 50%. (Earlier post.)The time required for biofuels to overcome the GHG emissions resulting from land use change (the “carbon debt”) and to begin providing cumulative greenhouse gas benefits is referred to as “payback period” and has been estimated to be 100-1000 years depending on the specific ecosystem involved in the land use change event. There are two mechanisms for land use change:

“Direct” land use change, in which the land use change occurs as part of a specific supply chain for a specific biofuel production facility; and “Indirect” land use change, in which market forces act to produce land use change in land that is not part of a specific biofuel supply chain, including, for example, hypothetical land use change on another continent.

MSU Professor Bruce Dale and his co-authors point out in a paper published in the January online edition of the journal Environmental Science & Technology, that existing land use change studies did not consider many of the potentially important variables that might affect the greenhouse gas emissions of biofuels.

For example, they note, their analysis shows that cropping management is a key factor in estimating greenhouse gas emissions associated with land use change. Sustainable cropping management practices (no-till and no-till plus cover crops) reduce the payback period to 3 years for a grassland conversion case and to 14 years for a forest conversion case.

No-till and cover crop practices also yield higher soil organic carbon (SOC) levels in corn fields derived from former grasslands or forests than the SOC levels that result if these grasslands or forests are allowed to continue undisturbed.

The debate over the causes and effects of land use change has significant implications for the future of the US biofuels industry. As required by EISA, the US Environmental Protection Agency (EPA) is establishing a methodology for determining the lifecycle greenhouse gas (GHG) emissions from the production of various biofuels, including GHGs from indirect land use changes.

In their paper, Dale and his co-authors note that since the US currently does not hold any of its domestic industries responsible for their greenhouse gas emissions, the greenhouse gas standards established for renewable fuels set a higher standard for that industry than for any other domestic industry.

Holding domestic industries responsible for the environmental performance of their own supply chain over which they may exert some control is perhaps desirable (direct land use change in the case of biofuels production), they write. However, holding domestic industries responsible for greenhouse gas emissions by their competitors worldwide through market forces (via indirect land use change in this case) is “fraught with a host of ethical and pragmatic difficulties”.

Greenhouse gas emissions associated with indirect land use change depend strongly on assumptions regarding social and environmental responsibilities for actions taken, cropping management approaches, and time frames involved, among other issues. The discrepancies between the time it will take biofuels to offer environmental benefits is due to the models used for each analysis, Dale notes.

There are no real data on what actually happens as demand increases for land for biofuel production in one part of the world potentially leads to land clearing, because it is impossible to track these relationships in the real world. All the estimates are based on economic relationships and theoretical models with various data and assumptions. It’s really one set of assumptions versus another set. The other scientists believe their assumptions are more reasonable, and we believe ours are more reasonable.

How land is managed after it’s converted to cropland is very important. The authors of the Science paper assumed the worst-case scenario—plow tillage—which we don’t think is accurate. The actual use of sustainable management practices—no till, reduced till and other approaches—is more than 50 percent and increasing.

—Bruce Dale

Resources

Timothy Searchinger et. al. Use of US Croplands for Biofuels Increases Greenhouse Gases Through Emissions from Land Use Change. Science 7 February 2008 DOI: 10.1126/science.1151861 Hyungtae Kim, Seungdo Kim and Bruce E. Dale (2009) Biofuels, Land Use Change, and Greenhouse Gas Emissions: Some Unexplored Variables. Environ. Sci. Technol., Article ASAP doi: 10.1021/es802681k