I’ve been paying a lot of attention recently to new analyses attempting to model carbon emissions from indirect land use change, which is the conversion of land needed to maintain an international balance of supply and demand for agricultural crops, an effect that is heavily determined by crop prices. These new analyses raise a question about the existing assumption that oil has zero effect on land use change.
Tim Searchinger, the lead author of one of the Science papers that brought this debate to national attention, says, for instance,
The amount of land used to produce a gallon of gasoline is extremely small — according to some energy experts we have quickly consulted, it is less than 1 percent of the amount of land used to produce a gallon-equivalent of ethanol. Much of the world’s oil is either produced in deserts or offshore or on land that still remains in productive agricultural use. Because the effect of oil production on emissions from land use change is small, it is reasonable to omit it.”
Similarly, Dan Kammen and Thomas Hertel, et al., in a recent letter to the administrator of California’s Air Resources Board encouraging the inclusion of a large indirect land use emission number for biofuels in California’s Low Carbon Fuel Standard, say,
Our judgment incorporates recognition that land use effects of fossil fuels need to be compared to those of biofuels. Briefly, petroleum (with the important exception of strip-mined oil sands and oil shale) affects tiny amounts of land compared to biofuels per unit of energy obtained. Oil is extracted from open water, from deserts, and in any case from very small land footprints.”
The statements primarily address the direct land use change emissions of petroleum, assuming that because oil does not displace crop production it does not have an indirect effect on land use. However, indirect land use change is heavily mediated by crop prices. And as we’ve seen over the past year, oil has a significant impact on crop prices.
For biofuels to meet the new U.S. Renewable Fuel Standard, they must achieve “at least a 20 percent reduction in lifecycle greenhouse gas emissions compared to baseline lifecycle greenhouse gas emissions … for gasoline or diesel … sold or distributed as transportation fuel in 2005.”
A recent paper from Purdue University professors Thomas Hertel, Wallace Tyner, and Dileep Birur, assesses land use change in the 2001-2006 timeframe as a baseline for predicting land use change through 2015 in response to the U.S. and EU renewable fuel standards. The researchers find that in 2006, grain output in the U.S. increased by 7 percent. “The majority of this (5.6% output growth) was driven by higher oil prices,” and the change did lead to declines in output of other agriculture and forestry.
Searchinger’s original paper cites an estimate of the baseline carbon emissions for gasoline of 92 tons of CO2 per megajoule, and most analyses appear to adopt that figure. And Searchinger has publicly stated that it “makes little sense to reduce fossil fuels at expense of greater land conversion” when calculating the carbon emissions.
However, there is a need to study and model the true effect of biofuels and petroleum on land conversion and carbon emissions before drawing a final conclusion.