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Widespread cultivation of perennial grasses for ethanol production could lower regional surface temperatures by nearly 2 degrees F, according to Stanford researchers. Credit: Chung-Ho Lin, Agricultural Research Service, USDA
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Converting
large swaths of farmland to perennial grasses for biofuels could lower regional
surface temperatures, according to a recent Stanford study.
The study,
published online in Proceedings of the National Academy
of Sciences (PNAS),
comes on the heels of federal initiatives to wean the United States off fossil fuels by
mandating significant increases in ethanol production. The Department of
Agriculture forecasts
that by 2018, more than one-third of the country's corn harvest will be used to
produce ethanol.
But concerns
about the impact of corn ethanol on food prices, deforestation, and global
warming have raised interest in the cultivation of perennial grasses—such as
switchgrass—as alternative sources of biofuel. Previous studies suggest that
ethanol made from switchgrass emits less carbon dioxide than corn-derived
ethanol and would therefore have less of an impact on global warming.
In the PNAS study, researchers found that
widespread cultivation of perennial grasses could reduce the surface
temperature of Earth at a regional scale.
"We've
shown that planting perennial bioenergy crops can lower surface temperatures by
about 2 degrees Fahrenheit locally, averaged over the entire growing
season," said study co-author David Lobell, assistant professor of environmental
Earth system science and a center fellow at Stanford's Program on Food
Security and the Environment. "That's a pretty big effect, enough to dominate any effects
of carbon savings on the regional climate."
In the study,
Lobell and his colleagues used a computer simulation to forecast the
climatic effects of converting farmland in the Midwest
from annual crops—like corn and soybeans—to perennial grasses. The results
showed that large-scale perennial cultivation in the 12-state area would pump
significantly more water from the soil to the atmosphere, producing enough
water vapor to cool the local surface temperature by 1.8 F.
"Locally,
the simulated cooling is sufficiently large to partially offset projected
warming due to increasing greenhouse gases over the next few decades," the
authors wrote.
"A key
issue remaining is whether the additional water being pumped from the soil gets
fully replenished by rainfall, or whether in the long term the soil dries and
can't support the same amount of crop production," Lobell said.
"More study is needed to understand the long-term implication for
regional water balance," added lead author Matei Georgescu of the Center
for Environmental Fluid Dynamics at Arizona State Univ. "This study
focused on temperature, but the more general point is that simply assessing the
impacts on carbon and greenhouse gases overlooks important features that we
cannot ignore if we want a bioenergy path that is sustainable over the long
haul."
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