Scientists identify new implications for perennial bioenergy crops

Feb 28, 2011

A team of researchers from Arizona State University, Stanford University and Carnegie Institution for Science has found that converting large swaths of land to bioenergy crops could have a wide range of effects on regional climate.

In an effort to help wean itself off fossil fuels, the U.S. has mandated significant increases in renewable fuels, with more than one-third of the domestic corn harvest to be used for conversion to ethanol by 2018. But concerns about effects of corn ethanol on food prices and deforestation had led to research suggesting that ethanol be derived from perennial crops, like the giant grasses Miscanthus and . Nearly all of this research, though, has focused on the effects of ethanol on , which drive global warming.

"Almost all of the work performed to date has focused on the carbon effects," said Matei Georgescu, a climate modeler working in ASU's Center for Environmental Fluid Dynamics. "We've tried to expand our perspective to look at a more complete picture. What we've shown is that it's not all about , and that modifying the landscape can be just as important."

Georgescu and his colleagues report their findings in the early online edition (Feb. 28, 2011) of the . Co-authors are David Lobell of Stanford University and Christopher Field of the Carnegie Institution for Science, both located in Stanford, Calif.

In their study, the researchers simulated an entire growing season with a state-of-the-art regional climate model. They ran two sets of experiments – one with an annual crop representation over the central U.S. and one with an extended growing season to represent perennial grasses. In the model, the perennial plants pumped more water from the soil to the atmosphere, leading to large local cooling.

"We've shown that planting perennial bioenergy crops can lower surface temperatures by about a degree Celsius locally, averaged over the entire growing season. That's a pretty big effect, enough to dominate any effects of carbon savings on the regional climate," said Lobell.

The primary physical process at work is based on greater evapotranspiration (combination of evaporated water from the soil surface and plant canopy and transpired water from within the soil) for perennial crops compared to annual crops.

"More study is needed to understand the long-term implication for regional water balance," Georgescu said. "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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Sean_W
5 / 5 (1) Feb 28, 2011
If these grasses are also being planted in areas that would not be used for harvesting and would have less vegetation naturally they are likely also producing particulates and aerosols that result in cloud nucleation and more rain down wind. None of this is necessarily bad, especially if irrigation is from a sustainable source like reclaimed waste water/grey water or low energy desalinization or from rivers which are not over taxed already. If the area down wind is also a dry climate it can result in more diverse and productive wilderness or replenish aquifers.