New study proves it: Farms are cool.

05-13-09 RODALE NEWS, EMMAUS, PA—Can farmland cool the planet? A new study published in the journal Climate Dynamics has found that, at a very local level, the air above farms is cooler than the air above forests, suggesting that the evaporation of water from the earth may be helping to combat climate change. “There’s a lot of evidence that land cover influences climate,” says Noah Diffenbaugh, PhD, the study’s author and interim director of Purdue University’s Climate Change Research Center. “The science certainly points to crops having a general cooling effect overall, and that they have some slight effect on the warming trend.”

THE DETAILS: Using computer modeling and historical data, Diffenbaugh compared temperatures over the U.S. based on what the landscape looks like today (more farms and fewer forests) to those seen when our landscape was covered with more forests and fewer farms. The farms, he found, had a definite cooling effect at the local level; the air above them was a few degrees cooler in the modern land cover model than it was in the historically forested model, at some points as much as 6 degrees Centigrade cooler.

Water released by the crops seems to have an effect on local air that’s similar to the way sweat cools the body. “Energy is required for the transition of water from liquid to vapor,” Diffenbaugh says. “There’s a cooling of air associated with it.” That mechanism may explain why forests didn’t have the same effect. We still need forests, of course, but they pull water out of the air and store it underground so we have drinking water. (Though this study didn’t include urban and suburban areas, previous research suggests they’re big contributors to heating up their local environment.)