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.)
WHAT IT MEANS: Farms grow food that keeps us healthy, and we need them to keep our atmosphere cool—which gives you one more good reason to patronize your local farmer’s market. In tough economic times, we don’t need farmers going out of business and having their cooling croplands converted to a highway or suburban subdivision.
Diffenbaugh’s study didn’t get down to microlevel comparisons of the size of each farm, or determine whether the farms used organic farming methods. But research at the Rodale Institute has found that unlike chemical-based agriculture, organic farming adds carbon to the soil, rather than releasing it into the atmosphere, where it contributes to global warming. So seeking out organic farms gives you an opportunity to do double duty in fighting climate change. You can locate a farmer’s market, and find local farms to support, at www.localharvest.org.