Irrigation may lose to global warming

California's Central Valley has been buffered against global warming by the expansion of irrigated cropland, but the cooling effect may not help much in the future, according to scientists at Lawrence Livermore Laboratory. Evaporation from irrigation cools the land surface, and the steady addition of newly irrigated land during the past century has counteracted rising temperatures in agricultural areas. The average cooling effect has slowly increased as irrigation expanded to more than 12,700 square miles for a total of between 3.2 and 5.8 degrees.