Climate change is caused by human activities — and maybe by more of them than previously thought. That was the conclusion of a report released today by NASA, which found that land-use changes such as farming, irrigation, and urban sprawl contribute as much if not more to climate change than does the burning of fossil fuels. According to the report, changing land-uses in North America, Europe, and Southeast Asia are redistributing heat regionally and globally; for example, irrigated farmlands in Colorado have contributed to a cooler, wetter climate in the area by adding moisture to the atmosphere, and deforestation in the tropics has led to higher temperatures there and elsewhere. Steve Running, an ecology professor at the University of Montana and one of the authors of the study, said international dialogue about climate change has neglected the impact of land-use change: “All of [the Kyoto Protocol on climate change] was based on reducing greenhouse gas emissions. … We’re not trying to replace [Kyoto] but instead bring in an additional variable that has been ignored.”