Wind farms are supposed to be environmentally friendly, but research reported in Nature indicates that large wind farms actually contribute to warmer temperatures, at least at the local level. At nighttime, after the sun goes down, the earth’s temperature usually decreases. Large wind farms mix that cold air with warmer air aloft, increasing the local temperature. This could have an eventual effect on wildlife in the area and could also affect the weather regionally, since warmer air contributes to cloud formation and wind speeds. The research was done in Texas, which has four of the largest wind farms in the world. China is reportedly erecting 36 wind turbines a day (Telegraph, April 29).