Methane is a greenhouse gas with dual personalities. It heats Earth's atmosphere 28 times as potently as carbon dioxide, gram for gram. But its absorption of the sun's radiation high in the atmosphere also alters cloud patterns - casting a bit of shadow on its warming effect. So rather than adding even more thermal energy to the atmosphere, as previously thought, methane's solar absorption sets off a cascade of events that reduces its overall warming effect by about 30 percent, researchers report March 16 in Nature Geoscience.