As global warming’s effects become evident researchers have turned to geoengineering schemes that could slow the warming process, like a global “sunshade” produced by spraying sulfur aerosols into the atmosphere to reflect sunlight back into space. But a new study points out an (obvious in retrospect) drawback of that idea: It would seriously reduce the effectiveness of some solar energy facilities, which proponents hope would reduce our dependence on fossil fuels and thus prevent further global warming.