With nations incapable so far of taking drastic steps to cut emissions of heat-trapping greenhouse gases, many scientists and policy specialists have started talking more openly about geoengineering, the deliberate manipulation of the environment to reverse the effects of climate change.

For them, geoengineering may be “a bad idea whose time has come,” said Eli Kintisch, a reporter for Science, at a AAAS forum on the topic.