“The big thing nuclear weapons did wasn't all the details,” says Harvard climate scientist David Keith. “The really big thing is, they changed what it means to be a nation-state.” It’s on his mind because as the next century unfolds, Keith expects it to happen again.

Scientists usually shy away from Oppenheimer comparisons, but in the case of geoengineering, they’re a given. Spend enough time at geoengineering conferences, and you’re guaranteed to hear a reference to The Bomb. Keith, who has grown into geoengineering’s leading advocate after his recent book on the topic, says the technology would be “as disruptive to the political order of the 21st century as nuclear weapons were for the 20th." It’s an exciting, dangerous idea — and it already has its opponents. In the years that he's been researching geoengineering, Keith says he's received two death threats serious enough to warrant calls to the police.