The failure to make much progress at the UN Climate Change Conference in Doha, Qatar this winter was yet another reminder that the world might soon face extreme climate shifts. In response, it is becoming increasingly likely that governments will adopt risky strategies, known as “geoengineering,” to rapidly cool the planet. Four years ago, in order to raise awareness about geoengineering, we published “The Geoengineering Option” in Foreign Affairs. Almost nobody thought that such tactics -- which included spraying particles into the upper atmosphere to make the earth more reflective, akin to how big volcanoes cool the planet -- were a particularly good option. The risks were simply too great and the unknowns too many. Still, if reliable data and specific models showed that climate change was about to get out of hand, we wrote, such drastic measures might start to look more appealing. The world could no longer ignore the geoengineering option, and we argued that a major science program should begin to explore it.