The risks of global warming are pressing and potentially vast. The difficulty of doing without fossil fuels is daunting, possibly even insurmountable. So there is an urgent need to rethink our responses to the crisis. To meet that need, a small but increasingly influential group of scientists is exploring proposals for planned human intervention in the climate system: a stratospheric veil against the sun, the cultivation of photosynthetic plankton, fleets of unmanned ships seeding the clouds. These are the technologies of geoengineering--and as Oliver Morton argues in this visionary book,...