Right now, a group of scientists is working on ways to minimize the catastrophic impact of global warming. But they're not designing hybrids or fuel cells or wind turbines. They're trying to lower the temperature of the entire planet. And they're doing it with huge contraptions that suck CO2 from the air, machines that brighten clouds and deflect sunlight away from the earth, even artificial volcanoes that spray heat-reflecting particles into the atmosphere. This is the radical and controversial world of geo-engineering, which only five years ago was considered to be 'fringe'. But as Jeff Goodell points out, the economic crisis, combined with global political realities, is making these ideas look sane, even inspired. Goodell himself started out as a sceptic, concerned about tinkering with the planet's thermostat. We can't even predict next week's weather, so how are we going to change the temperature of whole regions? What if a wealthy entrepreneur shoots particles into the stratosphere on his own? Who gets blamed if something goes terribly wrong? And perhaps most disturbing, what about wars waged with climate control as the primary weapon? There are certainly risks, but Goodell believes the alternatives could be worse. In the end, he persuades us that geoengineering may just be our last best hope - a Plan B for the environment. His compelling tale of scientific hubris and technical daring is sure to jump-start the next big debate about the future of life on earth.