The planet is heading for feverish temperatures. With each increase in degrees, the climate is changing dramatically: sea levels are rising, Arctic ice is disappearing and entire species of animals are being wiped out. Of course, we need to reduce CO2 emissions. But despite 25 years of climate agreements and fine promises, emissions are still increasing. If we don't act vigorously, we are lost.

Could climate engineering be the emergency solution we need? Can these techniques and ideas cool the planet? And how risky are they?