The thermostat. What an invention! Your house gets too hot, just crank the thermostat down a few degrees and you’re good to go.

Now, what if we could put a thermostat on our too-hot planet?

As it happens, we could. A few billion dollars is all it would take to deploy a version of solar-radiation management (SRM), a form of geoengineering that would seed the stratosphere with reflective aerosols, creating a sort of sunshade for the planet.