It's the option climate negotiators here are loath to talk about.
What if they fail to curb global warming and the environment gets so dangerous that someone decides to do something drastic and play mad scientist? Should nations purposely pollute the planet to try to counteract man-made warming and cool the world? Scientists are pretty sure they can do it, but should they?
The issue is called geoengineering — purposely tinkering with the planet as opposed to the unintentional warming that's happening now. The most talked about and advanced method involves putting heat-reflecting particles high in the air, but there also have been proposals to seed clouds other ways, put mirrors in space and seed the oceans with iron.
Scientists noticed a temporary but pronounced cooling after the 1991 eruption of Mount Pinatubo in the Philippines. What's in mind would be, essentially, an artificial and constant man-made volcano with material released by aircraft or cannons.
No one is talking about doing it — yet. But some scientists want to study it to find about side effects and other issues. And earlier this year, the U.S. National Academy of Sciences said small-scale and controlled experiments could be helpful to inform future decisions.