More than 300 watts per square meter of sunshine hits the top of Earth's atmosphere each year. A third is reflected and the sky, sea and land absorb the rest. Much of that warmth tries to escape back to space but only a little over half makes it each year. That proportion is declining as concentrations of gases in the atmosphere, notably carbon dioxide, edges ever upward. The result: global warming.
To a tinkerer's mind there is an obvious solution: block some of that sunlight from coming in. That's the solution known as geoengineering—the large-scale manipulation of the planet’s environment, in this case the sky. As negotiators at the climate talks underway here spar over what to do about adding more CO2 to the air, geoengineering becomes more and more attractive to those with this tinkerer's bent—a group dubbed the "geoclique" by journalist Eli Kintisch in his 2010 book Hack the Planet: Science’s Best Hope—or Worst Nightmare—for Averting Climate Catastrophe. These scientists, engineers and businessmen want to at least study options for blocking sunlight, which they say can be relatively inexpensive when compared with the bill for transforming the trillion-dollar global energy system that largely burns fossil fuels.
Geoengineering is also part of the appeal of big physics, once reserved for hydrogen bombs and subatomic particles. Figuring out how droplets of sulfuric acid sprayed into the stratosphere might offset rising CO2 offers physicists a chance to have a literal global impact. As journalist Oliver Morton details in his new book "The Planet Remade: How Geoengineering Could Change the World," the geoclique is calling the approach "solar-radiation management," to fend off critics who call the sulfur idea far-fetched, or dangerous.