1 SUPERCHARGE THE STRATOSPHERE
Instead of making clouds brighter, another idea is to release particles into the atmosphere that can reflect the Sun’s radiation themselves. This year, Harvard professors David Keith and Frank Keutsch, designers of the Stratospheric Controlled Perturbation Experiment (SCoPEx), plan to launch a high-altitude balloon 20km into the air near Tucson, Arizona, and spray a small quantity of calcium carbonate particles to see what happens.
2 OCEAN SEEDING
“Give me half a tanker of iron, and I will give you an ice age,” said the late oceanographer John Martin in 1988. Although he was half joking, Martin stood by his idea of using iron to boost plankton and increase the carbon dioxide taken up from the atmosphere. Since then, several tests have been carried out. A key question is how much of the plankton will actually sink to the seabed, locking the carbon away from the atmosphere.
3 SPACE REFLECTORS
It sounds implausible – place a giant reflective sunshade in space to block off some of the sunlight that reaches Earth. Wacky as it sounds, this idea has been receiving some consideration: in a report by the Royal Society, it was suggested that in the long-term, some form of space sunshade may be cheaper and less risky than a geoengineering project in the stratosphere. Tests are currently confined to modelling effects of various approaches.