Dec. 21, 2006 — For those hot days at the ocean, a beach umbrella can help block the sun's heat and ultraviolet radiation. Now an orbiting sunshade could do the same for the planet, in the event of a global warming emergency.
The sunshade, proposed by Roger Angel of the University of Arizona in a recent issue of Proceedings of the National Academy of Sciences, would be made of trillions of transparent, platter-sized spacecraft
flying together in an elliptical formation.
Like a light-blocking cirrus cloud, the flock of spacecraft would diffuse about two percent of the sun's
energy away from the Earth.
"You wouldn't notice anything at all. Aesthetically it's not too bad," said Angel, who is director of the university's Steward Observatory Mirror Laboratory and its Center for Astronomical Adaptive Optics. "But frankly I'm at the point that even if it produced a nasty black spot on the sun, it's what I'd take to fix global warming."
According to Angel, the idea of blocking some of the sun's energy to reduce global warming has been around for about 20 years. Some have envisioned a large shade, while others have proposed increasing the whiteness
of clouds to reflect sunlight back into space.
Angel preferred the shade solution because it change the Earth's atmospheric chemistry, but he knew that deploying a large structure would be a challenge.
So instead of one shade, he devised a plan to launch trillions of disc-like craft, each 2 feet in
diameter. Made from a lightweight film, each vehicle would weigh as little as a butterfly.
