A Swarm of Umbrellas vs. Global Warming: Astronomer thinks small to save Earth

Some wives ask their husbands to take out the garbage. Roger Angel’s wife asked him to get rid of global warming.

COOLING CONCEPT. Miniature flyers made of transparent film would deflect sunlight from Earth. Three solar-reflecting tabs on each flyer direct its course. This illustration shows background starlight blurred into doughnuts by the film. Angel, T. Connors/Univ. of Arizona

Prompted by her plea, Angel, an astronomer and acclaimed telescope-mirror designer at the University of Arizona in Tucson, began pursuing a space-based solution.

In the plan he came up with, a trillion miniature spacecraft, each about a gram in mass and carrying a half-meter-diameter sunshade, would shield Earth.

This cloud of sun-orbiting flyers, about 1.5 million kilometers from Earth and stretching over a distance of about 100,000 km, would act as a mostly transparent umbrella for the entire planet.

The cloud would reduce by 1.8 percent the amount of sunlight reaching Earth, and that shading would significantly cut global warming, Angel calculates. He describes his ambitious plan, which he says could be deployed in about 25 years at a cost of several trillion dollars, in the Nov. 14 Proceedings of the National Academy of Sciences.

Previous schemes to reduce the sunlight reaching Earth had required far heavier craft with larger shades. Such vehicles would have to be built in space from lunar material or asteroids.

In contrast, Angel’s proposed flyers, which include shades made of transparent film and riddled with holes, can be built and assembled on Earth, he asserts.

Rather than requiring rocket fuel, which could further contribute to global warming, the flyers would be accelerated into space by a large magnetic field applied along 2,000-m-long tracks. With each such launch sending out 800,000 flyers, the project would require 20 million launches over a decade.

The flyers would rely on ion propulsion to reach their destination—a position between the sun and Earth in which the craft would take the same amount of time to orbit the sun as Earth does. They would then maintain a fixed position relative to Earth and shade it for about 50 years.

The flyers would need to continuously modify their trajectories. The pressure of sunlight on a trio of tiltable solar reflectors, embedded with electronics, would automatically redirect each craft, keeping the cloud intact or dispersing it as needed.

Several scientists say that there are less-expensive and easier ways to reduce global warming. Aluminized Mylar stretched across the ground or white paint covering large areas to reflect visible light from Earth into space “would be vastly cheaper,” says astronomer Webster Cash of the University of Colorado at Boulder.

“It makes much more economic sense to find ways to address the climate problem directly by reducing the pollution that causes it,” says climatologist James Hansen, director of NASA’s Goddard Institute for Space Studies in New York City.

No word has come yet on what Angel’s wife thinks.

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