Could Space Mirrors Stop Global Warming?

Space Mirrors Climate Change — A constellation of billions of mirrors free-floating at the Earth-Sun Lagrange point blocks solar radiation and cools earthly global warming.

(Image credit: Dan Roam)

The record-breaking temperatures of the past few years are getting more people thinking about bigger solutions to climate change. Ideas once thought of as wacky are now receiving careful consideration, including an idea that sounds straight out of science fiction: cooling the earth by launching reflective mirrors into space.

Lowell Wood of Lawrence Livermore National Laboratory proposed a giant space mirror in the early 2000s, though he cautioned that the mirror should be considered only as a measure of last resort. Why? Because the mirror would have to have an area of 600,000 square miles – a slightly smaller area than Greenland – and launching something that big would be prohibitively expensive. Another option: billions of smaller mirrors. Roger Angel, researcher and optics expert at the University of Arizona, proposed that idea in 2006.

In either case, the mirror or mirrors would orbit at Lagrange point L1, a gravitationally stable point between the Earth and the sun that's about four times the distance from the Earth to the moon. The mirrors would barely be visible from Earth and would block just 1 percent to 2 percent of the sun's light, but that would be enough, advocates of the schemes say, to cool the planet. Even with Angel's plan, the current cost of launching a trillion mirrors would be $10,000 per pound, or, in total, 26 times more than the current U.S. national debt.

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But such an approach could generate problems. Report author and Star Technology president Jerome Pearson calculated it would take 5 million spacecraft to achieve the desired result, and even if each individual craft could last 100 years, that means 137 ships would have to be replaced or repaired per day. And the craft would produce "stars" that would be visible from the ground. (Pearson's other hypothetical proposal, a ring of reflective rocks in the same position, would light the night sky with the equivalent of 12 full moons.)

Even if a space mirror scheme was technically and financially feasible, it could result in unintended consequences, like drought. A recent study from the Max Planck Institute for Meteorology added the effect of space mirrors to four climate models. In each model, the space shades lowered the average global temperature to preindustrial levels, but unevenly. The poles warmed while the tropics cooled, fewer clouds formed, and the planet received less rainfall, especially in the Americas and northern Eurasia.

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Rachel is a writer and editor based in Washington, D.C., who covers a range of topics for Live Science, from animals and global warming to technology and human behavior. Rachel also contributes to National Geographic News, Smithsonian Magazine and Scientific American, and she is currently a senior editor at Next City, a national urban affairs magazine. She has an English degree with a journalism concentration from Adelphi University in New York.