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Global Warming: Can We Shade the Sun?

We've recently written about how important clouds are when it comes to global warming. Maybe what we need to do is create a huge, artificial cloud?or space shade?to block the sun's rays from reaching the earth so we can gain extra time to clean up the atmosphere.

Astronomer Roger Angel has developed a plan to launch a constellation of trillions of small free-flying spacecraft a million miles above Earth into an orbit aligned with the sun, called the L-1 orbit. The craft would form a long, cylindrical cloud that would have a diameter about half that of the earth, and would be about 10 times longer. This space shade would divert about 10% of the sunlight passing through the 60,000-mile length of the cloud away from us, reducing sunlight by about 2% over the entire planet. Even if we doubled the amount of carbon dioxide in the earth's atmosphere, this space shade would still cool the earth down.

The idea for a space shade to deflect sunlight from earth was first proposed by James Early in 1989, but he thought it would be a single, large structure which, Angel says, would have to be launched "from the moon, which is pretty futuristic." Instead, Angel proposed to "make the sunshade from small 'flyers,' small, light and extremely thin spacecraft that could be completely assembled and launched from Earth, in stacks of a million at a time. When they reached L1, they would be dealt off the stack into a cloud. There's nothing to assemble in space."

Another approach to creating a cooling cloud would be to spray aerosols into space, although this would have to be repeated at regular intervals. Tom Wigley, of the National Center for Atmospheric Research (NCAR), got this idea from the way that exploding volcanoes cool the atmosphere, by injecting millions of particles into the atmosphere thatdeflect the heat of the sun. He thinks that it might be wise to inject sulfate particles into the stratosphere every one to four years, in amounts equal to those lofted by the volcanic eruption of Mt. Pintabuto in 1991. If found to be environmentally and technologically viable, such injections could provide a ?grace period? of up to 20 years before major cutbacks in greenhouse gas emissions would be required.

There's no word about what all this might do to our view of the sky from here on earth.

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