Angel’s plan calls for small “flyers”: transparent sheets two feet in diameter and 1/5,000 of an inch thick, each weighing approximately one gram under Earth’s gravity. Trillions of these objects, according to Angel, could together form a cylindrical cloud having a diameter half that of Earth’s and a length of 60,000 miles. Interposed lengthwise between the Sun and Earth at L1, this cloud would uniformly reduce sunlight on our planet’s surface by 2 percent, which would be sufficient to offset the warming produced by even a doubling of atmospheric carbon dioxide.
Angel stresses that his plan is an emergency option, for use only if climate change so accelerates that global catastrophe looms within a decade or two. It is, he says, “no substitute for developing renewable energy, the only permanent solution.” It’s just as well that Angel makes that qualification, since he estimates that the total mass of all the flyers composing his cloud would be 20 million tons and a total of 20 electromagnetic launchers. At $10,000 a pound, conventional rockets are a prohibitively expensive way of getting that much mass into orbit. Human beings would have to launch a stack of flyers every five minutes for 10 years to put the whole structure in place.
Gregory Benford, a professor of plasma physics and astrophysics at the University of California, comments, “This whole L1 idea is neat, but it’s going to cost trillions of dollars, we can’t do it right away, and it gets used to label the entire field of geoengineering as smoke and mirrors.” Benford, besides having been an advisor for NASA, the Department of Energy, and the White House Council on Space Policy, has been a science-fiction writer, and he distinguishes carefully between currently feasible technological solutions and the kinds of advanced possibilities that he writes about in his fiction. “These are fun ideas for the year 2,100. But we don’t live there. People don’t quite understand that we will never again in our lifetime see the level of CO2 in the atmosphere that we enjoyed just yesterday. Our grandchildren likely won’t, either.”
What’s to be done? Other scientists have proposed Earth-based environmental megamodifications, such as reflective films laid over the planet’s deserts or fertilizing the seas with iron to create vast blooms of plants that would then consume tons of carbon dioxideand, as the plants died, drag the carbon into the sea. But even these measures are problematical and grandiose when most European and North American environmentalists remain committed to an international regime of carbon emissions caps and reject the idea of radical new technologies to mitigate the climate change that technological society has already created.