Global warming is a reality and increasingly its consequences are upon us. We may think that global warming does not affect us but the fact is it has already started to have disastrous consequences. Flash floods, droughts, receding icebergs, cyclones are some of the manifestations of global warming. Although we are aware and worried about it and trying our best to control it but no significant impact could be seen.

Scientists have come up with new strategies to tackle the problem. Now a scientist has suggested an ambitious idea to contain global warming. Put sunshades in space. That’s right. University of Arizona astronomer Roger Angel suggests putting sunshades in space and has detailed his idea in a paper “Feasibility of cooling the Earth with a cloud of small spacecraft near L1” in the Proceedings of the National Academy of Sciences. He suggests launching 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.

This spacecraft would form a long, cylindrical cloud and would have a diameter about half that of Earth, and about 10 times longer. It is suggested that about 10 percent of the sunlight passing through the 60,000-mile length of the cloud, pointing lengthwise between the Earth and the sun, would be diverted away from our planet. This would result in uniformly reduced sunlight by about 2 percent over the entire planet and would balance the heating of carbon dioxide in Earth's atmosphere.

The use of space shade was first mooted by James Early of the Lawrence Livermore National Laboratory in 1989.

"The earlier ideas were for bigger, heavier structures that would have needed manufacture and launch from the moon, which is pretty futuristic," Angel said. "I wanted 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."

Angel proposes to design lightweight flyers made of transparent film pierced with small holes and would be two feet in diameter, 1/5000 of an inch thick and weigh about a gram, the same as a large butterfly. He suggests using “MEMS” technology mirrors as tiny sails that tilt to hold the flyers position in the orbiting constellation.

The weight of all flyers would be 20 millions tons. But conventional rocket launch system at $10,000 a pound would be too prohibitive. His alternative would cost only around $20 a pound.

He suggests deploying a total 20 electromagnetic launchers launching a stack of flyers every 5 minutes for 10 years. The electromagnetic launchers would use hydroelectric power but even if it uses coal-generated electricity, each ton of carbon used would reduce the effect of 1000 tons of atmospheric carbon.

Once propelled beyond Earth’s atmosphere the flyer stacks would be steered to L-1 orbit by solar-powered ion propulsion, pioneered by European Space Agency's SMART-1 moon orbiter and NASA's Deep Space 1 probe.

"The concept builds on existing technologies," Angel said. "It seems feasible that it could be developed and deployed in about 25 years at a cost of a few trillion dollars. With care, the solar shade should last about 50 years. So the average cost is about $100 billion a year, or about two-tenths of one percent of the global domestic product."

He added, "The sunshade is no substitute for developing renewable energy, the only permanent solution. A similar massive level of technological innovation and financial investment could ensure that.

"But if the planet gets into an abrupt climate crisis that can only be fixed by cooling, it would be good to be ready with some shading solutions that have been worked out."