Surrounding the Earth with reflective satellites could reduce the amount of light hitting the planet.

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Reflecting Sunlight

The Earth's heat ultimately comes from the sun, so the proposed plans to fight global warming focus on reducing the amount of heat the Earth receives from the sun. That means finding a way to redirect or block some light from the sun.

This need has prompted some interesting proposals from scientists and engineers. Some of them sound like science fiction. One method would require us to put reflective surfaces in orbit around Earth to reduce the amount of energy hitting the planet from the sun.

In 2005, astrophysicist Gregory Benford suggested that we build a concave lens and position it in orbit around the Earth so that it reduces the light hitting Earth from the sun. The lens would be 1,000 kilometers (621 miles) across and would require engines to keep it spinning in the proper alignment with the Earth.

That same year, another proposal suggested we create a ring of either reflective particles or spacecraft with reflective surfaces to block some light from the sun. The proposal had a hefty price tag: $500 billion to $200 trillion, depending on the method [source: Britt].

Another proposal in 2006 came from a scientist at the University of Arizona's Steward Observatory named Roger Angel. Angel's idea was to launch trillions of round lenses to circle the Earth. He also suggested using an electromagnetic gun to fire the lenses up into position [source: Christensen]. The gun would need a renewable energy source to power it. Since then, even more scientists have suggested similar approaches involving putting reflective objects in orbit.

But not every suggestion involves putting junk into space. Another option is to change the nature of low-flying clouds over the ocean. By seeding the clouds with the right mixture, scientists can make the clouds more reflective. The best part of this plan is that it involves spraying sea water into the air -- there's no need to use harmful chemicals. John Latham of the National Center for Atmospheric Research suggested that we design a fleet of autonomous ships that can spray sea water across the ocean to redirect sunlight and reduce global warming [source: PhysicsWorld].

In an interview with the Science Channel, scientist and advisor to the Canadian government David Keith cautioned against relying too heavily on these climate engineering techniques. It's not that the techniques might not work -- if engineered correctly they should work. The bigger problem in Keith's mind is that if we design a system that reduces global warming, we may not feel an incentive to change our carbon-emitting lifestyles. But eventually, the problem will just build up again until our quick fix isn't enough to save us and we'll be back at square one [source: The Science Channel].

Reversing climate change is one of the biggest challenges humans have ever faced. There are technological, economic and political considerations that we must make if we are to reverse a trend that might otherwise threaten our very existence.

Learn more about climate change and what we can do about it by following the links on the next page.