I think it's a very good solution because it can be easily undone. If we "over-tip" the energy balance, we could also use mirrors at the polls to add energy in case of 'global cooling'. The only real problem with the idea is the expense of deploying it.

An alternative I thought of a while ago would be to find an oil-like substance which floats on water and is both reflective, gas permeable, and quickly biodegradable. The substance could then be poured out on the ocean's surface and self-spread. You could create acre sized "ocean mirrors" just by pouring out a barrel of the stuff at sea. So long as it is non-toxic and breaks down quickly, you won't harm the ocean. You could design a similar substance which absorbs light to add energy to the earth.

We need to find ways to control our planet's environment. Nature has done a pretty fantastic job for us over the last several hundred thousand years, but that's just a drop in the time-line bucket as far as the universe is concerned. Just because we've been lucky so far doesn't mean our luck will continue.
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Mirrors in orbit around Mars could create Earth-like conditions on a small patch of the planet's surface, according to a NASA-funded study. The extra sunlight would provide warmth and solar power for human explorers, but some experts say the mirrors may be hard to deploy. So to answer your question, it could both harm and benefit
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It will NEITHER save NOR destroy earth. It's life span, cost, maintainance and power are all extremely limiting and there is little or no chance for it (as it stands, at least) to anyhow affact Earth in any signficant way.
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I think giant mirrors, if created, will do nothing to stem or accelerate climate change. I think we've already reached a peak, and that now we are heading towards extreme global cooling due to extreme changes in water circulation in the Atlantic.

The ice caps will melt AND it will get colder. What would the pundits say!?
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This is more from those with green delusions! Humans don't cause global warming, it is a natural geological and astronomical occurrence of the earth axial wobble, solar orbit and magnetic field fluctuation. What these global warming nuts are not saying (and now NASA has confirmed) is that the Earth is rapidly cooling and will face another Ice Age in as short a period as a decade.

The ice caps have melted before (1938) and recouped again in 1948. Mirrors in space, that is just a bunch nonsense! People should be investing in property on the Earth equator or at least into some warmer retreating locations.
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I will like to put forward some points----


*Putting a layer of reflective material around the Earth's atmosphere is not addressing the real issue which is the depletion of the planet's natural resources. We should be working towards a society that is not so wasteful. Also what side effects would this proposed layer have?

*You would get complaints from people living along the orbital path of these mirrors, of course, since it would change their climate and agriculture, perhaps more drastically than global warming would.

*There’s two types of orbits that could be used. You could have mirrors in geosynchronous orbits, 25,000 miles up, which would stay over the same part of the planet’s face. Since the sun isn’t in geosynchronous orbit, this means that each day the shadow would move from west to east along the section of earth passing directly under the mirror and the sun. The other is non-geosynchronous orbit, which means that the mirror would orbit the earth anywhere from every 90 minutes to (realistically) every 28 days. This would cause brief artificial nights at various odd times.

http://i43.tinypic.com/nga7v4.jpg

*One problem is that of scale. The earth’ surface is nearly 200 million square miles in area, and they want to reduce the amount of sunlight by 1%. That would require, at a minimum, 3 million square miles of mirrors in orbit, because the shadow cast by the mirrors wouldn’t be as large in area, or as opaque at the edges. That’s a lot of tinfoil.

*Depressingly, the reality of modern space programmes is that of a vast expenditure of money, energy and pollutants, justified by appeals to a mixture of scientific research and nationalist propaganda at best, and corporate profit at worst.

http://www.popsci.com/files/imagecache/article_image_large/files/articles/space0805eng_485x326.jpg


*CS Lewis’s science fiction novels contemptuously dismiss the idea ‘that humanity, having now sufficiently corrupted the planet where it arose, must at all costs contrive to seed itself over a larger area’.

http://space.newscientist.com/data/images/ns/cms/dn10573/dn10573-1_800.jpg
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