Another stab at PutTheCarbonBack. Particulates in the atmosphere, along with the extra clouds they seeded, supposedly helped check GlobalWarming through the latter half of the 20th century. Can we create similar particulates from inert substances like, say, finely powdered graphite, and put together a network of dispensers - planes, cars, and smokestacks - to dim the planet further?
This has been seriously proposed before and it seems respectable. Of course graphite isn't the best idea. Can we say lung cancer? Ah, hell, it's not like China isn't implementing this anyways.
What's a good substance to use? Or maybe I'm aiming too low. How about a big solar sail in solarsynchronous orbit? Can't have accusations of respectability dogging me now ...
Damn, I forgot about that. That's actually a very good idea since it would be very low maintenance once unfurled. Also, most of the technology to do it (space launch, robots, thin films) is either already here or getting there. It's only the scale required that's new, and that might render it impractical. The other consideration is that the cheapest solar sail would only occlude the tropics and that would really fuck with global weather patterns. On the other hand, it would be a first step towards Planetary Weather Control.
What would be ideal is developing something that floats on water, forms a thin film, is completely non-toxic, reasonably reflective ...
Thus killing off all plant life, on land and sea! Brilliant! -- CallumLerwick
20% reflective would do, you know.
Like water, you mean?
But seriously, you can't really put a huge solar sail at L1, for the simple reason that the pressure of the solar wind and of the light (yes, photons have momentum too, just very very little of it) would cause it to fly away. Some have suggested placing a giant Fresnel lens at L1 (more info at http://ww.kuro5hin.org/story/2005/4/7/41932/19363), with the appropriate rocketry to keep it in place. Theoretically that could work, but in practice it turns out that you'd need quite a bit more space-grade plastic than can currently be produced. -- WouterCoene