If we had had the good sense to do what Dr Gerard K. O'Neill et al suggested around the time of the U.S. Bicentennial we would RIGHT NOW have a large scale orbital manufacturing infrastructure supported by lunar resource bases already building L5 colonies and solar power satellites...and IF so-called 'global warming' turned out to be a REAL problem it would be little trouble to retask the manufacturing efforts from building more L5 colonies to building additional solar power satellites @ Lagrange 1 where they could not only be used to reduce insolation, which would help any global warming effects if any REGARDLESS of whether such are natural or human origin as presently hotly debated, but would also be able to generate enormous amounts of extra energy as a result...yes we might have to delay moving humanity off the planet [which is the REAL solution to any human caused global 'environmental' problems] for a few extra decades but we'd have enormous amounts of extra energy [and therefore vast surplus industrial capacity if we planned it right] when we did.
Instead we didnt bother to TCB for the Future's sake so now IF there is global warming [and not merely microclimate warming from increased urbanization] then regardless of whether it's man made or natural [insolation variance or other] we don't have the extraplanetary assets to do much about it...
...but hey we've got laptop computers and Tivos and Playstations and cellphones in 2006 instead of L5, SPS, Helium-3 fusion and microgravity manufacturing...
...brilliant choices there Homo sapiens...posthumous Darwin award coming?
Subterranean colonies are just as important and maybe cheaper and easier to get to. It should be possible to build a colony deep underground that gets all its energy from the Earth's nuclear powered molten core and not have any cares about the surface.