I had a long posting about this in one of the recent AGW threads (and I'm too lazy to search it out). My gut feeling is that humans will not undertake any of these large scale "terraforming" projects (iron seeding, sun shades in orbit, etc.). We barely seem to have the technological ability and political will to do things like increasing efficiency, look at alternative energy sources, and slow down our rate of deforrestation. But that's just my opinion.

I also think, whether we admit it or not, that we are doing large-scale modifications of our planet's atmosphere, by introducing all the CO2 and other polutants. I'm not arguing that this large-scale modification justifies another one, and I agree that if we decided to go ahead and "do" something, we have to be mightly careful that we don't make things worse with our fix.

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At night the stars put on a show for free (Carole King)

One Earth, One Sky - IYA 2009