Scientists: Trying to change earth's climate is tricky

"Scientists are exploring global warming solutions that sound wholly far-fetched, including giant artificial "trees" to filter carbon dioxide out of the air, a bizarre "solar shade" created by a trillion flying saucers that lower Earth's temperature, and a scheme that mimics a volcano by spewing light-reflecting sulfates high in the sky.
These are costly projects of last resort -- in case Earth's citizens don't cut back fast enough on greenhouse gas emissions and the worst of the climate predictions appear not too far away. Unfortunately, the solutions could cause problems of their own -- beyond their exorbitant costs -- including making the arid Middle East even drier and polluting the air enough to increase respiratory illnesses.
Kevin Trenberth, climate analysis chief at the National Center for Atmospheric Research, said mankind already has harmed Earth's climate inadvertently, so it's foolish to think people can now fix it with a few drastic measures."