Now here’s a novel idea. Why not dump fine iron sulphates into the world’s seas, thus helping avert the massive build-up of carbon in the atmosphere – one of the key causes of adverse climate change? Actually, the concept’s been bounced around for some years, though it didn’t seem to be taken very seriously until 2007.
See http://www.minesandcommunities.org/article.php?a=11826&l=1.