Here's just a small sample of the evidence that shows it's for real. Corals are bleaching by the mile as sea temperatures climb and waters become more acidic due to higher carbon-dioxide levels.
Mass death can follow.
Colonies in the Indian Ocean, western and eastern Pacific now resemble graveyards. Caribbean corals which help protect coastlines are also endangered. Fish that depend on the ecosystems created by them are suffering. And as Australia's Great Barrier Reef crumbles, so also could the livelihoods of thousands of people dependent on the tourists who come to see the gemlike creatures. Cracked For 20,000 years the Larsen B ice-shelf had lain undisturbed, until in 1998 this gigantic fissure opened up.