I disagree with the irreversible part, it may take say a couple million years but if snowball earth and all the other earth climate shifts reversed a slight global rise in temp shouldn't have any prob doing so.
http://news.yahoo.com/s/nm/20071127/...OfyflyVLx34T0D
BRASILIA (Reuters) - Unless the international community agrees to cut carbon emissions by half over the next generation, climate change is likely to cause large-scale human and economic setbacks and
irreversible ecological catastrophes, a U.N. report said on Tuesday.