Just saw an interesting episode of the BBC science programme Horizon about "Global Dimming". The theory runs that whilst excess Carbon Dioxide in the atmosphere promotes global warming by trapping heat and infrared radiation close, particulate matter in pollution, especially in the high atmosphere, reflects heat away from the earth before it can reach the surface and be trapped. Purely from the grounding of all air civilian air traffic over the US in the three days following September 11th, 2001, the temperature dropped by 1 degree centigrade (to be precise the day/night temperature differential increased by 1 degree).
In a bitter irony our attempts to reduce pollution has reduced global dimming and so reduced its moderation of global warming. Hence the recent jumps in temperature that lead to the deaths from heat accross Europe over the last few summers. Previous models of global warming, before the effects of global dimming were known, predicted a 6 degree rise by the year 2100. Now we're looking at that rise by 2040.
Predictions now indicate that we're looking at the Northern European climate becoming like that of North Africa, death of the Amazon rainforest followed by it burning and becoming savannah (perhaps even desert), melting of the Greenland ice sheet and the release of methane currently trapped deep undersea. By the time we get to 2025 reversing the effects will be difficult, according to the updated models, by 2040 it may be impossible.