According to this article on Wired Magazine, and many other places, we have now burned our way through half of the fossilised carbon that would take global average temperature levels above the danger point. We are predicted to burn the next half within 40 years.

You’ve seen my view. The human race is like a man who has discovered that they are overweight. We have to decide if we are going to keep eating or go on a diet. If we wait things will just get worse. Cutting back CO2 emissions will be harder later. It’s not impossible to reduce CO2 now, but we have to start… all of us.