Preliminary release of information from Copenhagen shows that with the best case scenario of CO2 emissions reductions, where CO2 emission decline by 3% per year by 2015 (this is a very aggressive reduction rate), there is still a 50% chance that the earth will warm 3.6 to 5 degrees F by 2100. A 3.6 degree rise is an amount that is widely acknowledged to create major disruptions to society. CO2 levels on the planet today are increasing at 3% per year and this rate is increasing rapidly, barring a slight slowing of the rate because of the economic crisis.
If reductions of CO2 emission of 3% per year are delayed or otherwise do not occur until 2025, temperatures will become increasingly difficult to control and increases will be at least another 1.8 degrees F. If they are delayed until 2035, another 1.8 degrees increase can be expected.
If CO2 emission reductions are sluggish or 0%, temperature increases by 2100 will increase by 10 to 13 degrees F. This amount of warming is an increase that will make much of life on Earth impossible.
These calculations are also done based on increases above pre Industrial Revolution temperatures. Since the Industrial Revolution began we have already seen half, or 1.8 degrees F. of warming out of our allowable 3.6 degrees.