CO2

Science Daily: Reconciling predictions of climate change - New framework accounts for conflicting estimates of global temperature increases

summary - Researchers have resolved a major conflict in estimates of how much the Earth will warm in response to a doubling of CO2 in the atmosphere -- finding that the lower range of estimates offered by historical observations does not take into account long-term patterns of warming. The research finds a range of 1.5 to 4.5 degrees Celsius, even up to 6 degrees, may also be possible due to a doubling of CO2.