If measuring greenhouse gas levels is so precise, why is there so much confusion and uncertainty over global warming?
There is no easy formula for predicting what CO2 increases will do to global temperatures. While we can calculate that a doubling of atmospheric CO2 will force roughly 1°C of warming, the planet is more complex than that. It could magnify the effect, but it could also conceivably dampen down warming. Global processes such as the formation of ice and clouds, the circulation of the oceans and biological activity all interact to provide feedback effects.