If the planet goes from friend to foe, then our mitigation policies for emission reductions will make little difference. Because as impressive as they might be, human impacts on the climate system pale by comparison to the warming feedbacks the Earth system itself can trigger. If the carbon contained in just the top 50 cm (19.6 inches) of soil in the Arctic were to be released, for example, it would exceed all the carbon humans have emitted since the industrial revolution began 250 years ago.
