Temperature and concentration feedbacks in the carbon cycle

Feedback processes in the carbon budget are investigated in a manner that parallels the treatment of feedback processes in the energy budget. The analysis is applied to simulations with the CCCma earth system model CanESM1 using a range of emission scenarios. For the atmosphere there is a positive “carbon‐temperature” feedback which acts to increase CO 2 flux to the atmosphere as temperatures warm. There is also a negative “carbon‐concentration” feedback which acts to remove CO 2 from the atmosphere via enhanced uptake of CO 2 by the land and ocean as CO 2 concentration increases. While the positive feedback associated with temperature change is reasonably linear and consistent as temperature increases, the feedback associated with CO 2 concentration is not. The negative carbon‐concentration feedback weakens with increasing CO 2 concentration thereby enhancing atmospheric CO 2 and accelerating global warming. The behaviour of the inferred carbon‐concentration feedback is different for different emission scenarios implying a dependence on state variables other than CO 2 concentration. The carbon‐concentration feedback behaviour inferred for a particular scenario may not, therefore, be used to infer system behaviour for other scenarios.