Temperature and concentration feedbacks in the carbon cycle

Abstract

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 CO2 flux to the atmosphere as temperatures warm. There is also a negative “carbon‐concentration” feedback which acts to remove CO2 from the atmosphere via enhanced uptake of CO2 by the land and ocean as CO2 concentration increases. While the positive feedback associated with temperature change is reasonably linear and consistent as temperature increases, the feedback associated with CO2 concentration is not. The negative carbon‐concentration feedback weakens with increasing CO2 concentration thereby enhancing atmospheric CO2 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 CO2 concentration. The carbon‐concentration feedback behaviour inferred for a particular scenario may not, therefore, be used to infer system behaviour for other scenarios.