Positive feedback between future climate change and the carbon cycle

Future climate change due to increased atmospheric CO 2 may affect land and ocean efficiency to absorb atmospheric CO 2 . Here, using climate and carbon three‐dimensional models forced by a 1% per year increase in atmospheric CO 2 , we show that there is a positive feedback between the climate system and the carbon cycle. Climate change reduces land and ocean uptake of CO 2 , respectively by 54% and 35% at 4 × CO 2 . This negative impact implies that for prescribed anthropogenic CO 2 emissions, the atmospheric CO 2 would be higher than the level reached if climate change does not affect the carbon cycle. We estimate the gain of this climate‐carbon cycle feedback to be 10% at 2 × CO 2 and 20% at 4 × CO 2 . This translates into a 15% higher mean temperature increase.