Decrease of emissions required to stabilize atmospheric CO2 due to positive carbon cycle-climate feedbacks -: art. no. L21707

Positive feedbacks between the carbon cycle and climate have the potential to accelerate the accumulation of atmospheric CO2 over the next century. Here, I address the question of how climate-induced carbon cycle changes could affect the emissions required to stabilize atmospheric CO2 at 1000 ppmv. From a coupled climate-carbon cycle simulation, I calculated emissions that are consistent with a prescribed CO2 stabilization pathway. By comparing a coupled simulation with a second constant-climate simulation, I show that carbon cycle-climate feedbacks lead to large decreases in allowable emissions. Cumulative emissions are reduced by 94, 230 and 754 GtC between 2005 and years 2050, 2100 and 2350 respectively. Annual differences are largest at 2080, where emissions are reduced by 2.8 GtC/year. Further, while terrestrial feedbacks dominate for the next two centuries, the effect of ocean feedbacks on allowable emissions begin to exceed that of terrestrial feedbacks around the year 2250.