Impact of climate-carbon cycle feedbacks on emissions scenarios to achieve stabilisation

Abstract

As atmospheric concentrations of CO2 increase due to burning of fossil fuels, stabilisation scenarios are receiving increasing amounts of interest both politically and scientifically, leading to the question, ‘what emissions pathway is required to lead us to a given climate/CO2 state?’ At present, about half of anthropogenic CO2 emissions are absorbed naturally, but there is growing consensus that this fraction will reduce due to the action of climate change on the natural carbon cycle. Such climate-carbon cycle feedbacks will therefore influence the amount of carbon emissions required to stabilise atmospheric CO2 levels. Here we quantify the impact that climate change will have on the world’s natural carbon cycle and how this will affect the amount of CO2 emissions which are permissible to achieve a stabilised climate in the future. Our simulated feedbacks between the climate and the carbon cycle imply a reduction of 21–33% in the integrated emissions (between 2000 and 2300) for stabilisation, with higher fractional reductions necessary for higher stabilisation concentrations. Any mitigation or stabilisation policy which aims to stabilise atmospheric CO2 levels must take into account climate-carbon cycle feedbacks or risk significant underestimate of the action required to achieve stabilisation.