Dependence of Regional Climate Change on Greenhouse Gas Emission Pathway

This study explores the dependence of the coupled climate-carbon cycle response on greenhouse gas emission pathway. An Earth System model of Intermediate Complexity is forced with 24 idealized emissions scenarios across five cumulative emission groups (1300 GtC - 5300 GtC) with varying emission rates. The global mean response, and regional responses of Arctic sea ice, the Meridional Overturning Circulation (MOC) and the Amazon are investigated. The ratio of global mean temperature to cumulative carbon emissions is found to decline with increasing cumulative emissions, unlike in previous studies. The long-term response of the MOC and Arctic sea ice is independent of emission rate and proportional to cumulative emissions, with the threshold for an ice free Arctic in September found between 1300-2300 GtC. Both global land carbon and Amazonian broadleaf carbon display non-monotonic long-term responses to cumulative emissions, whereby carbon uptake declines beyond a certain threshold (2300 GtC and 3300 GtC respectively).