Abstract
Throughout the Holocene, northern peatlands have both accumulated carbon and emitted methane. Their impact on climate radiative forcing has been the net of cooling (persistent CO 2 uptake) and warming (persistent CH 4 emission). We evaluated this by developing very simple Holocene peatland carbon flux trajectories, and using these as inputs to a simple atmospheric perturbation model. Flux trajectories are based on estimates of contemporary CH 4 flux (15–50 Tg CH 4 yr −1 ), total accumulated peat C (250–450 Pg C), and peatland initiation dates. The contemporary perturbations to the atmosphere due to northern peatlands are an increase of ∼100 ppbv CH 4 and a decrease of ∼35 ppmv CO 2 . The net radiative forcing impact northern peatlands is currently about −0.2 to −0.5 W m −2 (a cooling). It is likely that peatlands initially caused a net warming of up to +0.1 W m −2 , but have been causing an increasing net cooling for the past 8000–11 000 years. A series of sensitivity simulations indicate that the current radiative forcing impact is determined primarily by the magnitude of the contemporary methane flux and the magnitude of the total C accumulated as peat, and that radiative forcing dynamics during the Holocene depended on flux trajectory, but the overall pattern was similar in all cases.