NORTHERN PEATLAND CARBON ACCUMULATION THROUGH THE HOLOCENE AND ITS IMPACT ON CLIMATE - A FRAMEWORK FOR ANALYSIS

Throughout the Holocene, northern peatlands have both accumulated carbon as CO2 from the atmosphere and emitted methane (CH4). Their combined impact on climate radiative forcing should be the net balance (or imbalance) of a cooling due to persistent CO2 uptake and a warming due to persistent CH4 emissions. We evaluated this combined impact by incorporating very simple scenarios of Holocene peatland carbon fluxes as inputs into a simple atmospheric perturbation model. Flux scenarios are based on estimates of contemporary CH4 flux (15-50 Tg/yr), total accumulated peat C (250-450 Pg C), and peatland initiation dates. The contemporary perturbations to the atmosphere from northern peatlands are an increase of ~100 ppbv in CH4 and a decrease of ~35 ppmv in CO2. The net radiative forcing impact of northern peatlands is currently about -0.2 to -0.5 W/m2 – that is, a net cooling. It is likely that peatlands initially caused a net warming during their first millennium of up to +0.1 W/m2, but have been causing an increasing net cooling for the past 8000-11,000 years. Sensitivity analysis indicates that the current radiative forcing impact is determined primarily by the magnitude of the contemporary methane flux and by the magnitude of the total C accumulated as peat. Also, radiative forcing during the Holocene depends on flux history but follows a fairly predictable trajectory in general.