Holocene radiative forcing impact of northern peatland carbon accumulation and methane emissions

TLDR

Northern peatlands have simultaneously sequestered carbon and emitted methane, producing a climate radiative forcing that balances cooling from CO₂ uptake with warming from CH₄ emission. The authors aimed to quantify this balance by constructing simple Holocene peatland carbon flux trajectories and feeding them into a basic atmospheric perturbation model. These trajectories were derived from estimates of contemporary CH₄ flux (15–50 Tg yr⁻¹), total accumulated peat carbon (250–450 Pg), and peatland initiation dates. The results show that present peatlands raise atmospheric CH₄ by ~100 ppbv and lower CO₂ by ~35 ppmv, yielding a net cooling forcing of –0.2 to –0.5 W m⁻², while early Holocene peatlands likely produced a net warming of up to +0.1 W m⁻² before shifting to a progressively stronger cooling over the past 8–11 kyr, with current forcing mainly governed by methane flux magnitude and total peat carbon.

Abstract

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.