Background
The authors note that "throughout the Holocene, northern peatlands have both accumulated carbon and emitted methane," so that "their impact on climate radiative forcing has been the net of cooling (persistent CO2 uptake) and warming (persistent CH4 emission)."

What was done
Frolking and Roulet analyzed this situation by developing Holocene peatland carbon flux trajectories based on estimates of contemporary CH4 flux, total accumulated peat C, and peatland initiation dates, which they used as inputs to a simple atmospheric perturbation model to calculate the net radiative impetus for surface air temperature change.

What was learned
The two researchers calculated that "the impact on the current atmosphere of northern peatland development and carbon cycling through the Holocene is a net deficit of 40-80 Pg CO2-C (~20-40 ppm [of atmospheric CO2]) and a net excess of ~200-400 Tg CH4 (~75-150 ppb [of atmospheric CH4])."

What it means
Early in the Holocene, according to Frolking and Roulet, the capture of CO2 and emission of CH4 by earth's northern peatlands is likely to have produced a net warming impetus of up to +0.1 W m^-2. Over the following eight to eleven thousand years, however, they say earth's peatlands have been doing just the opposite, and that the current radiative forcing due to these atmospheric CO2 and CH4 perturbations represents a net cooling force on the order of -0.22 to -0.56 W m^-2. Hence, it can be appreciated that the impetus for global cooling due to carbon sequestration by earth's peatlands historically has been - and currently is - significantly greater than the global warming potential produced by their emissions of methane.