How northern peatlands influence the Earth's radiative budget: Sustained methane emission versus sustained carbon sequestration

Abstract

Northern peatlands sequester carbon and emit methane, and thus have both cooling and warming impacts on the climate system through their influence on atmospheric burdens of CO 2 and CH 4 . These competing impacts are usually compared by the global warming potential (GWP) methodology, which determines the equivalent CO 2 annual emission that would have the same integrated radiative forcing impact over a chosen time horizon as the annual CH 4 emission. We use a simple model of CH 4 and CO 2 pools in the atmosphere to extend this analysis to quantify the dynamics, over years to millennia, of the net radiative forcing impact of a peatland that continuously emits CH 4 and sequesters C. We find that for observed ratios of CH 4 emission to C sequestration (roughly 0.1–2 mol mol −1 ), the radiative forcing impact of a northern peatland begins, at peatland formation, as a net warming that peaks after about 50 years, remains a diminishing net warming for the next several hundred to several thousand years, depending on the rate of C sequestration, and thereafter is or will be an ever increasing net cooling impact. We then use the model to evaluate the radiative forcing impact of various changes in CH 4 and/or CO 2 emissions. In all cases, the impact of a change in CH 4 emissions dominates the radiative forcing impact in the first few decades, and then the impact of the change in CO 2 emissions slowly exerts its influence.