Global peatland area and carbon dynamics from the Last Glacial Maximum to the present - a process-based model investigation

Peatlands are an essential part of the terrestrial carbon cycle and the climate system. Understanding their history is key to understanding future and past land-atmosphere carbon fluxes. We performed transient simulations over the last 22 000 years with a dynamic global peat and vegetation model forced by Earth system model climate output, thereby complementing data-based reconstructions for peatlands. Our novel results demonstrate a highly dynamic evolution with concomitant gains and losses of active peatland areas. Modeled gross area changes exceed net changes several fold, while net peat area increases by 60% over the deglaciation. Peatlands expand to higher northern latitudes in response to warmer and wetter conditions and retreating ice sheets, and they are partly lost in midlatitude regions. In the tropics, peatlands are partly lost due to the flooding of continental shelves and are regained through nonlinear responses to the combined changes in temperature, precipitation, and CO2. Large north-south shifts of tropical peatlands are driven by shifts in the position of the intertropical convergence zone associated with the abrupt climate events of the glacial termination. Time slice simulations for the Last Glacial Maximum (LGM) demonstrate large uncertainties in modeled peatland extent (global range from 1.5 to 3.4 Mkm(2), million square kilometers) stemming from uncertainties in climate forcing. The net uptake of atmospheric CO2 by peatlands, modeled at 351 GtC since the LGM, considers decay from former peatlands. Carbon uptake would be misestimated, in particular during periods of rapid climate change and subsequent shifts in peatland distribution, when considering only changes in the area of currently active peatlands. Our study highlights the dynamic nature of peatland distribution and calls for an improved understanding of former peatlands to better constrain peat carbon sources and sinks.