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Abstract

The present study investigates the response of the high latitude's carbon cycle to in- and decreasing atmospheric greenhouse gas (GHG) concentrations in idealized climate change scenarios. For this, we use an adapted version of JSBACH – the land-surface component of the Max-Planck-Institute for Meteorology's Earth system model (MPI-ESM) – that accounts for the organic matter stored in the permafrost-affected soils of the high northern latitudes. To force the model, we use different climate scenarios that assume an increase in GHG concentrations, following the Shared Socioeconomic Pathway 5, until peaks in the years 2025, 2050, 2075 or 2100, respectively. The peaks are followed by a decrease in atmospheric GHGs that returns the concentrations to the levels at the beginning of the 21st century. We show that the soil CO2 emissions exhibit an almost linear dependency on the global mean surface temperatures that are simulated for the different climate scenarios. Here, each degree of warming increases the fluxes by, very roughly, 50 % of their initial value, while each degree of cooling decreases them correspondingly. However, the linear dependency does not mean that the processes governing the soil CO2 emissions are fully reversible on short timescales, but rather that two strongly hysteretic factors offset each other – namely the vegetation's net primary productivity and the availability of formerly frozen soil organic matter. In contrast, the soil methane emissions show almost no increase with rising temperatures and they are consistently lower after than prior to a peak in the GHG concentrations. Here, the fluxes can even become negative and we find that methane emissions will play only a minor role in the northern high latitudes' contribution to global warming, even when considering the gas's high global warming potential. Finally, we find that the high-latitude ecosystem acts as a source of atmospheric CO2 rather than a sink, with the net fluxes into the atmosphere increasing substantially with rising atmospheric GHG concentrations. This is very different to scenario simulations with the standard version of the MPI-ESM in which the region continues to take up atmospheric CO2 throughout the entire 21st century, confirming that the omission of permafrost-related processes and the organic matter stored in the frozen soils leads to a fundamental misrepresentation of the carbon dynamics in the Arctic