Abstract. The present study investigates the response of the high-latitude carbon cycle
to changes in atmospheric greenhouse gas (GHG) concentrations in idealized
climate change scenarios. To this end we use an adapted version of JSBACH –
the land surface component of the Max Planck Institute for Meteorology Earth
System Model (MPI-ESM) – that accounts for the organic matter stored in the
permafrost-affected soils of the high northern latitudes. The model is run
under different climate scenarios that assume an increase in GHG
concentrations, based on the Shared Socioeconomic Pathway 5 and the
Representative Concentration Pathway 8.5, which 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, reversing the imposed climate change. We show
that the soil CO2 emissions exhibit an almost linear dependence 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 dependence 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 net primary productivity and the availability of formerly
frozen soil organic matter. In contrast, the soil methane emissions show a
less pronounced increase with rising temperatures, and they are consistently
lower after the peak in the GHG concentrations than prior to it. Here, the net
fluxes could even become negative, and we find that methane emissions will play
only a minor role in the northern high-latitude contribution to global
warming, even when considering the high global warming potential of the
gas. Finally, we find that at a global mean temperature of roughly
1.75 K (±0.5 K) above pre-industrial levels the high-latitude ecosystem turns from a CO2 sink into a source of atmospheric
carbon, with the net fluxes into the atmosphere increasing substantially with
rising atmospheric GHG concentrations. This is very different from 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.
Extreme Wildfire occurrence in response to Global Change type
Droughts in the Northern Mediterranean
