Abstract

Permafrost carbon feedback (PCF) modeling has focused on gradual thaw of near-surface permafrost leading to enhanced carbon dioxide and methane emissions that accelerate global climate warming. These state-of-the-art land models have yet to incorporate deeper, abrupt thaw in the PCF. Here we use model data, supported by field observations, radiocarbon dating, and remote sensing, to show that methane and carbon dioxide emissions from abrupt thaw beneath thermokarst lakes will more than double radiative forcing from circumpolar permafrost-soil carbon fluxes this century. Abrupt thaw lake emissions are similar under moderate and high representative concentration pathways (RCP4.5 and RCP8.5), but their relative contribution to the PCF is much larger under the moderate warming scenario. Abrupt thaw accelerates mobilization of deeply frozen, ancient carbon, increasing 14C-depleted permafrost soil carbon emissions by ~125–190% compared to gradual thaw alone. These findings demonstrate the need to incorporate abrupt thaw processes in earth system models for more comprehensive projection of the PCF this century.

Highlights

  • We capture a wide range of uncertainty in net lake formation and drainage trajectories by varying two key model parameters: The maximum net lake area, FTKLmax, and the optimum high latitude surface temperature increase, dT′TKLmax (Supplementary Fig. 5)

  • Permafrost-region 21st-century soil carbon emissions are compared between two model types using IPCC RCP4.5 and RCP8.5

  • We utilized CLM4.5BGC emission data for years 1950–2100 partitioned according to non-permafrost carbon, originating from present-day active layer horizons, and permafrost carbon, which becomes thawed from the top down as active layer gradually deepens

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Summary

Introduction

We capture a wide range of uncertainty in net lake formation and drainage trajectories by varying two key model parameters: The maximum net lake area, FTKLmax, and the optimum high latitude surface temperature increase, dT′TKLmax (Supplementary Fig. 5). AThaw simulates typical talik depth beneath lakes of 11 m (7.8–13.4 m, 68% uncertainty range; 20 m max) in warm permafrost environments (i.e., mean annual soil temperatures close to 0 °C) with mineral soils by the year 2050 under RCP8.5.

Results
Conclusion

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