Evaluating permafrost physics in the Coupled Model Intercomparison Project 6 (CMIP6) models and their sensitivity to climate change

Abstract

Abstract. Permafrost is a ubiquitous phenomenon in the Arctic. Its future evolution is likely to control changes in northern high-latitude hydrology and biogeochemistry. Here we evaluate the permafrost dynamics in the global models participating in the Coupled Model Intercomparison Project (present generation – CMIP6; previous generation – CMIP5) along with the sensitivity of permafrost to climate change. Whilst the northern high-latitude air temperatures are relatively well simulated by the climate models, they do introduce a bias into any subsequent model estimate of permafrost. Therefore evaluation metrics are defined in relation to the air temperature. This paper shows that the climate, snow and permafrost physics of the CMIP6 multi-model ensemble is very similar to that of the CMIP5 multi-model ensemble. The main differences are that a small number of models have demonstrably better snow insulation in CMIP6 than in CMIP5 and a small number have a deeper soil profile. These changes lead to a small overall improvement in the representation of the permafrost extent. There is little improvement in the simulation of maximum summer thaw depth between CMIP5 and CMIP6. We suggest that more models should include a better-resolved and deeper soil profile as a first step towards addressing this. We use the annual mean thawed volume of the top 2 m of the soil defined from the model soil profiles for the permafrost region to quantify changes in permafrost dynamics. The CMIP6 models project that the annual mean frozen volume in the top 2 m of the soil could decrease by 10 %–40 %∘C-1 of global mean surface air temperature increase.

Hydrologic-land surface modelling of the Canadian sporadic-discontinuous permafrost: initialization and uncertainty propagation

“…CMIP5 results showed a projected areal loss of permafrost in the northern regions of between 30% to 90%, with most of the loss occurring by the end of the 21 st century (McGuireet al, 2018). Similarly, Burke et al (2020) reported projected permafrost degradation of the upper 2m of soil of 10% -40% per 1.0°C increase in global mean air temperature from the CMIP6 multi-model ensemble. Notably, permafrost contains twice the amount of carbon stored in the atmosphere, the release of which would accelerate the pace of global warming via a positive feedback mechanism (Schuuret al , 2015;Walvoord and Kurylyk, 2016).…”

Effects of multi-scale heterogeneity on the simulated evolution of ice-rich permafrost lowlands under a warming climate

“…The presence of permafrost in high-latitude landscapes crucially affects hydrological and biogeochemical processes and makes their realistic representation within macro-scale LSM frameworks challenging (Chadburn et al, 2017;Andresen et al, 2020;Burke et al, 2020). Beyond the requirement to accurately simulate freeze-thaw processes near the surface, the presence of excess ice in the subsurface is an additional source of complexity.…”

Model improvement and future projection of permafrost processes in a global land surface model

“…9 ). Burke et al ( 2020 ) reported that permafrost sensitivity—the change in permafrost volume per degree of global mean surface air temperature change—is 20–30% using CMIP5/CMIP6 data. Although these authors analyzed the uncertainty ranges in multi-model ensembles of CMIPs, the present study could examine the response of a global land surface model by considering the uncertainty in atmospheric model projection.…”