Atmospheric circulation-constrained model sensitivity recalibrates Arctic climate projections

The Arctic climate system has been suggested to be ‘en route’ to a new state with seasonally ice-free conditions expected within two-three decades under high-emissions scenarios. Here we show the prospect of its delayed emergence stemming from a consideration of observed and modelled Arctic cryosphere sensitivity to atmospheric circulation changes. While the observed Arctic warming contains a substantial contribution from large-scale circulation, it is not reflected in the modelled forced response. Numerical model simulations with the CESM2 with an active Greenland ice sheet model (CISM2), where model winds are nudged towards the observed state, advocate for the need to have a circulation-based model sensitivity evaluation metric. Hence a recalibration is proposed by matching the warming signals free of atmospheric circulation impacts in observations and models over 1979-2020. This constraint yields a ~decade delay in the projected timing of the first seasonally sea-ice free Arctic and widespread Greenland melting. Accounting for the role of large-scale atmospheric forcing in Arctic climate change offers new perspectives of estimating Arctic sea- and land-ice sensitivity to anthropogenic forcing and understanding the recently emerging issue of some CMIP6 climate models being ‘too hot’.