The model-projected first Arctic ice-free year significantly depends on the model’s two climate sensitivities. The two constraints are complementary and nearly scenario-independent. Thus, two constraints are proposed: the Arctic sea ice sensitivity that measures Arctic sea ice response to the local warming, and the Arctic amplification sensitivity that assesses how well the model responds to anthropogenic forcing and allocates heat to the Arctic region. To establish a physical basis for the constraints, we first demonstrate, with numerical experiments, that the observed trend of Arctic ice loss is primarily driven by the Arctic near-surface air temperature.
Finding emergent constraints to reduce the projection uncertainties has been a foremost challenge.
However, the Coupled Model Intercomparison Project Phase 6 models’ projected occurrence remains notoriously uncertain. Further efforts toward investigating causes of the model limitations and quantifying the contribution of local and remote component to Arctic sea ice on different timescales may help to improve the future sea ice prediction.Īn ice-free Arctic summer is a landmark of global change and has the far-reaching climate, environmental, and economic impacts. Our quantitative estimation of the contribution of the internal atmospheric circulation to SSIE during the next three decades may be underestimated due to models’ inability to capture the observed Rossby wave train originating from the tropical Pacific Ocean propagating into the Arctic.
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The tropical Pacific Ocean may act as a remote driver for the sea ice melting but the coupling between them is more intense on decadal timescales than that on year-to-year scales. We used a 40-member ensemble of simulation by the Community Earth System Model Version 1 (CESM1) and a 100-member ensemble simulation by the Max Planck Institute Earth System Model (MPI-ESM) to reveal that the internal variability of the local atmosphere circulation change can contribute 12%-17% to the uncertainties in the projected SSIE changes during 2016-2045 in both CESM-LE and MPI-ESM.
Reasons previously identified for the accelerated decrease in SSIE are largely related to the tendency toward a barotropic geopotential height rise in summer over the Arctic. The September sea ice extent (SSIE) in the multi-model ensemble mean of climate models shows a large divergence from observations since the 2000s, which indicates the potential influence of internal variability on SSIE decadal variations. The Arctic sea ice has undergone rapid loss in all months of the year in recent decades, especially in September.
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