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We establish the first intermodel comparison of seasonal to interannual predictability of present-day Arctic climate by performing coordinated sets of idealized ensemble predictions with four state-of-the-art global climate models. For Arctic sea ice extent and volume, there is potential predictive skill for lead times of up to 3 years, and potential prediction errors have similar growth rates and magnitudes across the models. Spatial patterns of potential prediction errors differ substantially between the models, but some features are robust. Sea ice concentration errors are largest in the marginal ice zone, and in winter they are almost zero away from the ice edge. Sea ice thickness errors are amplified along the coasts of the Arctic Ocean, an effect that is dominated by sea ice advection. These results give an upper bound on the ability of current global climate models to predict important aspects of Arctic climate.

We establish the first inter-model comparison of seasonal to interannual predictability of present-day Arctic climate by performing coordinated sets of idealized ensemble predictions with four state-of-the-art global climate models. For Arctic sea-ice extent and volume, there is potential predictive skill for lead times of up to three years, and potential prediction errors have similar growth rates and magnitudes across the models. Spatial patterns of potential prediction errors differ substantially between the models, but some features are robust. Sea-ice concentration errors are largest in the marginal ice zone, and in winter they are almost zero away from the ice edge. Sea-ice thickness errors are amplified along the coasts of the Arctic Ocean, an effect that is dominated by sea-ice advection. These results give an upper bound on the ability of current global climate models to predict important aspects of Arctic climate.

The Atlantic thermohaline circulation (THC) is an important part of the earth’s climate system. Previousresearch has shown large uncertainties in simulating future changes in this critical system. The simulatedTHC response to idealized freshwater perturbations and the associated climate changes have been intercomparedas an activity of World Climate Research Program (WCRP) Coupled Model IntercomparisonProject/Paleo-Modeling Intercomparison Project (CMIP/PMIP) committees. This intercomparison amongmodels ranging from the earth system models of intermediate complexity (EMICs) to the fully coupledatmosphere–ocean general circulation models (AOGCMs) seeks to document and improve understandingof the causes of the wide variations in the modeled THC response. The robustness of particular simulationfeatures has been evaluated across the model results. In response to 0.1-Sv (1 Sv 106 m3 s 1) freshwaterinput in the northern North Atlantic, the multimodel ensemble mean THC weakens by 30% after 100 yr.All models simulate some weakening of the THC, but no model simulates a complete shutdown of the THC.The multimodel ensemble indicates that the surface air temperature could present a complex anomalypattern with cooling south of Greenland and warming over the Barents and Nordic Seas. The Atlantic ITCZtends to shift southward. In response to 1.0-Sv freshwater input, the THC switches off rapidly in all modelsimulations. A large cooling occurs over the North Atlantic. The annual mean Atlantic ITCZ moves intothe Southern Hemisphere. Models disagree in terms of the reversibility of the THC after its shutdown. Ingeneral, the EMICs and AOGCMs obtain similar THC responses and climate changes with more pronouncedand sharper patterns in the AOGCMs