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This animation shows the variability of the fourteen general circulation models (GCMs) in simulating surface air temperature over the Arctic. The variability is defined here as the standard deviation (wikipedia link) of simulated surface air temperatures across the fourteen GCMs for each calendar month.
Regions of highest variability are indicated in yellows and reds, while blues and greens indicated regions and times when the GCMs agree well on their simulations.
Winter surface air temperatures over the Arctic Ocean can vary by 20-30 (deg. C) depending on whether the underlying ocean surface is sea ice covered, or not. With an insulating sea ice cover, the air temperature is isolated from the relatively warm surface ocean temperatures and the temperatures can drop to -30 to -40 deg. C. When sea ice cover is not present, the surface air temperatures are exposed to the relatively warm (near freezing) ocean surface and the air temperatures are confined to near the freezing point.
In these animations, the largest disagreement between model surface air temperature simulations occurs in the winter months, predominantly over the Arctic Ocean. The maximum in variance is generally found over the southern boundary of the climatological sea ice extent, indicating that the models disagree on the precise extent of the Northern Hemisphere sea ice cover. The variations in winter sea ice extent from one model to the next result in widely varying simulations of surface air temperatures over these same regions.
By contrast, the melting of snow and sea ice in the summer months acts to constrain the surface air temperatures to near the melting point of water. Additional energy at the surface is used to melt snow and ice at the expense of increasing the surface air temperatures beyond the melting point. Since all of the general circulation models capture this melting physics, and hence, the summer surface air temperatures for all models are near 0 deg. C, the across-model variability over the Arctic Ocean in summer is very small.