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The coupled climate response to high-latitude forcing

Using coupled simulations in which the response to Arctic sea-ice loss has
been isolated, a multi-model comparison of the near-surface atmospheric and
oceanic response is carried out. To account for the differing amounts of
lower latitude warming in these simulations, a two-parameter pattern
scaling technique is used to separate out the part of the response that
scales with Arctic sea-ice loss from that which scales with lower latitude
warming. The response to high-latitude forcing is found to be quite robust
across models in the near-surface atmosphere despite differences in the way
the sea-ice loss is carried out in each set of simulations. Despite
previous work showing that using a model with full ocean dynamics is
integral for creating these robust near-surface atmospheric response
patterns, the response to high-latitude forcing in the ocean in the various
models is less robust. A warming of the sea surface occurs in all seasons
in the Arctic and subpolar seas where ice is lost, however some models also
find a cooling of the North Atlantic to scale with sea-ice loss. Most
models find some freshening of the Arctic Ocean as a result of the sea-ice
melt, but most of the freshening appears to scale with lower latitude
warming and some salinification patterns scaling with sea-ice loss are
robust, e.g. in Hudson’s Bay. The way in which the circulation and mixed
layer responds in the North Atlantic to sea-ice loss and to lower latitude
warming is model-dependent. Finally, there is little consensus amongst the
models whether sea-ice loss or lower latitude warming would drive changes
in the strength of the Atlantic Meridional Overturning circulation, and in
what direction that change would be.