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We explore the global impacts of Arctic sea ice decline in climate model perturbation experiments focusing on the temporal evolution of induced changes. We find that climate response to a realistic reduction in sea ice cover varies dramatically between shorter decadal and longer multidecadal to centennial timescales. During the first two decades, when atmospheric processes dominate, sea ice decline induces a "bipolar seesaw" pattern in surface temperature with warming in the Northern and cooling in the Southern Hemisphere, leading to a northward displacement of the Intertropical Convergence Zone and an expansion of Antarctic sea ice. In contrast, on multidecadal and longer timescales, the weakening of the Atlantic meridional overturning circulation, caused by upper-ocean buoyancy anomalies spreading from the Arctic, mediates direct sea ice impacts and nearly reverses the original response pattern outside the Arctic. The Southern Hemisphere warms, a Warming Hole emerges in the North Atlantic, the Intertropical Convergence Zone shifts southward, and Antarctic sea ice contracts.

Plain Language Summary To understand how the recent Arctic sea ice decline may affect global climate, we conduct model experiments in which we modify the properties of Arctic sea ice, in order to simulate an Arctic sea ice loss similar to the observed. We find that climate response shows dramatically different patterns during different periods after the imposed sea ice decline. During the first one or two decades, Arctic sea ice decline allows more solar energy into the Northern Hemisphere, altering the Earth's energy balance. As the Northern Hemisphere warms while the Southern Hemisphere cools, the tropical rain belt moves northward, and Antarctic sea ice expands. However, after several more decades to a century, the impacts from changes in the deep ocean become more important and eventually overwhelm the direct effects of sea ice loss on the atmosphere. The weakening of the Atlantic deep ocean circulation causes a cooling in the North Atlantic and a warming in the Southern Hemisphere. Antarctic sea ice contracts and the tropical rain belt shifts back to its original position and further south.