One of the bigger risks we’re running with our planetary warming experiment is the melting of the vulnerable West Antarctic Ice Sheet, raising sea levels much more rapidly than we expect. It’s a scenario scientists assess both by studying present conditions and by examining the past.
One time period of particular interest is the previous interglacial—a warm intermission between ice ages—about 120,000 years ago. Sea level appears to have been 5 to 9 meters higher during this time when the configuration of Earth’s orbit made for a little more summer sunshine (and warmer temperatures) in the Northern Hemisphere.
The West Antarctic Ice Sheet is a candidate to have supplied about 3 meters of that sea level rise. Unfortunately, evidence of its history is hard to come by, as the regrowth of the ice sheet destroyed some of it and now conceals even more. Sediment cores show the ice sheet shrank drastically in the past, but it’s unclear when in the past.
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