Science Focus
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Earth’s climate system will respond to the stronger greenhouse effect we’ve produced in various ways. But one key question about its response is how much ice will be lost from the great ice sheets of Greenland and Antarctica. Push them too far outside their climatic comfort zone, we know, and a large retreat of glacial ice can follow, raising global sea levels.
Given that the innards of these ice sheets are complicated and inaccessible, researchers rely heavily on what we can discover about their pasts. One key point in the past has been the warm interglacial period around 400,000 years ago. The cycles in Earth’s orbit that govern the timing of the ice ages conspired to produce an exceptionally long respite from the cold at this time—twice as long or more than the most recent interglacial period about 120,000 years ago. It may have been warmer, as well, and some estimates put sea level in the vicinity of six to 13 meters higher than it is today.
Did that sea level rise come mostly from a smaller Greenland ice sheet, loss of ice from Antarctica, or some mixture of the two? We don’t know, and it’s difficult to answer since glaciers destroy the evidence of their past retreat when they expand again. A new study led by Alberto Reyes (now at the University of Alberta) and Oregon State’s Anders Carlson sifted sediments off Greenland’s coast to find clues about what the ice sheet was up to at that time.
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