The climate of past interglacials: polar warmth and sea level rise

Future projections of climate change imply our planet is moving into a ‘super-interglacial' with sea level rise of conservatively 20 to 60 centimeters by the end of this century. Within the last million years, there are previous interglacials that are known to have been warmer than present at the poles, with a near to ice-free Arctic Ocean and sea level many meters above present, therefore providing a natural analogue for what the future might hold. Past periods may not be complete analogues for anthropogenic-driven climate change, but the mechanisms that operated at different times can provide analogues of climate processes for the future and provide excellent tests of climate models.

Climate during the Last Interglacial (130,000 to 116,000 years ago) provides an excellent ‘process analogue' for future changes of summer sea ice and melting of the Greenland ice sheet. We will present climate modeling results from the NCAR Community Climate System Model that demonstrates that these changes were a result of an orbitally-driven excess of Northern Hemisphere summer insolation. The Last Interglacial simulated climate is warmer than present, particularly in the Arctic, with summer temperatures up to 5°C warmer than present. Reduced summer sea ice is important for this response. We also will show ice-sheet modeling results that provide strong evidence for a reduced Greenland ice sheet (equivalent to a few metres of sea level change) at the Last Interglacial. Portions of the West Antarctic ice sheet may also have been vulnerable to basal melting by warmer ocean waters, leading to additional warming of the East Antarctic ice sheet. Interglacials previous to the Last Interglacial will also be discussed.