Last month, we summarized evidence for the long-term stability of Greenland’s ice cap, even in the face of dramatically warmed summer temperatures. We drew particular attention to the heat in northwest Greenland at the beginning of the previous (as opposed to the current) interglacial. A detailed ice core shows around 6000 years of summer temperatures averaging 6-8oC (11-14oF) warmer than the 20th century average, beginning around 118,000 years ago. Despite six millenia of temperatures that are likely warmer than we can get them for a mere 500 years, Greenland only lost about 30% of its ice. That translates to only about five inches of sea level rise per century from meltwater.
We also cited evidence that after the beginning of the current interglacial (nominally 10,800 years ago) it was also several degrees warmer than the 20th century, but not as warm as it was at the beginning of the previous interglacial.
Not so fast. Work just published online in the Proceedings of the National Academy of Sciences by Jamie McFarlin (Northwestern University) and several coauthors now shows July temperatures averaged 4-7oC (7-13oF) warmer than the 1952-2014 average over northwestern Greenland from 8 to 10 thousand years ago. She also had some less precise data for maximum temperatures in the last interglacial, and they are in agreement (maybe even a tad warmer) with what was found in the ice core data mentioned in the first paragraph.
Award McFarlin some serious hard duty points. Her paleoclimate indicator was the assembly of midges buried in the annual sediments under Wax Lips Lake (we don’t make this stuff up), a small freshwater body in northwest Greenland between the ice cap and Thule Air Base, on the shore of the channel between Greenland and Ellesmere Island. Midges are horrifically irritating, tiny biting flies that infest most high-latitude summer locations. They’re also known as no-see-ums, and they are just as nasty now as they were thousands of years ago.
Getting the core samples form Wax Lips Lake means being out there during the height of midge season.
She acknowledges the seeming paradox of the ice core data: how could it have been so warm even as Greenland retained so much of its ice? Her (reasonable) hypothesis is that it must have snowed more over the ice cap—recently demonstrated to be occurring for the last 200 years in Antarctica as the surrounding ocean warmed a tad.
The major moisture source for snow in northwesternmost Greenland is the Arctic Ocean and the broad passage between Greenland and Ellesmere. The only way it would snow so much as to compensate for the two massive warmings that have now been detected, is for the water to have been warmer, increasing the amount of moisture in the air. As we noted in our last Greenland piece, the Arctic Ocean was periodically ice-free for millenia after the ice age.
McFarlin’s results are further consistent, at least in spirit, with other research showing northern Eurasia to have been much warmer than previously thought at the beginning of the current interglacial.
Global warming apocalypse scenarios are driven largely by the rapid loss of massive amounts of Greenland ice, but the evidence keeps coming in that, in toto, it’s remarkably immune to extreme changes in temperature, and that an ice-free Arctic Ocean has been common in both the current and the last interglacial period.