A profile of an ice sheet in northwest Greenland
Photo: Yarrow Axford, Northwestern University

In the not-too-distant geologic past when global temperatures weren’t too much warmer than they are today, black flies called midges buzzed around a lake in northwest Greenland. Their discovery suggests temperatures could have routinely reached a balmy 50 degrees Fahrenheit in the summertime—a profound climactic switch that could foreshadow Greenland’s future.

The findings, published Monday in the Proceedings of the National Academies of Science, are the latest evidence that ancient Greenland was nothing like the icy island we know today. The Northwestern University and Dartmouth researchers reached their conclusions through a glamorous analysis of very old fly corpses preserved in mud at the bottom of the Wax Lips Lake, which is situated along the coastline due east of Canada’s Ellesmere Island and just over a mile from the edge of the Greenland Ice Sheet.

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“Midges are largely stenothermic, meaning many midge species are sensitive to temperature and thrive only in a narrow temperature range,” lead study author Jamie McFarlin, a Ph.D. student at Northwestern, told Earther via email.

To produce temperature estimates through time, the researchers looked at the composition of the midge population as it changed from more cold- to heat-loving species and back again.

Casts shed by lake fly larva found in sediments from Wax Lips Lake in northwestern Greenland.
Photo: Jamie M. McFarlin

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Their analysis suggests air temperatures in the peak of summer were 4-7 degrees Celsius (7-13 degrees Fahrenheit) warmer during the early Holocene (8,000-10,000 years ago) than they are today and 5.5-8.5 Celsius degrees (10-15 Fahrenheit) hotter during the Last Interglacial (116,000-130,000 years ago). On average, global temperatures were about a degree to two Celsius higher than pre-industrial temperatures during these time periods, owing to slight differences in its orbit around the Sun.

“Those are really high numbers,” Gifford Miller, a paleoclimate researcher at Colorado University who wasn’t involved in the study told Earther, referring to the study’s temperature estimates for the Last Interglacial.

Other studies have attempted to determine Greenland’s past climate using models or different proxies (physical evidence of past temperatures, like fly corpses or pollen grains), and all have arrived at somewhat different answers. Most of those answers clocked in cooler than the new study. That means while it is provocative, the new findings still warrant further analysis, especially because as Miller noted, the study offers a pretty big range of potential temperatures.

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“I think we’d all like to see those numbers replicated by another tool,” he said.

McFarlin agreed her team’s numbers were on the high end compared with estimates of Greenland’s past climate derived from models, but said they agree with several nearby temperature estimates from ice cores, “which provides confidence in strong regional warming during these periods.”

Understanding just how much warmer Greenland was in the past is more than an academic curiosity. Our current warming trend is on track to usher in global temperatures not seen since the Last Interglacial. If the 25 feet of global sea level currently locked away in Greenland’s ice was prone to melting during that time, the same is likely to be true today.

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As the authors put it, “such strong warming at WLL [the lake] may portend even larger changes over this region than predicted in the coming century.”