Greenland Ice Sheet Lost a Record Level of Ice in 2019, Study Finds

The Greenland ice sheet saw record levels of ice loss in 2019, a situation caused by high temperatures and certain atmospheric circulation patterns. Scientists writing in the journal Cryosphere say climate models that ignore these atmospheric patterns could drastically underestimate levels of future ice loss.

The Greenland ice sheet, in the Arctic, is the second largest ice sheet on the planet. It is three times the size of Texas (656,000 square miles), and covers most of Greenland, the world's largest island. The sheet contains so much ice that if it was to melt in its entirety, global sea levels could rise 20 feet—drowning coastal cities like Miami.

To calculate levels of ice loss on the Greenland ice sheet, the study's authors used a combination of satellite data, ground measurements and climate models. Machine learning tools were used to help identify patterns within the data.

From this information, the scientists worked out the ice sheet's "surface mass balance," which considers ice lost through surface meltwater runoff and mass gained—for example, through snowfall. They liken the losses and gains to a bank account.

"In some periods you spend more, and in some periods you earn more. If you spend too much you go negative. This is what happened to Greenland recently," lead author Marco Tedesco, a climate scientist at Columbia University, said in a statement.

Tedesco and Xavier Fettweis, a polar climate scientists at University of Liège in Beligium, found the surface mass gained around 50 billion tons in 2019. At the same time, the sheet lost around 560 billion tons.

According to Tedesco and Fettweis, the total surface mass balance was roughly 300 billion tons below the 1981-2010 average, and was lower than the previous record for lowest surface mass balance—610 billion tons—recorded in 2012. These results suggest that in 2019, the Greenland ice sheet experienced the highest levels of ice loss since records began in 1948.

However, temperatures were not as high as they were in 2012. Researchers also note levels of surface runoff—the amount of water that "runs off" the surface—were lower in 2019. In theory, this means levels of ice loss should have been less than in 2012.

The researchers say there was a specific set of atmospheric conditions in 2019 that exacerbated melt and contributed to record-breaking ice loss. These include long periods of anticyclonic conditions, which prevented clouds from forming in the southern section of the ice sheet. Not only does this mean the region experiences lower levels of snowfall but clearer skies allow more sunlight to reach the sheet's surface, which causes the ice to thaw.

Further north, high pressure systems brought warmer, wetter air from the lower latitudes. These formed heat-trapping clouds to create a greenhouse-like effect that, again, increased levels of meltwater runoff and contributed to 2019's record-breaking ice loss.

Tedesco explained these atmospheric conditions have increased in frequency over recent decades. This is an effect he attributes to changes in the jet stream—a current of strong winds that sit 5 to 7 miles above the Earth's surface—triggered by global temperature changes and the disappearance of sea ice and snow cover in Siberia.

Models that do not account for changes in the jet stream will be unable to project ice loss in the future—"It's almost like missing half of the melting," he said in a statement.

Tedesco and Fettweis urge scientists to consider the involvement of atmospheric conditions and the jet stream in climate projection models. A better understanding of these processes would improve predictions relating to ice loss.

This is important because knowing when and how much ice will be lost can help countries prepare for the consequences, such as rising sea levels. According to current projections from the Intergovernmental Panel on Climate Change (IPCC), the sea levels could rise 3.6 feet higher by the end of the century if nothing is done to cut greenhouse gas emissions. A study from 2019 also found as many as 187 million people could be displaced by the end of the century as a result of rising sea levels.

Greenland ice sheet
In this view from an airplane the Greenland ice sheet lies near the Sermeq Kujalleq glacier, also called the Jakobshavn glacier, on August 04, 2019 near Ilulissat, Greenland. 2019 saw record breaking ice loss on the Greenland ice sheet. Sean Gallup/Getty
Greenland Ice Sheet Lost a Record Level of Ice in 2019, Study Finds | Tech & Science