The West Greenland Ice Sheet has melted at a dramatically higher rate over the last 20 years than any other time in at least 450 years.
Researchers from Dartmouth College and Boise State University are studying the importance of long-term warming trends to account for the recent upswing in melting rates in recent years. Their findings indicate that greenhouse gas emissions as the likely cause for the additional warming. The study also revealed that the loss of ice from Greenland is one of the largest contributors to global sea level rise.
“We see that west Greenland melt really started accelerating about 20 years ago,” Erich Osterberg, an assistant professor of earth sciences at Dartmouth and the lead scientist on the project, said in a statement. “Our study shows that the rapid rise in west Greenland melt is a combination of specific weather patterns and an additional long-term warming trend over the last century.”
While glaciers calving into the ocean cause much of the ice loss in Greenland, the researchers found that most of the ice loss in recent years is caused by an increased surface melt and runoff.
In the study, the researchers spent two months on snowmobiles in the region collecting seven ice cores from the remote percolation zone of the ice sheet.
In the percolation zone, when warm temperatures melt the snow on the surface, the melt water trickles down into the deeper snow and then refreezes into ice layers. The team was able to distinguish the ice layers from the surrounding compacted snow in the cores to preserve a history of how much melt occurred through time.
“Most ice cores are collected from the middle of the ice sheet where it rarely ever melts, or on the ice sheet edge where the meltwater flows into the ocean,” Karina Graeter, the lead author of the study as a graduate student in Dartmouth’s Department of Earth Sciences, said in a statement. “We focused on the percolation zone because that’s where we find the best record of Greenland melt going back through time in the form of the refrozen ice layers.”
The cores, which could be as long as 100-feet, where then transported to Dartmouth and measurements of thickness and frequency of the ice layers using a light table. The cores were also sampled for chemical measurements in Dartmouth’s Ice Core Laboratory to determine the age of each ice layer.
“The ice core record ends about 450 years ago, so the modern melt rates in these cores are the highest of the whole record that we can see,” Osterberg said. “The advantage of the ice cores is that they show us just how unusual it is for Greenland to be melting this fast.”
The researchers also found that an additional summertime warming factor of 2.2 degrees Fahrenheit is needed to explain the strong melting observed in the last 20 years.
“It is striking to see how a seemingly small warming of only 2.2 degrees Fahrenheit can have such a large impact on melt rates in west Greenland,” said Graeter.
The study concludes that North Atlantic ocean temperatures and summer blocking activity will continue to control year-to-year changes in Greenland melt into the future.
“Cooler North Atlantic Ocean temperatures and less summer blocking activity might slow down Greenland melt for a few years or even a couple decades, but it would not help us in the long run,” said Osterberg. “Beyond a few decades, Greenland melting will almost certainly increase and raise sea level as long as we continue to emit greenhouse gases.”