Report: Greenland is losing more ice than we thought
The Greenland ice sheet has lost 20% more ice than scientists previously thought, posing potential problems for ocean circulation patterns and sea level rise, according to a new study.
Researchers had previously estimated the Greenland ice sheet lost about 5,000 gigatons of ice in recent decades, enough to cover Texas in a sheet 26 feet high. The new estimate adds 1,000 gigatons to that period, the equivalent of piling about five more feet of ice on top of that fictitious Texas-sized sheet.
The additional loss comes from an area previously unaccounted for in estimates: ice lost at a glacier’s edges, where it meets the water. Before this study, estimates primarily considered mass changes in the interior of the ice sheet, which are driven by melting on the surface and glaciers thinning from their base on the ice sheet.
The study, released Wednesday in Nature, provides improved measurements of ice loss and meltwater discharge in the ocean, which can advance sea level and ocean models.
Loss from the edges of glaciers won’t directly affect sea level rise because they usually sit within deep fjords below sea level, but the freshwater melt could affect ocean circulation patterns in the Atlantic Ocean.
“We can take a look at the glaciers we have now and see how they’re behaving,” said Michael Wood, a study co-author and glaciologist. “That will give us a sense of what the future might hold for future ice loss from Greenland.”
The researchers tracked changes in 207 glaciers in Greenland (constituting 90% of the ice sheet’s mass) each month from 1985 to 2022. Analyzing more than 236,000 satellite images, they manually marked differences along the edges of glaciers and eventually trained algorithms to do the same. From the area measurements, the team could calculate the volume and mass of the changes in ice.
Glaciers can lose ice in many ways. One change can happen when large ice chunks break off at the edge, known as calving.
They can also lose ice when it melts faster than it can form, causing the end of a glacier to retreat and move to higher elevations.
Scientists found that a total of 1,034 gigatons of ice was lost across all glaciers because of this retreat and calving on their peripheries. The loss accelerated since January 2000, with the glaciers losing a total of 42 gigatons each year. It has shown no signs of slowing down.
Most striking, nearly every glacier was shrinking — and in every corner of the ice sheet.
“This is a signal that’s touching every part of Greenland,” said Chad Greene, the study’s lead author and a scientist at NASA’s Jet Propulsion Laboratory. “There’s basically no part of Greenland that’s safe from climate change.”
Polar scientist Twila Moon, who was not involved in the research, said scientists have known the ice sheet is experiencing long-term retreat on the coasts, but she called the study “the most complete quantification of that change published to date.”
The research “emphasizes that we have to remain attentive to the extensive peripheral changes happening across Greenland,” said Moon, a researcher at the National Snow and Ice Data Center.
The largest losses came from glaciers that experienced the biggest changes from season to season. Glaciers in Greenland accumulate mass and grow throughout the winter, then experience ice loss throughout the summer.
A number of factors play into the seasonal variations, including how much ocean water the glacier is in contact with, whether it has a steep or shallow bedrock slope, and how much meltwater it is receiving upstream, Wood said.
Unfortunately, some of the glaciers with wild swings from season to season also happen to be very large, posing significant threats for global sea levels.
Losing the most at its front, the Zachariae Isstrom glacier in northeast Greenland shed 160 gigatons over the past four decades. The glacier holds enough water to add more than 18 inches to the global sea level if it were to melt completely.
West Greenland’s Jakobshavn Glacier, said to have released the iceberg that is believed to have sunk the Titanic, lost 88 gigatons over the time period. One of the ice sheet’s fastest-moving glaciers, it was responsible for nearly 4% of sea level rise during the 20th century.
The Humboldt Glacier in northern Greenland, the ice sheet’s widest glacier that ends in the sea, lost 87 gigatons. If it melted completely, it could raise global sea level by 7 inches.
“The rapid loss from the Greenland ice sheet started in the 1990s and is ongoing,” said physical oceanographer Fiamma Straneo, who was not involved in the study.