Melting Misconceptions: NASA’s Startling Findings on Greenland’s Ice Loss

A brand new, complete evaluation of satellite tv for pc knowledge finds extra Greenland ice misplaced than beforehand estimated and that almost all of glaciers on the landmass have retreated considerably.

The Greenland Ice Sheet has shed about one-fifth extra ice mass prior to now 4 a long time than beforehand estimated, researchers at NASA’s Jet Propulsion Laboratory in Southern California reported in a brand new paper. The vast majority of glaciers on the landmass have retreated considerably, and icebergs are falling into the ocean at an accelerating charge. This extra ice loss has had solely an oblique influence on sea ranges, however may maintain implications for ocean circulation sooner or later.

Printed in Nature on January 17, the evaluation affords a complete take a look at retreat across the edges of your complete ice sheet from 1985 to 2022, drawing from practically 1 / 4 million items of satellite tv for pc knowledge on glacier positions. Of the 207 glaciers within the research, 179 retreated considerably since 1985, 27 held regular, and one superior barely.

Many of the ice loss got here from under sea degree, in fjords on Greenland’s periphery. As soon as occupied by historical glacial ice, many of those deep coastal valleys have stuffed with seawater – which means the ice that broke off made little web contribution to sea degree. However the loss possible accelerated the motion of ice flowing down from greater elevations, which in flip added to sea degree rise.

“When the ice on the finish of a glacier calves and retreats, it’s like pulling the plug out of the fjord, which lets ice drain into the ocean quicker,” mentioned Chad Greene, a glacier scientist at JPL and the research’s lead creator.

Jakobshavn Isbrae, a glacier on Greenland’s western coast, is proven in imagery taken on September 5, 1985, by the Landsat 5 satellite tv for pc. Jakobshavn receded from 1985 to 2022, dropping about 97 billion tons (88 billion metric tons) of ice, a latest research of the Greenland Ice Sheet’s glacial retreat discovered. Credit score: NASA/USGS

Accounting for Glacial Retreat

For many years researchers have studied the Greenland Ice Sheet’s direct contributions to international sea degree rise by ice circulation and melting. Scientists collaborating within the worldwide Ice sheet Mass Stability Inter-comparison Train (IMBIE) estimated that the ice sheet had misplaced 5,390 billion tons (4,890 billion metric tons) between 1992 and 2020, including about 0.531 inches (13.5 millimeters) to international imply sea degree, in accordance with the Intergovernmental Panel on Local weather Change.

However the IMBIE measurements don’t account for ice misplaced as a result of retreat of terminal glaciers alongside the perimeters of Greenland. (These glacier edges have been already within the water, whether or not submerged or floating.) The brand new research quantifies this quantity: For the 1985 to 2022 interval within the new paper, the ice sheet was estimated to have misplaced about 1,140 billion tons (1,034 billion metric tons) – 21% extra mass misplaced than within the IMBIE evaluation.

Though it doesn’t add to sea ranges, the extra ice represents a major inflow of recent water to the ocean. Current research have advised that modifications within the salinity of the North Atlantic Ocean from melting icebergs may weaken the Atlantic Meridional Overturning Circulation, a part of the worldwide “conveyor belt” of currents that transport warmth and salt across the ocean. This might affect climate patterns worldwide, in addition to have an effect on ecosystems, the authors mentioned.

The oceans play a major function in absorbing greenhouse gases, like carbon dioxide, and warmth from the environment. This absorption might help mitigate the early results of human-emissions of carbon dioxide. The Atlantic Meridional Overturning Circulation acts as a conveyor belt of ocean water from Florida to Greenland. Alongside the journey north, water close to the floor absorbs greenhouse gases, which sink down because the water cools close to Greenland. On this approach, the ocean successfully buries the gases deep under the floor. Credit score: NASA’s Goddard House Flight Heart

A Complete View of Glacial Retreat

Icebergs have tumbled from Greenland’s glaciers for 1000’s of years as a part of a pure cycle that usually balanced glacier development within the winter with melting and retreat in the summertime. The brand new research finds that ice retreat has far outpaced development all through the twenty first century.

The researchers additionally discovered that Greenland’s ice extent remained comparatively regular from 1985 to 2000, then began a marked recession that continues to at the present time.

A Landsat 8 picture from August 22, 2022, exhibits icebergs breaking from Zachariae Isstrom. From 1985 to 2022, as icebergs fell into the ocean at an accelerating charge, the Greenland Ice Sheet shed about 1,140 billion tons (1,034 billion metric tons) – one-fifth extra mass than beforehand estimated. Credit score: NASA/USGS

The info confirmed a glacier in northeast Greenland known as Zachariae Isstrom misplaced essentially the most ice, dropping 176 billion tons (160 billion metric tons) of mass resulting from retreat. It was adopted by Jakobshavn Isbrae on the western coast, which misplaced an estimated 97 billion tons (88 billion metric tons), and Humboldt Gletscher within the northwest, which misplaced 96 billion tons (87 billion metric tons).

Just one glacier, Qajuuttap Sermia in southern Greenland, skilled any development over the research interval, however its features have been too small to offset the losses from different glaciers.

Imagery from the Landsat 7 satellite tv for pc taken on August 5, 1999, exhibits Zachariae Isstrom, a glacier in northeast Greenland. This glacier misplaced about 176 billion tons (160 billion metric tons) of ice throughout its retreat from 1985 to 2022, a latest research discovered. Credit score: NASA/USGS

The researchers additionally discovered that glaciers with the most important seasonal fluctuations within the place of their ice entrance skilled the best general retreat. The correlation suggests the glaciers which are most delicate to warming every summer season might be most impacted by local weather change within the coming a long time.

The invention of a large-scale sample of glacier retreat and its hyperlink to glacier sensitivity on seasonal time scales was the results of a big-data synthesis that appears in any respect elements of the ice sheet over time, mentioned JPL cryosphere scientist Alex Gardner, a co-author of the paper. Scientists drew from 5 publicly out there datasets that cumulatively tracked the month-to-month positions of 236,328 glacier edges as detected, both manually or by pc algorithms, in photographs collected by optical and radar satellites.

“Beforehand, we had bits and items – numerous native research,” Gardner mentioned. “However what this research affords is a scientific and complete view that has led to some fairly vital insights that we didn’t have in regards to the ice sheet earlier than.”

Reference: “Ubiquitous acceleration in Greenland Ice Sheet calving from 1985 to 2022” by Chad A. Greene, Alex S. Gardner, Michael Wooden and Joshua Ok. Cuzzone, 17 January 2024, Nature.
DOI: 10.1038/s41586-023-06863-2