NASA's surprising findings about ice melting in Greenland

Ice loss in Greenland exceeds previous estimates

A new in-depth analysis of satellite data has revealed that Greenland has lost more ice than previously estimated and that most of the island's glaciers have retreated significantly.

The Greenland ice sheet has lost about a fifth more ice mass than previously estimated in the past 40 years, according to researchers at Jet Propulsion Laboratory From NASA in California in a new study. ‍Most of the island's glaciers have retreated significantly, and icebergs are falling into the ocean at an accelerating rate. This additional ice loss only had an indirect effect on sea levels, but could have future effects on ocean circulation.

Retreat of glaciers

Published on nature On January 17, the analysis provides a comprehensive view of retreat along the edges of the entire ice sheet from 1985 to 2022, based on nearly a quarter of a million pieces of satellite data on the locations of glaciers. Of the 207 glaciers studied, 179 have retreated. Icy. Remarkably since 1985, 27 countries have remained stable and one has advanced slightly.

Most of the ice loss occurred below sea level, in the fjords on the outskirts of Greenland. Many of these deep coastal valleys, once occupied by ancient glacial ice, were filled with seawater, meaning that the breaking ice contributed little to rising sea levels. However, the loss of ice likely accelerated the movement of ice flowing from higher elevations. . Which contributes to sea level rise.

“When the ice at the end of a glacier breaks off and retreats, it's like pulling the plug out of the fjord, allowing the ice to flow more quickly into the ocean,” glacier scientist Chad Green said. Glacier at JPL and lead author of the study.

Contribution of glaciers to sea level

For decades, researchers have studied the direct contributions of the Greenland ice sheet to global sea level rise through ice flow and melting. Scientists participating inMass balance comparison exercise for ice sheets IMBIE estimated that the ice sheet lost 5,390 billion tons (4,890 billion metric tons) between 1992 and 2020, adding about 13.5 mm to global average sea level, according to the IMBIE report. ⁤ Intergovernmental Panel on Climate Change.

However, IMBIE's measurements do not take into account ice lost due to the retreat of peripheral glaciers along Greenland's edges. (These ice ledges‌ were already in the water, submerged and floating.) The new study quantifies this amount: For the period 1985 to 2022, the ice sheet is estimated to have lost about 1,140 billion metric tons (1,034 billion metric tons). tons)⁤ – 21% greater mass loss than IMBIE rating.

Even if it does not contribute to sea level rise, the additional ice represents a significant influx of fresh water into the ocean. Recent studies have indicated that changes in the salinity of the North Atlantic caused by melting icebergs could weaken the Atlantic Ocean Circulation in the South AtlanticIt is part of the global “conveyor belt” of currents that transport heat and salt across the ocean. This could affect weather patterns around the world, as well as ecosystems, the authors said.

A bird's-eye view of the glacial retreat

Balance between growth and retreat of glaciers

Icebergs have calved from Greenland's glaciers for thousands of years as part of a natural cycle that typically balances glacier growth in winter with melting and retreat in summer. The new study finds that ice retreat has far outpaced growth throughout the 21st century.

The researchers also found that Greenland's ice extent remained relatively stable from 1985 to 2000, then began a marked recession that continues today.

Ice loss from individual glaciers

A glacier in northeastern Greenland called Zechariah Istrom lost most of its ice, losing 176 billion metric tons (160 billion metric tons) of its mass to retreat, the data showed. It is followed by Jakobshavn⁣Espray on the west coast, which lost about 97 billion tons⁢ (88 billion metric tons), and Humboldt Gletscher in the northwest, which lost ⁤96 billion tons⁢ (87 billion metric tons).

Only one glacier, the Cajutap-Sirmia in southern Greenland, saw growth during the study period, but its gains were too small to offset the losses of other glaciers.

The relationship between seasonal fluctuations and glacier retreat

The researchers also found that glaciers with the greatest seasonal fluctuations in the location of the ice front experienced the greatest overall retreat. The correlation suggests that glaciers that are most sensitive to summer warming will be the most affected by climate change in the coming decades.

“The discovery of a large-scale pattern of glacier retreat and its association with glacier sensitivity on seasonal time scales was the result of a massive data compilation that examined all parts of the ice sheet over time,” said Alex Gardner, a cryospheric scientist at Harvard University. Jet Propulsion Laboratory (JPL) and co-author of the study. The scientists relied on five publicly available datasets that collectively mapped the monthly locations of 236,328 ice edges detected, both manually and through computer algorithms, in images collected by optical and radar satellites.

“Previously, we had snippets of information — a lot of local studies,” Gardner said. “But what this study provides is a systematic, comprehensive insight that has led to some very important insights that we didn't have about the ice sheet before.”