NASA’s surprising discovery about Greenland’s ice loss

A comprehensive new analysis of satellite data shows that Greenland has lost more ice than previously estimated, with most of its land glaciers in deep retreat.

Greenland’s ice sheet has shed about a fifth more ice mass over the past 40 years than previously estimated, researchers said. NASAThe Jet Propulsion Laboratory in Southern California reports in a new paper. Most of the continent’s glaciers are retreating significantly, and icebergs are falling into the ocean at an accelerating rate. Although this additional ice loss has only an indirect effect on sea levels, it could affect ocean circulation in the future.

was announced on Nature The analysis, published Jan. 17, provides a comprehensive look at retreat near the edges of the entire ice sheet from 1985 to 2022, based on nearly 250,000 satellite data on glacier positions. ing. Of the 207 glaciers studied, 179 have retreated significantly since 1985, 27 have remained stable and one has advanced slightly.

Most of the ice loss occurred below sea level in the fjords around Greenland. Many of these deep coastal valleys, once occupied by ancient glaciers, are now filled with seawater, meaning that cracked ice contributes little to sea level rise. But this loss may have accelerated the movement of ice downhill from highlands, further accelerating sea level rise.

“When the ice at the edge of a glacier shrinks and retreats, it’s like pulling a cork out of a fjord, allowing the ice to flow into the ocean faster,” says glacier scientist Chad Green. JPL and lead author of this study.

An image taken by the Landsat 5 satellite on September 5, 1985 shows Jakobshavn Isbrae, a glacier on the west coast of Greenland. A recent study of the Greenland Ice Sheet’s retreat found that Jakobshavn retreated from 1985 to 2022, losing about 97 billion tons (88 billion metric tons) of ice. Credit: NASA/USGS

Explanation of glacier retreat

For decades, researchers have studied the direct contribution of the Greenland Ice Sheet to global sea level rise through ice flow and melting. Scientists participating in the International Ice Sheet Mass Balance Intercomparison Exercise (Inbee) estimates that ice sheets lost 5.39 trillion tons (4.89 trillion tons) between 1992 and 2020, increasing global average sea level by about 0.531 inches (13.5 millimeters). Intergovernmental Panel on Climate Change.

However, IMBIE’s measurements do not take into account ice loss due to the retreat of terminal glaciers along Greenland’s edges. (The edges of these glaciers were already under water, whether submerged or floating.) A new study quantifies this amount. A new paper estimates that between 1985 and 2022, ice sheets lost about 1.14 trillion tonnes (1.34 trillion tonnes). ) – 21% more mass loss than IMBIE rating.

Although sea levels are not rising, increased ice means a large influx of fresh water into the ocean. A recent study found that changes in salinity in the North Atlantic due to melting icebergs could weaken the Atlantic Meridional Overturning Circulation, part of a “conveyor belt” of global ocean currents that transports heat and salt into the ocean. It suggests. This could not only affect ecosystems, but also affect weather patterns around the world, the authors said.

The ocean plays an important role in absorbing greenhouse gases such as carbon dioxide and heat from the atmosphere. This absorption helps reduce the initial impact of anthropogenic carbon dioxide emissions. The Atlantic Meridional Overturning Circulation acts as a conveyor belt transporting ocean water from Florida to Greenland. On its way north, water near the surface absorbs greenhouse gases, which sink as the water cools near Greenland. In this way, the ocean effectively buries gas deep beneath the earth’s surface.Credit: NASA’s Goddard Space Flight Center

Overall picture of Glacial Retreat

Icebergs have been rolling off Greenland’s glaciers for thousands of years, typically as part of a natural cycle that balances glacier growth in the winter with melting and retreat in the summer. A 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, but then began a marked recession that continues to this day.

Landsat 8 image from August 22, 2022 shows an iceberg breaking off from Zachariae Istrom. From 1985 to 2022, the Greenland Ice Sheet shed approximately 1.14 trillion tons (1.34 trillion tons) of mass as icebergs fell into the ocean at an accelerating rate. This is one-fifth more mass than previously estimated. Credit: NASA/USGS

According to the data, a glacier in northeast Greenland called Zachariae Istrom lost the most ice, losing 176 billion tonnes (160 billion tonnes) of mass due to retreat. This was followed by Jakobshavn-Isblae on the west coast with an estimated loss of 97 billion tonnes (88 billion tonnes) and Humboldt-Gletscher in the northwest with an estimated loss of 96 billion tonnes (87 billion tonnes).

Only one glacier, Kajuutap Selmia in southern Greenland, experienced growth during the study period, but the increase was too small to offset losses from other glaciers.

An image from the Landsat 7 satellite taken on August 5, 1999 shows the Zachariae Isstrom, a glacier in northeastern Greenland. According to a recent study, the glacier lost about 176 billion tons (160 billion tons) of ice during its retreat from 1985 to 2022. Credit: NASA/USGS

The researchers also found that glaciers with the greatest seasonal variation in ice front position had the greatest overall retreat. This correlation suggests that glaciers, which are most susceptible to warming each summer, will be the most affected by climate change in coming decades.

JPL cryosphere scientist Alex Gardner said the discovery of the link between large-scale patterns of glacier retreat and glacier susceptibility on seasonal scales is based on big data that look at all parts of the ice sheet over time. It was said to be the result of a synthesis. Co-author of the paper. Scientists cumulatively tracked the monthly positions of 236,328 glacier edges detected manually or by computer algorithms in images collected by optical and radar satellites, based on five publicly available used the dataset.

“Before, there was a lot of piecemeal, on-the-ground research,” Gardner said. “But what this study provides is a systematic and comprehensive view that leads to some pretty important insights about the ice sheet that we haven’t had before.”

Reference: Chad A. Green, Alex S. Gardner, Michael Wood, and Joshua K. Kuzon, “Ubiquitous Acceleration in Greenland Ice Sheet Melt from 1985 to 2022,” January 17, 2024 Day, Nature.
DOI: 10.1038/s41586-023-06863-2