The Greenland ice sheet may lose 20% more ice than previously measured

It is known that the expanding Greenland ice sheet has been shrinking, especially since the 1990s, due to global warming due to climate change. It's a fate shared by the Antarctic ice sheet as well as glaciers around the world. Now, a new study has revealed that about 20% more of Greenland's ice sheet is missing than previous estimates showed.

The missing ice was breaking off and melting from the tips of the glaciers around Greenland. new search, Published Wednesday in the journal NatureIt provides a detailed account of a process that scientists knew was occurring but had struggled to measure comprehensively.

“Almost all of Greenland's glaciers are retreating. This story is true no matter where you look,” said Chad Green, a glaciologist at NASA's Jet Propulsion Laboratory and lead author of the study. “This retreat is happening everywhere and simultaneously.”

Because the ends of these glaciers generally lie below sea level, within deep fjords, their retreat does not directly add a significant amount to sea level rise. But the melting ice still adds an influx of fresh water, which has implications for global climate models and projections, and for the system of ocean currents that regulate temperatures on both sides of the Atlantic.

Dr. Green's team collected more than 200,000 observations of glaciers' endpoints, covering almost all of Greenland, based on satellite images taken from 1985 to 2022. The researchers used observations from existing public datasets and combined them to create a bird's-eye view . From the shrinking edges of the Greenland ice sheet over the past 40 years.

“It provides a really important new dataset that captures the areal scale of the entire Greenland ice sheet“,” said Laura LaRocca, a climate scientist at Arizona State University who has also studied Greenland's glaciers but was not involved in this project.

Previous estimates of the changing size of the Greenland ice sheet were based on three types of measurements: the surface height of the sheet, the speed of ice passing through fixed locations, and the gravitational pull caused by the mass of the sheet.

By combining several of these estimates, scientists have reached a consensus that Greenland lost a total of Nearly five trillion metric tons Ice since 1992.

These traditional methods can track how much the ice sheet is contributing to sea level rise: approx 13 mm, or half an inch, Until now. But they don't capture everything that happens around the margins, at the foot of hundreds of glaciers that flow through the island's many fjords. This process, called glacial end retreat, represents an additional trillion metric tons of ice lost, according to the new study.

This amount is approximately equivalent to an ice cube It covers an area larger than Manhattan and taller than Mount EverestAccording to the European Space Agency.

Only one glacier out of more than 200 studied since 1985 has expanded permanently. Its gains have been small compared with losses elsewhere.

The erosion of the endpoints of these glaciers has an indirect effect on sea levels. Dr. Green compared the retreat of a glacier's end to a drain separation, which allows the entire glacier to flow faster and thinner, accelerating the melting of parts above sea level as well.

So, while this study is not measuring a direct addition to sea level rise, we are most likely measuring a cause of sea level rise.

The additional ice lost in Greenland is important for other reasons as well.

Once the ice melts, it adds a large amount of fresh water to the ocean, potentially weakening an important system of ocean currents called the Atlantic overturning circulation. This system includes the Gulf Stream, which brings warm tropical waters up the southeastern coast of the United States and across the Atlantic to Europe, contributing to relatively mild temperatures there.

The crumbling ends of Greenland's glaciers have been somewhat overlooked as scientists focus on the pressing issue of sea level rise. It will help scientists better understand the climate system as a whole and the way global warming is distributed among the atmosphere, said Vincent Verjans, a glaciologist at the IBS Center for Climate Physics at Busan National University in South Korea, who reviewed the study. Ocean and ice sheets.

Dr Vergans said it was a topic that was “barely covered”, but an “important one”.