Greenland’s Ice Sheet May Be Losing 20% More Ice Than Previously Measured

Greenland’s expansive ice sheet is known to be shrinking, especially since the 1990s, because of warming from climate change. It’s a fate shared by the Antarctic Ice Sheet as well as glaciers around the world. Now, a new study reveals that about 20 percent more of the Greenland ice sheet has disappeared than previous estimates show.

The missing ice has been breaking and melting from the ends of glaciers around Greenland’s perimeter. The new research, published Wednesday in the journal Nature, provides a detailed accounting of a process that scientists knew was happening but had struggled to measure comprehensively.

“Almost every glacier in Greenland is retreating. And that story is true no matter where you look,” said Chad Greene, a glaciologist at the NASA Jet Propulsion Laboratory and the lead author of the study. “This retreat is happening everywhere and all at once.”

Because the ends of these glaciers generally sit below sea level, within deep fjords, their retreat isn’t directly adding a significant amount to sea level rise. But melting ice still adds an influx of freshwater that has implications for global climate models and projections, and for the system of ocean currents that regulates temperatures on both sides of the Atlantic Ocean.

Dr. Greene’s team combined more than 200,000 observations of glaciers’ end points, covering almost all of Greenland, based on satellite images taken from 1985 to 2022. The researchers used observations from existing public data sets and combined them to create a comprehensive bird’s-eye view of the contracting edges of Greenland’s ice sheet over the past 40 years.

“They provide a really important new data set that captures the aerial extent 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.

Earlier estimates of the changing size of Greenland’s ice sheet were based on three types of measurements: the altitude of the ice sheet’s surface, the velocity of ice passing by fixed locations and the gravitational pull produced by the ice sheet’s mass.

Combining several of these estimates, scientists arrived at a consensus that Greenland has lost a total of nearly five trillion metric tons of ice since 1992.

These traditional methods can capture how much the ice sheet has contributed to sea level rise: about 13 millimeters, or half an inch, so far. But they don’t capture everything happening around the margins, at the feet of hundreds of glaciers that funnel through the island’s many fjords. This process, called glacial terminus retreat, accounts for an additional one trillion metric tons of lost ice, according to the new study.

That amount is roughly equivalent to an ice cube covering an area larger than Manhattan and taller than Mount Everest, according to the European Space Agency.

Only one glacier out of more than 200 included in the study had definitively expanded since 1985. Its gains were small compared to the losses elsewhere.

The erosion of these glaciers’ end points has an indirect effect on sea levels. Dr. Greene compared glacial terminus retreat with unplugging a drain, allowing the whole glacier to flow faster and thin out, accelerating melt from the parts above sea level as well.

So, while this study does not measure a direct addition to sea level rise, “we’re probably measuring a cause of sea level rise,” he said.

Greenland’s additional lost ice is important for other reasons, too.

Once the ice melts, it adds a significant amount of freshwater to the ocean, potentially weakening an important system of ocean currents called the Atlantic Meridional Overturning Circulation. This system includes the Gulf Stream, which brings warm tropical water up the southeast coast of the United States and across the Atlantic Ocean to Europe, contributing to relatively mild temperatures there.

The fraying ends of Greenland’s glaciers have been somewhat overlooked as scientists focused on the urgent question of sea level rise. Vincent Verjans, a glaciologist at the IBS Center for Climate Physics at Pusan National University in South Korea, who reviewed the study, said it would help scientists better understand the climate system as a whole and the way global warming is being distributed between the atmosphere, the ocean and the ice sheets.

It’s a topic that is “very barely covered,” Dr. Verjans said, but “it is an important topic.”