Greenland is careening toward a critical tipping point for ice loss

Frozen Greenland is on track to become significantly less frozen before the 21st century is over. By 2055, winter snowfall on the Greenland Ice Sheet will no longer be enough to replenish the ice that Greenland loses each summer, new research finds.

Rising global temperatures are driving this dramatic change. If Earth continues to heat up at its present pace, average global temperatures should climb by nearly 5 degrees Fahrenheit (2.7 degrees Celsius) by 2055. Regional averages in Greenland become even hotter, rising by about 8 F (4.5 C), scientists reported in a new study.

Under those conditions, Greenland's annual ice loss could increase sea levels by up to 5 inches (13 centimeters) by 2100 — unless drastic steps are taken, starting now, to curb greenhouse gas emissions and slow global warming trends.

Related: Photos of Greenland's gorgeous glaciers

Ice sheets are any thick masses of ice that cover more than 20,000 square miles (50,000 square kilometers) of land, and they grow their icy layers from snow that builds up over thousands of years, according to the National Snow and Ice Data Center (NSIDC). During the last ice age (around 115,000 to 11,700 years ago), ice sheets blanketed much of North America and Scandinavia. But today, only two ice sheets remain — in Greenland and in Antarctica — holding around 99% of Earth's freshwater reserves, NSIDC says.

Ice sheets aren't static — their own weight pushes them slowly toward the ocean, where they discharge ice and meltwater from ice shelves, streams and glaciers. An ice sheet can remain stable only so long as its lost ice is replenished seasonally by winter snowfall.

The Greenland Ice Sheet is roughly three times the size of Texas, measuring approximately 656,000 square miles (1.7 million square km), according to NSIDC. If all of Greenland's ice were to melt at once, sea levels would rise by about 20 feet (6 meters). While that catastrophic scenario is unlikely to happen anytime soon, Greenland has been steadily losing ice for decades, at a rate of about 500 gigatons per year since 1999, another study published in August 2020 found.

Those scientists said that Greenland was already losing more ice than it gained every winter. Their models factored in ice loss from iceberg calving, which can be substantial; a massive iceberg that separated and drifted alarmingly close to a Greenland village in 2018 was thought to weigh more than 12 million tons (11 million metric tons), Live Science previously reported. 

However, the processes that drive icebergs to separate from the ice sheet are complex and unpredictable, said Brice Noël, lead author of the new study and a researcher with the Institute for Marine and Atmospheric research (IMAU) at Utrecht University in the Netherlands. For the new study, the researchers analyzed the Greenland Ice Sheet's surface to determine when melt would surpass snowfall, Noël told Live Science in an email.

"We explore the sensitivity of the Greenland Ice Sheet mass loss to atmospheric warming using a much higher resolution climate model — 1 km — compared to previous work (20 to 100 km)," Noël said. "Higher spatial resolution means that we can now better capture the high mass loss rates of small outlet glaciers;" this source of melt runoff was previously excluded from models, but contributes significantly to the total mass of ice lost, he explained. 

"As a result, we can more accurately project the future evolution of the Greenland Ice Sheet mass loss and its contribution to sea-level rise," Noël said. 

Accelerated exposure

Stability of the ice sheet began to slip after the 1990s, as atmospheric warming boosted meltwater runoff during warm summer months, according to the study. Models showed that most of the runoff was produced at the margins of the ice sheet, in a narrow band called the ablation zone. As Earth warms, it melts the ablation zone's protective layer of tightly compressed snow. Once this layer is gone, the ice underneath — which is much less reflective than the bright snow — absorbs more sunlight, leading to more melt. 

"The accelerating exposure of bare ice amplifies the runoff production, and thus the surface mass loss," Noël said.

In a scenario where humans don't lower greenhouse gas emissions and present warming continues, ice loss in Greenland will cross a new threshold — in which the ice sheet gets smaller each year — within just a few decades, according to the study. And that's a conservative estimate; that threshold could be crossed even earlier, depending on how much additional ice is lost annually from calving icebergs, the authors reported. 

It could then take thousands of years for the ice sheet to melt completely, but saving Greenland's ice from disappearing would require halting or reversing global warming sooner rather than later — "during this century," Noël said.

The findings were published online Jan. 19 in the journal Geophysical Research Letters.

Originally published on Live Science.