The Greenland Ice Sheet is the largest ice mass in the Northern Hemisphere, and it’s melting rapidly. Climate change is causing more intense atmospheric rivers, which can deliver intense snowfall—enough to slow Greenland’s ice mass loss, a new study finds.

The work appears in Geophysical Research Letters.

Atmospheric rivers are bands of water vapor that transport moisture and heat from warm oceans to cooler high latitudes. Until recently, they were thought only to exacerbate Arctic ice loss. But in March 2022, an intense atmospheric river delivered 16 billion tons of snow to Greenland. That was enough snow to offset the sheet’s annual ice loss by 8%, the study reports. This massive dump of fresh snow also recharged the winter snowpack with fresh, reflective snow, increasing the snow’s albedo and delaying the onset of ice melt by almost 2 weeks.

Study co-author Alun Hubbard, a field glaciologist at the Universities of Oulu, Finland and the Arctic University of Tromsø, Norway, has worked on the impact of rainfall on Greenland’s ice melt and dynamics for over a decade.

“Sadly, the Greenland Ice Sheet won’t be saved by atmospheric rivers,” Hubbard said. “But what we see in this new study is that, contrary to prevailing opinions, under the right conditions, atmospheric rivers might not be all bad news.”

Tracing an epic snowstorm

As the Arctic has warmed almost four times faster than the global average since 1980, Greenland has been melting. Warmer temperatures from climate change mean more rain, less snow and more melt, even farther inland, which has historically been the frigid heart of the ice sheet. If the entire Greenland Ice Sheet melts, sea level would rise by more than 7 meters (23 feet).

Atmospheric rivers are expected to become larger, more frequent and more intense in response to climate change, so understanding their impacts on the Greenland Ice Sheet is crucial.

Hannah Bailey, a geochemist at the University of Oulu and the study’s lead author, was working in Svalbard in March 2022 when the intense atmospheric river hit. Heavy rain fell across Svalbard for days, turning winter snowpack into a quagmire and bringing fieldwork to an abrupt halt. Bailey wondered what the storm’s impact was on the Greenland ice sheet.

A year later, Bailey and Hubbard went searching for traces of the storm in southeastern Greenland. There, around 2,000 meters (6,562 feet) above sea level, it’s cold enough that snow accumulates year after year, compressing into denser snow, called firn, and eventually compacting into glacial ice. In this “firn zone,” the researchers dug a deep pit in the snow and collected a 15-meter-long firn core, which captured nearly a decade of snow accumulation. Bailey used oxygen isotopes and the density of different layers to calculate the age profile and snow accumulation rates in the core. She then compared them to local weather and climate data over the same period.

“Using high-elevation firn core sampling and isotopic analysis allowed us to pinpoint the extraordinary snowfall from this atmospheric river,” Bailey said. “It’s a rare opportunity to directly link such an event to Greenland ice sheet surface mass balance and dynamics.”

Atmospheric rivers: Not all bad

The atmospheric river had pelted Svalbard with rain, but 2,000 kilometers (1,245 miles) away in southeastern Greenland, it delivered snow—and lots of it. On March 14, 11.6 billion tons of snow fell on the ice sheet, with an additional 4.5 billion tons over the next few days. One gigaton of snow roughly equates to one cubic kilometer of fresh water, which could completely fill the U.S. capitol building more than 2,200 times. In a matter of three days, this atmospheric river delivered enough snow to offset Greenland Ice Sheet mass loss by 8% in the 2021-2022 hydrologic year.

“I was surprised by just how much snow was dumped on the ice sheet over such a short period,” Hubbard said. “I thought it’d be a minute amount, but it’s a gobsmacking contribution to Greenland’s annual ice mass.”

By adding so much fresh snow, the atmospheric river delayed the onset of summer ice melt by about 11 days despite warmer than average spring temperatures, the study finds.

More research is needed to understand the net effect of atmospheric rivers on Greenland’s ice in the past and to predict how that may change in the future. If warming continues, all precipitation will eventually fall as rain in Greenland, exacerbating ice loss, Bailey said.

“Atmospheric rivers have a double-edged role in shaping Greenland’s—as well as the wider Arctic’s—futures.”