UArctic Chair Alun Hubbard along with his colleague Hannah Bailey, both from the University of Oulu, published a study in Geophysical Research Letters, an open-access AGU journal that publishes high-impact, short-format reports with immediate implications spanning all Earth and space sciences. The study can be found here.
A single storm on March 2022 delivered more than 11 billion metric tons of snow in one day, offsetting Greenland’s ice loss to global sea level rise and delaying summer melt. The Greenland Ice Sheet is the largest ice mass in the Northern Hemisphere and as the Arctic has warmed almost four times faster than the global average since 1980, melting of Greenland’s ice has accelerated rapidly. Climate change is also causing more intense atmospheric rivers, which up until recently were thought only to exacerbate Arctic ice loss. However, a new study shows that they can also deliver more intense snowfall events that can slow Greenland’s mass loss and help offset global sea level rise. Atmospheric rivers are intense bands of water vapor transport that deliver vast amounts of moisture and heat from warm oceans to higher latitudes. A particularly intense atmospheric river in March 2022 delivered a total of 16 billion metric tons of snow - enough to offset Greenland’s annual ice loss by 8%, the study reports. This massive dump of snow also recharged the winter snowpack, delaying the onset of summer ice melt by 11 days. “Sadly, the Greenland Ice Sheet won’t be saved by atmospheric rivers,” said co-author Prof Alun Hubbard. “I’ve been working on the impact of rainfall on Greenland’s ice melt and dynamics for over a decade, but what we see in this new study and, contrary to prevailing wisdom, is that under the right conditions atmospheric rivers might not be all bad news.”
In Greenland, warmer temperatures from climate change mean more rain, less snow, and more melt, even farther inland, into what has historically been the frigid heart of the ice sheet. If the entire Greenland Ice Sheet melts, sea level would rise by over 7 meters (23 feet). Atmospheric rivers are expected to become more intense in response to climate change, so understanding their role on the Greenland Ice Sheet is crucial. Hannah Bailey, a geochemist and the study’s lead author also based at Oulu University, was working on Arctic Svalbard in March 2022 when this intense atmospheric river brought incredibly moist and warm air - around 20 degrees Celsius above typical for that time of year. Heavy rain fell across Svalbard for days, turning winter snowpack into a quagmire. The deluge was so intense that Svalbard’s glaciers took a massive pounding, and she wondered what its impact was on the Greenland ice sheet.
A year later Bailey and Hubbard went searching for the storm high up on SE Greenland’s accumulation area, at ~2435 m elevation on the ice sheet. This is in the firn zone, where year-on-year fresh snow accumulates into denser ice layers, which eventually compress into true glacial ice. They dug a deep pit into the snow and collected a 15-meter long core, which captured nearly a decade of past snow accumulation. Bailey used oxygen isotopes and the density of different layers to calculate the age profile and snow accumulation rates in the core and compared them to local weather and climate data over the same period. “Our use of high-elevation firn core sampling and isotopic analysis allowed us to pinpoint the extraordinary snowfall from this atmospheric river. It’s a rare opportunity to directly link such an event to Greenland ice sheet surface mass balance and dynamics,” said Dr. Hannah Bailey. “What sets this study apart is its foundation in real, empirical observations. While many studies rely on models alone to infer impacts, we cored the ice sheet to ground-truth our findings, relating them to local weather data and the synoptic picture. ” Whilst Svalbard had been pelted with rain, they found that 2000 km away in SE Greenland, the same atmospheric river delivered snow: and lots of it! On March 14, 11.6 billion tonnes of snow fell on the ice sheet, with an additional 4.5 billion metric tons over the next few days. Just one billion metric tons is 1 gigaton of snow which equates to one cubic kilometer of fresh water, enough to completely flood the entire U.S. Capitol Building 2200 times over. In a matter of three days, this atmospheric river delivered sufficient snowfall to offset Greenland’s annual ice mass loss by 8%. “I was surprised by just how much snow was dumped on the ice sheet over such a short period. I thought it’d be a minute amount but thinking outside the Box - it’s a gobsmacking quantity”, Hubbard says, “particularly when fully accounted in Greenland’s mass budget.”
Fresh snowfall is white and highly reflective, so it also changes the ice sheet’s albedo, reducing melt due to the intense solar radiation over spring and summer. The March 2022 event not only recharged the snowpack but delayed the onset of summer ice melt by a further 11 days despite warmer than average spring temperatures, the study finds. In the right conditions, atmospheric rivers can help, not hinder, the plight of the Greenland Ice Sheet - at least for now. If warming continues though, precipitation will eventually all fall as rain, amplifying Greenland’s ice loss; more research is needed to learn if, when, and the long-term impact of this transition. Bailey has been taking more firn cores to fully understand the role of increased atmospheric river activity across the wider Arctic. “Our hands-on approach reveals how atmospheric rivers, often portrayed as a destructive force due to rainfall and flood-induced loss, can also deliver immense snowfall and replenish ice sheet health. It’s a nuanced perspective on their double-edged role in shaping Greenland’s - as well the wider Arctic’s - future,” said Bailey.