Extreme weather has become the new normal—whether it’s precipitation, drought, wind, heat, or cold. The question of how the ever-shrinking layer of Arctic sea ice has contributed to any of these changes has prompted some lively discussion over the past few years. Researchers have proposed that a weakened jet stream driven by vanishing Arctic sea ice might play a large role in extreme winter events like the descending polar vortex that struck North America earlier this year. But the idea hasn’t held up well in light of more recent evidence.

But now, researchers have identified a direct link between extreme winter weather and sea ice loss. The 2018 “Beast of the East” winter storm hit Europe with record-breaking snowfall and low temperatures. And potentially as much as 88 percent of that snowfall originated from increased evaporation of the Barents Sea.

The working hypothesis is that Arctic sea ice acts as a cap for Arctic waters, limiting evaporation. Less sea ice and warmer Arctic temperatures mean more evaporation, potentially explaining the increased severity of winter storms like the Beast of the East. Until now, it’s been tough to measure direct evidence linking sea ice loss to extreme European winters, but recent advances in technology are making this a little less challenging.

Secrets of the north

With sub-freezing temperatures, 24-hour darkness in winter, and, well, not very much land, the Arctic is among the world’s most hostile research environments. To date, much of the direct data from the region has been collected by hands-on research boats, but these expeditions are expensive and limited in where and when they can be used.

Instead, this latest research used a recent technology—an isotope and gas-concentration analyzer—that automatically collects real-time data at the impressive frequency of nearly one measurement per second. Although the researchers haven’t installed the instrument in the furthest reaches of the Arctic, they have added one at a weather station in Pallas-Yllästunturi National Park, northern Finland, just a few hundred kilometers from the Norwegian Sea.

They installed the instrument in late 2017, and it’s been allowing them to detect the naturally occurring stable isotopes in water vapor—i.e., hydrogen and oxygen—since then. Two of these isotopes, ¹⁸O and ²H, have been widely used for tracking hydrological processes over the last 70 years. Because these isotopes are a little heavier, they are less likely to evaporate, creating unique isotope “fingerprints” for phase transitions such as evaporation, cloud formation, rain, and snow. This has made it possible to trace the origins of storm systems—and the research team put this instrument in place just in time for a whopper of a storm.

The Beast

Within months of installing the instrument, the team noticed a huge isotope spike in March of 2018, just as the Beast of the East arrived in Europe. The researchers could trace this spike in vapor back to unusually high amounts of evaporation from the Barents Sea, which was warmer and more ice-free than historical norms.

“The data from our study represent the first ‘real measurements’ that prove that sea ice loss through enhanced evaporation is contributing to extreme mid-latitude snowfall events,” says first author Hannah Bailey. “Up until now scientists have explored the link between Arctic sea ice loss and extreme snowfalls using climate models and, without this technology we’re using, it simply wouldn’t be possible to capture these types of natural events and processes in real-time.”

The team also combined satellite data and modeling to calculate that up to 88 percent of the snow from the Beast storm—140 billion tons—may have come from the Barents Sea.

Less ice, more snowfall

The team focused on the Barents Sea because it is a literal “hotspot” of decreasing sea ice in the Arctic. Maximum March sea ice levels there have dropped 54 percent since 1979. Using historical satellite observations and atmospheric models, the team confirmed that smaller amounts of Barents Sea ice have regularly correlated with higher evaporation and heavier March snowfall across northern Europe over the last 30 years.

This evidence also suggests that this trend may intensify with further sea ice loss in the Barents Sea, which some researchers have predicted may be ice-free by 2061-2088. The team hopes to establish a network of these isotope monitoring instruments throughout the Arctic—both on ships and on land—in order to better measure these changes moving forward.

“There is scientific consensus that the decline of Arctic sea ice impacts mid-latitude weather, but there is a lack of consensus among the models used to investigate these processes,” says Bailey. “There’s huge potential for atmospheric vapor isotope data to improve weather forecasting, as well as aid in the prediction of extreme weather events that impact society.”

Nature Geoscience, 2021. DOI: 10.1038/s41561-021-00719-y  (About DOIs).

K.E.D. Coan is a freelance journalist covering climate and environment stories at Ars Technica. She has a Ph.D. in Chemistry and Chemical Biology.

https://arstechnica.com/?p=1758076