Snowpack is shrinking across the Northern Hemisphere thanks to climate change, and many communities could soon face a “snow-loss cliff,” according to the most comprehensive assessment yet.
The effects of climate change can vary dramatically from place to place, which is why it’s been difficult to suss out the bigger picture with snowpack until recently. Now we can see that many of the hardest hit places also happen to be those that depend on snowpack for their water. Other communities that have seen relatively little impact so far are on track to pass a temperature threshold that would suddenly speed up snow loss, new research published in the journal Nature shows.
“Where the majority of people live and where the majority of people put increasingly competitive uses on water availability, particularly from snow — they live in places that are at or on this snow-loss cliff,” said Justin Mankin, an associate professor of geography at Dartmouth and senior author of the new research paper.
What is the snow-loss cliff? The researchers found that once average winter temperatures for a watershed rise above 17 degrees Fahrenheit (minus 8 degrees Celsius), even modest increases in temperature can significantly speed up snow loss.
“Once a basin has fallen off that cliff, it’s no longer about managing a short-term emergency until the next big snow. Instead, they will be adapting to permanent changes to water availability,” Mankin said in a press release.
Previous research has documented losses of snow cover in a warming world — but that’s different than this study on snowpack, which measures how much water is in the snow rather than the geographic range of snow cover. Most of the water rushing through rivers in the Northern Hemisphere comes from snow. That makes it really important to understand how snowpack is changing with the climate, especially as communities face dwindling resources.
To conduct their study, the authors studied datasets on on 169 Northern Hemisphere river basins between 1981 and 2020. They compared real-world observations to climate model simulations of a world with and without humans’ historical fossil fuel emissions. Then they used machine learning to zoom in and study snowpack trends at a river basin scale. That’s how they were able to link snow trends over the past 40 years to climate change.
“We were able to identify a really clear fingerprint of anthropogenic emissions,” says Alex Gottlieb, first author of the new study and a PhD student at Dartmouth. In other words, they could clearly see the impact that pollution from fossil fuels had on snow trends across the Northern Hemisphere.
It’s been hard to make this connection until now because global warming leads to both higher temperatures and more precipitation, which can counteract each other. You might have warmer average temperatures, for instance, but heavier snowfall in a storm.
“The study reveals a surprising nonlinear relationship between snow mass and temperature, which has complex ramifications,” Jouni Pulliainen, a research professor at the Finnish Meteorological Institute, writes in an accompanying article that comments on the new research.
The researchers only saw minimal snowpack loss in 80 percent of the Northern Hemisphere where winters tend to be colder. Parts of Alaska, Canada, and Central Asia even experienced increased snowpack. Eventually, though, if the planet keeps heating up, even those places could fall off the snow-loss cliff.
The remaining 20 percent of the hemisphere that lost the most snowpack happens to be where a majority of people in the Northern Hemisphere live. That includes the Southwestern and Northeastern US, and central and eastern Europe, where snowpack diminished by as much as 20 percent per decade.
By the end of the century, parts of the Southwestern and Northeastern United States could be nearly snow-free by the tail end of March, the month when there’s typically the most snow mass in the Northern Hemisphere. That loss of snow is a big problem for communities whose local economies depend on it. Smaller ski towns at lower elevations could quickly see business dry up as they approach that snow-loss cliff. The Southwest, meanwhile, has been in the grip of a two-decade-long mega drought and can’t afford to lose snowmelt that provides water during dry summers.
“[The study] really just highlights the vulnerabilities of this region, things like drought, water availability, and so on just because we are so dependent on both the Colorado River Basin and Sierra Nevada in California,” says Chad Thackeray, climate science lead at the University of California, Los Angeles Institute of the Environment & Sustainability, who was not involved in the study.