Snow masses are shrinking throughout the Northern Hemisphere

Snowpack is shrinking across the Northern Hemisphere due to climate change, and many communities may soon face a “snow loss cliff,” according to the most comprehensive assessment to date.

The effects of climate change can vary greatly from place to place, which is why it has been difficult to envision the bigger picture of snow until recently. Now we can see that many of the most affected places are those that depend on snowpack for their water. Other communities that haven't seen a relatively large impact so far are on track to surpass a temperature threshold that would suddenly accelerate snow loss, a new study shows. published In the magazine nature Offers.

“Where the majority of people live and where the majority of people are making increasingly competitive uses of the availability of water, especially from snow, they live in places that are at or on this snow-losing escarpment,” said Justin Mankin, assistant professor of geography. at Dartmouth and senior author of the new paper.

What is a snow loss shovel? The researchers found that once average winter temperatures for watersheds rise above 17 degrees Fahrenheit (minus 8 degrees Celsius), even modest increases in temperature can dramatically accelerate snow loss.

“Once the aquarium falls off that cliff, it is no longer a matter of managing a short-term emergency until the next big snowfall. Instead, they will adapt to permanent changes in water availability,” Mankin said in a press release.

Previous research has documented Snow losses cover In a warming world – but that is different from this study snow, which measures the amount of water in the snow rather than the geographic extent of the snow cover. Most of the water that flows through rivers in the Northern Hemisphere comes from snow. This makes it really important to understand how snowpack changes with climate, especially as communities face dwindling resources.

To conduct their study, the authors studied datasets on 169 river basins in the Northern Hemisphere between 1981 and 2020. They compared real-world observations with climate model simulations of a world with and without humans' historical fossil fuel emissions. They then used machine learning to zoom in and study snowpack trends at the river basin scale. In this way they were able to link snow trends over the past 40 years to climate change.

“We were able to identify a really clear signature of anthropogenic emissions,” says Alex Gottlieb, first author of the new study and a doctoral student at Dartmouth. In other words, they can clearly see the impact of fossil fuel pollution on snow trends across the Northern Hemisphere.

This connection has been difficult to make until now because global warming is causing temperatures to rise And More precipitation, which can conflict with each other. For example, average temperatures may be warmer, but heavier snowfall in a storm.

“The study reveals a surprising non-linear relationship between snow mass and temperature, which has complex implications,” Jouni Poliainen, a research professor at the Finnish Meteorological Institute, wrote in an accompanying article commenting on the new research.

The researchers observed only minimal snow loss in 80% of the Northern Hemisphere, where winters tend to be colder. Parts of Alaska, Canada and Central Asia saw an increase in snow density. Eventually, however, if the planet continues to warm, even those places could fall off the slope of snow loss.

The remaining 20 percent of the hemisphere that lost the most snow is where the majority of people in the Northern Hemisphere live. This includes the southwestern and northeastern United States, and central and eastern Europe, where snowpack density has diminished by up to 20% per decade.

By the end of the century, parts of the southwestern and northeastern United States could be nearly snow-free by the end of March, the month when there is typically the greatest snowpack in the Northern Hemisphere. Snow loss is a major problem for communities whose local economies depend on it. Small ski towns located at lower elevations can see business dry up quickly as they approach the slope of snow loss. Meanwhile, the Southwest has been in the grip for two decades Mega drought They cannot afford to lose the melting snow that provides water during dry summers.

“[The study] “It really highlights the vulnerabilities of this region, like drought and water availability and so on, just because we're so dependent on both the Colorado River Basin and the Sierra Nevada in California,” says Chad Thackeray, climate science lead at UCLA. , Los Angeles Environment and Sustainability Institute, which was not involved in the study.