Snowpack is shrinking in the Northern Hemisphere

Snowpack is shrinking in the Northern Hemisphere thanks to climate change, and many communities could soon face a ‘snow cliff’, according to the most comprehensive assessment yet.

The effects of climate change can vary dramatically from place to place. That is why until recently it was difficult to map the bigger picture with snow layers. Now we can see that many of the hardest hit places are also places that rely on snowpack for their water. Other communities that have seen relatively little impact so far are on track to cross a temperature threshold that would suddenly accelerate snow loss, according to new research published in the journal Nature shows.

“Where the majority of people live and where the majority of people are making increasingly competitive use of water availability, especially snow — they live in places that are on or on this snow loss cliff,” said Justin Mankin, associate professor of geography . at Dartmouth and senior author of the new research paper.

“Once a basin falls off that cliff, it’s no longer about managing a short-term emergency until the next big snowfall. Instead, they will adapt to permanent changes in water availability.”

What is the snow loss cliff? The researchers found that once the average winter temperature for a watershed rises above 17 degrees Fahrenheit (minus 8 degrees Celsius), even modest increases in temperature can significantly accelerate snow loss.

“Once a basin falls off that cliff, it’s no longer about managing a short-term emergency until the next big snowfall. Instead, they will adapt to permanent changes in water availability,” Mankin said in a news release.

Previous research has documented snow loss cover in a warming world – but that is different from this research snowsuit, which measures how much water is in the snow rather than the geographic range of snow cover. Most of the water flowing through rivers in the Northern Hemisphere comes from snow. That makes it very important to understand how the snowpack changes with climate, especially as communities face declining resources.

To conduct their research, the authors studied datasets covering 169 Northern Hemisphere river basins between 1981 and 2020. They compared real-world observations with climate model simulations of a world with and without historical human emissions of fossil fuels. They then used machine learning to zoom in and study trends in snowpack at the watershed scale. This allowed them to link snow trends of the past 40 years to climate change.

“We were able to identify a very clear fingerprint of anthropogenic emissions,” said Alex Gottlieb, first author of the new study and a PhD candidate at Dartmouth. In other words, they could clearly see the impact that fossil fuel pollution was having on snow trends in the Northern Hemisphere.

Until now, it has been difficult to make this connection because global warming is leading to higher temperatures And more precipitation, which can counteract each other. For example, you can have warmer average temperatures but heavier snowfall during a storm.

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

The researchers saw only minimal snow loss in 80 percent of the Northern Hemisphere, where winters tend to be colder. Parts of Alaska, Canada and Central Asia even experienced an increase in snow cover. But eventually, as the planet continues to warm, even those places could fall off the snow-loss cliff.

The remaining 20 percent of the hemisphere that has lost the most snow is where the majority of people in the Northern Hemisphere live. That includes the southwestern and northeastern US, and central and eastern Europe, where snow cover has declined 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 end of March, the month that typically sees the most snowpack in the Northern Hemisphere. That snow loss is a major problem for communities whose local economies depend on it. Smaller resorts at lower elevations could see things dry up quickly as they approach the snow-lost cliff. The Southwest, meanwhile, is in the grip of a 20-year megadrought and cannot 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, etc., just because we are so dependent on both the Colorado River Basin and California’s Sierra Nevada,” said Chad Thackeray, chief of climate science at the University of California. , Los Angeles Institute of the Environment & Sustainability, who was not involved in the study.

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