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WASHINGTON — Vast swaths of the U.S. have been hit with powerful storms, including blizzards that have blanketed parts of the Midwest and Northeast in snow. But something's amiss: Many states accustomed to white winters are now getting more rain than snow.
A new study published on Wednesday shows that the human-caused climate crisis has reduced snowpack in most parts of the Northern Hemisphere in the last 40 years, threatening crucial water resources for millions of people.
It might seem logical a warmer world would be less hospitable to snow, but the relationship between snow and climate change is complex, and scientists have for many years struggled to make a clear connection between the two.
Part of the problem has been that snowfall is notoriously difficult to measure accurately, and scientific data from ground observations, satellites and climate models have given contradictory signals on the role of climate change in declining snowpacks. Some areas have even experienced more snow in our warmer world.
But Wednesday's study, published by researchers at Dartmouth College in the journal Nature, offers the big picture — climate change has caused significant drops in snow in the world's north since the 1980s. Areas in the U.S. Southwest and Northeast, as well as in Central and Eastern Europe, have experienced the steepest global warming-related declines of between 10% and 20% per decade.
"It's very clear that climate change has been having negative impacts on snow and water," said Alexander Gottlieb, lead author of the study and a doctoral student at Dartmouth College. "And every additional degree of warming is going to take away a bigger and bigger chunk of your snow water resources."
Less snow means less water supply
The researchers found that snowpack loss accelerates when average winter temperatures at a location rise above 17 degrees Fahrenheit, a point they refer to as a "snow-loss cliff." Past that, snow loss accelerates with even modest rises in temperature.
That's a huge problem for communities that depend on snow for water. Many of the world's water supplies are already threatened by climate change through drought and heat waves that are becoming more frequent and intense. As the planet continues to warm, the study found that many highly populated areas that rely on snow are going to see increased losses in water availability over the next few decades.
"When you have a regime shifting to one that's no longer snow-dominated in the winter, but instead is rain-dominated, you have a situation where you can have reservoirs at half full, or less," Justin Mankin, senior author of the study and associate professor of geography in Dartmouth, told CNN. "Then the question becomes 'Well, are we going to have a rainy spring?'" to compensate for water withdrawals from places downstream.
They also looked at river basins to measure how much snow water resource had dropped. The study found a declining trend in snowpack across 82 out of 169 major Northern Hemisphere river basins, including the Colorado River in the U.S. and the Danube River in Europe, with 31 of those confidently showing the fingerprints of human-caused climate change.
"Most of the world's people live in river basins that are at this precipice of falling off an accelerating snow-loss cliff, whereby every additional degree of warming means greater and greater snowpack loss," Mankin said.
To reach their conclusions, the researchers specifically analyzed snowpack declines in March between 1981 and 2020, because it provides a "convenient summary of all winter weather," Mankin said. He noted that the amount of snow on the ground in March indicates what the winter conditions were like that season before spring melts the reservoir that trickles downstream to supply water for households and agriculture.
"March snowpack is emblematic of everything that happened over the winter, and we do test the sensitivity of that measure," Mankin said.
Back-to-back years of less snowpack in the western U.S. have already given a preview of what future winters and springs could look like in many parts of the Northern Hemisphere, from unprecedented water shortages to worsening wildfires, said Mankin.
Snow also helps prevent wildfires or can reduce their intensity. Unlike rain, which can run off quickly, snow melts slowly over time and can provide a slow and sustained release of water into the soil, making it less likely to ignite and providing less fuel for fires to spread.
Less snowpack also carries a significant toll for places that rely on winter recreational activities, such as skiing and snowboarding, as key economic drivers. Many ski resorts in the Northern Hemisphere are facing such challenges already, with many now relying on snow cannons to ensure there's enough snow to keep businesses operational. Some places are approaching temperature thresholds that will make even machine-made snow unviable.
Mona Hemmati, postdoctoral research scientist at the Columbia Climate School, who was not involved with the study, said the research provided "compelling evidence" of how human-caused climate change is influencing snow patterns.
"What makes this study groundbreaking is its approach to isolating the effects of anthropogenic climate change from natural climate variability," Hemmati told CNN. "This study serves as a crucial reminder of the escalating impacts of climate change and the imperative for immediate and concerted action to address this global challenge."
