Large swathes of the United States were hit by powerful storms, including blizzards that blanketed parts of the Midwest and Northeast with snow. But something is wrong: In many states accustomed to white winters, it is now raining more than snow.
A new study published Wednesday shows that the human-caused climate crisis has reduced snowpack across much of the Northern Hemisphere over the past 40 years, threatening important water supplies for millions of people.
It might seem logical that a warmer world would be less conducive to snow, but the relationship between snow and climate change is complex, and scientists have tried to establish a clear link between the two for many years.
Part of the problem was that measuring snowfall accurately was extremely difficult, and scientific data from ground observations, satellites, and climate models gave conflicting signals about the role of climate change in reducing snowpacks. In our hot world, there was more snow in some regions.
But Wednesday’s study, published in the journal Nature by researchers at Dartmouth College, reveals the big picture: Climate change has caused significant declines in snow in the world’s north since the 1980s. Regions in the U.S. Southwest and Northeast, as well as Central and Eastern Europe, experienced the steepest global warming-related declines of 10% to 20% per decade.
“It’s very clear that climate change is having negative effects on snow and water,” said Alexander Gottlieb, the study’s lead author and a doctoral student at Dartmouth College. “And each additional degree of warming will destroy more and more of your snow water supplies.”
Less snow means less water supply
Researchers found that snow cover loss accelerated when average winter temperatures in a region rose above minus 8 degrees Celsius (about 17 degrees Fahrenheit); they called this point the “profit loss cliff.” Beyond this, snow loss accelerates with slight increases in temperature.
This is a big problem for communities that depend on snow for water. Many of the world’s water resources are already threatened by climate change, with droughts and increasingly frequent and intense heat waves. The research found that as the planet continues to warm, many regions with high land-based population densities will face increasing losses in water availability over the next few decades.
“When you transition to a regime in the winter where snow is no longer dominant, but instead is dominated by rain, you end up with a situation where reservoirs may be half full or less full,” said senior author Justin Mankin. professor of geography and research assistant at Dartmouth, told CNN. “The question then becomes, ‘Well, are we going to see a rainy spring?’” To make up for water withdrawals from places downstream.
They also looked at river basins to measure how much snow water supplies were falling. The study found a decreasing trend in snowpack in 82 of 169 major river basins in the Northern Hemisphere, including the Colorado River in the US and the Danube in Europe, and 31 of these confidently show the fingerprints of human-caused climate change.
“Most of the world’s people live in river basins on the verge of falling off the cliff, where snow loss is increasing rapidly, so every additional degree of warming means more and more snowpack loss,” Mankin said.
To reach the results, researchers specifically analyzed declines in March snow cover between 1981 and 2020 because it provides a “convenient summary of all winter weather conditions,” Mankin said. He noted that the amount of snow on the ground in March shows what winter conditions were like that season before melting the reservoir, which drips downward to supply water to homes and agriculture.
“Snow cover in March is symbolic of everything that happens during the winter, and we are testing the sensitivity of this measure,” Mankin said.
Mankin said successive periods of less snowpack in the Western U.S. are giving 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.
Snow also helps prevent wildfires or can reduce the intensity of fires. Unlike rain, which can run off quickly, snow melts slowly over time, allowing water to be released slowly and steadily into the ground, making it less likely to ignite and providing less fuel for fires to spread.
Less snowpack also carries a significant price for places that rely on winter recreation activities such as skiing and snowboarding as key economic drivers. Many ski resorts in the Northern Hemisphere are already facing such challenges; many now rely on snow machines to ensure there is enough snow to keep their businesses running. Some places are approaching temperature thresholds that would make even machine-made snow uninhabitable.
Mona Hemmati, a postdoctoral research scientist at the Columbia Climate School who was not involved in the research, said the research provides “compelling evidence” about how human-caused climate change affects snow patterns.
“What makes this study groundbreaking is the approach of separating the effects of anthropogenic climate change from natural climate variability,” Hemmati told CNN. “This study is an important reminder of the increasing impacts of climate change and the imperative for urgent and concerted action to address this global problem.”
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