Snow disappears as the planet warms. A new study shows who loses more

(CNN) — Large areas of the United States were hit by strong storms, including blizzards that covered parts of the Midwest and Northeast in snow. But something is wrong: Many states that were accustomed to white winters are now getting more rain than snow.

a A new study was published this Wednesday It indicates that the crisis Man-made climate Snow cover has declined across much of the Northern Hemisphere over the past 40 years, threatening vital water resources for millions of people.

It may seem logical that a warmer world would be less hospitable to snow, but the relationship between snow and climate change is complex, and scientists have struggled for many years to establish a clear connection between the two.

Part of the problem is that snowfall is difficult to accurately measure, and scientific data from ground-based observations, satellites and climate models have given conflicting signals about the role of climate change in the decline in snowfall. Some areas have even seen more snow in our warmer world.

Percentage change in snow cover due to climate change in river basins between 1981 and 2020. Red indicates a decrease, blue indicates an increase. Snow cover has increased in some northern basins as climate change brings more rain. Alexander R. Gottlieb and Justin Mankin/Dartmouth College

Lack of snow means limited water supplies

The researchers found that snow loss accelerates when average winter temperatures rise somewhere above -8 degrees Celsius (about 17 degrees Fahrenheit), a point they refer to as the “snow loss cliff.” Moreover, snow loss accelerates with modest increases in temperature.

This is a big problem for communities that rely on snow for water. Many of the world's water supplies are already threatened by climate change, with droughts and heat waves becoming more frequent and severe. As the planet continues to warm, the study found that many densely populated areas that rely on snow will see greater losses in water availability in the coming decades.

“When the regime changes to one where the winter is not snow-dominated, but rain-dominated, you get a situation where the reservoirs may be half full, or less,” said study lead author Justin Mankin. The study and assistant professor of geography at Dartmouth told CNN. “So the question is: Well, are we going to have a wet spring?” To compensate for the withdrawal of water from places located downstream.

They also studied river basins to measure the extent of declining snow water resources. The study found a downward trend in snow accumulation in 82 of the 169 major river basins in the Northern Hemisphere, including the Colorado River in the United States and the Danube River in Europe, 31 of which reliably showed the effects of human-induced climate change. .

“The majority of the world's population lives in river basins on the verge of falling off a cliff due to accelerating snow loss, so every additional degree of warming means increased snow cover loss,” Mankin said.

To reach their conclusions, the researchers looked specifically at the decline 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 indicates what winter conditions were like that season before the spring thawed the reservoir that flows downstream to provide water for homes and agriculture.

“The March snowpack is a symbol of everything that happened during the winter, and we tested the sensitivity of this measure,” Mankin said.

Percentage change in snow cover caused by climate change in North American river basins between 1981 and 2020. Red indicates a decrease, blue indicates an increase. Alexander R. Gottlieb and Justin Mankin/Dartmouth College

Consecutive years of reduced snowpack in the western United States have already offered a glimpse of what future winters and springs could look like in many parts of the Northern Hemisphere, from unprecedented water shortages to worsening wildfires, Mankin said.

Snow also helps prevent wildfires or can reduce their severity. Unlike rain, which can pour quickly, snow melts slowly over time and can provide a slow, sustained release of water into the ground, making it less likely to ignite and providing less fuel to burn.

Low snow density also comes at a significant cost to places that rely on winter recreational activities, such as skiing and snowboarding, as major economic drivers. Many ski resorts in the northern hemisphere Already facing such challenges Many are now relying on snow cannons to ensure there is enough snow to keep businesses operating. Some places are approaching temperature thresholds that would make even mechanically produced snow unviable.

Mona Hemmati, a postdoctoral research scientist at Columbia University's climate school, who was not involved in the study, said the research provided “compelling evidence” about how human-caused climate change is affecting snow patterns.

“What makes this study innovative is its approach to isolating the effects of human-induced climate change from natural climate fluctuations,” Hemmati told CNN. “This study serves as a critical reminder of the growing impacts of climate change and the need for immediate and concerted action to address this global challenge.”