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Changing snow patterns have far-reaching consequences, from water shortages to shuttered ski resorts. A new study confirms that human-caused climate change has affected snow patterns across the Northern Hemisphere, including clear declines of snowpack in at least 31 individual river basins.
What’s more, the researchers found that when a region warms to an average temperature of 17 degrees Fahrenheit, or minus 8 degrees Celsius, over the whole winter, it appears to reach a tipping point that snow starts to melt away quickly.
“Beyond that threshold, we kind of see everybody go off a cliff,” said Justin Mankin, a professor of geography at Dartmouth College and co-author of the study, which was published on Wednesday in Nature.
Declines in snowpack, the total mass of snow on the ground, have serious implications for places that depend on spring snow melt as a water source.
Large storms this week across the United States dumped a lot of snow, but the snow now on the ground may not last through winter. In the short term, climate change can create deeper snow from blizzards because of increased precipitation, but, with warmer temperatures, this snow is likely going to melt faster and may not stick around as snowpack.
The researchers studied data from more than 160 river basins to review how much snow was left in March each year from 1981 to 2020. In about 20 percent of these areas, they found clear declines of snowpack that could be attributed to human-caused climate change.
The Northeast and Southwest of the United States are among the regions losing snowpack the fastest, along with much of Europe.
These changes haven’t been even or linear around the world. Even as temperatures warm, places that were colder to begin with may not exceed the freezing point of water (32 degrees Fahrenheit, or 0 degrees Celsius) enough during the winter to lose much snowpack.
But after an area hits a winter average of 17 degrees Fahrenheit, the losses accelerate exponentially.
“Each degree of warming beyond this cliff is taking more and more,” said Alexander Gottlieb, a Ph.D. student in Dr. Mankin’s group and the study’s lead author.
In much of the American West, snowpack has historically acted as a frozen reservoir that stores water during winter and releases it in spring and summer, when demand is highest. When snow doesn’t accumulate during the winter, droughts during the summer can be exacerbated.
In the Northeast, snow is less important for water supply, but it’s a foundation for winter recreation, tourism and culture.
Mr. Gottlieb and Dr. Mankin combined existing snowpack, temperature and precipitation data to reconstruct snowpack patterns over the past 40 years. While direct measurements of snowpack are available for some places, to cover larger areas scientists have to fill in the blanks with calculated estimates.
The researchers also modeled snowpack in a hypothetical world without climate change over the same period, to see if taking global warming out of the equation would yield significantly different results. In 31 of the river basins they studied, or about 20 percent of the total, it did, meaning that the influence of climate change is clear in those places.
“There are these handful of basins where we see this really clear signal,” Mr. Gottlieb said. By and large, these river basins have warmed beyond the 17 degrees Fahrenheit tipping point that the researchers identified. Because humans tend to live in places with milder climates, these warmer regions are the ones with the biggest populations.
“With further warming, you’re just going to have more and more of these highly populated river basins pushed beyond that edge,” Mr. Gottlieb added.
This paper was “very well-researched,” said Stephen Young, a professor of geography at Salem State University who was not involved in the study.
Dr. Young has examined the effects of climate change on snow cover, a measure of whether or not there is any snow on the ground, regardless of depth. Unlike snowpack, snow cover can be measured reliably by satellites. Global annual snow cover has decreased by about 5 percent since 2000, according to a separate study published last year by Dr. Young.
While studying snowpack is useful for revealing the potential consequences for water supply, studying snow cover illuminates another problem: White snow reflects sunlight back into the atmosphere, while darker, exposed ground absorbs sunlight. So once snowpack declines to the point where there’s no snow cover on the ground at all, a feedback loop warms the planet even more.
“It becomes another way that our world is heating up,” Dr. Young said.
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