Changing snow patterns have far-reaching consequences, from water shortages to closed ski resorts. A new study confirms that human-induced climate change has affected snow patterns across the Northern Hemisphere, including a clear decrease in snow in at least 31 individual river basins.
In addition, the researchers found that when an area warms to an average temperature of 17 degrees Fahrenheit, or minus 8 degrees Celsius, over the course of the entire winter, it appears to reach a tipping point where snow begins to melt rapidly.
“Beyond that threshold, we see everybody falling off a cliff,” said Justin Mankin, a geography professor at Dartmouth College and co-author of the study, which was was published Wednesday in Nature.
Reductions in snowpack, the total mass of snow on the ground, have serious implications for places that depend on spring snowmelt as a source of water.
Big storms this week across the United States dropped a lot of snow, but the snow now on the ground may not last through the winter. In the short term, climate change may create deeper snow from blizzards due to increased precipitation, but, with warmer temperatures, this snow is likely to melt faster and may not stick as a blizzard.
The researchers studied data from more than 160 river basins to examine how much snow was left in March each year from 1981 to 2020. In about 20 percent of those areas, they found clear declines in snowpack that could be attributed to climate change. human-caused change.
The northeastern and southwestern United States are among the areas losing snow the fastest, along with much of Europe.
These changes have not been uniform or linear across the globe. Even when temperatures are warm, places that were coldest to begin with may not rise above the freezing point of water (32 degrees Fahrenheit or 0 degrees Celsius) enough during the winter to lose much snow.
But once an area hits a winter average of 17 degrees Fahrenheit, losses accelerate exponentially.
“Every degree of warming beyond that cliff gets more and more,” said Alexander Gottlieb, Ph.D. student in the group of Dr. Mankin and lead author of the study.
In much of the American West, the snowpack has historically functioned as a frozen reservoir that stores water during the winter and releases it in the spring and summer when demand is greatest. When the snow doesn’t pile up in winter, droughts during the summer it can get worse.
In the Northeast, snow is less important for water supply, but is a foundation for winter recreation, tourism, and culture.
Mr. Gottlieb and Dr. Mankin combined existing snow, temperature and precipitation data to reconstruct snowpack patterns over the past 40 years. While direct measurements of snow are available for some places, to cover larger areas scientists must fill in the gaps with calculated estimates.
The researchers also modeled snow in a hypothetical world without climate change over the same period to see if taking global warming out of the equation would produce significantly different results. In 31 of the river basins they studied, or about 20 percent of the total, it did, meaning the impact of climate change is clear in these places.
“There are these few basins where we see this really clear signal,” Mr. Gottlieb said. In general, these river basins have warmed beyond the 17 degrees Fahrenheit threshold identified by the researchers. Because people tend to live in places with milder climates, these warmer areas are the ones with the largest populations.
“With further warming, you’re just going to have more and more of these highly populated river basins beyond that threshold,” Mr Gottlieb added.
That paper was “very well researched,” said Stephen Young, a geography professor at Salem State University who was not involved in the study.
Dr Young looked at the effects of climate change on snow cover, a measure of whether or not there is snow on the ground, regardless of depth. Unlike snowpack, snow cover can be reliably measured by satellites. Global annual snow cover has declined by about 5 percent since 2000, according to a separate study published last year by Dr. Yang.
While studying snow is useful for revealing potential consequences for water supplies, studying snow cover illuminates another problem: white snow reflects sunlight back into the atmosphere, while darker, exposed ground absorbs it. Sun’s light. So once the snow falls to the point where there is no snow on the ground at all, a feedback loop warms the planet even more.
“It’s becoming another way our world is warming,” Dr Young said.