Climate Change Behind the Precipitous Decline in Snowpack Since the 1980s

Snow is one of the most contradictory pieces of evidence we have for understanding climate change.

As in many recent winters, December's lack of snowfall seemed to portend a global warming future, with peaks from Oregon to New Hampshire more brown than white and the American Southwest facing a severe snow drought.

On the other hand, January brought heavy snow to New England, and blizzards in early 2023 buried California's mountain communities, replenished dried-up reservoirs, and dumped 11 feet of snow on northern Arizona, defying our notions of life on one planet. which is heated.

Similarly, scientific data from ground-based observations, satellites, and climate models disagree on whether global warming is consistently wiping out the snowfall that accumulates on high-elevation mountains and provides water when it melts in the spring, complicating efforts to manage water scarcity. which would result in many population centers.

Now, a new Dartmouth study limits the uncertainty in these observations and provides evidence that seasonal snowfall over most of the Northern Hemisphere has indeed shrunk significantly over the past 40 years due to human-induced climate change. The sharpest snowfall declines associated with global warming—between 10% and 20% per decade—occur in the Southwestern and Northeastern United States, as well as Central and Eastern Europe.

Researchers Alexander Gottlieb and Justin Mankin report in the journal Nature that the extent and speed of this loss potentially puts hundreds of millions of people in North America, Europe and Asia who depend on snow for their water on the brink of a crisis that will be exacerbated by continued warming.

“We were more concerned with how warming affects the amount of water stored in snow. The loss of this reservoir is the most immediate and powerful risk that climate change poses to society in terms of reduced snowfall and accumulation,” says Gottlieb, the study's first author and Guarini School of Graduate and Advanced Studies PhD candidate in Mankin's research group and Ecology, Evolution, Environment and Society graduation program.

“Our work identifies watersheds that have experienced historical snow loss and those that will be most vulnerable to rapid snowpack decline with further warming,” says Gottlieb. “The train has left the station for areas such as the southwestern and northeastern United States. By the end of the 21st century, we expect these parts to be almost snow-free by the end of March. We're on that path and we're not particularly adapted when it comes to water scarcity.”

Water security is only one dimension of snow loss, says Mankin, associate professor geography and the paper's senior writer.

The Hudson, Susquehanna, Delaware, Connecticut and Merrimack watersheds in the northeastern US, where water scarcity is not as dire, saw some of the sharpest declines in snowfall. But those big losses threaten economies in states like Vermont, New York and New Hampshire that depend on winter recreation, Mankin says — even machine-made snow has a temperature limit many areas are quickly approaching.

“Recreational impacts are emblematic of the ways in which global warming disproportionately affects the most vulnerable communities,” he says. “Ski resorts at lower elevations and latitudes are already experiencing year-over-year snow loss. This will only accelerate, making the business model unviable.”

“We are likely to see further consolidation of skiing into large, well-equipped resorts at the expense of the small and medium-sized ski areas that have such critical local economic and cultural values. It will be a loss that will ripple through the communities,” says Mankin.

In the study, Gottlieb and Mankin focused on how the effect of global warming on temperature and precipitation drove changes in snowpack in 169 river basins across the Northern Hemisphere from 1981 to 2020. The loss of snowpack potentially means less meltwater in the spring for rivers, streams and soils downstream when ecosystems and people require water.

Gottlieb and Mankin programmed a machine learning model to examine thousands of observations and climate model experiments that recorded snow, temperature, precipitation and runoff data for Northern Hemisphere watersheds.

This not only allowed them to pinpoint where snow loss occurred due to warming, but also allowed them to look at the offsetting effect of climate change on temperature and precipitation, which reduce and increase snowboard thickness, respectively.

The researchers identified the uncertainties shared by models and observations so they could understand what scientists had previously missed when measuring the effect of climate change on snow. A 2021 study by Gottlieb and Mankin used similar uncertainties in how scientists measure snow depth and define snow dryness to improve predictions of water availability.

Snow comes with uncertainties that have masked the effects of global warming, Mankin says. “People assume that snow is easy to measure, that it just decreases with warming, and that losing it has the same effects everywhere. None of that is true,” he says.

“Snow observations are difficult at the regional scales that are most relevant for water security assessment,” says Mankin. “Snow is very sensitive to variations in temperature and precipitation within the winter, and the dangers of snow loss are not the same in New England as in the Southwest, or for a village in the Alps as in high Asia.”

Gottlieb and Mankin actually found that 80% of Northern Hemisphere avalanches – which are located in the north and at high altitude – experienced minimal losses. Snowpack actually expanded over vast areas of Alaska, Canada, and Central Asia as climate change increased precipitation falling as snow in these frozen regions.

But it is the remaining 20% ​​of snow that surrounds – and provides water for – many of the hemisphere's major population centers that has declined. Since 1981, documented snow declines for these regions have been largely inconsistent due to uncertainty in observations and natural climate variations.

But Gottlieb and Mankin found that a steady pattern of annual decline in snowpack sets in quickly—and leaves population centers suddenly and chronically short of new water supplies from melting snow.

Many snow-dependent watersheds are now dangerously close to a temperature threshold that Gottlieb and Mankin call the “snow loss cliff.” This means that as average winter temperatures in a watershed rise beyond 17 degrees Fahrenheit (minus 8 degrees Celsius), snow loss accelerates even with only modest increases in local average temperatures.

Many densely populated watersheds that rely on snow for their water supply are set to see accelerated losses in the coming decades, Mankin says.

“It means that water managers who rely on snowmelt cannot wait for all observations about snow loss to agree before preparing for permanent changes in water supplies. By then, it's too late,” he says. “Once a basin falls off that cliff, it's no longer about managing a short-term emergency until the next big snow. Instead, they will adapt to permanent changes in water availability.”