Our Spring Snowpack Keeps Getting Smaller

If you've been wondering where all the snow's gone—historically speaking—you're not alone. A new study in the journal Nature suggests that snowpack throughout the Northern Hemisphere has dropped sharply over the last 40 years, the New York Times reports. Snowpack is seasonally stable snow that packs the ground throughout colder months. As winter wanes, it gradually melts, feeding rivers and streams as a vital water source in dryer regions. The study documents a drop in 31 different river basins. The researchers say snowpack is dropping fastest (between 10% and 20% per decade) in the Southwestern and Northeastern US, as well as in Central and Eastern Europe, according to the Los Angeles Times. And they say its connection to human-caused climate change is undeniable.

"We were able to provide the most compelling evidence to date that there's a really clear anthropogenic signal in all of our snowpack data," says the study's lead author, Alexander Gottlieb, adding there was "almost no chance" they'd see these trends without human influence on the planet's climate. The researchers determined a tipping point of average winter temperatures—hitting 17 degrees Fahrenheit—when snowpack will melt too quickly to sustain watersheds. "Beyond that threshold, we kind of see everybody go off a cliff," says paper co-author Justin Mankin, a geography professor at Dartmouth College.

Snow cover—meaning any snow on the ground—is also on the decline, which only contributes to the problem, say the researchers. That's because snow reflects sunlight back into the atmosphere, while darker ground absorbs it. "It becomes another way that our world is heating up," Dr. Stephen Young, a geography professor at Salem State University, tells the New York Times. One of the biggest threats that continuing loss of snowpack poses is to drought-prone areas, especially in the US Southwest. In their paper, the researchers warn that "human-forced snow losses and their water consequences ... will accelerate and homogenize with near-term warming, posing risks to water resources in the absence of substantial climate mitigation." (A climate researcher delivers an unusual message: hope.)