Winter snowpack in the Northern Hemisphere may fall off the “snow cliff”



Snow is falling across much of the United States this week, but a new study says it’s the exception rather than the norm, with seasonal snowfall in the Northern Hemisphere decreasing over the past 40 years due to climate change.

Still, snow responds to global warming in different ways.

“A warmer atmosphere is also an atmosphere that can hold more water,” says Alex Gottlieb, a graduate student at Dartmouth College and lead author of the new study published in the journal Nature. This could lead to increased precipitation, enhanced snowfall, and even extreme storms and snowstorms, offsetting the effects of snowmelt amid rising temperatures.

That makes it difficult for scientists to calculate how the snowpack has changed over time. But new research reveals that regions of the United States and Europe are nearing a tipping point where they could face catastrophic snow loss for decades to come.

“Once you cross this threshold, which we call the snow loss cliff, even modest amounts of warming can cause this really accelerated snow loss,” Gottlieb said.

Cut noisy data

When Gottlieb and his co-author, Dartmouth geography professor Justin Mankin, started investigating this, they were surprised by how inconclusive previous analyzes had been. A recent report from the United Nations’ Intergovernmental Panel on Climate Change did not assess a decline in snow cover in the Northern Hemisphere or globally.

Researchers said snowfall amounts are difficult to measure and link to human-induced climate change.

Because there is so much variation and so many methods researchers use to observe snowpack, estimates don’t always agree with each other.

To get around this problem, Dartmouth researchers collected every snowpack dataset they could find to identify parts that matched each other. They looked at his March snow levels from 1981 to 2020 to capture all the variations in the previous winter’s weather, from episodic snowstorms to midwinter thaws.

They then used modeling to examine snowpack levels with and without greenhouse gas emissions.

“When you look at any of these snow datasets, you see patterns of snow change that don’t necessarily match each other, but only match human emissions,” Gottlieb said.

Falling from the “Snow Cliff”

Researchers found that the relationship between rising temperatures and snowfall is not linear. Little snow disappears until temperatures rise above a certain threshold near the melting point (-8 degrees Celsius (17.6 degrees Fahrenheit)). Then the snow level falls off the “cliff” and snow melting accelerates rapidly.

Mankin said this makes snowfall a “bad canary in the coal mine” for detecting human-induced climate impacts.

“Once you see snow loss, you’re either on top of that snow loss cliff or coming down,” Mankin said. This means that communities that rely on snow for water are not only facing temporary water shortages and emergencies, but also “fundamental regime change.”

Researchers have found that more than 2 billion people who rely on snow are at or near that tipping point, and predict that future warming will accelerate the crisis.

What does it mean for the Northern Hemisphere?

The researchers didn’t see snowfall anywhere, but they believe this is another reason this effect has not been quantified until now. There is a non-linear relationship between rising temperatures and snowfall, so in very cold regions of North America, Asia, and Europe, snowfall may remain nearly constant or even more due to increased precipitation. .

But the places that are seeing significant snow reductions are precisely the places that need it the most. In previous research, Mankin found that around 2 billion people in the Northern Hemisphere rely on snowmelt as a critical water source and tend to live in warmer places where snow is more sensitive to rising temperatures.

Snow runoff could decline sharply in the western United States, scientists wrote. In California, the first snow surveys of the season found snow depths to be well below average this year, and researchers predict snow loss will accelerate as temperatures rise.

The researchers focused on the effects of snowfall on water supplies, but also on local economies that rely on snow for recreation and tourism, and on ecosystems that have historically been protected from disease and pests by snow. , there are other influences as well.

“I think what’s really clear is that we are systematically underestimating the cost of global warming to humans and ecosystems,” Mankin said, adding that policymakers need to act now. Snow added that there is a need to reduce global warming emissions and adapt to a world with lower emissions.

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