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Climate change is altering the smell of snow

Its scent is getting stronger as both the atmosphere and the land get warmer, researchers say

Researcher Johan Lundstrom's cabin in Bjurstrask, which is about 60 miles from the Arctic Circle. He says the snow there smells “extremely clean.” But he says snow in a city has a different odor to it, whether it is exhaust from vehicles or the rubber from tires. (Jens Lundstrom)

How would you describe the scent of winter?

Unlike spring, summer and fall, which have strongly defined aromas (flowers in bloom, beaches, decaying leaves), the current season is marked by the scent of nothing. Nothing’s growing. Nothing’s dying. It’s a kind of olfactory pause.

But snow has a scent, and researchers say that scent depends on what’s in the ground and the air. And as both the atmosphere and the land are getting warmer, the scent of snow is getting stronger.

Johan Lundstrom, a professor of clinical neuroscience who describes himself as a “smell researcher” at Monell Chemical Senses Center in Philadelphia, said because snow’s smell reflects the impurities in the air, the flakes in Wisconsin smell different from snow in Sweden, and from snow in a city.

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Lundstrom said that people notice smells more in the summer because the humid and warmer air intensifies odor molecules, in the same way perfume smells more intense and different on the skin than when it is sprayed in the air. But the cold and dry air of winter makes for a “poor odor environment.”

“It’s the same reason why the worst place to smell things is on a transcontinental airplane,” he said. “You have dry air, you have different air pressure, and it’s often colder than we would normally have in a room.”

The snow — particularly the top layer covering the ground — picks up compounds mostly from the air, Lundstrom said. As time passes, the snow absorbs more of those odor compounds, increasing the scent. And some molecules hit the nose harder than others.

“For example, decaying biological material creates the chemical geosmin, a chemical we are so sensitive to [it’s the odor of mold] so that if you take one drop and put that in an Olympic-size swimming pool and stir the water well, you can still smell the odor,” he said. “In other words, it often does not take much pollution for us being able to smell it.”

Climate change is affecting the way snow smells, said Parisa A. Ariya, a chemist and chair of the Atmospheric and Oceanic Sciences Department at McGill University. As the ground and air get warmer, that encourages the circulation — and intensity — of the odor molecules.

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Climate change is also affecting the amount of snow that the United States receives. Nationally, the contiguous United States has warmed 1.7 degrees since the 1901-1930 period, when climate normals were first calculated, according to the National Oceanic and Atmospheric Administration. That means it’s getting wetter, but not snowier, with 80 percent of weather stations seeing a decrease in snow, according to an Environmental Protection Agency analysis.

When snow falls, Ariya said, it’s “a snapshot of the atmospheric process.” In 2017, she helped conduct a study looking at how snow absorbs the pollution from gasoline engine exhaust, which could then contaminate the water and soil on the ground as it melts.

What’s on the ground gets pulled into the air, so a polluted area might see more trace metals in the snow, and an agricultural area might have more nitrogen [from fertilizer], Ariya said. Once the snow melts, some of that pollution is released into the soil, the water supply and back into the atmosphere. And the cycle begins again.

“The increases in temperature have been suggested to increase the toxicity of certain contaminants and enhance the chemical reaction rates and degradation processes,” Ariya said.

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The reason people often say they can “smell snow coming” is similar to differences in the air when a thunderstorm comes in during the summer, Lundstrom said. The air feels a little warmer, and gets more humid, which carries scent better, and there’s a change in the barometric pressure.

Lundstrom, who heads two research centers, one at Monell, another at the Department of Clinical Neuroscience at Karolinska Institutet in Sweden, said that snow in the city has an odor to it, whether it is exhaust from cars or the rubber from tires.

But when he goes to his cabin in Bjurstrask, which is about 60 miles from the Arctic Circle, it smells “extremely clean,” he said.

It’s not only snow that carries a scent, he said. Ice does as well. Think of old ice in the fridge — it smells odd and musty, as it has absorbed food odors. But ice can also carry fragrances that invoke happy memories.

When Lundstrom was 4 years old, growing up in Sweden, he would go ice fishing with his father and grandfather. He distinctly remembers the smell of the ice shavings as they drilled a hole for perch and pike.

“I would lie on a reindeer fur, and your face is right there next to the hole and you smell the shavings, and it smells like the lake,” he said, adding that it’s a sweet water lake, so ice smells fresh with a tinge of sea grass and sediment. “So every time I go back with my daughter and make a hole in the ice I’m right back, I’m 4-years-old lying on the reindeer fur trying to get fish. It’s a very positive emotion.”

Trying to explain what snow smells like is a challenge. When perfumer Christopher Brosius was creating the scent he called “Snow,” he was looking for a burst of something fresh and cold. Nothing really worked — until he talked to a friend about her first snow.

“She reminded me of a line from a French book, ‘Claudine at School,’ where she bites into a snowball and says ‘It always smells a little of dust, this first [snow]fall,’ ” Brosius, founder of the “CB I Hate Perfume” line, said. “So I had something that was earthy and wet and slightly green, but the thing missing was dust. That’s when I grabbed a bunch of bottles out of the archive and started creating.”

The result, which he created for his former perfume line Demeter, won awards for both male and female fragrance of the year in 2000. Brosius, who goes by “CB,” later created other snow iterations, including “Winter 1972,” and “Walking in the Air,” each of them slightly different based on the place and time of the snowfall.

In 2018, he created an art installation based on the smell of snow for the Cooper Hewitt, the Smithsonian Design Museum based in New York. The project involved a room with a wool carpet below and pale blue balls of felted wool above, both of which were infused with a scent of snow. Compared with his other “snow” scents, he described this one as “fresher, wetter, more frozen and colder.”

“It was about that smell of snow when you put woolen mittens up to your face to keep your nose warm, with a bit of pine trees that were about 50 to 75 yards away at the edge of a field,” CB said. “Some people said that it even smelled cold.”