Dirty snow may be altering our climate, scientists say

That white blanket of snow may look pure, but don’t let it deceive you.

According to a new extensive survey of North America’s snowfall published in the Journal of Geophysical Research, all that fluffy white stuff may not be as pristine as we thought.

University of Washington scientists found regional patterns of impurities contaminating snow caused by dark soot and dirt particles. Questions have arisen as to whether this may actually have an impact on our climate, both globally and locally.

The survey shows that snow covering the countrysides outside of cities, for the most part, is about as pristine as that found in the Arctic. But in some areas, particularly mid-west America, the purity of snow may be more at risk and the source turns out to be of a bit of a surprise.

The project involved collecting snow samples from 67 sites, bringing them back to the laboratory, and carrying out chemical analyses to find contaminants. They zeroed in on the light absorbing black carbon particles released through burning diesel, coal and wood. Researchers are interested in these particles because of their ability to darken snow, allowing it to absorb sunlight and speed melting rates.

The cleanest samples were found to be from northern Canada. Pacific Northwest and Rocky Mountain states were a tad more polluted, according to the study. But it was the Great Plains region that appeared to have three or more times higher levels of black carbon.

In their 10,000 mile voyage across the continent, over much of the northwestern U.S. states and Canadian provinces, one hot spot the team focused on was the Bakken oil fields in northwest North Dakota.

“With all this oil exploration, diesel trucks and new oil wells, people wondered: Is there a huge amount of air pollution making the snowpack darker?” lead author Sarah Doherty, a research scientist at the UW’s Joint Institute for the Study of the Atmosphere and Ocean said in a press statement.

While their finding indicated that the truck traffic on unpaved roads and construction seen in this industry did contribute to snow pollution, researchers discovered that agricultural practices—even those quite a distance away from the oil fields—led to soil being disturbed.

“Our work suggests that land use and farming practices might matter as much as diesel emissions in many parts of the Great Plains,” Doherty said.

“When the wind blows the dirt gets lofted, maybe just 10 feet off the ground, and gets mixed in with the snow.”

Our snowpack is darkened in part by organics, dust and soil. Climate models that have focused mainly on just black carbon may need to take this into account.

For the Great Plains region, the team found that up to half of the darkening was due to organic matter like soil mixing in with the snow.

And snow pollution is not just regulated to carbon and soil but also road-salt. According to a five year Environment Canada study, the use of this de-icing agent can be quite detrimental to plant, animal and aquatic life too.

Another Toronto based study looked at how melting snow in springtime is contaminated by chemicals leaked from pesticides, car exhaust, telecommunications wiring insulation, water repellent clothing, and paints that seep into the surrounding groundwater.

It is too early to tell what practical effects the carbon and organics may have and more data will have to be collected to see if this pollution could actually affect snow melt timing.

But it’s easy to see if the spring melt is shifted. Because of changes in snow reflectivity, farmers may have to worry about the timing for the meltwater to drain out of their fields.

“But first the models have to do a more accurate job of representing the amount of dirt that’s in the snowpack,” Doherty added.