Off-White Christmas : Dirty Snow

Thanks to a few December snowstorms, the Boston area had its first “White Christmas” in several years. Although the snow buried the urban grime for a few days, pristine snow doesn’t last long in the city. Here’s a pile near my apartment. Eww.

But dirty snow isn’t just an aesthetic issue. It also contributes to global warming. A study by students at UC Irvine proposed that dirty snow in the Arctic might be responsible for one-third of the alarming temperature increases in the region, which is most often attributed to greenhouse gases like carbon dioxide and methane.

Normally, clean snow reflects sunlight back to space (which is why fresh snow appears so bright to our eyes on sunny days). But tiny particles of soot from forest fires, dust storms, and burning fossil fuels are settling on top of snow, and acting like billions of “tiny toaster ovens.” The dark-colored particles absorb sunlight, causing them to heat up and melt surrounding snow.

Dust storms from the American Southwest and even China are sprinkling the snowy Colorado Rockies with particles, and causing snow to melt earlier in spring. This is already impacting ski resorts, hydropower companies, white water rafting guides, and farmers whose crops rely on spring melt water.

I always think of greenhouse gases as the primary cause of global warming. I read about taxes, cap-and-trade systems, and sequestration projects for carbon dioxide every day in the newspapers. But this research reminded me that there are other culprits as well.