But the greenhouse effect isn't the only man-made mechanism responsible for why things are heating up. Scientists at the University of California, Irvine have found that snow is also responsible.

Dirty snow, that is, especially in the Arctic, but also in East Asia, Northern Europe, and the Northeastern United States. Snow becomes soiled when soot from smokestacks, car tailpipes, forest fires, and other sources swirls up into the atmosphere and eventually falls back to earth. As we know from wearing a black shirt on a hot, sunny day, dark colors absorb light. Ditto for dark snow, which absorbs more sunlight than clean, white snow, and reflects less light back into the atmosphere. And so the darker snow is, the warmer it gets.

To be clear, this finding doesn't get greenhouse gasses off the hook. The greenhouse effect still accounts for the majority of global warming, while dirty snow may be responsible for something in the ballpark of nineteen percent of the total warming.

In the Arctic, though, the impact of dirty snow is more significant, accounting for perhaps one-third of the warming there. And when enough snow melts to expose much darker sea ice or soil, even more sunlight is absorbed, increasing Arctic warming.

The fix here, of course, is to clean up the snow by using cleaner fuels. Putting less soot into the atmosphere won't solve global warming, but at least it would be a start.  

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