We all know that carbon dioxide emissions contribute to global warming by trapping light and heat near the earth's surface.
However, the greenhouse effect is not the only man made mechanism responsible for things 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 sunny day, dark colors absorb light. The same goes for dark snow, which absorbs more sunlight than clean, white snow, and reflects less light back into the atmosphere. Therefore, the darker snow is, the warmer it gets.
To be clear, this finding doesn't let greenhouse gases off the hook. The greenhouse effect still accounts for the majority of global warming, while dirty snow may be responsible for something like 19% of warming.
In the Arctic, however, the impact of dirty snow is more significant, accounting for perhaps one-third of the warming there. Moreover, 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.