N Dakota famr field and melting snow
Snow samples show that dirt disturbed by human activity darkens snow as speeds melting.

Snow is not as white as it looks. Mixed in with the reflective flakes are tiny, dark particles of pollution. University of Washington scientists recently published the first large-scale survey of impurities in North American snow, to see whether they might absorb enough sunlight to speed melt rates and influence climate. The results, published in the Journal of Geophysical Research, show that North American snow away from cities is similar to Arctic snow in many places, with more pollution in the U.S. Great Plains. They also show that agricultural practices, not just smokestacks and tailpipes, may have a big impact on snow purity.

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