Ice core drilling at Summit, Greenland in June 2007.
Joel Savarino, LGGE

The rise and fall of acid rain is a global experiment whose results are preserved in the geologic record. By analyzing samples from the Greenland ice sheet, University of Washington atmospheric scientists found clear evidence of the U.S. Clean Air Act. They also discovered a link between air acidity and how nitrogen is preserved in layers of snow, according to a paper published this week in the Proceedings of the National Academy of Sciences.

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Photo credit on homepage: Rita Willaert (license).