Humans have polluted the air much longer than thought

01/29/2013 | Smithsonian Magazine

Scientists studying ice cores taken from Greenland have determined that methane levels have been affected by human activity as far back as about 100 B.C. "It used to be that before 1750, everything was considered 'natural,' so the baseline needs to be reconsidered, and we need to look farther back in time to see how much methane there was before humans got involved," said scientist Célia Sapart of Utrecht University.

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