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Carbon dioxide levels hit landmark in Northern Hemisphere.

April was the first month in recorded history with average carbon dioxide levels at or above 400 parts per million across the Northern Hemisphere, according to a May 26 announcement by the World Meteorological Organization. Climate scientists first recorded levels that high for the greenhouse gas in the Arctic in 2012 and in Hawaii last year (SN: 12/28/13, p. 26), but the rest of the globe had yet to consistently hit the high mark. Researchers expect the entire Earth will experience annual C[O.sub.2] levels averaging 400 ppm or higher in 2015 or 2016. The 400 ppm milestone is largely symbolic, representing nearly 150 percent of the C[O.sub.2] levels of preindustrial times.

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Author:Mole, Beth
Publication:Science News
Article Type:Brief article
Date:Jun 28, 2014
Words:130
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