<p>A flock of Geese fly past the smokestacks at the Jeffrey Energy Center coal power plant as the suns sets on Dec. 2, 2012 near Emmett, Kan. Worldwide levels of the chief greenhouse gas that causes global warming have hit a milestone, reaching an amount never before encountered by humans, federal scientists said Friday.</p>
May 11, 2013
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May 11, 2013 9 p.m.
Greenhouse gas levels set record
WASHINGTON - Worldwide levels of the chief greenhouse gas that causes global warming have hit a milestone, reaching an amount never before encountered by humans, federal scientists said Friday.