Science and technology

Associated Press
FILE - in this June 25, 2012 file photo, a crew works on a drilling rig at a well site for shale based natural gas in Zelienople, Pa. In a surprising turnaround, the amount of carbon dioxide being released into the atmosphere in the U.S. has fallen dramatically to its lowest level in 20 years, and government officials say the biggest reason is that cheap and plentiful natural gas has led many power plant operators to switch from dirtier-burning coal. Many of the world's leading climate scientists didn't see the drop coming, in large part because it happened as a result of market forces rather than direct government action against carbon dioxide, a greenhouse gas that traps heat in the atmosphere. (AP Photo/Keith Srakocic)

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