Global carbon dioxide levels reach highest point ever, likely for good - 400 parts per million has long been considered a benchmark of irreversible damage.

Global carbon dioxide levels in the atmosphere have surpassed 400 parts per million, and will almost certainly remain there indefinitely, according to new numbers from the Scripps carbon dioxide monitoring program at the Mauna Loa observatory in Hawaii.The 400-level has long been considered a benchmark of irreversible damage to the environment."We're really in uncharted territory," said Ralph Keeling from the Scripps Institution of Oceanography, who directs the program. "It's too bad we're this deep into it already, but that's the fact." 

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