CO2 Levels Highest in Human History Carbon dioxide reaches 400ppm milestone By John Johnson, Newser Staff Posted May 10, 2013 5:40 PM CDT 315 comments Comments A coal plant at sunset in Emmett, Kansas. (AP Photo/Charlie Riedel) (Newser) – Scientists have been anticipating this milestone for a while, but they won't be breaking out the champagne now that it's here: Carbon-dioxide levels in the atmosphere passed the mark of 400 parts per million yesterday for the first time in human history, reports the BBC. The National Oceanic and Atmospheric Administration made the declaration based on readings of the heat-trapping gas at a station on the Mauna Loa volcano in Hawaii. (Another monitoring program run by the Scripps Institution of Oceanography hasn't quite gotten to 400 yet, but it supports the NOAA figure and chalks up the difference to a technicality.) A few reactions: New York Times: It's "just an odometer moment in one sense, but also a sobering reminder that decades of efforts to bring human-produced emissions under control are faltering." National Geographic: "The last time the concentration of CO2 was as high as 400 ppm was probably in the Pliocene Epoch, between 2.6 and 5.3 million years ago. Until the 20th century, it certainly hadn't exceeded 300 ppm, let alone 400 ppm, for at least 800,000 years." “It symbolizes that so far we have failed miserably in tackling this problem,” says the NOAA's Pieter P. Tans.