2013-05-09. Carbon dioxide passes symbolic mark.

posted May 10, 2013, 1:28 PM by Alan Gould   [ updated May 10, 2013, 2:29 PM ]
BBC News. For GSS Climate Change chapter 6. Excerpt: ...Carbon dioxide levels in the atmosphere have broken through a symbolic mark. Daily measurements of CO2 at a US government agency lab on Hawaii have topped 400 parts per million for the first time. The station, which sits on the Mauna Loa volcano, feeds its numbers into a continuous record of the concentration of the gas stretching back to 1958. The last time CO2 was regularly above 400ppm was three to five million years ago - before modern humans existed. Scientists say the climate back then was also considerably warmer than it is today. ...The usual trend seen at the volcano is for the CO2 concentration to rise in winter months and then to fall back as the northern hemisphere growing season kicks in. Forests and other vegetation pull some of the gas out of the atmosphere. This means the number can be expected to decline by a few ppm below 400 in the coming weeks. But the long-term trend is upwards.... http://www.bbc.co.uk/news/science-environment-22486153.  See also New York Times article.