2013 was the first time planet Earth passed 400ppm carbon dioxide in the atmosphere since the Pliocene perod. Instruments at the Mauna Loa Observatory in Hawaii have been measuring atmospheric CO2 and other greenhouse gases for over 50 years. Other sites like CSIRO's Cape Grim observatory in Tasmania and New Zealand's National Institute of Water and Atmospheric Research (NIWA) at Baring Head Station near Wellington also take baseline measurements of atmospheric greenhouse gases.
The Keeling curve shows the rising levels of atmospheric carbon dioxide trend and is one of the most well known climate graphs. It was named after Charles Keeling from the Scripps Institute for Oceanography who started measuring CO2 at Mauna Loa in 1958 and continued up to his death in 2005. The graph clearly shows the northern hemisphere season cycle of carbon dioxide as part of the biological seasonal processes as CO2 is taken up by vegetation in Spring and Summer, then expired in Autumn and Winter, but the long term trend has been a gradual rising of CO2 by about 2ppm per year.
The significance of reaching 400ppm is that the planet has not seen this level of carbon dioxide for 3 to 5 million years, in the Pliocene Period. It was a warmer world then. By examining this geological period we can gain some insight on what we might expect to happen to temperatures, sea levels, the impact on ice sheets, and some signs of how our climate might change later this century and further into the future.
