Two and a half years ago I photographed a climate change story for The New York Times at the Mauna Loa Observatory in Hawaii. While on assignment, one of the NOAA scientists was kind enough to give me the tube (pictured below), with a admonition that I should hang on to it – as it is a historical sample of the CO2 levels below 400ppm – probably the last years it will be under this benchmark in our lifetimes. His prediction came to pass this May as the concentration of CO2 in the earths atmosphere passed the 400ppm mark.
Robert Kunzig, a senior editor for National Geographic magazine, wrote a brilliant piece explaining some of the history behind the Keeling curve and putting the 400 ppm CO2 threshold in historical context. It is well worth the read.