Earlier this month, the Mauna Loa Observatory in Hawaii recorded a carbon dioxide concentration of 400 parts per million for the first time. Atmospheric CO2 levels are now at 40 per cent higher than before the Industrial Revolution.
In an interview with New Scientist magazine, atmospheric scientist Ralph Keeping said: “At 400 ppm, we’ve perturbed Earth enough already that things could unfold that will be catastrophic.”
Scientists associate 400 ppm with the Pliocene epoch, from about 3 to 5 million years ago, when the world was 3°C warmer, the seas 25 metres higher, and the Greenland ice sheet was impermanent.
The Keeling Curve, named after Ralph Keeling, has kept a daily record of CO2 records since the 1950s. You can access that record here http://keelingcurve.ucsd.edu/