Inevitable Headline in 2014: ‘Planet’s CO2 Level Reaches 400 Ppm for First Time in Human Existence.’
Sometime, about one year from now, the front pages of whatever decent newspapers are left will carry a headline like the one above, announcing that for the first time in human existence (or in nearly a million years, or 3 million years, or 15 million years), the global atmospheric concentration of carbon dioxide - the principal gas causing climate change - will have passed 400 parts per million.
That’s a significant and shocking figure. Unfortunately, it is only a temporary marker on the way to even higher and higher levels. Here (Figure 1 below) are the most recent (March 2013) data from the Mauna Loa observatory showing the inexorable increase in atmospheric CO2 and the rapid approach to 400 ppm.
Figure 1. The concentration of CO2 in the atmosphere measured by Scripps/NOAA at Mauna Loa. We’re rapidly approaching 400 parts per million.
There is a range of estimates around the detailed time record of atmospheric composition, and the study of changes in atmospheric carbon dioxide concentrations over the billions of years of the Earth’s existence is an exciting area for research. A commonly cited figure with strong evidence comes from measurements of air trapped in ancient ice cores obtained from Antarctic ice. We now have a detailed 800,000 year record, which shows clearly that atmospheric CO2 levels never approached 400 ppm during this period