The May 11 issue of The Economist has an interesting, though disturbing, short article on one measure of global climate change: the percentage of carbon dioxide [CO2] in the atmosphere. This has recently reached a new high in recent history.
AT NOON on May 4th the carbon-dioxide concentration in the atmosphere around the Mauna Loa Observatory in Hawaii hit 400 parts per million (ppm).
Now, 400 ppm does not sound very high; after all, it is only 0.04%. However, as the article goes on to point out, this concentration of CO2 has not been routinely present since the Pliocene epoch, about 4 million years ago.
The data series is from the observatory at Mauna Loa in Hawaii, run by the Scripps Institution of Oceanography, part of the University of California at San Diego. This series (sometimes called the Keeling Curve in honor of the scientists who initiated the project) is of particular interest for two reasons:
- The observation site is remote from large centers of human population, minimizing fluctuations due to temporary pollution spikes.
- The observations have been made consistently, at the same place, since 1958.
There is a regular seasonal fluctuation in CO2 levels, tied to plants’ growth cycles. In the northern hemisphere, levels tend to peak in May, and then fall until about October, as plants’ growth removes carbon dioxide from the atmosphere.
The seasonal pattern is clearly visible in the graph. The more striking thing, of course, is the steady rise in the carbon dioxide levels, an increase of more than 25% over the observation period. And there is no evidence that the rate of increase is getting smaller.