The History of Atmospheric Carbon Dioxide on Earth
2010-01-19 from:planetforlife author:
The black wiggles record the breathing of all the plants and animals on Earth. Plants must inhale carbon dioxide to grow and as they do so, they remove carbon dioxide from the atmosphere. Almost all animals and bacteria exhale carbon dioxide as they go about living. Animals and bacteria are always active and so carbon dioxide concentration increases whenever plants are inactive. There are more plants growing in the Northern Hemisphere because there is more land mass in the Northern Hemisphere, as a glance at a globe will confirm. When all the plants in the Northern Hemisphere are growing during the summer, they remove significant amounts of carbon dioxide. The maximums occurs every year in May, at the beginning of the growing season. The minimums occurs every year in November, at the end of the growing season. All of this is quite visible on the graph.
The red line shows the same data but with the yearly variations removed. There are several ways this might have been done. Here, it was accomplished by fitting a curve called a 4th order polynomial to the data. The blue parts of the polynomial curve extend the record forward and backward in time. The red line is based on real data, the blue lines are plausible projections.
Interpretation of the Keeling curve
Clearly the amount of carbon dioxide in the atmosphere is increasing. Equally clearly, the rate of increase is increasing. In 1960 the rate of increase per year was 0.71 PPM (parts per million). The 2005 rate of increase was 2.14 PPM per year. However, the increase is not perfectly steady. The Pinatubo volcanic eruption of 1991 is credited with the slowing of the increase for a few years. The massive release of sulfur dioxide resulted in an increase in cloud cover which resulted in cooling which increased the solubility of carbon dioxide in sea water. The resulting slight pause beginning in 1992 is visible. The pause, whatever its origin, was canceled by an acceleration in the next decade. The Southern Oscillation also known as the El Niño--La Niña cycle also seems to have an effect. The general trend, however, is unmistakable.
Implications
If the general trend continues, the concentration of carbon dioxide will be 400 PPM within ten years. It is hard to avoid this conclusion. Nothing short of a large volcanic eruption or a nuclear war or a large meteorite strike would change this conclusion.
There is no doubt that the carbon dioxide increase is anthropogenic. The circumstantial evidence is strong. Human population increases track carbon dioxide increases. However, there is proof. Carbon dioxide circulating between plants, animals and the atmosphere is made slightly radioactive in the upper atmosphere by the sun. Carbon dioxide formed by burning fossil fuels is not radioactive because the carbon has not been in the upper atmosphere for millions of years. That makes it possible to distinguish anthropogenic fossil fuel derived carbon dioxide from the carbon dioxide circulating between plants and animals by measuring its radioactivity.