I do not want any person concerned with global warming, of the natural or human variety, to discuss the issue without at least pondering this vastly informative graph for at least ten minutes. It affords a rare and cheap education.
Note especially the little coloured insert near the top. Atmospheric CO2 has been sharply declining since the age of the dinosaurs, from about the middle Jurassic period onward, from about 2,750 parts per million to about 300 parts per million. Average global temperature has dropped from a balmy 25 degrees Centigrade about 50 million years ago to about 10C today. The temperature drop began around 100 million years after the drop in atmospheric CO2. That is some lag time!
I am not saying this is the complete or final picture of atmospheric or temperature changes over time. Rather, I am saying that it successfully shows
- the immensity of time over which the planet has been changing from one dominated by CO2 in the atmosphere to one where CO2 is a trace element;
- the irrelevance of man to most of this picture; and
- the possible relevance of human-produced CO2 to the latest warm period, post 1860. Note the sharp upswing in average global temperature post-1980 (see bottom right inset into chart).