ATMOSPHERIC CARBON DIOXIDE

3. Atmospheric carbon dioxide is being increased by human activities (primarily the burning of coal, oil, and natural gas), but this increase is not causing a significant increase in global temperature.

4. The increase of atmospheric carbon dioxide is actually beneficial because it causes an increase in the amount of plants and animals. Even if global temperature does rise, plants, animals, and humans will benefit from better nutrition and a warmer, more hospitable climate.

This is reminiscent of the Texas trial lawyer's shifting defense which asserted: "My client's dog did not bite your client; my client's dog doesn't bite; my client's dog wasn't there; and, moreover, my client doesn't have a dog.'' Our friends look a little confused for two reasons. First, they are participating in a debate concerning a subject for which the essential scientific knowledge is not yet available. This is not the fault of science. Global carbon balance and its atmospheric and environmental interactions is a difficult, as yet poorly understood subject.

Why not just add "5. Neither we nor anyone else knows enough about atmospheric composition and global environments to reliably comment on their interactions or to suggest political action or inaction?'' This truth is, unfortunately, rhetorically weak. You say you don't know; your opponent says he does know; you look foolish; and everyone listens to him (and gives him a big tax-financed grant).

1. Why do some people think that atmospheric carbon dioxide is not increasing? The reason is that the carbon dioxide content of arctic and antarctic ice cores has been cited in support of the popular graphs of atmospheric carbon dioxide vs. time (see Access to Energy, 21-3, p. 3 and Figure 2a below).

Drilling cores from ice far under the earth's surface (some more than a mile deep) initially seemed to be a good way in which to obtain historical information about the atmosphere. Atmospheric components are deposited in falling snow which is eventually frozen in the ice record, and bubbles of air also become entrained in the ice.

Unfortunately, the engineering problems involved in obtaining ice samples lead to such severe contamination that data from this source is of little value, especially for a volatile, water soluble gas like carbon dioxide. The history and details of these efforts are carefully reviewed in "Do glaciers tell a true atmospheric CO 2 story?'' by Jaworowski, Z., Segalstad, T. V., and Ono, N., The Science of the Total Environment, 114 , pp. 227-284 (1992), which is the source of Figures 1 and 2.

In addition, carbon dioxide is soluble in the water layer on the surface of ice and also forms inclusion clathrates within the ice under some circumstances. These and other difficulties make carbon dioxide measurements of ice cores almost valueless. Reported measurements of carbon dioxide tend to correlate with drilling parameters as is shown in Figure 1. Notice the similarities between CO 2, ice crystal size, and pressure and expansion of the cores. Accordingly, reported ice core CO2 values have varied over a range of about 10-fold with 2 to 3-fold typical of the narrower ranges - until 1985.

In 1985, in an effort to make their measurements consistent with the actual atmospheric record that began in the 1950s and "relevant'' to the increasingly popular global warming debate, investigators began simply discarding measurements that were outside of the popular range. Worse, when the newly cleansed data did not match the curvature of actual measurements, a fortuitous hypothesis was introduced: the air in the ice was assumed to be younger than the ice - just enough

younger to shift the values into register. (See Figure 2b which shows the actual "cleansed'' data and 2a which shows the newly fabricated data after the "young air shift''.) This dishonesty has led some to reject the CO2 increase shown by these indirect measurements.

Shenanigans cannot, however, alter truth nor be used as an excuse to ignore truth. Direct measurements of atmospheric carbon dioxide were made about 100 years ago. For example, the Encyclopedia Americana for 1908 gives an atmospheric CO2 value of 290 ppm. The carbon dioxide section of the International Critical Tables of 1926 was written by W. J. Humphreys, who cites his own work published in 1921 and gives a value (which we calculate from his total atmospheric mass values) of 280 ppm. Almost 40 years ago, direct and continuous measurements began and have now been extended to numerous sites.

Figures 3 and 4 are from "Trends '93: A Compendium of Data on Global Change'' available from Oak Ridge National Laboratory, Oak Ridge, TN 37831 as Publication No. ORNL/CDIAC-65, which contains complete literature citations. These values from Hawaii and the South Pole are consistent with other world-wide stations. CO 2 has definitely risen substantially during the past century.

2. There is serious doubt, however, about the source and effects of this rise. Since the atmospheric increase during the 1980s has been about 3 Gt C (gigatons carbon) per year and the estimated human release is about 5 Gt C per year, most people have assumed that the increase is of human origin. For these values and Figure 5 see "Terrestrial ecosystems and the carbon cycle'' by D. S. Schimel, Global Change Biology 1, in press (1995). F. Seitz, however, (see Access to Energy 22-1, p 3) has suggested that this assumption is not consistent with atmospheric turnover rates of ¹⁴CO2 from atomic testing.

It is entirely possible that atmospheric CO2 ordinarily fluctuates and that the past 50 to 100 years have been an upward period on that curve. During this time, atmospheric temperature has risen about 0.5°C (apparently from solar variation and not from CO2 effects - see Access to Energy 22-1, p3). The solubility of CO2 in sea water (see International Critical Tables) diminishes about 2.5% per °C increase in temperature. Therefore, making the imperfect assumption for purposes of estimation that equilibrium is maintained, a total ocean warming of 0.3°C per century would lead to ocean outgassing of 3 Gt C per year - the observed atmospheric increase. (We calculate (40,000)(0.3)(.025)/(100) = 3 Gt C using the ocean value of 40,000 from Figure 5.) Interestingly, the observed increase in atmospheric CO2 does lag behind the increase in temperature as expected from this hypothesis.