How does rising atmospheric CO2 affect marine organisms?

Learn how plants respond to higher atmospheric CO2 concentrations

Click to locate material archived on our website by topic

Assessing the Potential for Serious Global Warming
Volume 4, Number 30: 25 July 2001

The 20 July 2001 issue of Science magazine contains three different items dealing with the subject of certainty -- or, depending upon one's point of view, uncertainty -- relative to the topic of CO2-induced global warming (Allen et al., 2001; Reilly et al., 2001; Wigley and Raper, 2001). None of the articles are anywhere near as provocative as the news stories generated in their wake. The Wigley and Raper report, however, has been the source of much public discussion, leading to a false sense of certitude about the future state of earth's climate. Hence, we felt it would be instructive to review what these two climate scientists have done that evokes such strident reporting by the popular press, as well as what they have not done, which should have greatly tempered the sense of the dramatic with which their conclusions were reported.

First of all, the attention-grabbing study considered, in the words of its authors, only a "limited subset" of the "many different uncertain quantities or model parameters that may influence future warming rates," which immediately raises concern about the confidence one can have in the study's conclusions. The authors, however, insist -- "we show," they say -- that the specific factors they consider "capture the main contributions to output uncertainty."

But, we yet wonder, how can Wigley and Raper be certain this assumption is correct? And what about the rest of us? Do we kneel at their feet, honoring them as the new high priests of an order that demands their declarations be accepted on faith? Or, do we think a little deeper about the subject? We know not the inclinations of others, but as for us, we choose to think. Hence, we here elucidate but a single example of one ignored phenomenon that makes almost every aspect of Wigley and Raper's analysis an exercise in futility.

Consider droplet clouds, which according to Charlson et al. (2001) "are the most important factor controlling the albedo (reflectivity) and hence the temperature of our planet." Man-made aerosols, according to these scientists, "have a strong influence on cloud albedo, with a global mean forcing estimated to be of the same order (but opposite in sign) as that of greenhouse gases."

Knowledge of the existence of the delicate balance between these two opposing forces is all that is needed to refute the conclusions of Wigley and Raper, i.e., that "in the absence of climate-mitigation policies, the 90% probability interval for 1990 to 2100 warming is 1.7 to 4.9C." It is abundantly clear, for example, that a slight perturbation of but a single factor on one side or the other of this delicate balance could readily produce either a slight warming or a slight cooling. What is more, in view of the empirical findings of several recent studies, Charlson et al. note that the magnitude of the man-made impetus for cooling "may be even larger than anticipated." This work thus suggests that man's net climatic influence may actually be one of cooling, which is a far, far cry from the 90% probability of a planetary warming on the order of 1.7 to 4.9C that is implied by the assumption-laden analysis of Wigley and Raper.

But how could that be? Don't the IPCC's results and those of Wigley and Raper include the phenomena described by Charlson et al.? No, they don't. And that lack of inclusion, in the words of the latter investigators, "poses additional uncertainty beyond that already recognized by the Intergovernmental Panel on Climate Change, making the largest uncertainty in estimating climate forcing even larger."

In subsequent Journal Reviews and/or Editorials, we will deal with various aspects of this subject in more detail. Suffice it to say for now, there is no compelling reason to believe there will necessarily be any global warming as a result of the activities of man, especially those activities that result in CO2 emissions to the atmosphere. In fact, atmospheric CO2 enrichment actually stimulates a number of phenomena that tend to enhance cloud albedo via the mechanisms described by Charlson et al., which clearly result in cooling.

So stay tuned. As the popular press brings you ever more dramatic stories of increasingly probable global warming -- courtesy of theoretical, assumption-laden models -- we'll be reporting the results of real-world physical measurements that suggest just the opposite.

And remember, reality always beats hypotheses.

Dr. Craig D. Idso
Dr. Keith E. Idso
Vice President

Allen, M., Raper, S. and Mitchell, J. 2001. Uncertainty in the IPCC's Third Assessment Report. Science 293: 430-433.

Charlson, R.J., Seinfeld, J.H., Nenes, A., Kulmala, M., Laaksonen, A. and Facchini, M.C. 2001. Reshaping the theory of cloud formation. Science 292: 2025-2026.

Reilly, J., Stone, P.H., Forest, C.E., Webster, M.D., Jacoby, H.D. and Prinn, R.G. 2001. Uncertainty and climate change assessments. Science 293: 430-433.

Wigley, T.M.L. and Raper, S.C.B. 2001. Interpretation of high projections for global-mean warming. Science 293: 451-454.