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 # 349  

 August 2001

Climate Change Science? National Academy of Sciences Global Warming Report Fails to Live Up to Its Billing

by Gerald Marsh


"Greenhouse gases are accumulating in Earth's atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise."

Thus begins the summary of the June 2001 National Academy of Sciences report "Climate Change Science," which made headlines across the world for (supposedly) providing additional "proof" that mankind is causing global warming.

But the headline writers didn't read the fine print.

This often quoted, categorical statement is not supported by the rest of the NAS report - or the scientific report of Working Group I of the Intergovernmental Panel on Climate Change (IPCC), the United Nations body frequently cited as a key authority on global warming.

Two sentences later in the NAS summary, readers are told that "The changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes are also a reflection of natural variability." "Likely mostly due to human activities"? "Some significant part"? Given these qualifications, and the very large uncertainties in the science, how could the National Research Council (NRC) - the research arm of the NAS - approve such a categorical opening sentence?

The NAS report is a summary rather than a critical review of the IPCC reports. It was prepared and approved in less than a month after the White House submitted its formal request. NRC reports, to quote Richard Lewontin of Harvard University, "always speak with one voice. Such reports... can produce only a slight rocking of the extremely well gyrostabilized ship of state, no matter how high the winds and waves. Any member of the crew who mutinies is put off at the first port of call."1 In other words, there is a forced consensus, one that tends to provide an oversimplified picture of the state of scientific research and of the uncertainties.

One must dig carefully through the report to discover that water vapor and cloud droplets are in fact the dominant cause of greenhouse warming. We are not told, however, what fraction of the greenhouse effect is due to water vapor and clouds.2 Nor are we told that carbon dioxide is a minor greenhouse gas - one that accounts for less than ten percent of the greenhouse effect - whose ability to absorb heat is quite limited.3 Adding more carbon dioxide to the atmosphere only increases greenhouse warming very slowly. Similarly, decreasing the amount of carbon dioxide in the atmosphere only decreases greenhouse warming very slowly.

Thus, the relatively small changes in the emission of carbon dioxide agreed to in the Kyoto Protocol would have an insignificant impact on global warming. The provisions of the Protocol seem singularly innocent of this fact.

The NAS study also notes that increased radiation from the sun could be responsible for a significant part of climate change during part of the industrial era. But the study does not tell us that the warming due to the increase in solar output4 is comparable to that alleged to be a consequence of the 25% rise in atmospheric carbon dioxide concentration since the end of the 18th century. Because carbon dioxide is a minor greenhouse gas, and increased carbon dioxide concentration in the atmosphere does not proportionately increase its greenhouse effect, this rise has had only a minimal impact on the earth's temperature.

Most people assume that the rise in atmospheric carbon dioxide is due to human activity. However, our understanding of the carbon cycle is so poor that we cannot be certain this is the case.5 Nonetheless, deforestation and the burning of fossil fuels (which, on a yearly basis, comprises only some three-and-a-half percent of the two-way exchange of carbon between the earth and its atmosphere), most likely does contribute to the increased concentration of this gas.

In 1976, when the earth had been cooling for some three decades, "mainstream scientists" believed that we were sliding into a new ice age. There has been significant improvement in modeling the ocean and atmosphere since then, but the predictions of these models still do not form a sound basis for public policy decisions. As put by Ahilleas Maurellis of the Space Research Organization Netherlands, "Until we understand the full picture, perhaps the best reaction to global warming is for everybody to just keep their cool."6

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Gerald Marsh, a physicist, is a member of the National Advisory Board of The National Center for Public Policy Research. He served with the U.S. START delegation and was a consultant to the Office of the Chief of Naval Operations on strategic nuclear policy and technology for many years. He is on the Editorial board of the Bulletin of the Atomic Scientists. Comments may be sent to [email protected].


1 Richard Lewontin, "Genes in the Food!," New York Review of Books, June 21, 2001.

2 J. T. Houghton, et al., eds, Climate Change: The IPCC Scientific Assessment, Cambridge University Press, Cambridge, 1991. Notice that the IPCC estimate of 60-70% is for a clear sky, thereby neglecting the contribution from water vapor in clouds. The clear sky greenhouse effect, measured in watts per square meter is 146 w/m2; clouds contribute an additional 33 w/m2 to the clear-sky value, an increase of 23% over the IPCC estimate. See also M. Z. Jacobson, Fundamentals of Atmospheric Modeling, Cambridge University Press, Cambridge, 1999.

3 Houghton, et. al., Section 2.2.2.

4 A. Eddy, Science 192, 1189, 1976; E. N. Parker, Nature 399, 416, 1999; E. W. Cliver, et al., Geophysical Research Letters 25, 1035, 1998; T. J. Crowley and K. Y. Kim, Geophysical Research Letters 23, 359, 1996; G. C. Reid, Journal of Geophysical Research 96, 2835, 1990; E. Friis-Christensen and K. Lassen, Science 254, 698, 1991; J. Lean, et al., Geophysical Research Letters 22, 3195, 1995 and R. A. Kerr, Science 271, 1360, 1996.

5 W. M. Post, et al., "The Global Carbon Cycle," American Scientist 78, 310, 1990.

6 Ahilleas Maurellis, Physics World, February 2001.


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