TCS Daily

The Science and Politics of Climate

By Freeman J. Dyson - April 26, 2001 12:00 AM

Another highly successful program of local measurements is called Acoustic Thermometry of Ocean Climate (ATOC). It is the brainchild of Walter Munk at the Scripps Institution of Oceanography. ATOC uses low-frequency underwater sound to measure ocean temperatures. A signal is transmitted from a source on top of a seamount at a depth of three thousand feet near San Francisco, and received at six receivers in deep water around the north Pacific. The times of arrival of signals at the receivers are accurately measured. Since the speed of propagation depends on temperature, average temperatures of the water along the propagation paths can be deduced.

The main obstacle that Walter Munk had to overcome to get the AOTC project started was the opposition of environmental activists. This is a long and sad story which I don`t have time to tell. The activists decided that Munk was an evil character and that his acoustic transmissions would endanger the whales in the ocean by interfering with their social communications. They harassed him with lawsuits, delaying the project for several years. Munk tried in vain to convince them that he also cared about the whales and was determined not to do them any unintentional harm. In the end, the project was allowed to go forward with less than half of the small budget spent on monitoring the ocean and more than half spent on monitoring the whales. No evidence was found that any whale ever paid any attention to the transmissions. But the activities are continuing their opposition to the project and its future is still in doubt.

During the two years that the ATOC system has been operating, seasonal variations of temperature have been observed, giving important new information about energy transport in the ocean. If measurements are continued for ten years and extended to other oceans, it should be possible to separate a steady increase of temperature due to global warming from fluctuations due to processes like El Ni¤o that vary from year to year. Since the ocean is the major reservoir of heat for the entire climate system, a measurement of ocean temperature is the most reliable indicator of global warming. We may hope that the activists will one day admit that an understanding of climate change is as essential to the preservation of wildlife as it is to the progress of science.

To summarize what we have learned, there is good news and bad news. The good news is that we are at last putting serious effort and money into local observations. Local observations are laborious and slow, but they are essential if we are ever to have an accurate picture of climate. The bad news is that the climate models on which so much effort is expended are unreliable because they still use fudge-factors rather than physics to represent important things like evaporation and convection, clouds and rainfall.

Besides the general prevalence of fudge-factors, the latest and biggest climate models have other defects that make them unreliable. With one exception, they do not predict the existence of El Ni¤o. Since El Ni¤o is a major feature of the observed climate, any model that fails to predict it is clearly deficient. The bad news does not mean that climate models are worthless. They are, as Manabe said thirty years ago, essential tools for understanding climate. They are not yet adequate tools for predicting climate. If we persevere patiently with observing the real world and improving the models, the time will come when we are able both to understand and to predict. Until then, we must continue to warn the politicians and the public: don`t believe the numbers just because they come out of a supercomputer.

Freeman J. Dyson, professor emeritus of physics at the Institute for Advanced Study in Princeton, New Jersey, is the recipient of the 1999 APS Joseph Burton Forum Award, and author of a number of books about science for the general public. His most recent is The Sun, the Genome, and the Internet, which will be published this year.

Printed with permission of APS News

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