Global Climate Change: Panel Agrees:"In 10 Years We Will Know"
by Martin M. Cassidy
On Friday, September 25, 1999, a distinguished panel of eight scientists (Table 1), all active in research on global climate change, met at the Houston Club under the sponsorship of the Houston Forum to present a reasoned scientific discussion about global climate change. The half-day panel discussion was a welcome relief from the strident cries of special pleaders on either side of the question of global warming.
Ed Powell, Houston Forum leader, turned the meeting over to Dr. David R. Legates to moderate. He stated that the objective of the meeting was to present what is known and the limits of accuracy of the data that we have. During the morning session, four general topics were discussed:
- The greenhouse effect and related issues
- Temperature and other weather data
- Anthropomorphic vs. natural climate change
- The state of atmospheric general circulation modeling
Dr. Richard Kerr, senior scientific writer with Science magazine, led off by pointing out that the greenhouse effect is a physical fact, but how much mankind has affected it is in doubt. That C02 in air has risen from 310 ppm in 1959 to 360 ppm today is a fact. How much it has affected the climate is an open question. Other greenhouse gases, including methane and water vapor, have a powerful effect.
A primary question is: "If you perturb the climate, how will it change?" or, put another way, "If you kick it, how high will it jump?" It is not simple; there are surprises. One must get accurate, pertinent data to put into models to make accurate predictions. Predictions of warming of 1.5' C all the way to 4.5' C have been made if C02 content of the air doubles. Computer models are improving and including more and more factors, but, as Dr. Richard Lindzen points out, the error bars on input data are still large.
Dr. John Christi of the University of Alabama spoke about temperature and weather records. He presented data from 50 years of land weather data that show cooling from 1940 to 1978 and warming from 1979 to 1998 in the northern hemisphere.
Satellite data do not show the latest warming on a worldwide basis; it shows a cooling instead. However, these data include ocean data, and also it may not be accurately measuring surface temperature. On the other hand, the average data may be correct but land in the northern hemisphere may be warming while the ocean cools. Satellite data agree with those from meteorological balloons that measure atmospheric temperature. However, the instruments vary enough in that data set that it may not be representative.
Dr. Christi showed that extreme droughts and heat have occurred before. The droughts of the 1930s were much more severe than the recent ones. It is still difficult to separate man's influence on the climate from natural variability. Weather is variable. If it has happened before, it will happen again.
Dr. Jim Hurrell spoke further about the problem of satellite data failing to match the trend of ground data. Ground data are assumed to be true. However, changes of ground temperature caused by a warm bubble of air over cities were not addressed. The discrepancy is now attributed to bad calibration and decaying orbit of the satellite, and perhaps measuring different levels in the atmosphere.
There was not a consensus about the reasons for the discrepancy between surface and satellite data.
After a break, the question of man's influence vs. natural climate change was addressed by Dr. Gerald North of Texas A&M. He showed that the natural variation in the climate has been large enough that the man-made signal is hard to find. Volcanic eruptions are obvious in the data. Statistical tests of probability of events using earlier records to test for later effects of man are attempted, but results are only suggestive of possible effects.
Dr. Lindzen of MIT was the speaker most skeptical of the proof of global warming. He pointed out that the greenhouse signal is buried in natural variability and that details of the present models do not match the real world even though general agreement with the past can be achieved. Natural oscillations in the North Pacific have not been predicted by the model. A quick retort from the i-nodelers was that a new (unpublished) model does achieve that.
Dr. Jeffery Kiehl was the speaker most confident of global warming froi-n man's activities. fie pointed out that 20 years of climate modeling, which didn't match Earth's climate at first, has matched from the 1970s on. Now the model can even predict correctly the distribution of water vapor vertically in the atmosphere. I found this the least convincing portion of the conference.
The civil level of discourse was a pleasureto observe. Statements of respect and appreciation often preceded the words "but I disagree" followed by a mildly worded but sharp rebuttal.
At the end of the morning meeting there was a consensus that in 10 years, with new and refined data, we will be able to tell confidently how much climate will be changed based upon man's behavior.
The need for such reasoned discussion was well shown by a slick 20-page brochure "Climate Change, State of Knowledge" published under the seal of the executive office of the President of the United States, which was available at the door. The publication is not a summary of State of Knowledge but an infomercial giving part of the truth and selling a viewpoint with emotional language. It is just as annoying in print as such things are on TV.
In summary, it may be said that, "A preponderance of evidence is that man has influenced the climate." How much and how much more man could change the climate is still heavily debated. Measurements can be made that will reduce uncertainty and give much more definite answers. We need to make them as soon as possible.
Luncheon was served in the renovated dining area of the Rice Hotel. A "Scientific Debate Over Global Warming" was held between Stephen H. Schneider, Stanford University, against counterpoint "The Retreating Case for Global Warming Alarmism" by Richard Lindzen, MIT. It was moderated by Gerald R. North of Texas A&M.