]]]]]]]]] LINDZEN CRITICAL OF GLOBAL WARMING PREDICTION [[[[[[[[ (10/17/1989) by Eugene F. Mallove M.I.T. TECH TALK, 9/27/1989 Dire predictions of global warming through the greenhouse effect were roundly criticized last week by Professor Richard Lindzen of the Department of Earth, Atmospheric and Planetary Sciences. "I argue that the greenhouse effect does not seem to be as significant as suggested." Professor Lindzen said. He spoke last week before an audience of 250 scientists at the Alexander von Humboldt Foundation Colloquium at Kresge Auditorium. "I personally feel that the likelihood over the next century of greenhouse warming reaching magnitudes comparable to natural variability seems small," he said. "And I certainly feel that there is time and need for research before making major policy decisions." Professor Lindzen characterized the question of possible global warming as "a region in which the uncertainty is vast." He then proceeded systematically to expose major difficulties with projections of global climate. Has warming already occurred? What does the temperature record already show about global warming? Do the data conclusively indicate about one-half degree centigrade (plus or minus 0.2 degree) global warming over the last century, as some proponents suggest? No, contends Professor Lindzen. Professor Lindzen cited many problems with the temperature records, an example being the representation of the Atlantic Ocean with only four island measurement sites. Urbanization also creates problems in interpreting the temperature record, he said. There is the problem of making corrections for the greater inherent warming over cities--in moving weather stations from a city to an outlying airport, for example. "The trouble with many of these records," he said, "is that the corrections are of the order of the effects, and most of us know that when we're in that boat we need a long series and great care to derive a meaningful signal." Nor, he said, was the temperature data collected in a very systematic and uniform way prior to 1880, so comparisons often begin with temperatures around 1880. "The trouble is that the earlier data suggest that one is starting at what probably was an anomalous minimum near 1880. The entire record would more likely be saying that the rise is 0.1 degree plus or minus 0.3 degree." He referred to MIT Professor Reginald Newell's work that suggests that between the 19th century and the present there appears to be no change in ocean surface temperatures. Moreover, the record for the 48 contiguous states shows no evidence for warming over the past century. "As far as the data goes, I would argue that we really don't have the basis for saying it's a half degree plus or minus 0.2. That is false use of science. What we have is data that says that maybe it occurs, but it's within the noise." Problems with models Climate inherently has a natural variability that is often attributed to possible variations in solar output, volcanic dust, etc. However, Professor Lindzen highlighted a more fundamental source of natural variability. "The point we have to keep in mind is that without any of this at all our climate would wander--at least within limits. The reason is that we don't have a closed system. "Even if the Sun's output were fixed, even if the radiative input were absolutely constant, even if there were no change in the absorbing gases, the ocean itself can take up and store heat and release it. It has a stable layer that normally does not communicate with lower levels, but every so often there is upwelling that suddenly presents the atmosphere and the surface world with an erratic energy source." The ocean is extremely complex and not well handled in computer models of climate change, Dr. Lindzen argued. He said that the models showing that warming will occur with increasing CO2 predict after-the-fact (post-predict) that since the 19th century we should have seen between about one and two degrees of warming. "Clearly by any standards this is only marginally compatible with the temperature record." The models overpredict warming from 1880 to present and greatly overpredict the estimated warming from earlier, he claimed. "I would say, and I don't think I'm going out on a very big limb, that the data as we have it does not support a warming. Whether it contradicts it is a matter of taste. "It is interesting that before this last appearance of 'greenhouse warming' (1970 to present), there were actually quite a log of books on the coming ice age. Now a new set of books on the coming warming are hitting the stands." Professor Lindzen said that in 1983 a panel of the National Academy of Sciences recommended a technique to validate climate models known as "fingerprinting"--efforts to find at least regional effects in modeling that are correct. "This has turned out to be a disaster in methodology, because all the models differ even in their signs [directions] of predicted change, and they don't even agree on these features for the present climate." "The only thing they agree on is the occurrence of enhanced warming at high latitudes. This has been a period of almost steady cooling in those latitudes--exactly the opposit to what one would have expected from climate theory." Complexity of the problem Getting most attention as the source of warming is the emission of infrared radiation by the atmosphere's trace but growing amount of carbon dioxide that is heated by sunlight. However, Professor Lindzen pointed out that "in the upper atmosphere around 50 kilometers, this is the dominant mode of cooling, so an increase in CO2 undoubtedly means that the upper atmosphere will cool more." He said, "That has implications for ozone, because the colder that part of the atmosphere, the less destruction of ozone. Several people have already commented that these may be compensating problems." He characterized water as much more important source of potential warming. "Water is terrifically absorptive. We see the bumps [in the absorption spectrum] from CO2 and ozone and methane only because they occur in a window of the water vapor absorption spectrum. Water vapor is far and away the most important greenhouse gas, except for one form which isn't a greenhouse gas: clouds. "Clouds themselves as liquid water are as important to the infrared budget as water vapor. Both swamp by orders of magnitude all the others. With CO2 one is talking about three watts per square meter at most, compared to a hundred or more watts per square meter for water." Thermal radiation alone does not explain the temperature of the atmosphere. Professor Lindzen emphasized that the atmosphere must convect--vertically circulate--to bring about its present temperature. Radiative cooling by itself would mean an atmosphere that would already be some 20 degrees hotter today. "Upper level humidity--especially above five kilometers--is rather important and the models are lousy at handling this. In the models, most warming comes from the increase in water that accompanies the warming. Whether such an increase in water vapor above five kilometers actually accompanies warming is doubtful. "We don't know how to calculate cloudiness," Professor Lindzen said. Some studies have found that the dominant radiative effect of clouds is cooling. Only a few percent change in cloud cover will more than swamp the estimated CO2 effect, he suggested. In the current models, for reasons that puzzle almost everyone, the cloud feedbacks are positive rather than negative." That is, they increase the temperature. "There are other tricky things that no one has explored," he said. One example: the feedback through albedo--the reflectivity of the Earth such as can be affected by snow cover. In the models this feedback is positive, but it could as well be negative in certain ranges of temperature, he said. "On the planet the most wonderful constituent is water with its remarkable thermodynamic properties. It's the obvious candidate for the thermostat of our system, and yet in most of these models, all water-related feedbacks are positive. I don't think we would have existed if that were true. "All of you know that the greenhouse warming has become a 'happening'--some would say a circus. It has engaged us in a realm of argument that is in some ways foreign to us." He criticized editorials that simultaneously state that we don't know whether warming will occur, but that we shold nonetheless undertake "virtuous things"--altered energy policy, forestation, etc. To call for action, he said, "has become a litmus test of morality." Comparing the greenhouse warming debate to an earlier controversy, he found fault with a statement by Princeton physicist Freeman Dyson that "nuclear winter" was "bad science but good politics." "It seems to me," said Professor Lindzen, "that if science doesn't have integrity, it isn't of much use to people." * * *
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