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 
     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 
     "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 
     "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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