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climate has warmed about 0.5°C over the past century and that added greenhouse gases quite likely would "explain" a portion of that warming.

That there would be considerable disagreement on what portion of that 0.5°C warming is "greenhouse explainable"? 50%? 100%? 150%?

That high levels of agreement would be reached on the legitimate sources of disagreement. The key contenders would be identified as: measurement uncertainty; natural variability; shortness of records; and poor ability to quantify other climate change forcing factors, such as sulfate aerosols.

A group of social scientists who deal with the possible impacts of Climate Change would have little difficulty agreeing:

That difficulties of mitigating such effects are formidable; the potential impacts of not mitigating CO2 emissions are likely to be very daunting in the long term.

a)

b)

How such a global warming would affect life on earth remains uncertain and problematic, but certainly worrisome.

c)

d)

That the "do much" vs. "do little" policy dilemma is putting considerable pressure on the science community to provide sharper answers soon about how the climate is likely to change.

That it is reasonable for policymakers to ask if the model projections are good enough to guide major policy decisions (to either mitigate or to ignore).

Because almost all serious climate scientists would agree on the first list of key points, why then are the policy and public debates so intense? Here are my answers to this question:

a)

b)

c)

d)

We start by noting that the first "we climate scientists all agree" list is not controversial among climate scientists.

People have a wide variety of agendas and personal biases that have little to do with the state of the science. Some would wish to protect the environment at all costs, thus strongly favoring a "mitigate now" stance. This type of position seems inclined to exaggerate the sense of confidence in greenhouse warming science. Others would wish to protect the economy and the status quo at all costs, thus strongly favoring a "do little" stance. This "do little" position seems inclined to minimize the confidence In greenhouse warming science.

Thus, one extreme seeks to overstate the level of scientific confidence, while the other extreme seeks to understate the confidence.

Real scientific uncertainty "just is". It has neither ideology or willful blas. It should not be manipulable because scientists' "best guesses" are designed to split the difference between erring on the high side and erring on the low side.

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The media exaggerate the sense of controversy; this is because conflict is always much more "newsy" than consensus or progress.

Finally, Congressional hearings tend to exaggerate the sense of controversy because most of the time is spent buttressing positions, rather than seeking Information. Fortunately, there are important exceptions to this, in the House Science Committee, and elsewhere in Congress.

In normal times, the artificial Intensity of the public debates does neither much harm nor good. Unfortunately, these do not appear to be normal times.

When the seeking of proper and reliable scientific information about the present and future state of the environment is regarded as "tainted science", something disturbingly dysfunctional is going on. Why?

Why is improved Information regarded as being so threatening that the very creation of that information must be sharply reduced or even eliminated? Is the goal to have the United States depend on other countries for its scientific assessments? As a participant in the production of non-ideological scientific information that has already demonstrated an enormous societal value, I find these trends deeply distressing. I fear for the future of our country's world-leading science and I fear for a United States that allows such "thinking" to sérve as a substitute for real leadership.

Jerry D. Mahlman

References

Hansen, J., et al., 1995: Satellite and Surface Temperature Data at Odds? Climate Change, 30(1), 103-117.

IPCC, 1990: Climate Change; the IPCC Scientific Assessment, J.T. Houghton, et al., eds. Cambridge University Press, 365 pp.

IPCC, 1992: Climate Change 1992: The Supplementary Report to IPCC Scientific Assessment, J.T. Houghton, et al., eds. Cambridge University Press, 200 pp.. Manabe, S., R.J. Stouffer, M.J. Spelman, and K. Bryan, 1991: Transient Responses of a Coupled Atmosphere-Ocean Model to Gradual Changes of Atmospheric CO, Part I: Annual Mean Response. Journal of Climate, 4:785-818.

Santer, B.D., 1995: A Search for Human Influences on the Thermal Structure of the Atmosphere, PCMDI Report No. 27, U. California, Lawrence Livermore National Laboratory, UCRL-ID-121956, 26 pp, (also submitted to Nature).

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I want to express my appreciation for your participation in the Committee's recent hearing on Global Change modelling. Your testimony was of great value to me and to the Committee.

Enclosed, you will find some additional questions which are intended to clarify certain points raised in the hearing and develop additional information for the Committee's use. Your written responses will be included as part of the hearing record. I ask that you provide your responses by February 15. You may contact Dr. William S. Smith of my staff at 202/225-4439 if you have any questions regarding this request.

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