Global Change and Our Common Future Papers from a Forum (1989) / Chapter Skim
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22. Global Warming: Is It Real and Should It Be Part of a Global Change Program?
22. Global Warming: Is It Real and Should It Be Part of a Global Change Program?
Pages 209-220
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From page 209... ...
On June 23, 1988, James Hansen of the National Aeronautics and Space Administration's Goddard Institute for Space Studies (GISS) stated before the Senate Committee on Energy and Natural Resources that he considered there was a "99 percent' chance that the unusually warm globally averaged temperature records he and a colleague had constructed for the 1980s could not have occurred by chance but rather were the result of the buildup of greenhouse gases.2 He went on to point out that increasing the global temperature would increase the likelihood of extreme heat waves such as those occurring in 1988.
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From page 210... ...
National Climate Program Office helped to sponsor a workshop on climate trends at the National Academy of Sciences on September 29, 1988. It focused on several difficulties with the observational record used to reconstruct global temperature trends, including the fact that many thermometers have had cities grow around them, which causes an unnatural urban heat island effect.
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From page 211... ...
Michaels listed a number of issues he believed were improperly reported or underreported in the press, giving examples of "a few recent revelations that somehow got lost with the ozone." He disparaged Hansen's June testimony forecasting that 1988 would be the warmest year on record, even though recent evidence now suggests that indeed it was.6 He went on to refute the greenhouse explanation of drought by citing Trenberth's work to the effect that the drought of 1988 was caused by cold tropical ocean temperatures, something that was never doubted by other scientists. He cited the very recent results of National Oceanic and Atmospheric Administration scientist Tom Karl, who, Michaels said, "arguably knows more about regional climate variation than anyone in the world." Michaels described Karl as saying that the NASA-GISS calculations for warming over the United States were too high by nearly 1°F for this century because of the urban heat island effect.
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From page 212... ...
Goddard Institute for Soace Studies It ·- - -- -- - Annual Mean —5 Year Mean —o 8 1900 1920 1940 1960 1980 2000 YEAR FIGURE 22.1 A comparison of the global surface temperature trends of the past 100 years constructed (a) from land and island stations and ocean surface temperature data sets at the Climatic Research Unit and (b)
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From page 213... ...
global warming for the past century. This is not consistent with the frequent statements in the press that urban biases are likely to eliminate the global warming trend over the past century.
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From page 214... ...
The policy process is advanced when scientists provide what they are technically competent to offer: estimates of specific consequences of greenhouse gas buildups and their likelihood of occurrence -- even if estimates of the latter are based on intuitive judgments of technical experts. Any statements beyond that are the personal opinions of those scientists.
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From page 215... ...
Quite simply, the "bottom line" of the evolving greenhouse gas buildup is that we are insulting the environment at a rate greater than our ability to predict the consequences and that, under these conditions, surprises are virtually certain. NEED FOR ONGOING SCIENTIFIC INVESTIGATION Continued Observation and Monitoring To establish that the greenhouse effect signal has clearly been detected in the climatic record, we will require another decade or possibly 2 to be sure that the warming of the 1980s (which does appear to be the warmest decade recorded on a global basis)
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From page 216... ...
Let us consider in more detail the important issue of model validation. Perhaps the most perplexing question about climate models is whether they can ever be trusted enough to provide grounds for altering social policies, such as those governing carbon dioxide emissions.
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From page 217... ...
modelers have not properly accounted for the large heat capacity of the oceans taking up some of the heating of the greenhouse effect and delaying, but not ultimately reducing, warming of the lower atmosphere; (6) both present model forecasts and observed climatic trends could in fact be consistent because models are typically run for equivalent doubling of carbon dioxide, whereas the world has only experienced one-quarter of this increase, so that nonlinear processes have been properly modeled and have produced a sensitivity appropriate for a doubling but not for a 25 percent increase; and (7)
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From page 218... ...
I hope that recent shrill or irrelevant debates or headlines do not mask the already large scientific consensus that exists over the basic physical phenomenon known as the greenhouse effect, a scientific proposition over which I have heard virtually no scientific dissent. In any case, regardless of whether society chooses vigorous prevention policies as a response to global warming, nearly all analysts agree that some growth in greenhouse gases will continue into the twenty-first century.
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From page 219... ...
Karl and P.D. Jones, 1989, Urban bias in area-averaged surface air temperature trends, Bulletin of the American Meteorological Society 70:265-270.
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