Climate Change: The IPCC Scientific Assessment ("IPCC Report"), published in the summer of 1990, forms the scientif- ic basis for the climate treaty of the 1992 UN Conference on the Environment and Development. It has also prompted unilat- eral announcements by many governments--and legislative proposals in the U.S. Congress--concerning plans to stabilize or even cut back emissions of carbon dioxide (CO2).
Only a year later, in response to the flood of new research results, the Intergovernmental Panel on Climate Change (IPCC) began to assemble a Supplement, which was published in March 1992. Its 21-page Summary (labeled "Scientific Assessment") contends there has been no change in the principal 1990 conclusions, namely, (1) an observed increase in the global mean temperature during the past 100 years in broad accord with theoretical model calculations, and (2) an expected increase of 0.3øC per decade--as a result of an enhanced greenhouse (GH) effect due to human activities that release CO2 and other GH gases.
This is not so: These conclusions, contained in the 1990 Policymakers Summary, are not supported by the body of the 1990 Report nor by the Supplement. Consider, for example, the statement (on page 254 of the Report): "It is not possible to attribute all, or even a large part, of the observed global- mean warming to the enhanced greenhouse effect on the basis of observational data currently available".
Furthermore, as we shall show, there have been major scientific changes and new findings during the past two years, not adequately dealt with in the Supplement, that cast further doubts on the 1990 conclusions.
The preface of the IPCC Report states that it is "the most authoritative and strongly supported statement on climate change that has ever been made by the international scientific community. The issues confronted with full rigour include: global warming, greenhouse gases, the greenhouse effect, sea level changes, forcing of climate, and the history of the Earth's changing climate.
The information presented here is of the highest quality."This claim has fostered the view that the hundreds of climate specialists from dozens of countries, listed at the end of the Report, all agree that there is a serious and urgent climate problem. This is not the case. An indepen- dent survey, conducted by the Washington-based Science & Environmental Policy Project (SEPP) demonstrates that scien- tists who worked on the Report are skeptical about the 1990 Policymakers Summary, that most do not see evidence for anthropogenic global warming in the climate record and do not consider current climate models as reliable tools to forecast global warming.
Another problem: The IPCC documents were never "peer- reviewed" in the generally accepted sense--in spite of such claims. (See p.12). The IPCC core group, whose members were co-authors and prepared the summaries, also selected the reviewers. The existence of a "minority of opinions" among scientists who worked on the IPCC Report was mentioned (in the Foreword of the 1990 Report), but they were not described further or "accommodated" by the IPCC.
The tone of the two documents, 1990 Summary and 1990 Report, is markedly different. While the IPCC Report proper is a useful compilation of then current knowledge--and filled with appropriate qualifying statements--the Policymakers Summary throws all caution to the winds. By selectively extracting from the often conflicting statements in the Report that express existing doubts and uncertainties, the Summary's firm tone leads policymakers to believe that the existence of a climate problem has been confirmed by "scientific consen- sus."
The IPCC's action of binding the Policymakers Summary with the full Report gives the misleading impression that it arose out of the full Report. But the Summary is essentially a document of governments not of scientists. It was prepared for and agreed to by the official representatives to the Intergovernmental Panel on Climate Change, and influenced by accredited delegates from other organizations, including environmental pressure groups.
It is worth noting that at the time of the Second Session of the IPCC, in June 1989, IPCC Chairman Prof. Bert Bolin [of the University of Stockholm] stated that its primary objective was to produce a document to provide guidelines for the formulation of global policy. He also said that the IPCC document should be a proposal for action and that the world community cannot afford delays in safeguarding the future of the planet. The Policymakers Summary seems to have satisfied these objectives despite the fact that the full Report finds no compelling evidence for an impending climate problem.
The fact that this "most authoritative Report" required a major updating only one year later calls into question the robustness of the Report and any support it may give for an enhanced greenhouse warming. Will it require another update a year from now? Two years from now? The scientific situa- tion, as we shall show, is fluid and unsettled, and is unlikely to be resolved within a few years or even a decade.
What follows is a summary of the main scientific issues discussed in the body of our Analysis and Critique, and in the Attachments prepared by individual authors.
In general, the IPCC documents can be faulted in three distinct ways:
In addition to our own analysis, we will also present the views of IPCC scientists themselves, as determined by two independent surveys: one conducted in August 1991 by the Science & Environmental Policy Project, and the other in January 1992 by Greenpeace International. As already men- tioned, the SEPP survey shows that scientists who worked on the Report are skeptical about its Summary: most do not see evidence for anthropogenic global warming in the climate record and do not view current climate models as reliable tools to forecast global warming.
Summary of Scientific Issues: Our scientific discussion is divided into three general areas:
1. How much of the increase in carbon dioxide (CO2) is due to fossil fuel burning? While recent CO2 growth appears to parallel the use of fossil fuels, land use--including defores- tation and biomass burning--continues to make a major, but difficult-to-quantify contribution. With carbon reservoirs in the ocean and biosphere some fifty times larger than the atmospheric reservoir of CO2, even minor fluctuations in the rates of release and absorption can produce increases or decreases of atmospheric CO2 that dwarf any fossil-fuel effects. To gain further perspective on this issue, it should be stressed that the geologic record shows large-scale natural variations of CO2, with concentrations 10-fold the present value during the paleozoic era. In the last 100 million years, the concentration has been generally declining. In the last 2 million years, an era of frequent ice ages, there have been large swings in connection with the periodic glaciations and warm interglacial periods.
2. Will CO2 double or triple by 2100? Recent carbon models that consider an interactive ocean and biosphere, for example that of the Max Planck Institute of Hamburg, raise serious doubt that an atmospheric CO2 doubling will ever be reached. Furthermore, the 1990 IPCC emission scenario labeled "business as usual" (visualizing a complete phase-out of nuclear power) was recognized as unrealistic and has since been abandoned by the IPCC. These developments would, of course, lower the rates of global warming predicted in the IPCC Policymakers Summary; but this finding is not spelled out in the 1992 Supplement.
3. Does a CO2 stabilization scheme make sense? First, it must be recognized that stabilizing CO2 emissions, the currently announced policy for many nations, would not stabilize CO2 concentration. It would simply diminish the rate of increase and thus postpone the date of doubling by a few years--if indeed doubling occurs at all. In order to stabilize concen- tration, worldwide emissions would have to be rolled back by more than 60 percent--if one accepts the carbon model and the long lifetime of atmospheric CO2 used by the IPCC vs the shorter value derived by the Hamburg model. At this point, industrialized nations must consider carefully the wisdom of such policies; developing nations will require large increases in energy use as their populations and GNPs rise in the next century and will therefore dominate CO2 emissions.
One would also need to consider carefully the effects of the remaining greenhouse gases, principally methane, which would become relatively more important as the contribution from CO2 diminishes. If one factors in also the indirect greenhouse (GH) effects of methane (mentioned but not quanti- fied by IPCC) and the more realistic lifetime for CO2, then stabilization of the GH effect becomes an even more daunting task.
4. Is there radiative forcing of climate from other human activities? Aside from the conventional greenhouse gases, there may be other effects that will become more important as populations and economic activities grow. One example is the indirect effects of increasing methane, which adds water vapor to the stratosphere and also influences ozone chemistry. Another important source of water vapor in the upper tropo- sphere and stratosphere comes from the increase in air traffic, which routinely penetrates the region of the tropopause. Airplane exhausts cause condensation trails, enhanced by decreasing stratospheric temperatures. Contrails are just one source of high-altitude cirrus, which could lead to substantial radiative forcing and affect surface tempera- tures.
Another important omission in the 1990 Report is sulfur dioxide and its global distribution. Surface sources, mainly power plants and other industrial plants, create sulfates that can increase regional cloud albedo and produce cooling in the lower troposphere. Pollution controls in western nations and rapid industrial development elsewhere are changing the geographic distribution of SO2 emissions and of cloud albedo. Aircraft sources can add sulfate aerosols to the stratosphere, mainly in the northern hemisphere, and increase the climate effects of the existing aerosol layer.
5. Does the existing climate record support greenhouse warming-- and the model predictions of a major warming in the next century? The record, based on temperature measurements of the last hundred years or so, cannot be said to support the warming scenarios of existing computer models. On the contrary, even if all the warming experienced in the last 130 years were due to GH effects--a quite unrealistic assumption-- the temperature increase (corresponding to an increase in all GH gases--equivalent in radiative forcing to a doubling of CO2) would be less than 1øC instead of 2.5øC as claimed by the IPCC.
The fact that global temperature data first became available 130 years ago, during an unusually cold period, distorts the IPCC conclusions. If examination of the climate record were to start around 1940 (or during the warm period around 1780) rather than in 1860, then the projected tempera- ture increase becomes even less. In the U.S. climate record the warmest years occurred in the 1930s, not in the 1980s.
(The well-known urban heat island effect reduces further any temperature increase that could be ascribed to anthropo- genic GH effects. On the other hand, lower tropospheric sulfates, formed as a result of SO2 pollution, scatter and absorb incoming solar radiation and reduce a GH surface temperature increase.)
The finding that an observed average warming, possibly from natural causes, constitutes an increase in the minimum (nocturnal and winter) temperatures, originally noted for the United States, has now been confirmed also for Russia and China. This important feature, which determines the economic and ecological impact of a possible climate warming, had been neglected in the original IPCC Report. The explanation for the observed effect is not yet certain: it could be the result of increased cloudiness during the day, thus increasing the albedo; or an increased nighttime greenhouse effect of rising CO2 levels or of clouds.
But perhaps the most important of the observations that the IPCC documents fail to address fully are the satellite microwave data, which show no appreciable global temperature trend during the 12-year period, 1979 to 1991, of existing observations. Although the record is still too short, the data at this point would be consistent with a future tempera- ture increase--due to a rise in all greenhouse gases, equiva- lent to a doubling of CO2--of only about 0.5øC. This is about one-third of the lowest model calculation and one-fifth of the IPCC "best value."
In addition to the usually quoted "annual global mean" temperature, other important features of the climate record are the temperature trends in each hemisphere, as a function of latitude, as a function of altitude, and as a function of season. The agreement of these "fingerprints" with the model predictions is poor, as has been pointed out by Hugh Ellsaes- ser [Lawrence Livermore National Laboratory] and other investigators. To be considered valid, improved GCMs must reproduce these details of the climate record.
The IPCC response to this has been: "We do not yet know what the detailed `signal' looks like because we have limited confidence in our predictions of climate change patterns" [1990 IPCC Report, p. xxix]. (One is left to wonder by what logic the model-produced mean global warming is credible, but the model-produced "fingerprint" of the warming is not.)
Another feature of the climate record in dispute is the trend in sea surface temperatures (SST). The IPCC does not take account recent work (by Donald Atwood et al [NOAA Marine Lab, Miami]) that shows bleaching of corals taking place without any increase in the SST, nor does the IPCC do justice to the small trends reported by Reginald Newell [MIT]; the "corrections" that others applied to his data may have distorted the trend.
Finally, there is a growing body of satellite data measuring increased thickness of the Greenland ice sheets. These trends, if confirmed for the Antarctic as well, would further lower predictions of sea level rise, which have already gone from 10 meters down to about 20 centimeters (cited in the 1990 IPCC Report), in response to a CO2-equiva- lent greenhouse gas doubling in the next century.
6. Are current global climate models (GCMs) reliable? While the IPCC Report and Supplement give fairly comprehensive discussions of model deficiencies and while improvements will surely be made, shortcomings of current models are glossed over in the Policymakers Summary of the IPCC Report and the Science Assessment section of the Supplement. Some of these are:
7. Have global climate models (GCMs) been validated? The answer must be a resounding "no". As explained above, current models cannot explain the global mean temperature variations recorded during the past 100 years, nor the "fingerprints." Even assuming that natural variations are offsetting some of the greenhouse warming, the enhanced GH effect falls well below that calculated from even the lowest temperature change derived from model simulations.
Clearly, the physics of the GCMs is not yet complete and much effort will be required to make them agree more closely with observations. The IPCC Report does not give adequate emphasis to the uncertainties in the modeling of clouds, ocean circulation, and the terrestrial biosphere. Nor does the Supplement discuss the many research efforts now underway to intercompare and improve models, e.g. the Electric Power Research Institute program to investigate the sensitivity of models to various physical assumptions, techniques, and procedures.
One of the weakest points of the models lies in the treatment of feedback due to water vapor, by far the most important greenhouse gas. As pointed out independently by Hugh Ellsaesser and Richard Lindzen [MIT], the feedback may not be as large as assumed in the models--and might even be negative, reducing the greenhouse effects of CO2. In view of the unsatisfactory way in which the GCMs now handle water vapor, by not including the relevant physics, it would be inappropriate to rely on their forecasts to formulate policy on CO2 control.
8. Can the climate record be explained by natural variations? Since many natural events have climate consequences, it behooves scientists to investigate these to the fullest before recommending far-reaching control policies. Certainly, the substantial warming observed before 1940 must be ascribed largely to natural causes-- most likely a recovery from the "Little Ice Age" that prevailed until about 1850.
Many investigators have reported climate effects from natural causes; but these are not followed up extensively by the IPCC. For example, correlations with solar variations have been suggested in the past by Wallace Broecker [Lamont Labs, Columbia Univ.], P.R. Bell [Oak Ridge National Lab], George Reid [NOAA Labs, Boulder], Robert Jastrow [Dartmouth College], Harry van Loon [NCAR, Boulder] and Karen Labitzke [Meteorol. Institute, Berlin]. Other temperature correlations have been published and require critical discussion; e.g. with volcanoes (Paul Handler [Univ. of Illinois]).
In a 1991 article in Science, Eigil Friis-Christensen and Knud Lassen [Danish Meteorol. Institute] showed a near-perfect correlation between global temperature and length of solar cycle. If confirmed, this would further reduce any warming that could be ascribed to greenhouse effects. It would also imply that the GCMs have failed to include a large negative feedback.
9. Can the existence of ice age cycles be ignored? The IPCC documents, claiming to be an authoritative scientific assess- ment, should discuss fully the possibility that the present interglacial (warm) period will soon come to an end. Many would consider a return of glaciation to have a much higher probability than a catastrophic or even an appreciable greenhouse warming. One may recall here the fears about the onset of another ice age, so prevalent in the 1960's and 1970's. Economists even published estimates of the enormous damage expected from a cooling of only a degree or so.
Finally, one would like to see a mention of the fact that a slight warming, say less than 1øC for a CO2-doubling, would not entail disastrous consequences, but should rather be considered as beneficial--in light of the evidence available from climate history. This positive view of a possible modest climate warming is reinforced by the more certain benefits to agriculture from the higher levels of carbon dioxide, which speed up the growth of many plants, and from expected higher levels of precipitation due to higher levels of ocean evaporation.
Surveys of IPCC Scientists:
Since the IPCC Report has been referred to as a "scien- tific consensus" and since the IPCC Supplement will undoubted- ly be so labeled, it is useful to present the views of the scientists who wrote the Report, either by contributing to it or by reviewing it. The existence of minority views is mentioned in the Foreword of the 1990 Report, but they are nowhere identified; the Report "was not able to accommodate them." Many reviewers report privately that their critical comments were ignored--and certainly were not published. Again, this procedure calls into question t
he IPCC claim that its Report was "peer-reviewed."During the summer of 1991, the Science & Environmental Policy Project mailed questionnaires to the more than 100 U.S. IPCC contributors and reviewers, as well as to a group of atmospheric scientists, active in research but not involved in IPCC. Of the 126 surveys mailed, 37 percent were returned, many with signatures.
Only about half of the respondents thought that the Policymakers Summary reflects the text accurately; a majority said that the Summary did not reflect their own views and might convey a misleading message to policymakers. About 90 percent agreed with the following statement (on page 254 of the Report): "It is not possible to attribute all, or even a large part, of the observed global-mean warming to the enhanced greenhouse effect on the basis of observational data currently available". Only 15 percent believed that current GCMs accurately portrayed the atmosphere-ocean system, and less than 10 percent thought that current GCMs had been adequately validated by the climate record.
The other survey, conducted by Greenpeace International, polled 400 climate scientists who had worked on the IPCC study or had published on relevant issues during 1991. The key question was: "Do you think there will be a point of no return, at some [unspecified] time in the future at which continued business-as-usual policies run a serious risk of instigating a runaway greenhouse effect?" Of the 113 respon- dents, 13 percent said "Probably" and 47 percent said "Proba- bly not." This result appears consistent with the results of the SEPP survey.
But here is how Greenpeace interpreted its survey in a press release of February 9, 1992: "This result reveals an as- yet poorly expressed fear among a growing number of climate scientists that global warming could lead not just to severe problems but complete ecological collapse." (Emphases added)
Conclusions:
The Policymakers Summary of the 1990 IPCC Report indulges in bold statements and predictions about future climate warming, not supported by current science nor indeed by the Report itself.
The 1990 IPCC Report and the 1992 Supplement do not deal adequately with available scientific evidence which throws doubt on the reality of any appreciable human-induced greenhouse warming, now or in the future.
There is no scientific consensus backing the idea of an appreciable greenhouse warming. On the contrary, as shown by independent surveys, a majority of active climate specialists are skeptical about the importance and urgency of the greenhouse problem.