Aspen Global Change Institute Elements of Change 1996

AGCI Session II: Characterizing and Communicating Scientific Uncertainty

Session Chairs: Dr. Richard H. Moss and Dr. Stephen H. Schneider

July 31 to August 8, 1996

Why the IPCC Detection Chapter Was So Controversial

Michael MacCracken

U. S. Global Change Research Program

Washington, DC

Chapter 8 of the IPCC WGI report discusses the detection and attribution of anthropogenic climate change. Understanding why this chapter has raised significant attention may provide lessons for the future. Thus, MacCracken began with the rather intriguing question: Why did the IPCC chapter on detection of a human influence on climate receive so much attention when other areas of research involved even greater uncertainties? The process used by the authors of Chapter 8 was elegant and rigorous; key conclusions had multiple supporting evidence; and the result was not so surprising. So why did this chapter lead to such a commotion, and what can we learn from this?

The process used by the authors of Chapter 8 was elegant and rigorous; key conclusions had multiple supporting evidence; and the result was not so surprising. So why did this chapter lead to such a commotion, and what can we learn from this?

MacCracken suggests that the answer lies in a number of contributing factors:

1. The key conclusions of the detection chapter crossed an important psychological barrier, sometimes even nearing the "religious" belief that humans can not affect the global environment. Thus, saying that we can is an important paradigm shift. Detecting a human influence on climate crossed this line, saying that humans can and are changing the planet on a global scale.

2. Procedural issues were called into question by a number of the critics, although nothing out of the ordinary actually occurred procedurally (e. g., other chapters were also changed late in the process). The question thus arises whether such a seemingly strong conclusion might have threatened a trillion dollar industry, such that all means, even apparent procedural ones, might be used to discredit the IPCC conclusions and those who reported them.

3. There were misperceptions about whether any substantive changes were actually made in the chapter. MacCracken suggests that, contrary to claims, no changes actually were substantial if the chapter is read as a whole in contrast to focusing on specific phrases that were deleted.

4. Detection was one of the first areas in which there was an effort to be statistically rigorous. Was the jump to being quantitative, instead of just qualitative, part of the problem?

5. Some of the key critics apparently felt offended by the IPCC process; they felt insufficient attention was paid to their points of view in the chapter development process. The set of critics in this area, sometimes referred to as the "contrarians," have been well funded and have access to the media and thus were able to gain attention.

6. There was confusion on the part of some between the Summary for Policymakers and the chapter itself. Because the summary integrates across all chapters, it cannot contain all the caveats and explanations of each chapter.

7. Another problem may have been the manner in which the key conclusions of the detection chapter were first communicated to the public in The New York Times, which is perceived by some as a "pro-environment" newspaper, rather than directly from the IPCC (although the IPCC report was put out for review with a notice in the Federal Register a month before The New York Times article).

8. The lead authors of this chapter tried to be as up-to-date as possible in a rapidly changing field. Some of the newest materials hadn't been vetted for very long in the scientific literature and community, and some of the points were not sufficiently elaborated upon or fully reconciled ( e. g., the Microwave Sounding Unit data).

9. The manner in which the IPCC chooses authors was also a possible point of controversy. The aim was to have a comprehensive review, but questions were raised about whether some of the expert authors might have slanted the content of their chapters to their own views. This is a potential issue across the IPCC in that experts in fields are selected as authors and will often cite their own work or may omit the work of others.

10. Did the reaction of the scientists involved in the IPCC exacerbate the problem (e. g., could they have chosen not to respond to the opinion pieces in the newspapers)? Would a different response to the critics have been appropriate and not ballooned the issue to as much prominence? Did the critics receive enough attention during the process? Is there a way to include them more effectively in the future?

Contrary to claims, no changes actually were substantial if the chapter is read as a whole in contrast to focusing on specific phrases that were deleted.

Discussion

Discussion ensued regarding ways to try to avoid such pitfalls in the future. One suggestion was that the IPCC lead authors should not be the final authority for checking that adequate responses were made to reviewers' comments. Instead, an appointed editor for each chapter could be responsible for overseeing comments and making sure they are adequately incorporated. It was also suggested that adequate time to study, document and incorporate comments is needed.

It was also pointed out that the conclusions of the detection chapter present a direct threat to the world view that climate change is just a theory that warrants study. The model for many powerful people is that it's fine to study this subject but we should not take action until there is certainty. As soon as information in the climate debate approached a "smoking gun," as it did in the IPCC chapter on detection and attribution, it became more politically charged. It was suggested that other issues might stir a similar response in the future ( e. g., ecological impacts, economic costs).

As soon as information in the climate debate approached a "smoking gun," as it did in the IPCC chapter on detection and attribution, it became more politically charged.

Santer pointed out that there is no unique set of words that will make everyone happy, so criticism will be an ultimate consequence. How to word key conclusions will often be contentious, even among the authors. Even if there were more time and additional changes made, the authors could still iterate endlessly and still leave some people unhappy. So who should ultimately decide how to word conclusions? Would involving more individuals at the lead author level help? Santer suggests that the scientists closest to the work are most appropriate to serve this function.

It was further pointed out that the language of the chapter was originally written as a communication from expert to expert and thus included implicit messages about statistics in phrases such as "we cannot positively attribute..." When read by those not versed in scientific subtleties, the implicit messages are missed. Thus, there seems to be a real communication problem between experts and laypeople. Having to write the chapters as well as the Summary for Policymakers for laypeople would seem to make the overall process much more difficult.

It was suggested that there will likely be topics that will become flash points in future IPCC assessments. Identifying them early in the process might lead to more focused attention on how to best deal with them.

How to word key conclusions will often be contentious, even among the authors. Even if there were more time and additional changes made, the authors could still iterate endlessly and still leave some people unhappy.

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