Controversy erupts over climate report.

In a war over words, critics of an influential United Nations' climate report have charged its authors with "scientific cleansing"-altering the text to downplay uncertainties about humanity's influence on climate. The scientists who wrote the document counter that the critics have misrepresented the situation to divert attention from the report's basic conclusion, approved by 96 countries, that "the balance of evidence suggests that there is a discernible human influence on global climate."

The skirmish centers on chapter 8 of the 1995 scientific assessment by the Intergovernmental Panel on Climate Change (IPCC), published last month by Cambridge University Press. This chapter, written by 4 scientists, with contributions by 32 others, is titled "Detection of climate change and attribution of causes."

The Global Climate Coalition, a lobbying group funded in part by the energy, transportation, and manufacturing industries, argues that the authors of chapter 8 altered the text improperly after representatives of the IPCC had accepted the document at a meeting in Madrid in November 1995. "There was a total breakdown of IPCC's agreed procedure for preparation and publication of this assessment report," says John Shlaes, executive director of the Global Climate Coalition in Washington, D.C.

Leaders of the IPCC disagree. In a letter to the Wall Street Journal on June 25, Bert Bolin, chairman of the IPCC, and the two cochairmen of the science panel assert that "in accordance with IPCC procedures, the changes to the draft of Chapter 8 were under the full scientific control of its convening lead author, Benjamin D. Santer. No one could have been more thorough and honest in undertaking that task."

Santer, an atmospheric researcher at Lawrence Livermore (Calif.) National Laboratory, says that he made the changes to reflect comments and criticisms he received in Madrid, as well as to assess the science better. The Global Climate Coalition argues that these changes eliminate or diminish caveats regarding studies linking human activities with changes in climate. The published chapter, for instance, lacks a concluding summary-present in an earlier draft-that discussed scientific uncertainties.

Santer says he dropped the section after receiving criticism in Madrid that chapter 8 was the only one with a concluding summary in addition to the summary at the beginning, which all the chapters had. Half of the material in the excised conclusion now appears in the body of the chapter, which devotes roughly 20 percent of its total space to the issue of uncertainties, Santer says.

"This issue of cleansing somehow suggests that [the uncertainties] have been purged from the chapter. That's ridiculous," he says.

The Global Climate Coalition's charges have received widespread attention, especially among global warming skeptics who disagree with the IPCC's main conclusions, which remain unchanged in the final report. Among those skeptics is Frederick Seitz, past president of the National Academy of Sciences and chairman of the George C. Marshall Institute, a Washington, D.C.-based conservative think tank. In an essay in the June 12 Wall Street Journal, Seitz wrote that "it would be best to abandon the entire IPCC process, or at least that part that is concerned with the scientific evidence on climate change." Santer responded in a letter in the June 25 Wall Street Journal, saying that Seitz is not a climate scientist, was not involved in putting together the IPCC report, did not attend the Madrid meeting, and did not attempt to obtain an explanation for the changes. Santer's letter was signed by 40 scientists, all of whom were contributors to the 1995 IPCC science report.