PARIS (January 31, 2007) — Beneath the twinkling lights of the Eiffel Tower, scientists and diplomats are working until midnight tonight to produce a global consensus on climate change. The process is at times contentious, but mostly painstakingly slow as every line in a 14-page "summary for policymakers" is scrutinized word by word.

After presentations by lead authors of the 11 chapters of the final report—due to be fully released this fall—governments peruse the text of the final summary, probably the most read section of a 1,600 page document. In it, scientists attempt to convey in accessible English the most up-to-date findings on climate change, from forecasts of temperature sensitivity to global average sea level rise. As the report is displayed on a giant screen, various countries raise their flags to be recognized so they may comment or make suggestions—or question why previously submitted comments were not included, of which there were 30,000, according to the Intergovernmental Panel on Climate Change (IPCC). "We are talking about nothing," jokes Arthur Petersen, senior policy analyst at the Netherlands Environmental Assessment Agency (MNP), and part of that country's delegation. "We will never get perfect, so we should be satisfied with good as long as the science is okay."

Adds Yoshiro Tanaka of the Japanese Meteorological Agency: "Whether wordings or expressions are right is hard for a non-nativer speaker to say. ... I am worried whether it will be finished or not."

Particularly contentious issues thus far have included the effect of global warming on hurricane activity and intensity as well as the role of carbon dioxide (CO2) as a driver of climate change, according to participants. These issues are dealt with by banishing them to smaller working groups, where interested countries negotiate final language that is then resubmitted to the larger session. In the case of CO2, while the U.K. pushed for stronger language on its overall role, other countries debated the relative contributions of deforestation and fossil fuel burning to CO2 levels. "It was resolved in the group but it still has to be presented to the plenary," says one participant, who asked not to be quoted by name. "Some were not enthusiastic about the final language and may try to block it again."

"One thing to note is that scientists can object to any rephrasing they find not supported by the technical chapters of the report," says Gabriele Hegerl, a research director at Duke University and a coordinating lead author of the chapter on "Understanding and Attributing Climate Change." "For me as a scientist, it is fascinating to watch how our findings are of interest to countries, and reassuring that the wording has to stay consistent with the science, so we can object if we think its not."

Hegerl and others have been leading the effort to marshal all the peer-reviewed science on climate change to date into succinct chapters for this fourth iteration of the IPCC report as well as extract the work's refined essence in a clear summary. But the end result is a worldwide consensus: "The soon to be released report is not the IPCC's opinion. Rather it is the IPCC's assessment of what the peer-reviewed scientific literature, reporting on results of reproducible analysis, indicates," says Thomas Peterson, a climate analyst with the U.S. National Oceanic and Atmospheric Administration (NOAA) and lead author of the "Historical Overview of Climate Change Science" chapter. "That is a far cry from opinion."

The effort, despite its slowness, is progressing more cooperatively than in the past, participants note, with some countries relaxing their opposition to certain basic science. "The U.S. is very much more constructive," says another participant who asked not to be identified. And while Canada, China and Saudi Arabia have all shown concern over particular wordings, according to a participant, "the spirit is cooperative," says MNP's Petersen.

But with much of the document remaining to approve—and much contentious subject matter to cover, such as the appropriate boundaries for sea level rise—the final product (or language) remains to be seen. "The projections [for sea level rise] will stay what they are," Petersen speculates, noting that current computer models cannot take into account melting from Greenland or Antarctica. "The uncertainties on predictions of sea level rise are difficult to project. We really don't know. You can't say what is the upper limit."

Already, anomalous extreme weather events such as storm surges have begun to destroy property or poison fields with salt in the island nation of Kiribati, according to Riibeta Abeta, climate change planning officer for Kiribati's Ministry of Environment and sole delegate from the smaller island nations of the Pacific. "We notice the level of the sea, it is rising," he says. "It is always difficult to find the words to express science."

But the IPCC summary aims to be clear and unequivocal in its main finding: that the globe is warming and scientists are 90 percent certain—a category dubbed "very likely" (just behind "extremely likely" at 95 percent certainty and "virtually certain" at 99 percent certainty)—that humanity is behind it. "If everyone agrees, you cannot ignore it," adds another participant, who declined to be identified. "If all governments say glaciers are retreating, it is hard to deny."