The head of the Intergovernmental Panel on Climate Change said yesterday that he welcomes "vigorous debate" on climate science.

"We who are on the side of the consensus must remind ourselves that the evolution of knowledge thrives on debate," Rajendra Pachauri said in an essay published on the website of the BBC.

But Pachauri, whose panel has come under fire in recent months after revelations of multiple errors in its last major report, said he also believes that "many people either do not know, or have forgotten, what the IPCC actually is."

Pachauri's comments came as the independent panel charged with reviewing the IPCC's operations held its second meeting. Gathering in Montreal yesterday, the panel assembled by the world's science academies heard from a number of scientists who worked on previous IPCC reports, as well as the head of the World Meteorological Organization.

One major point of agreement for those experts: The IPCC needs to develop a mechanism to correct any errors found in its reports, even after they're published.

The IPCC was slow to react to news that its 2007 report contained an error-riddled paragraph that said, among other things, that Himalayan glaciers could disappear by 2035. Although the group eventually issued a statement admitting the error, the head of one of the IPCC's three scientific working groups said making a "more definitive fix" has been a challenge.

"Even though everyone recognizes the statement in the report is wrong, nobody is really sure whether it requires plenary approval to get a correction out," said Carnegie Institution climate scientist Chris Field, who is serving as chairman of IPCC's Working Group 2 -- which covers "impacts, adaptation and vulnerability" -- for the panel's fifth report, due in 2013.

'Atrocious' delayed reaction
The error in the glacier paragraph came to light after IPCC's October 2009 plenary meeting, Field noted, and the next plenary meeting is set for October 2010.

That kind of delayed reaction is "atrocious," said former IPCC chairman Robert Watson, who oversaw development of the science group's 2001 report.

"To me the basic problem was as much the way the situation was handled once the error had been found as much as the error itself," said Watson, chief scientific adviser to the United Kingdom's Department for Food, Environment and Rural Affairs.

But Watson said he's not sure whether the errors in the IPCC's report -- including the incorrect projections of how quickly Himalayan glaciers would retreat and how much of the Netherlands lies below sea level -- are out of the ordinary.

"I think there is a question of how big of a problem does the IPCC have," he said. "No error is acceptable, but there is such a thing called human error."

Experts who spoke before the review panel yesterday also debated the role of so-called "gray literature" -- information that has not undergone scientific peer review -- in the IPCC process.

The Himalayan glacier flap has put the spotlight on such sources. The IPCC's error-riddled paragraph on the glaciers cited a report by the World Wildlife Fund, although scientists who identified the mistakes say they believe the science panel actually relied on news accounts that appear to misquote a scientific paper.

Field said the IPCC working group he heads is especially reliant on what he called "non-journal-based literature," sometimes drawn from everything from the U.S. National Academy of Sciences' peer-reviewed reports to documents produced by non-governmental organizations who are implementing different climate adaptation strategies in communities around the world.

Michel Jarraud, secretary general of the World Meteorological Organization -- one of two United Nations bodies that established the IPCC -- said he doesn't think that's a problem.

The pros and cons of 'gray literature'
"I don't think there is anything wrong with using gray literature, because it was a deliberate choice of the members of the IPCC in order to get enough input from developing countries," he said. But the problems with the last IPCC report suggest that review processes for evaluating gray literature need to be strengthened, Jarraud added.

Hans von Storch, a climate scientist at GKSS Research Center and the University of Hamburg, agreed.

"We have to make very sure that if there is no material, we do not say anything," said von Storch, who worked on the IPCC's 1995 and 2001 reports.

Meanwhile, Field said he believes making a major change in the IPCC's report process would help limit errors.

Each IPCC working group completes its report, then prepares a summary for policymakers. That summary is approved line-by-line in long, often highly charged, meetings with representatives of the governments that participate in the IPCC process.

"It's hard to imagine the best thing we can come up with is the pressure-cooker environment where there is no chance to go back and see if you've got it right," he said.

As yesterday's meeting in Montreal came to a close, the head of the panel reviewing the IPCC said his group was still on track to deliver its report by the Aug. 30 deadline set by the IPCC.

Harold Shapiro, an economist at Princeton University, said the panel hoped to complete a draft of its report five weeks from now, then send it off for a one-week peer review.

"We're going to be moving very quickly, but I'm very optimistic we can do it," he said. "Like many here, I'm new to this area, but in my mind I can see this report developing."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500