The scientific community was buzzing Tuesday over a leaked draft summary of a highly anticipated intergovernmental climate change report, which cautions sea levels could rise more than 3 feet by this century's end and also more strongly ties global warming to human activity.

Two scientists at the National Center for Atmospheric Research who participated in the report, which will be debated and fine-tuned in Stockholm, Sweden, late next month, said confidentiality agreements bar them from discussing the Intergovernmental Panel on Climate Change report in detail.

Kevin Trenberth, a distinguished scientist in the climate analysis section at NCAR and a review editor on the report, didn't strongly dispute a projected sea rise that could transform low-lying cities from New York to Shanghai.

"We can't really predict at that high end," Trenberth said. Three feet by 2100 is "generally not in the likely category. It's at the limits of ranges of what we can conceive."

Trenberth put about a 5 percent probability on seeing the high end of a 10 inch- to 3-feet rise by 2100. Such a surge, scientists believe, could possibly be triggered by an event such as a mammoth chunk of polar ice sheet melting and collapsing into the sea.

"I think it is likely we will get there" to a 3-foot rise, Trenberth said, "but a little later than 2100."

The IPCC, established in 1988 by the United Nations, issues scientists' comprehensive assessments on the risk of climate change every few years, the most recent in 2007, with the next due by 2014. It is divided into three so-called working groups, and it is Working Group I, charged with addressing the physical science basis of climate change, which will be hammering out its summary for policy makers next month in Stockholm.

The complete IPCC Fifth Assessment Synthesis Report, incorporating the work of 830 authors around the world in all three working groups, will be unveiled in October 2014 in Denmark.

In the 2007 report, IPCC scientists put the chances that human activity was warming the planet at 90 percent. The coming report reportedly places that probability higher.

A draft of the group's summary for policy makers, obtained by the New York Times, stated, "It is extremely likely that human influence on climate caused more than half of the observed increase in global average surface temperature from 1951 to 2010."

Gerald Meehl, a senior scientist at NCAR who authored the chapter on near-term climate change for the coming IPCC report, said, "It's obvious that the New York Times got a hold of the summary for policy makers.

"But how these things get portrayed, and the wording used to describe them, may change, to try to make it more clear. The caveat is that that's not the final version."

That was seconded by Trenberth -- who has attended the IPCC sessions in the past but won't be doing so this year.

"It's going to change a lot," he said. "How it gets said, and the wording, and what gets emphasized and what gets dismissed is decided by the government representatives. And there is usually a war of sorts that goes on in that room, between governments who are determined to have a clear and accurate report, and some governments who are trying to muddy the language and downgrade the language.

"For the 1990, '95 and 2001 reports, the main countries that were working to obfuscate and diminish the language were the OPEC countries, led by Saudi Arabia," Trenberth said. "And the 2007 report, the country with a strong delegation and strong objections was China, backed up by Saudi Arabia.

"There is supposed to be unanimous consensus. And that is very hard to achieve."

The struggle to reach consensus, Trenberth said, "is an interesting process, but it's a brutal process. The chair has to have an amazingly robust bladder."

Meehl said the presence at Stockholm of the dozens of scientists who have contributed to the assessment's 14 chapters helps guard against political considerations overriding the data. Each chapter, by this stage, has already been subjected to more than 1,000 readers' open-sourced comments -- each and every one of which the scientists are obligated to address.

"I've been involved in every one since 1990, and as we learn more about climate system and our modeling tools improve, the certainty with which we can say certain things increases generally," Meehl said. "But the general conclusions don't change too much from report to report -- which is a good thing. It's a very similar story (from report to report). We know more about it. We have more certainty. And we know more of the details."

Contact Camera Staff Writer Charlie Brennan at 303-473-1327 or brennanc@dailycamera.com.