Quality not quantity … climate scientist Professor Kevin Trenberth. Photo: Sahlan Hayes

AS THE world’s elite global warming experts began poring over the drafts of the latest Intergovernmental Panel on Climate Change report this week, one leading scientist believes the process shouldn’t be happening at all.

”I think it will be less successful than the last assessment, and I think it will be blander – I’m disappointed in what I’ve seen so far,” said Kevin Trenberth, the head of the climate analysis section at the US National Centre for Atmospheric Research.

Professor Trenberth’s misgivings are not based on doubts about the strength of the science underpinning human-induced climate change but on frustration with the bureaucratic nature of the IPCC’s work.

Dozens of Australian scientists are among hundreds of international experts who started reviewing the IPCC’s fifth summary report this week, with the final version to be published next September. The previous IPCC report, released in 2007, declared global warming ”unequivocal” and said it was ”very likely” it was driven by human emissions of greenhouse gases.

But Professor Trenberth believes too many researchers and too much ”second tier” science are diluting the report’s quality, and science is jumping far ahead of the lumbering process.

”There are more people, it’s more diffuse, it’s harder to gain a consensus – quite frankly I find the whole process very depressing,” he said. ”The science is solid, but with a larger group it’s harder to reach a consensus, and updates every six years are just too slow. After the fifth assessment, we should push on with a different format.”

Two other scientists involved with the IPCC process, who asked to remain anonymous, said the coming report contained improvements on the previous edition but few ”breakthroughs” would be included. ”What you are dealing with is some superb work, and some that’s not so relevant or current, but the process makes it difficult to weight these appropriately,” one said.

Professor Trenberth is a bruised survivor of the ”climategate” scandal, which involved the theft and publication of thousands of emails that had been sent between some of the world’s most influential climate researchers. While he and his colleagues were cleared by investigations, the people who hacked the email system at Britain’s University of East Anglia have never been caught.

Professor Trenberth believes it had a big impact on public debates about climate science.

”It made an immense difference – the level of vitriol and hate we received,” he said. ”Not only do we have waves of attacks when we publish and it ends up on a denialist website but it has affected politicians.”

He believes some specific uncertainties in some of the climate change models scientists rely upon is being falsely inflated as a general uncertainty about the status of climate change science. ”With the links between weather and climate, for instance – we know they are there, but the specific numbers need work,” Professor Trenberth said.

”Human influences are overlaid on normal ranges of weather extremes. There’s more precipitation, and the rain’s a bit harder. There is more heat and water over the oceans. The question is how much is a ‘bit’.

”An example would be Hurricane Katrina in New Orleans, where there was about 11 inches [28 centimetres] of rain. About one inch of that was due to human influence. Maybe that extra inch was enough to cause the levee to break.”