United Nations-backed climate-change science reports have largely passed their usefulness because they produce "unbelievably conservative" results and areas of uncertainty are wilfully distorted by corporate interests to avoid action on global warming, leading environmentalist David Suzuki says.
Dr Suzuki, who is visiting Australia, said the Intergovernmental Panel on Climate Change generates important information but "the enormous pollution of the communications sphere has rendered it far less effective" than at its inception almost a quarter of a century ago.
"The whole sector of public dialogue has been totally contaminated, deliberately, by the corporate sector," Dr Suzuki said. "The whole purpose is to sow confusion and doubt, and it's worked."
The IPCC is due to release the first of three working group reports for its Fifth Assessment this week. Leaked draft reports indicate scientists have agreed with 95 per cent certainty - up from 90 per cent in 2007 - that humans are responsible for more than half of the warming in the atmosphere.
Dr Suzuki said the IPCC's reliance on achieving consensus for each report meant the risks of increased extreme weather - from droughts to cyclones to bushfires for a country like Australia - are understated.
"The way these reports are made with input from all sides, they tend to be unbelievably conservative because they don't want to be accused of extremism and exaggeration," he said. "I think that's unfortunate."
UNSW's Professor Steve Sherwood, a contributing author to the latest IPCC report, said the UN process at least "gives a focal point for us to stop and talk about the science again".
Professor Sherwood, an expert in how clouds may behave on a warming planet, said the number of scientists willing to volunteer for IPCC work was up 20 per cent from the previous Assessment Report in 2007, despite reports of attacks on some scientists in the past for taking part.
"The idea that you can squash this by intimidating scientists - I think we've moved on from that idea," he said.
Dr Suzuki, meanwhile, said the early moves by the Abbott government to shut down debate about climate change - such as by closing the Climate Commission last week - should be worrying signs.
"We've done the same thing in Canada with a right-wing government (under Stephen Harper)," he said.
Mr Harper is "determined to shut down research, muzzle scientists, vet scientific reports so that they all get funnelled through the prime minister's office before they are released."
"This is the conservative agenda: shut down sources of credible information and then you run it on ideology," he said. "Certainly in the early stages of this new government, they seem hell-bent on following that agenda."
The New York Times at the weekend blasted the Harper government for making it harder in recent years "for publicly financed scientists to communicate with the public and with other scientists".
"The government is doing all it can to monitor and restrict the flow of scientific information, especially concerning research into climate change, fisheries and anything to do with the Alberta tarsands," the Times editorial board said.
Dr Suzuki, 77, said civil society had a responsibility to demand science be made public. Elders, in particular, had a role to play since they had paid for their lifetimes "with expensive lessons" that they should share.
"I'm urging elders all over the world get the hell off the golf course, get off the couch, this is the most important time in your life," he said. "Damn it all, get out there and speak and tell the truth."