Environment Secretary David Miliband says the government must do more to beat climate change.
Mr Miliband faced vehement criticism from other panellists
Speaking at the Hay Festival in Powys, he said there would have to be a bigger change "than has happened in the last 10 years" to meet the threat.
It was the closest that the man many see as a future Labour leader came to criticising the record of outgoing Prime Minister Tony Blair.
The minister spent the rest of the time defending his government's actions.
There was vehement criticism from the two other panellists, environmental authors Jeremy Leggett and Mark Lynas.
Mr Milliband said the UK was on course to deliver cuts in greenhouse gas emissions, including carbon dioxide, that were double what the Kyoto protocol had demanded.
No other government in the world could claim that, he said: "For the first time we have broken the link between strong economic growth and carbon."
However, the claim was strongly denied by Mark Lynas, author of Six Degrees, Our Future on a Hotter Planet.
Mr Lynas said that progress begun under the previous Conservative administration - when the country was moved off coal and into cleaner gas - had helped New Labour look better than it was.
He said: "Carbon emissions have been going up since 1997. The Conservatives reduced emissions massively by taking the miners out of business, so don't take credit for that!"
Mr Lynas said there were only eight years left to make massive global cuts in carbon dioxide emissions if a disastrous increase in temperatures was to be avoided.
"So how can you allow this runaway expansion in aviation?" he asked.
The minister pointed out that Chancellor Gordon Brown had doubled air passenger duty.
There was strong criticism of the government's alleged reluctance to support new forms of cleaner energy.
Mr Leggett, who also runs a solar panel company, said last week's energy white paper was a "fig-leaf for the nuclear industry" and "replete with consultation and light on policy".
Mr Miliband defended his government's renewed interest in nuclear power by saying that if reactors were not replaced in the coming years the resulting energy gap would mean we would turn instead to carbon rich fuels like coal and gas.
'Time running out'
He also denied nuclear energy would suck public money away from renewable clean energy, saying, "by 2010 we'll be spending one billion pounds on renewables".
However, there was much laughter when Mr Lynas said he had calculated that at present levels of government grants, it would take 76,000 years for every house in Britain to have a solar panel.
There was agreement on hardly anything. Mr Miliband appeared reluctant to respond to invitations to say there would be big changes on the environment when Mr Brown becomes PM shortly.
Both Mr Leggett and Mr Lynas said that with time running out so quickly for the planet, courageous political leadership was vital, and there was still no sign of it.