In his regular column, BBC environment analyst Roger Harrabin examines the claims by the chief economist at a major energy think-tank that it is virtually impossible to keep CO2 within "safe" limits.
It is virtually impossible for the world to keep within the CO2 limits defined as safe for the climate, according to the chief economist of the International Energy Agency think tank.
Dr Fatih Birol told an audience in London that key nations were not prepared to take the steps necessary to cut carbon growth.
He also applauded the UK's high fuel taxes, and warned that the shale gas revolution would put pressure on the development of renewable energy sources worldwide.
But it was his comments on climate change that seemed to cause the biggest buzz among the audience that packed a huge lecture theatre at Imperial College London
The world's governments at the recent climate conference in Cancun agreed that greenhouse gases should be kept within the limit associated by scientists with a 2C temperature rise.
But as progress in cutting emissions has crawled along in recent years that public position has looked like an increasingly unrealistic facade.
And there appeared widespread relief that Dr Birol said the unsayable - that peaking emissions by 2020 was virtually impossible, and that in those circumstances we could "kiss goodbye" to the 2C target.
"We would need to double decarbonisation efforts, then double them again to keep emissions (of CO2 and equivalent gases) within 450 parts per million," he said. "The bulk of the effort needs to take place in countries where climate change is not high on the policy agenda. We have to be realistic."
Dr Birol referred to the debate in Europe as to whether the EU would cut emissions by 20% or 30% by 2020 against 1990 levels. The difference between these two targets, he said, was equivalent to just two weeks of China's emissions.
He said the West could not blame China because per capita emissions and car ownership there were still comparatively very low and he urged the UK and EU continue with "climate leadership".
Dr Birol also warned that efforts to tackle climate change through renewable energy were under threat from the world revolution in unconventional gas sources. He said the shale gas boom in the US
has already led to a gas rush which had contributed to a 50% drop in investment in renewable energy.
And the US boom, he said, had a knock-on global effect. The fact that the US has suddenly found that it is independent in gas supplies means it doesn't have to import gas.
That means the nations gearing up to sell gas to the US have to find other markets, which is forcing down prices.
"There's suddenly much more gas available in the world than previously thought," he told BBC News.
"It's cheaper than it was and the supply is more assured. And it's only half as polluting as coal. There will be strong debates between energy and climate and finance ministries round the world about whether investment should continue to support renewables when the situation on gas has so radically changed."
This debate hasn't started in earnest in the UK but it surely will. Firms like Shell are already bidding to get carbon capture and storage on gas fired power stations treated to the same subsidies bestowed on renewables.
Ministers will be asked to explain why we should invest in expensive intermittent wind power if gas with the carbon captured can supply energy more reliably and possibly more cheaply.
End of an era
And the gas price may go cheaper still if purchasing nations succeed in de-coupling gas price rises from oil prices, in the way they have in the US.
Dr Birol also dipped his toe into another controversy - the UK's high road fuel taxes which have been criticised again by motoring groups now the global oil price is rising.
He told BBC News: "The policy of the UK government to have taxes on oil products is a very good one in order to slow down oil demand growth, improve energy efficiency and not to lead to wasteful use of oil production.
"At the same time the UK government needs to make a lot of investment in transport infrastructure with the proceeds of those taxes.
"If not next month, in the future we should be prepared to see higher oil prices. The age of cheap oil is over. If we don't take the necessary measures as consumers we should be prepared for the consequences of this. The way to get rid of this problem is moving quickly and radically from oil-based transport to electric cars."
Mr Birol also criticised emerging nations that are subsidising oil products for domestic consumers. "One of the reasons for the high oil price is that the huge subsidies of $150bn yearly to oil products which makes oil very cheap in China India and Middle East countries and gives an incentive to consumers to use oil in an inefficient manner."
The biggest fossil fuel subsidies are in Iran, Saudi Arabia, Russia, India and China. Governments say they are needed to help the poor.
But Dr Birol said: "According to our analysis, more than 85% of subsidies go to medium and high income levels because the bulk of the commercial energy services are used by richer people whereas poorer people use a very small amount of energy.
"The reality is that those countries are subsidising rich people rather than poor people."
He urged the G20 to press on with its stalled plans to phase our fossil fuel subsidies.