Britain is seeking international agreement on a global target for stabilisation of greenhouse gases, which would halt the progress of global warming, Tony Blair has told The Independent.
The radical measure would be a major leap forward from the Kyoto agreement and the biggest step yet in the fight to combat climate change.
The Prime Minister outlined his move in a wide-ranging interview, arguing a staunch defence of his Government's record in tackling the issue of global warming and repeating his assertion that climate change was the greatest long-term threat to the world.
"We're sometimes attacked as being back-markers here, but nowhere in the rest of the world sees us like that.
"Of course we've got to do more, but we have achieved a lot. The difference between being a politician responsible for taking decisions, and a pressure group that puts pressure on those who take the decisions, is that the pressure group can put forward maximum demands, but the politician who actually takes the decision has got to balance competing demands."
Mr Blair dismissed criticism of his opposition to annual targets to cut British carbon emissions as "posturing, not practical politics".
He also implicitly ruled out aviation taxes, another measure favoured by the green lobby, insisting that a much better way forward was to deal with aircraft emissions under the European Union's emissions trading scheme.
The Prime Minister, on a visit to the nuclear plant at Sellafield in Cumbria, launched a defence of his position on nuclear power.
He said: "There is a decision we now have to take, as to whether we're going to replace our nuclear power stations and develop a new generation of nuclear power. I believe we should. I've given my view that if we want to deal with energy security and climate change, we've got to have the right policy for the future, and it's got to include nuclear."
Mr Blair also revealed that Britain would seek agreements to make future EU coal-fired power stations carbon neutral through improved technology.
And he hinted that a planned Energy White Paper would address the issue of personal carbon allowances - the idea that each individual would have a carbon "budget" to spend on motor fuel, electricity and other activities that impact on the environment. The move has already been floated by David Miliband, the Environment Secretary.
But the measure that will be most welcomed by green campaigners is likely to be the proposal to set a global target for stabilisation of greenhouse gases.
If set by the leading nations of the world, such a target - meaning the point beyond which concentrations of carbon dioxide and other gases would not be allowed to grow - would be a decisive move, and the biggest step forward yet in the fight to combat climate change.
Mr Blair is hoping that agreement on the principle of a global goal can be agreed next spring by the G8 group of rich nations, currently the world's biggest CO2 emitters, in partnership with the five big developing countries, led by China, which will soon be emitting even more. China is likely to overtake the US as the biggest CO2 emitter by 2010.
At the G8 summit in Gleneagles in Scotland last year, Mr Blair persuaded the developing nations to talk about their emissions for the first time. If the Chinese - plus the Indians, Brazilians, Mexicans and South Africans - can be persuaded to sign up to a target, the Prime Minister hopes the US may sign too, and thus end its hugely damaging isolation from the main climate change policy process which has lasted since George Bush withdrew the US from the Kyoto protocol in 2001.
Although Kyoto set out a series of targets for nations to cut back their own greenhouse gas emissions, no one has yet agreed on aiming for a target the other way round - for stabilisation of the total amount of CO2 going into the atmosphere.
This is much more important, and if agreed, would offer governments and business all over the world the clearest possible signal of exactly what needed to be done.
At present the atmospheric CO2 level is about 382 parts per million by volume (ppm), and rising at more than 2ppm annually. When all the other greenhouse gases such as methane and nitrous oxide are included, and expressed in CO2 terms, the figure is about 430ppm. This is known as "carbon dioxide equivalent", or CO2e.
The target Mr Blair and his officials have in mind would seek to halt the growth of greenhouse gases somewhere below 550ppm CO2e, perhaps between 500 and 550 - the figures are still being discussed, but 550 is regarded as the upper limit.
It would involve legally binding cutback agreements from those who signed up to it, and has been put forward by the UK to be taken on during the German presidency of the G8 next spring. The initiative - which has German support - would offer a major way forward for when Kyoto comes to an end in 2012.
On the vexed question of compulsory annual emissions reductions, highlighted by The Independent earlier this week, Mr Blair said: "Look, the plain fact of the matter is, the reason why Kyoto and the European Trading System went for targets over longer periods, over five-year periods, is because even changes in weather or changes in fuel price can make a huge difference to whether you can meet an annual target or not, and it ís just too inflexible."
There was a difference between "practical politics, and posturing," he said. "The difference between serious policy-making and non-serious policy-making in this area is the difference between people who think they might actually have to implement the decision, and people who don't.
"The cold weather in 2001 produced a variation of, I think, an additional 3 per cent in CO2 emissions. If you had a binding target to reduce CO2 emissions by 3 per cent, you could find you were suddenly being asked to put up fuel duty massively. Governments aren't going to be doing that. So you've got to have sufficient flexibility built into your system, and targets over a longer run."
On the question of what should be done about the rapidly rising CO2 emissions from aviation, he struck a similar note: "Put it [aviation] in the European Emissions Trading System, that's the single most important thing you could do. But the danger - again it's the difference between practical politics and posturing - is that if we prevented people in Britain taking cheap flights, but people in Europe were still able to do it, you wouldn't make a great deal of difference except you'd make travel a lot harder for low-income families." Britain was pushing hard for aviation to be included in the ETS, he said.
But what Britain would be doing, he said, was to help people to come to terms with their own personal "carbon footprint" through measures in the forthcoming Energy White Paper. "I think the idea of saying to people, look, you can actually measure you own impact and do something about it, the idea of carbon budget, is very powerful," he said. "One of the things we will come out with in the Energy White Paper is how your ordinary citizen, each of us in our own way, make a difference."
Asked if he was talking about personal carbon allowances, he said: "We're looking at all those things for the purpose of the White Paper, but you'll have to wait until it comes out."
His hint will be widely welcomed by environmentalists. But another part of what he said will have many of them grinding their teeth. Despite fully sharing their belief in the seriousness of the climate threat, Mr Blair parts company with the likes of Greenpeace and Friends of the Earth over what he sees as a key part of the solution, and they do not - nuclear power.
Asked if he accepted that there were public fears about nuclear power, he said: "Yes, there are public fears, but they're often generated less by knowledge than by people saying well, if something has got the word 'nuclear' in it, then there must be a problem."
On the issue of nuclear waste he was equally unapologetic. (The Government has announced that Britain's long-term nuclear waste store will be deep underground, but only located in a community that volunteers to take it. It may yet be decades away.)
He was asked: "What do you say to people who say, you're creating more nuclear waste with a new generation of nuclear power stations, when we still don't have a site for disposal of the waste that's been created over the last 50 years?"
Mr Blair replied: "Well, we're going to have to get that site, in any event, and we said that's best done by people volunteering. And the new nuclear power stations generate about a tenth of the waste [of the old ones] - but in any event we're going to have to find storage for that.
"But when you actually go into the details of the science of that storage, some of the fears that are raised seem to me at any rate to be completely exaggerated."
Few would deny that Mr Blair has done more than any other world leader to raise the profile of the climate change issue on the international agenda, and - especially if the greenhouse gas stabilisation target can be achieved, or even initiated, on his watch, that will be seen as a major part of his political legacy. However, he dismissed the idea of a legacy and declined to use the personal pronoun, contenting himself with saying: "I think what we have done on climate is important."
He was then asked if he might consider continuing to work on the climate issue after he leaves office, perhaps for the UN. He said: "I don't know. I will retain a strong interest in it because I believe passionately in it. As I've said, it is the greatest long-term threat that faces the world. But I tend not to answer questions about what I'll do afterwards, because I'm not in afterwards - yet."
The PM's policies
Kyoto, Mark II: PM is seeking international deal to limit global greenhouse gas emissions
Aviation taxes: Blair believes it is better to deal with plane emissions on a Europe-wide scale
Cleaner coal: PM wants all new EU coal-fired power stations to be carbon neutral
Personal responsibility: A White Paper may address individuals' carbon allowances