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World leaders may pay a heavy price in history if they fail to tackle global warming, Tony Blair has warned.

He said politicians did not have to wait for chaotic climate change in order for them to act.

The risks of not cutting emissions, given the potentially massive consequences, was enough to justify action, he told ´óÏó´«Ã½ Radio 4.

The former prime minister added that it had always been a struggle to explain the uncertainties in climate science.

He told Radio 4's Uncertain Climate documentary: "It's very hard to say 'this is the precise warming there's going to be, this is the maximum amount you can allow this (emissions) to continue'."

He took advice while in 10 Downing Street from the government chief scientist at the time, Professor David King and the President of the Royal Society, Lord May.

"They were very rightly and properly saying there's areas of uncertainty here but if you want a judgement from us as government scientists, then our judgement is this is a serious problem that needs global action to deal with it," he added.

"I was never in the situation of total certainty here and indeed I always used to say to the NGO people (pressure groups) and others (to) be careful you don't end up in a situation where you are claiming that something is certain when it isn't absolutely certain.

"But it doesn't need to be certain for us to act. It just needs to be likely, probable or actually even - if you look at the consequences possible because if you find out 2030 or 2040 'that was a real problem, we should have dealt with that', you're going to pay a pretty heavy price in history."

In the first part of the documentary, broadcast last week, Mr Blair said he did not agree with Gordon Brown or Ed Miliband who called climate sceptics "flat earthers" and "deniers".

He said these were the wrong terms as the science contained uncertainties. He said it was far better to express the issue as one of risk.

The documentary points out that under Mr Blair's tenure as prime minister, emissions in the UK actually rose if embedded emissions from goods imported into the UK were included in the national figures.

The second part of Uncertain Climate will be broadcast on ´óÏó´«Ã½ Radio 4 on Monday, 6 September 2010 at 0900 BST and 2130 BST