Copenhagen Summit:

Mr Miliband said politicians face a "huge challenge" to convince people that action on global warming should be a priority since much of the evidence is invisible.

He conceded that the row over leaked emails from scientists in East Anglia which appeared to suggest data making the case for man-made climate change was manipulated had been "damaging".

But he insisted that there was "as close to a scientific consensus as possible" that global warming is happening and is man-made.

"I think what's really important for politicians like me is that scientific debate is put in context – there is an overwhelming consensus among scientists and the science community that this is really happening," he told BBC Breakfast.

"I think it's partly because this is a threat that you cannot see or feel – it's not an army massing on our borders and people are focused on other things in their lives.

"There are also people who want to cast doubt on the science therefore it's not surprising that some people are not convinced.

"Therefore, we have to redouble our efforts, the scientific community has to redouble its efforts to persuade people.

"Frankly, it would be irresponsible for me to pretend anything other than what the scientists are telling me so I don't disagree that there's a long way to go to absolutely convince people of this but I think it's important that we do."

His comments came as Gordon Brown called on world leaders attending the Copenhagen climate change summit which starts today to enshrine in law the promises to cut emissions they make this week within six months.

The Prime Minister said the summit representing a "historical turning point" and called on all countries to reach for "high level ambition" in their intended cuts.

On the eve of the summit, the UN's chief climate negotiator Yvo de Boer said the talks were in excellent shape and many countries were now making pledges over curbing greenhouse gas emissions.

"Never in 17 years of climate negotiations have so many different countries made so many pledges. It's unprecedented," he said.

But others were less optimistic about how much difference pledged cuts – including those most recently announced by the US, China and India – will make.

Professor Kevin Anderson, the director of the Tyndall Centre for Climate Change Research at the University of Manchester, said current proposals were "little more than token gestures" compared to what scientists deem necessary to stay below dangerous levels of emissions.

According to the Met Office's Hadley Centre for Climate Prediction and Research, if global emissions peak in 2015 or 2016 and then declined by four per cent annually, there is a 50-50 chance that the rise in world temperature will be limited to 2C, avoiding the most severe sea level rises and temperature fluctuations.

“The statements by the US, China and India, allied with commitments from other nations, suggest peaking global emissions between 2020 and 2030 is about as hard as the economic and political orthodoxy is prepared to push in terms of emission reductions," Professor Anderson wrote in The Independent.

“If peaking global emissions between 2020 and 2030 is left unquestioned, the cumulative quantity of greenhouse gases emitted will be sufficient to put temperatures on a 4 degrees C or higher trajectory.”

Mr Obama has called for legislation cutting emissions by 17 per cent below 2005 levels by 2020, while China has pledged to cut its "carbon intensity", the measure of carbon dioxide emissions per unit of GDP, by 40 per cent to 45 per cent by 2020 compared to 2005 levels.

The EU has promised to cut C02 to 20 per cent below 1990 levels by 2020, while Britain has pledged to cut emissions by 34 per cent by 2020. Japan has pledged a 25 per cent cut by the same date and Norway has pledged a cut of 40 per cent.

Mr Brown has called on the 100 or so world leaders expected to attend the summit on the last day to give their promises at Copenhagen the full weight of international law within six months.

Writing in The Guardian, he highlighted the historic nature of the event, which some have described as the most important international gathering since the end of the Second World War.

"Sometimes history comes to turning points," he writes. "For all our sakes the turning point of 2009 must be real."

"Our aim is a comprehensive and global agreement which is then converted to an internationally legally binding treaty in no more than six months."

Mr Brown was the first world leader to confirm his attendance of the summit, but his record on environmental issues has came under attack as the summit began.

His former chief scientist Professor Sir David King said he frequently urged Downing Street to spend money on energy saving measures in order to create jobs and cut carbon – but was repeatedly ignored.

And in a separate interview with the Daily Telegraph, the world’s top environmental watchdog Achim Steiner, the head of the United Nations Environment Programme (UNEP), also said the Labour Government failed to “pick the low hanging fruit” of insulating homes and investing in renewable energy.

However Ed Miliband, the Energy and Climate Change Secretary, insisted Britain is taking action on global warming.

He said “our credibility abroad is based on our ambition at home” and announced £4 million to give 500 homes in Birmingham, London and Sunderland “complete energy makeovers”.