In an exclusive interview with the Observer, Miliband spoke out for the first time about last month's revelations that climate scientists had withheld and covered up information and the apology made by the influential UN climate body, the Intergovernmental Panel on Climate Change (IPCC), which admitted it had exaggerated claims about the melting of Himalayan glaciers.
But in the government's first high-level recognition of the growing pressure on public opinion, Miliband declared a "battle" against the "siren voices" who denied global warming was real or caused by humans, or that there was a need to cut carbon emissions to tackle it.
"It's right that there's rigour applied to all the reports about climate change, but I think it would be wrong that when a mistake is made it's somehow used to undermine the overwhelming picture that's there," he said.
"We know there's a physical effect of carbon dioxide in the atmosphere leading to higher temperatures, that's a question of physics; we know CO2 concentrations are at their highest for 6,000 years; we know there are observed increases in temperatures; and we know there are observed effects that point to the existence of human-made climate change. That's what the vast majority of scientists tell us."
Mistakes and attempts to hide contradictory data had to be seen in the light of the thousands of pages of evidence in the IPCC's four-volume report in 2007, said Miliband. The most recent accusation about the panel's work is that its chairman, Rajendra Pachauri, may have known before the Copenhagen summit that its assessment report had seriously exaggerated the rate of melting of the Himalayan glaciers.
However, Miliband was adamant that the IPCC was on the right track. "It's worth saying that no doubt when the next report comes out it will suggest there have been areas where things have been happening more dramatically than the 2007 report implied," he said.
The danger of climate scepticism was that it would undermine public support for unpopular decisions needed to curb carbon emissions, including the likelihood of higher energy bills for households, and issues such as the visual impact of wind turbines, said Miliband, who is also energy secretary.
If the UK did not invest in renewable, clean energy, it would lose jobs and investment to other countries, have less energy security because of the dependence on oil and gas imports and contribute to damaging temperature rises for future generations. "There are a whole variety of people who are sceptical, but who they are is less important than what they are saying, and what they are saying is profoundly dangerous," he said. "Everything we know about life is that we should obey the precautionary principle; to take what the sceptics say seriously would be a profound risk."
The Copenhagen conference in December ended with no formal agreement to make deep cuts in global emissions, or even set a timetable, but Miliband warned activists against "despair".
The UN conference was a "disappointment", he said, but there were important achievements, including the agreement by countries responsible for 80% of emissions to set domestic carbon targets by today. "There's a message for people who take these things seriously: don't mourn, organise," said Miliband, who has previously called for a Make Poverty History-style mass public campaign to pressure politicians into cutting emissions.
Lord Smith, the Environment Agency chairman, said: "The [Himalayan] glaciers may not melt by 2035, but they are melting and there's a serious problem that's going to affect substantial parts of Asia over the course of the next 100 or more years."