A report from scientists which say they are 90% sure that humans are to blame for climate change is a "call to action," says David Miliband.
The environment secretary said there was a "global battle" ahead for the UK and other countries working together.
But the Tories said the government was not doing enough bring about the necessary "culture change".
And the Lib Dems urged Labour to back "green" taxes - and come up with policies rather than PR stunts.
The Intergovernmental Panel on Climate Change said temperatures were probably going to increase by 1.8-4C (3.2-7.2F) by the end of the century.
It also projected that sea levels were most likely to rise by 28-43cm, and global warming was likely to influence the intensity of tropical storms.
"Every country in the world [has] to sort out their own emissions," Mr Miliband said.
"That's why we're publishing a climate change bill, the world's first climate change bill that will set a path of emissions' reductions of 60 per cent for the UK by 2050."
IPCC PROJECTIONS
It was also important for nations to work together, he said.
"We need to make sure that countries like the United States and in the end China and India also play their part in this global battle against climate change."
Shadow environment secretary Peter Ainsworth said temperature changes would be "extremely significant".
"This report simply reinforces the need for urgent action.
"The science is clear - mankind is responsible for climate change. Now we must be responsible for preventing it."
'Culture change'
He said technology to tackle climate change already existed, but "a cultural change" was needed too, headed by the government.
The Conservatives want annual targets for emission reductions set.
Liberal Democrat environment spokesman Chris Huhne said the report was "a cautious and consensual statement of the overwhelming scientific evidence that we have to act quickly".
He warned of "disastrous consequences" if action is not taken immediately and urged Chancellor Gordon Brown to "make a serious effort to use the tax system to change people's behaviour. We need greener and fairer taxes, but not higher taxes overall."
His frontbench colleague, Sarah Teather, attacked the government for failing to match warm words on the environment with policies.
Commenting its decision to send copies of Al Gore's climate change film An Inconvenient Truth to schools, she said: "The sad fact is that policies seem to be a little too inconvenient for a government that has presided over rising carbon emissions and a fall in green taxes every year since they came to power."
Domestic emissions
Green Party MEP Jean Lambert warned that emissions from domestic houses could cause the UK to fail to meet targets.
She described government policies as "not robust enough".
Responding to the report, the UK government's chief scientific adviser, Professor Sir David King, said pressure was increasing on the US to sign an international agreement to combat climate change.
However, environmental group Greenpeace advocated action by individuals while longer-term alternatives to fossil fuels were introduced.
Friends of the Earth urged governments to act faster.
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