Gordon Brown has called for progress to be made on environmental legislation in order to avoid a "catastrophe".
Speaking at the Major Economies Forum in London, the prime minister said that the UK could face droughts, heatwaves and floods if world leaders do not agree to a deal.
He said that failure is not an option and that a "heavy price" will be paid if a new agreement is not achieved.
"Once the damage from unchecked emissions growth is done, no retrospective global agreement, in some future period, can undo that choice," Mr Brown said.
The prime minister made his comments ahead of the UN Climate Change Conference in Copenhagen, which is due to take place between December 7th and 18th.
It will be the 15th session of its kind to be held within the United Nations Framework Convention on Climate Change.
Emissions from the event will be offset by a climate change project in Bangladesh, which the organisers say will effectively make the event "climate neutral".
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