The UK faces a "catastrophe" of floods, droughts and killer heatwaves if world leaders fail to agree a deal on climate change, the prime minister has warned.
He told the Major Economies Forum in London, which brings together 17 of the world's biggest greenhouse gas-emitting countries, there was "no plan B".
World delegations meet in Copenhagen in December for talks on a new treaty.
The United Nations (UN) summit will aim to establish a deal to replace the 1997 Kyoto treaty as its targets for reducing emissions only apply to a small number of countries and expire in 2012.
Mr Brown warned that negotiators were not reaching agreement quickly enough and said it was a "profound moment" for the world involving "momentous choice".Read it all if you want.