Brown said the upcoming summit had to mark a "decisive global shift" towards tackling the issue, amid fears about the outcome of the crunch talks.

Brown made the comments in a letter to Danish Prime Minister Lars Rasmussen and released by Downing Street, confirming his attendance at the UN gathering.

"I am committed to doing everything in my power to secure an agreement that marks the decisive global shift towards combating climate change," the prime minister said.

"I believe all leaders have a responsibility to come together at Copenhagen to do this. We cannot afford to fail."

Sixty-five world leaders have so far confirmed they will attend the summit, said Rasmussen earlier Sunday.

Hopes have been dashed in recent weeks that the December 7-18 talks will result in a binding agreement on cutting emissions and giving poor countries access to green technologies and to cope with the ravages of climate change.

Instead countries attending are set to push for a political deal to prepare the way for a binding pact next year to follow on from the Kyoto Protocol, which expires in 2012.

The European Union has vowed to reduce its own greenhouse gas emissions by 20 percent by 2020, raising the target to 30 percent in the event of an international agreement on the issue.

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