In a letter to a coalition of green groups, Gordon Brown said "all developed countries" needed to commit to reduce emissions to tackle the problem.
"Climate change poses the most urgent challenge to humankind – a challenge that threatens not only the environment, but international peace, security, prosperity and development," agencies quoted the letter as saying.
It came ahead of a key week of talks in Washington and at the United Nations on developing a new international treaty to succeed the Kyoto Protocol in 2012.
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