Mr Rudd is in New York for the opening of the United Nations General Assembly, which comes as the world wrestles with some of the most difficult issues in 50 years: a global recession, a new climate change treaty, restarting Middle East peace talks and renewed nuclear threats.

The UN meeting will be followed later this week by a meeting of the G20 in Pittsburgh, which will review the progress made in combating the financial crisis as well as how to finance poorer countries' efforts to tackle climate change.

For the early part of the week, Mr Rudd will entreat fellow leaders to inject urgency into climate negotiations.

"There is a danger, speaking absolutely frankly, that options for final decision at Copenhagen are left too late because we are now less than 80 days away," he said. "There are big decisions to be made on targets for developed countries and verifiable commitments for developing countries all of which bring down greenhouse gas emissions - and also how that is made possible financially, as well as the technologies."

Mr Rudd has been asked by UN Secretary-General Ban Ki-moon to chair a round table at the climate talks - which recognises the contribution Australia has made to the global effort to strike a deal.

But there is scepticism about what the UN Summit on Climate can achieve.

"I think it's unrealistic to expect a concrete, immediate outcome on targets and commitments and the other elements of the package this week … [But] we do need building blocks along the road, otherwise you get to that last point, Copenhagen, and the wall is too high to scale," he warned.

Mr Rudd will stress that the impact of climate change is real and is being felt now.

He will point to Australia's experience with the Murray-Darling basin and the plight of Pacific nations feeling the effects of rising sea levels.