Speaking in Melbourne, Mr Gore rejected pessimism about negotiations on a climate deal due in Copenhagen in December, saying "the glass is very definitely half-full".

Mr Gore, who sparked widespread concern about climate change with his 2006 film An Inconvenient Truth, said there were striking similarities between the debates about emissions trading and greenhouse reduction targets in Australia and the US.

"I say at home that the legislation pending in my country is not what I would have written - I would have written it as a stronger bill - but I am realistic about what can be accomplished within the political system as it is."

He said a failure of the 1997 Kyoto Protocol to limit emissions was that the US and Australia did not ratify it.

"Now, with new leadership in both the United States and Australia, our two countries are providing leadership. When that leadership is most needed is in the run-up to Copenhagen. It can make a huge difference."

Mr Gore's comments follow Coalition emissions trading spokesman Andrew Robb strengthening his opposition to passing the Government's bill this year after a fact-finding trip to the US.

He said the Australian proposal offered less assistance to business than the US bill that last month passed its House of Representatives - a point disputed by the Government and some green groups.

The Greens are also opposed to the Government's bill, which is due to return to the Senate next month. They say targets of cutting emissions 5-25 per cent below 2000 levels by 2020 do not go far enough.

Family First senator Steve Fielding, a climate change sceptic, will today write to all senators asking them to consider whether temperatures have risen over the past 15 years before deciding how to vote.

Mr Gore's comment came in a break from training 300 activists from across Asia and the Pacific in ways to influence the climate debate.