The world's most powerful economies urge "strong and effective action" on climate change, catapulting the issue up the G20 agenda in a new boost for campaigners after a surprising Sino-US breakthrough.

The grouping, which includes the world's worst greenhouse gas polluters -- the United States and China, also threw its support behind a United Nations fund aimed at helping poorer countries deal with the problem.

"We support strong and effective action to address climate change," G20 leaders said in a communique after weekend talks in Brisbane.

"We reaffirm our support for mobilising finance for adaptation and mitigation, such as the Green Climate Fund."

The G20 talks follow the breakthrough between China and the United States on curbing carbon emissions last week, and calls from US President Barack Obama and European leaders demanding action at the G20 on climate.

Australian host Prime Minister Tony Abbott had pushed economic issues to be the main thrust of the two-day talks, focussing on a push towards extra economic growth of 2.1 percent and creating jobs.

Abbott, who since coming to power a year ago has dismantled a carbon tax designed to combat climate change, had resisted some language on climate proposed for the G20 communique, with one European diplomat likening the negotiations to "trench warfare".

But he insisted that it "goes without saying that G20 leaders, all of us, support strong and effective action to address climate change".

"Our actions will support sustainable development, economic growth and certainty for business and investment and of course we will all work constructively towards the climate change conference in Paris next year," he told reporters.

- Climate change real -

In their declaration, G20 leaders said they aimed to support sustainable development, economic growth, and certainty for business and investment and would press for a post-Kyoto deal in the French capital in December next year.

The declaration also called on members to communicate their national contributions well in advance of this meeting, preferably by the first quarter of 2015 if possible.

"Australia has always believed that climate change is real, that humanity makes a contribution and that strong and effective action against it should be taken," Abbott said, adding his government was committed to reducing harmful emissions.

"I don't say that there weren't at different times discussions about what is the 'mot juste' but certainly it has been a very harmonious, constructive and collegial process."

Japan confirmed plans to give up to $1.5 billion to the UN-backed Green Climate Fund, joining a US pledge of $3 billion to mitigate the impact of global warming on poorer nations.

The GCF is designed as a way for wealthy countries to help poorer ones to become greener and to bolster their defences against the effects of climate change.

France and Germany have already pledged to contribute $1 billion each to the UN's new climate framework while world leaders have spoken repeatedly of climate change ahead of the G20 summit.

In Brisbane, UN Secretary General Ban Ki-moon labelled it "the defining issue of our times" while Obama said he wanted to halt global warming so his grandchildren could visit Australia's Great Barrier Reef "50 years from now".

Indian Prime Minister Narendra Modi added his voice to the calls for action, saying Sunday the damage humans had done to the planet over the centuries was heavy.

Campaigners, who had taken to the sweltering streets of Brisbane in vibrant protests during the week, said climate change had prevailed as a dominant economic agenda item for G20 leaders.

"Brisbane G20 may well become known as the 'de facto' climate change summit," said WWF-Australia chief Dermot O'Gorman, adding that Turkey had promised to make climate change a top priority when it hosts the group next year.