A Sino-US breakthrough on curbing carbon emissions proves a global deal on climate change is achievable, US President Barack Obama said Saturday, as campaigners hailed new vibrancy in long-stalled talks.

Announcing a $3 billion contribution to a UN-backed climate change mitigation fund, the American leader said the China-US deal unveiled earlier this week showed the way forward.

"If China and the US can agree on this, then the world can agree on this -- we can get this done," he said in a speech on the sidelines of the G20 summit in Brisbane.

The UN and green campaigners welcomed the funding pledge, saying it confirmed global warming was now central to the world's political agenda following the surprise deal between Washington and Beijing to reduce their greenhouse emissions.

Climate experts conceded that Republican opposition may see Obama struggle to fulfil his $3 billion commitment, but said he was fuelling momentum for change in an area where talks have faltered since the historic Kyoto Protocol of 1997.

"You can sense the energy lifting in this critical conversation across the planet -- the game has changed," Greenpeace Australia chief executive David Ritter told AFP.

"A global deal has become more likely, no question. Climate is now front and centre for the US, it's front and centre for China, that means it's front and centre for all of us."

- 'Leapfrog' dirty development -

Obama outlined his pledge to the Green Climate Fund (GCF) at the University of Queensland, drawing applause when he told the audience he wanted to ensure his grandchildren could visit Australia's famed Great Barrier Reef "50 years from now".

He said the fund would help developing nations cope with climate-related issues such as rising seas while also backing environmentally friendly infrastructure projects.

"(It will) let them leapfrog some of the dirty industries that powered our development and go straight to a clean-energy economy," he said.

It was the American leader's most upbeat assessment about climate change since he was elected in 2008 promising to tackle the issue, only to see it relegated amid partisan bickering and economic woes.

His stance stymied efforts by G20 host Tony Abbott -- who questions the science of man-made global warming -- to reduce the issue to the margins of the Brisbane summit and emphasise economic growth.

Despite Prime Minister Abbott's reluctance, climate change appears set to be mentioned in the G20 leaders' final communique on Sunday, a concession to US and European pressure that was described as a "victory" by a French diplomatic source.

World Vision chief Tim Costello said Abbott was "like King Canute, trying to send back the tide of climate change when other leaders are saying this has to be discussed".

UN Secretary General Ban Ki-moon used the Brisbane meeting to call on other G20 leaders to contribute to the GCF, labelling climate change "the defining issue of our times".

"The transition towards a low-carbon, climate-resilient future is accelerating," said the UN leader, who will host talks in Paris in December next year aimed at reaching a global agreement to succeed Kyoto.

- 'Clear message' -

The GCF is designed to help poorer countries invest in green technologies and build up their defences against rising sea levels and increasingly extreme weather patterns.

UN climate chief Christiana Figueres said the US donation was timely, given the fund will hold a donors' meeting in Berlin next Thursday.

"(It) sets a new benchmark for GCF support and provides inspiration for other developed countries to act," she said.

Figueres has set the GCF a $10 billon target for the end of the year and Obama's pledge doubles existing commitments to $6 billion.

France and Germany have already promised $1 billion each, with Japan reportedly set to announce a $1.5 billion donation in Brisbane.

But Republican James Inhofe, an outspoken climate change sceptic in the US Congress, signalled he will fight to block the GCF funds following recent mid-term elections which left Obama facing lame-duck status in his final two years.

"President Obama's pledge to give unelected bureaucrats at the UN $3 billion for climate change initiatives is an unfortunate decision to not listen to voters in this most recent election cycle," Senator Inhofe said.