The Abbott government has been backed into a corner on climate change after US President Barack Obama firmly put the issue back on the G20 agenda.
Action on climate change was a major talking point on day one of the Brisbane leaders' summit, despite government efforts to keep the focus on economic growth and jobs.
After striking a bold deal with China to slash emissions, Mr Obama stole the limelight on Saturday when he urged developed nations to do their bit in the "global fight" against climate change.
"No nation is immune and every nation must play its part," he said.
In a direct appeal to Australia, which holds the 2014 G20 presidency, the president warned natural wonders like the Great Barrier Reef were under threat and urgent action was needed from all.
"I want my daughters to be able to come back and I want them to be able to bring their daughters or sons to visit," he told an audience at the University of Queensland to much applause.
"And I want that there 50 years from now."
He announced the US would give $US3 billion ($A3.3 billion) to the United Nations' Green Climate Fund to help poorer countries deal with the impacts of climate change, such as rising seas, higher temperatures and extreme weather.
The UN will now have about $US6 billion of the $US10 billion it hopes to raise.
Japan is also expected to unveil a $US1.5 billion contribution to the fund over the G20 summit weekend.
Civil society groups working on the G20 sidelines are urging Australia to make its own contribution, which could amount to $200 million in line with past injections to similar funds.
A number of G20 members - including the US and European Union - had criticised the government for refusing to put climate change on the formal agenda.
But it appears under pressure the government has backed down on the eve of the main G20 leaders' event.
UN secretary general Ban Ki-moon said G20 leaders would make a strong commitment to climate over the weekend.
"It's my understanding ... that they are actively discussing the issue of a climate change," he said.
"Of course climate change is the defining issue of our times, therefore it's only natural that G20 leaders should focus much more on this."
Climate change was not mentioned during Prime Minister Tony Abbott's opening address to G20 leaders on Saturday.
Labor leader Bill Shorten said Mr Abbott's focus on domestic politics before a global audience was "weird" and lamented his lack of attention on climate.
"Australia cannot afford to be left behind," he said in Brisbane.
"We would just ask the prime minister of Australia to be a modern leader and not one looking at the past."
The president's move also comes after the historic US and China deal to cut carbon dioxide emissions out to 2030.
"If China and the US can agree on this, then the world can agree on this - we can get this done," he said.
