Environmental campaigners on Saturday welcomed President Barack Obama's $3 billion pledge to a UN climate change mitigation fund, saying it confirmed global warming is now "front and center" of the world political agenda.
While climate experts conceded Republican opposition meant Obama could struggle to fulfill the vow, they said it added to momentum for change after an ambitious U.S.-China agreement on greenhouse gas emissions was unveiled earlier this week.
"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 center for the U.S., it's front and center for China, that means it's front and center for all of us. It's now up to all governments to build on these huge steps forward."
Obama is set to outline his pledge to the UN Green Climate Fund in a speech on Saturday in Brisbane on the sidelines of the G20 talks.
"To see the U.S. put $3 billion into the fund is further evidence that they're determined to see a global deal done by next year," said Tim Flannery of the Sydney-based Climate Council.
"It's a clear message to the world that the U.S. has moved on this issue and it expects the rest of the world to move."
UN Secretary General Ban Ki-moon, who will host talks in Paris next year aimed at reaching a global agreement, said he hoped other G20 leaders would contribute to the fund.
"The transition towards a low-carbon, climate-resilient future is accelerating," he told reporters.
"I urge other leaders and major economies, especially at the G20, to come forward with contributions that will sustain this momentum."
However, Republican James Inhofe, regarded as the chief climate change skeptic in the U.S. Congress, signaled Obama would struggle to get the funds through the legislature, particularly after recent mid-term elections.
"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," Inhofe said.
Flannery said there was no guarantee Inhofe's view would prevail on Capitol Hill.
"The Republicans are quite deeply divided, some of the Republican governors have been very strong proponents of clean energy technology, with Texas being one of the great examples," he said.
Michael Levi from the U.S.-based Council of Foreign Relations said the U.S.-China deal was a step forward but warned it amounted only to "incremental" change.
"I don't know if I'd use the term game changer," he said. "This constitutes progress, but when you're talking about climate policy the bar is often very low."