The surprise revelation that the United States would contribute $US3 billion to a global climate change fund appears to have been designed to increase pressure on Australia to take the issue more seriously, says a board member of the fund.

Hours before the President was due to address the G20 meetings in Brisbane – where Australia has sought to keep climate change from the agenda – news broke that the US would contribute $US3 billion to the Green Climate Fund, a global initiative to provide money to developing nations to ameliorate the impact of climate change and reduce emissions.

"It's pretty clear that the timing of this is meant to put some pressure on the Australian government," said Brandon Wu, who is one of two observer members of the board of the Green Climate Fund, and is a senior policy analyst with ActionAid USA, based in Washington, DC.

An administration official has confirmed the contribution to Fairfax Media.

"We want to encourage all major countries to contribute to the GCF in accordance with their resources, not just the traditional donors," she said.

"As the US and China showed earlier this week, we need to reach across traditional divides to tackle climate change, and that includes providing support to the poorest and most vulnerable."

The news comes days after the announcement of a historic agreement between China and the US to curb their greenhouse gas emissions.

Peter Ogden, a former director of climate change policy for President Obama, told Fairfax Media: "This is what happens when a leader wants to elevate climate change and put it on top of the agenda, and it is not a good time for a leader who wants to keep it off the agenda."

He said it seemed clear that President Obama saw a chance to take significant action during his meeting with China's President, Xi Jinping, and grabbed it, and decided to keep the momentum going at the G20 meetings.

Next week, an international pledging conference for the fund will be held in Berlin. Until the US' contribution, it had received pledges of only $US3 billion out of its slated $US10 billion.

So far, France and Germany have pledged $US1 billion each to the fund and there is speculation Britain is set to pledge the same amount. Japan has made an unofficial pledge of $US1 to 1.5 billion.

Next year, world leaders will meet in Paris in an effort to set a legally binding agreement on climate change.

Mr Ogden believes that this week's actions by both the US and China will increase pressure on the international community to make serious commitments.

"It is significant that the world's two largest economies and two largest emitters have declared they believe they can prosper in a low carbon environment," he said.

Mr Wu said the agreement made it harder for governments or political parties to use the excuse that action on climate change was pointless without China's involvement.

He said the two decisions were extremely significant, but warned they were only a first step. Developing nations would need billions more to cope with coming climate changes, and far broader international agreements would need to be made – and met – to avoid climate change of more than two degrees, he said.

Tony Abbott is known internationally for his scepticism of climate change science and his enthusiastic support of the coal industry.

Before his visit to the US earlier this year, Mr Abbott pointedly stopped in Canada where he and the Canadian Prime Minister, Stephen Harper, agreed not to introduce climate change policies that would harm their economies.

Some Republicans have already criticised President Obama for the pledge, including Senator Jim Inhofe, who said: "The president's climate change agenda has only siphoned precious taxpayer dollars away from the real problems facing the American people".

Senator Inhofe is the author of The Greatest Hoax: How Global Warming Conspiracy Threatens Your Future and is set to become the chairman of the Senate Environment and Public Works Committee.