The United States will pump $US3 billion ($A3.
3 billion) into a global climate fund, stepping up pressure on other nations such as Australia to follow suit.
US President Barack Obama used a speech on the sidelines of the G20 summit in Brisbane to make the announcement to contribute to the “global fight against climate change”.
“No nation is immune and every nation must play its part,” he said.
“We can get this done.”
The United Nations Green Climate Fund, was set up to support developing nations dealing with the impacts of climate change, such as rising seas, higher temperatures and extreme weather.
The US contribution is the biggest country pledge so far.
The UN will now have about $US6 billion of the $US10 billion it hopes to raise.
The announcement at the University of Queensland was made in an auditorium partly powered by a solar array.
It also comes just days after the US and China signed a pact to lower emissions out to 2030.
UN Secretary-General Ban Ki-moon earlier on Saturday urged G20 member countries to contribute to the fund.
Mr Obama used Australia as an example of what could happen if climate change wasn’t addressed, by pointing to risk to Great Barrier Reef and the prospect of longer droughts.
“Here in the Asia Pacific nobody has more at stake when it comes to thinking about and then acting on climate change,” he said.
“Here, a climate that increases in temperature will mean more extreme and frequent storms, more flooding, rising seas that submerge Pacific Islands.
“Here in Australia it means longer droughts, more wildfires. The incredible natural glory of the Great Barrier Reef is threatened.”
Mr Obama said the plan to cut carbon pollution in the US and reverse the course of China’s emissions was aimed at paving the way for a more ambitious deal in Paris next year when global leaders again meet.
“You’ve got to be able to overcome old divides, look squarely at the science and reach a strong global climate agreement next year,” he added.
“If China and the US can agree on this, then the world can agree on this – we can get this done and it is necessary for us to get it done.”
Australia, which holds the current G20 presidency, declined to put climate change on the official 2014 agenda.
This week lobby groups were clamouring for it to be included.
Prime Minister Tony Abbot has previously argued the G20 is an economic forum and there are other forums to discuss climate change.
However, the historic deal by China and the US has all but guaranteed it should be a G20 talking point at leaders’ meeting in Brisbane, which started on Saturday.
The federal government has maintained Australia’s commitment to reduce emissions by five per cent on 2000 levels by 2020.
It expects to address the post-2020 reduction target in the lead up to the Paris conference.
Labor called on the government to contribute to the fund but did not specify how much.
Deputy opposition leader Tanya Plibersek said it will mean developing countries won’t have to choose between economic development and climate change mitigation.
“Of course Australia should be part of this,” she told Sky News.
Ms Plibersek said it was “extraordinary” the prime minister highlighted the scrapping of the carbon tax as a coalition achievement to global leaders at a pre-summit meeting.
The Australian Greens said Mr Abbott had made “a fool of himself” boasting about the tax’s abolition shortly before President Obama’s speech.
While China and US had shown they would act, they said the government was taking Australia further from the rest of the world.
“This is more than an embarrassment, it is object of national shame,” Greens leader Christine Milne said.