Barack Obama has surprised policy watchers by announcing a $3bn US contribution to an international effort to help poor countries deal with climate change.
The contribution doubles what other countries have previously pledged ahead of a 20 November deadline and would be the second major move on climate change taken by the President in a week following a landmark climate deal with China struck on Wednesday.
An administration official broke the news earlier today but Obama is expected to announce the pledge at this weekend's meeting of G-20 industrial nations in Australia. The US will join other countries including Mexico, South Korea, Germany, France and Japan in pledging to the fund.
The fund is the result of a pledge in 2009 by rich countries to mobilise $100bn a year by 2020 to help developing countries tackle climate emissions and respond to the damage that it causes.
The fund is designed to complement private sector investment and help spur global markets in clean energy technologies, creating opportunities for entrepreneurs and manufacturers.
In the run-up to the major global climate talks being held in Paris next year, developing nations view finance as a vital part of any deal. Hela Cheikhrouhou, executive director of the fund, lauded the US pledge as a game-changer. "It could have a domino effect on all other contributions," she said.
Germany and France have already pledged $1bn each, and Mexico, South Korea, Japan and others have pledged smaller amounts, so the US pledge roughly doubles the $3bn already promised for the fund, which will hold a first donors' meeting in Berlin next Thursday.
The UN has set an informal goal of raising $10bn for the fund before a meeting of environment ministers in Peru next month. Developing nations have been urging $15bn.
Earlier this week Obama also announced a climate agreement with China, which will see the US strive to cut total greenhouse emissions by about 25 per cent by 2025, while China, whose greenhouse gas emissions are still rising, will aim for a peak in greenhouse gas emissions by 2030.
But both pledges follow big Democratic losses in last week's mid-term elections, which may make the deals largely symbolic as they will have to win support from the now Republican-dominated congress.