The pledge is directed to the Green Climate Fund, a financial institution created last year by the United Nations with headquarters in Incheon, South Korea. It comes ahead of a Nov. 20 climate meeting in Berlin, at which countries have been asked to make formal commitments to the fund.

In December, global climate negotiators will gather in Lima, Peru, to begin drafting the 2015 Paris accord.

The American contribution is meant to spur other countries to make similar pledges. Christiana Figueres, the executive secretary of the United Nations Framework Convention on Climate Change, has called for governments to create an initial fund of about $10 billion.

Even before Mr. Obama’s pledge, at least 10 countries, including France, Germany and South Korea, had pledged a total of around $3 billion to the fund. On Thursday, the Kyodo News Agency reported that Prime Minister Shinzo Abe of Japan would announce a contribution of about $1.5 billion at the Group of 20 meeting. The American contribution is expected to be the largest.

“The contribution by the U.S. will have a direct impact on mobilizing contributions from the other large economies,” said Hela Cheikhrouhou, executive director of the Green Climate Fund. “The other large economies — Japan, the U.K. — have been watching to see what the U.S. will do.”

David Waskow, an expert on climate change negotiations with the World Resources Institute, a research organization in Washington, said: “This continues the momentum and really builds on what they did with the announcement in China. I think we’ll now see a broader set of actors who are willing to make contributions.”

Money, and lots of it, is viewed as a crucial part of reaching a climate change deal in Paris in 2015. In particular, the world’s least developed economies insist that the world’s richest economies — which are also the largest greenhouse gas polluters — must commit to paying billions of dollars to help the world’s poorest adapt to the ravages of climate change.