The money would come from $1.2 billion assistance for international programmes, part of a 2010 budget currently pending U.S. Congress approval.
Prince Charles has championed the protection of tropical forests as a way to curb climate change and preserve wildlife, and wants funds to fill a policy vacuum before a new U.N. climate deal comes into force in 2013.
A climate summit in Copenhagen next month is expected to approve a new scheme whereby rich nations pay the developing world to protect tropical forests under a successor treaty to the existing Kyoto Protocol after 2012.
Funding has been a major stumbling block in faltering U.N. climate talks. At a ceremony in London U.S. Ambassador Louis Susman read out a letter, from senior Democrat Senator Patrick Leahy to Prince Charles pledging $275 million.
The funds would aim “to protect biodiversity and support sustainable landscapes in fiscal year 2010 … with a focus on protection of tropical forests”, a U.S. Embassy London spokesman confirmed. A lot of the money would go to the Amazon and Congo basins in South America and Africa, he added.
Destruction of tropical forests accounts for about 12 percent of global carbon emissions, scientists said this month, and paying countries to maintain their forests is considered one of the cheaper ways to fight global warming.
“Paying a relatively small amount to protect them is an absolute bargain,” said Greenpeace Executive Director John Sauven, welcoming the U.S. announcement.
The U.S. pledge follows an offer last week from Norway to pay Guyana up to $250 million by 2015, and which has illustrated the complexity of constructing such schemes.
Guyana’s forests have been far less logged than in many tropical nations, covering three-quarters of the country, and under the terms of the new deal with Norway, Guyana could actually be paid while chopping trees at a faster rate.
When asked whether Guyana will be allowed to increase deforestation under the agreement, Guyana’s President Bharrat Jagdeo said: “Basically yes,” speaking to reporters, campaigners and researchers in London late on Wednesday.
The memorandum states that Norway will compensate Guyana if it does not cut down more than 0.45 percent of its forests per year, but Guyana is felling trees at a far slower rate now.
“We are going to do some detailed work between now and October 2010 when we will know what that figure is … That may cause some adjustment,” said Jagdeo.