One of the UK's best known entrepreneurs, Sir Richard made the announcement in New York on the second day of the Clinton Global Initiative, an annual conference hosted by former US President Bill Clinton.

Sir Richard, 56, said that transport and energy companies "must be at the forefront of developing environmentally friendly business strategies".

Planes and trains

Sir Richard recently launched a new Virgin Fuels business, which will invest up to $400m in green energy projects.

It has already announced its backing for a California firm, Cilion which plans to make bio ethanol from corn.

Friends of the Earth broadly welcomed Sir Richard's announcement, but the environmental pressure group warned that the continued fast growth in air travel could not be maintained "without causing climatic disaster".

Worth an estimated £3bn, Sir Richard started his career in the record industry before moving into everything from mobile phones to credit cards.

He established his main airline Virgin Atlantic in 1984, starting services between London and New York.

He also owns two low-cost airlines, Virgin Express in Europe and Virgin Blue in Australia.

His Virgin Group owns a 51% stake in UK train company Virgin Trains.

This firm operates the UK's West Coast Main Line franchise between London and the west of Scotland, and the cross country franchise between the south west of England and Scotland.

Major donations

Mr Branson's investment pledge comes after US billionaire investor Warren Buffett announced in June that he was donating $37bn to charity.

Mr Buffett gave the money to the charitable foundation run by Microsoft founder Bill Gates, which works to reduce global poverty and improve health and access to education.

Mr Gates himself said in July that the charity, the Bill and Melinda Gates Foundation, was pledging $287m in a bid to speed-up the development of a vaccine for the HIV/Aids virus.

Sir Richard has previously given money to educational charities in Africa.