Branson announced the 25-million-dollar Earth Challenge prize at a joint press conference with Gore, who has turned into to a global environment campaigner after losing presidential elections in 2000.

"The Earth cannot wait 60 years," Branson said. "I want a future for my children and my children's children. The clock is ticking."

It is not the first time Gore and Branson have teamed up to promote green issues: last September Gore backed Branson's pledge to spend three billion dollars (2.3 billion euros) on reversing global warming.

The former vice-president, who brought global warming to prominence in his documentary film "An Inconvenient Truth", told the Virgin boss at the time that he was in a unique position to make a difference.

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