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Branson has said he hoped the prize would spur innovative and creative thought to save mankind from self-destruction.

"Man created the problem and therefore man should solve the problem," he told a news conference to reveal the Virgin Earth Challenge.

"Unless we can devise a way of removing CO2 (carbon dioxide) from the earth's atmosphere we will lose half of all species on earth, all the coral reefs, 100 million people will be displaced, farmlands will become deserts and rain forests wastelands."

Branson rejected suggestions that he, as an airline owner, was being hypocritical in announcing the prize.

"I could ground my airline today, but British Airways would simply take its place," he said, noting that he was investing heavily in cleaner engines and fuels.

Top scientists predict that global average temperatures will rise by between 1.8 and 4.0 degrees Celsius this century due to human activities like burning fossil fuels, putting millions at risk from rising sea levels, floods, famines and storms.

The prize will initially only be open for five years, with ideas assessed by a panel of judges including Branson, Gore and Tickell as well as U.S. climate scientist James Hansen, Briton James Lovelock and Australian environmentalist Tim Flannery.

The winner will have to come up with a way of removing one billion metric tons of carbon gases a year from the atmosphere for 10 years -- with $5 million of the prize being paid at the start and the remaining $20 million at the end.