Millions of pounds are on offer for the person who comes up with the best way of removing significant amounts of carbon dioxide from the atmosphere. Virgin boss Sir Richard Branson launched the competition today in London alongside former US vice-president Al Gore.

A panel of judges will oversee the prize, including James Lovelock and Nasa scientist James Hansen. Sir Richard said humankind must realise the scale of the crisis it faced.

"The Earth cannot wait 60 years," he said at the news conference. "I want a future for my children and my children's children. The clock is ticking."

He said if the planet was to survive, it was vital to find a way of getting rid of the greenhouse gas carbon dioxide.

He said he believed offering the $25m (£12.5m) Earth Challenge Prize was the best way of finding a solution.