Billionaire Richard Branson is on a tear these days. Last year at Bill Clinton’s Global Initiative meeting in New York, Branson announced that he would spend $3 billion of his Virgin profits to research and develop renewable-energy technologies. Now he has announced a $25 million prize for anyone who creates a system that removes at least one billion tons of carbon dioxide from the atmosphere in each of ten years.

Removing carbon dioxide is key here. Anyone who has read global-warming studies or seen Al Gore’s An Inconvenient Truth knows that even if we stop increasing greenhouse gases and level off carbon dioxide, much damage has already been done. Nearly every scientist in the field agrees that human consumption of fossil fuels has already caused global temperatures to climb and ancient ice in Greenland and Antarctica to melt as seas slowly begin to rise.

A panel of environmentalist heavyweights will judge Branson’s prize: former vice president Al “Inconvenient Truth” Gore; Jim Hansen, director of the NASA Goddard Institute; James Lovelock, the father of the Gaia theory; Australian conservationist Tim Flannery; and Crispin Tickell, director of the Policy Foresight Programme at Oxford University, UK.

One contender might be Craig Venter, cosequencer of the human genome and the man Time magazine once called the “bad boy of science.” Venter has been working with Nobel laureate Hamilton Smith to build from scratch a synthetic organism they want to program at the DNA level to consume carbon dioxide. Venter and Smith have been quiet about the project recently, suggesting that they are having a tough time.

As interesting as the prize is this burgeoning age of billionaires doing the work that nations used to. More accurately, we are returning to an era before governments took the lead in community efforts, when tycoons gave large chunks of their money to worthy causes. Think Andrew Carnegie and Leland Stanford in the nineteenth century. These fellows were robber barons, and Branson is not, as far as we know. Nor are his fellow billionaire givers Bill Gates and Warren Buffet, though Gates has been every bit as ruthless as any business titan from the 1800s. (Ask Jim Clark of Netscape.) The intent with all of these men is the same: to be remembered for doing great things rather than for being merely uber-rich.

Still, there are two excellent reasons for us to be pleased that Branson is offering his prize. First is the failure of world governments to take decisive action on even slowing the growth of human-produced greenhouse gases in the atmosphere, never mind removing the gases we have already pumped into our air. The lead ditherer is the Bush Administration, which still officially denies that increases in greenhouse gases are as dire as scientists say and that human activity is to blame.

Second, Branson has seized on the idea of a prize to encourage exactly what needs to be encouraged: innovation by individuals. As he noted in his announcement last week, this sort of prize has a great tradition going back to at least the eighteenth century, when the British Parliament offered a then princely sum of 20,000 pounds to the first inventor to come up with a method for accurately measuring longitude at sea. Clockmaker John Harrison won, as recounted in Dava Sobel’s wonderful little book, Longitude. Another model was Branson’s own $10 million X-Prize handed out in 2004 for inventing and flying the first privately built spaceship.

Branson has added a caveat to his prize. The winner gets $5 million up front but must wait ten years to validate the system to get the other $20 million. Winners will have to find their own financing in the meantime, though Branson has said that he will help promising technologies find funding if their inventors are having trouble.

With all of Branson’s do-good bravado, there is a dark cloud above his environmentalist credentials. His businesses include Virgin Air and the Virgin railway system, which contribute to greenhouse gases. I happened to fly a Virgin Boeing 747 to London just last week, and I rode to Manchester and back in one of Branson’s trains. They are cool and colorful and modern, but they also pollute.

This suggests that Branson’s $25 million, added to his $3 billion for research, should be considered a down payment on the billions he has made from businesses that spew carbon dioxide into the air. It is a payback to be emulated by others who have made billions, or even mere millions. A billionaire movement may already have begun. Late last year Google founders Larry Page and Sergey Brin promised $1 billion to their new charity Google.org, which lists alternative energy as a major focus.

If we are lucky, the billionaires will try to out-billion each other. Let’s hope it’s not too late.