Virgin's millions are up for grabs. What's a biologist to do? Tycoon Richard Branson offered another $25 million to combat global warming (he pledged $3 billion in September). This time he's taking a page from X-prize folks, offering the money as a prize for the best design of a plan for removing ?significant volumes of anthropogenic, atmospheric greenhouse gases.? Although the official rules are a bit hazy on what a ?significant amount? means (they are far less hazy on publicity rights and several other items), reports are generalizing the target to a billion tons or more yearly. Enrollment is open for three years, after which entries will be judged by none other than Al Gore. It will be interesting to see what comes of this. And I for one would like to see some imaginative biologists take this. So far, engineered algal blooms and genetically modified trees designed to sequester carbon in their roots are interesting, but I don?t think they're going to tip the scales at a billion tons a year. What's your idea?