It is, however, a potent greenhouse gas—the U.S. Environmental Protection Agency suggests that methane has a heat-trapping power 25 times greater than CO 2 . But fortunately, very little of it ever leaves the ocean, thanks to the expansive communities of marine microbes that eat it. Using methane to give ocean robots a power boost may sound like sci-fi, but it may be closer than you think. A prototype of what the researchers refer to as a ‘seafloor generator’ is being built for testing later this year. It’s roughly the size of a large dorm room fridge, and when deployed, sits above methane seeps bubbling up from the seafloor.