Nature: In 2007, scientists scouting the icy waters of the Arctic Ocean began to notice some troubling signs. In about half of their seawater chemistry samples, the concentration of dissolved methane was two to ten times higher than in samples taken during previous years from the same locations. Then, last summer, they observed large rings of gas — sometimes as wide as 30 centimetres in diameter — trapped in ice, as well as methane plumes bubbling to the surface over hundreds of square kilometres …