Methane bubbles form in bodies of water when dead organic matter (leaves and animals) falls into the water and sinks to the bottom.The bacteria munch and poop out methane, which turns to white floating blob when it comes into contact with frozen water. Methane is formed in thousands of lakes around the arctic, but decreasing permafrost means more and more of this methane is being released into the atmosphere, a worrying trend for climate scientists who note that methane is a more potent greenhouse gas than carbon dioxide.