Retreating ice sheets could be uncorking another new source of carbon pollution

There's mounting evidence that ice sheets are letting the lid off a previously unaccounted for source of methane.

Most people are familiar with the sudden appearance of bubbles in a bottle of soda after the lid is opened. The explanation for why that happens is that, with the lid on, the pressure inside the bottle keeps the carbon dioxide gas dissolved in the liquid soda. Open the lid, and the pressure falls. The fizziness is the carbon dioxide as it escapes from the now effervescent soda.