Some scientists suspect that permafrost acts as a cap that protects hydrates from melting, particularly in the shallow Arctic seafloor, where the hydrates are found only a few tens of feet deep. The more that sea or lake waters thaw the permafrost below, the more likely this cap is to blow suddenly, releasing jets of methane up through the water and into the atmosphere. A team that included two of Walter’s colleagues at Fairbanks found such plumes rising up from the shallow continental shelf of Siberia in 2008. Possibly, these releases have been happening for a long time, and we are only now noticing them. But the discoverers point out that the Siberian shelf alone holds an estimated 1.4 trillion tons of methane in the form of gas hydrates—equivalent to the newest estimates of the total greenhouse gases that would be released during a complete permafrost thaw.

Many researchers note that methane hydrates exist below the permafrost on land as well. The deposits are generally assumed to be too deep to be at risk of thawing. But that assumption, like others before it, has been cast in doubt. If Walter confirms indications from a field excursion earlier this year that Arctic lakes are tapping a methane source even older and greater than permafrost, her alerts would have to be cranked up considerably. And those bubbles she lights would take on an even more sinister glow.

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ABOUT THE AUTHOR(S)
Sarah Simpson is a freelance writer in Riverside, Calif., and a contributing editor to Scientific American.