Bubbling Away

I live in fear of my tiny gas stove.

It’s the first gas range I’ve ever lived with, and every day I come home to it carefully sniffing for gas leaks and feeling faintly relieved that it hasn’t blown up my apartment in my absence. I stand as far back as possible when turning it on, and startle every time a burner finally catches. In my kitchen, the stove calls the shots.

Most of my friends don’t seem to share my perfectly rational terror; after all, the natural gas that powers my stove is an important and familiar energy source in many other aspects of our lives. And methane, the simple molecule that makes up the majority of natural gas, is also a major player in our atmosphere.

Although methane makes up less than a thousandth of a percent of the air around and above us, its total global warming punch is third in line behind only water vapor and the notorious carbon dioxide. That’s because, gram for gram, methane has 20 times the warming potential of carbon dioxide.

And, while methane concentrations are low, they’re still twice what they were just a couple hundred years ago (before the Industrial Revolution). And they’re rising.

This rise is mostly driven by human activities that release methane, like rice farming and animal husbandry (wet paddies and cow guts are both full of methane-generating bacteria). But scientists worry that, in a future, warmer world, more methane could come from wetlands and shallow ocean basins in the Arctic.

Normally, these places are cold — very cold. In fact, they’re sealed by a layer of ground that’s frozen all year round, aptly named “permafrost.” A lot of carbon has been stored up in these regions, accumulated by plants during their bursts of summer growth, then sealed in by freezing that slows down the natural decay of the dead stems and leaves.

Over millennia, wetlands and permafrost soils have tucked away two times the amount of carbon as what’s currently floating around in our atmosphere.

But for how long?

Warmer temperatures are melting the permafrost all around the pole, unsealing the cap on these carbon stores. Some of the dead organic carbon will be released as carbon dioxide; much may leak out as methane.

Since these gases will also contribute to the greenhouse gas effect and the net warming of the polar regions, further melting the permafrost, this could lead to a run-away self-reinforcing feedback loop.

To understand the magnitude of this problem, you first have to understand how this methane might be released. And in order to do that, as a scientific report published late last year explains, you have to know something about bubbles.

The shallow seas that ring the Arctic Ocean rest on beds of sediment that are filled with methane. Though we’ve long believed that these methane sources, too, were capped by permafrost, the new study reveals that, at least in some places, they’re not.        Which means that methane gas bubbles can form and, where conditions are right, float to the surface and spill all that greenhouse gas potential directly into the atmosphere.

How fast these bubbles drift to the surface depends a lot on local conditions. Imagine sticking a straw into a jar of syrup. You have to blow a mighty big bubble before it breaks off the tip of your straw and rises.

And plenty of tiny bubbles are almost stationary in the thick liquid. On a finer scale, that’s what’s happening in the ocean, too: Big bubbles rise faster than small ones. And storms — which could become more frequent and more severe with changing climate — accelerate the bubbling process by shaking up the whole system.

By making a series of careful measurements of bubble flux, storm effects and methane concentrations, the authors of the new research more than doubled their previous estimate of methane release off the coast of Russia. Each year, they say, at least 17 million tons (17 Tg) of methane are released from the East Siberian Arctic Shelf.

The number sounds big — and indeed it is. But it’s only a small fraction of total “natural” methane release, at 180 Tg per year. And when you add in human activities, globally the land and sea exhale 440 Tg annually.

Yet the potential for imbalance remains alarming, especially given methane’s greenhouse gas potency. Unlike my visions of a spontaneously combusting kitchenette, runaway Arctic thawing is a real fear and one that’s worth keeping an eye on as it simmers on the back burner.

 

Holly welcomes reader feedback, especially stories confirming her fear of gas stoves, at hollyvm “at” stanford.edu.

About Holly Moeller

Holly is a Ph.D. student in Ecology and Evolution, with interests that range from marine microbes to trees and mushrooms to the future of human life on this swiftly tilting planet. She's been writing "Seeing Green" since 2007, and still hasn't run out of environmental issues to cover, so to stay sane she goes for long runs, communes with redwood trees and does yoga (badly).