Arctic Methane Bubbles Not As Foreboding As Once Feared

European scientists were alarmed in 2008 when they discovered streams of methane bubbles erupting from the seafloor in Norway's high Arctic. This gas, which contributes to global warming, was apparently coming from methane ice on the seafloor. A follow-up study finds that methane bubble plumes at this location have probably been forming for a few thousand years, so they are not the result of human-induced climate change. But continued warming of ocean water can trigger more methane releases in the Arctic, with potentially serious consequences to the climate.

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AUDIE CORNISH, BYLINE: A few years ago, European researchers caused a stir when they discovered streams of methane bubbles rising from the Arctic seabed. The bubbles were caused by an ice-like material breaking apart as the seawater warmed up. Scientists fear that the warming of the oceans could be triggering the release of methane gas. The problem? Methane can actually speed up global warming. NPR's Richard Harris has the latest on this story.

RICHARD HARRIS, BYLINE: The biggest worry about climate change is some natural system can reach a tipping point, where something stable like methane locked up in an ice-like material on the seafloor suddenly becomes unstable. Christian Berndt and his colleagues discovered worrisome streams of methane gas erupting from ice-like material called gas hydrates off the coast of Norway's Svalbard Islands in 2008, so they knew they had to go back for a closer look. In 2012, they explored the area with a two-person mini-sub.

CHRISTIAN BERNDT: First, we did some reconnaissance dives to look at nature of the sediments and at the site where the gas was coming out.

HARRIS: And during those dives, they discovered some mineral deposits on the sea floor. They pulled up samples and realized that they had been formed by previous bursts of escaping methane, including releases 8,000 yeas ago, 3,000 years ago and 500 years ago.

BERNDT: We can see that this bubbling at that site must have been active for a long time. So that means this bubbling cannot be just caused by new climate change.

HARRIS: Berndt, in Kiel, Germany, is the lead author of a paper in the latest Science magazine that details their discoveries. It's reassuring news because it means that the bubbles near Svalbard aren't signs of a tipping point. But Carolyn Ruppel, who heads research on gas hydrates for the U.S. Geological Survey, says there's a huge amount of methane locked up in these hydrates around the world. There's no sign now of a runaway meltdown as the ocean gradually warms. But still, she says, these icy materials are sensitive to temperature change.

CAROLYN RUPPEL: Any time those waters may warm a little bit, you can break those down and potentially produce methane that then can come out of the seafloor.

HARRIS: In fact, Ruppel says small amounts of methane are emerging from hydrates along the continental shelves worldwide. As it turns out, though, most of the methane dissolves in the seawater long before it can bubble up to the surface.

RUPPEL: Our theory right now is that very little of that methane actually makes it to the atmosphere. So we're not talking necessarily here about a direct input of methane from the sea to the atmosphere.

HARRIS: The methane can alter ocean chemistry in a way that can affect sea life, so there are still consequences. And Ruppel now has her eyes on some areas in the Arctic where methane deposits are in shallow water. If those deposits were to break down, the gas could well make its way into the air. And scientists are trying to figure out just how stable those deposits are, so we haven't heard the last word on this subject. Richard Harris, NPR News.

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