Gas Attack?

by Bill McKibben

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A new study in Nature describes a new possible climate threat. We’ve known for some time that there is lots of methane stored in frozen form in the world’s oceans. The best known of these clathrate formations are in the Arctic, but today’s study finds them across the Atlantic, and by implication around the rest of the seafloor. Methane appears to be bubbling up out of these vents–which is bad news, since methane is a potent greenhouse gas, molecule for molecule much stronger than carbon dioxide:

The seeps were discovered in a stretch of ocean waters from Cape Hatteras, N.C., to Georges Bank, Mass. The majority are located at a depth of about 1,640 feet, which is at the upper level of stability for gas hydrate.

“Warming of the ocean waters could cause this ice to melt and release gas,”Adam Skarke, a geoscientist at Mississippi State University and the study’s lead author, told NBC News. “So there may be some connection here to intermediate ocean warming, though we need to carry out further investigations to confirm if that is the case,” he added.

The theory is, much of the heat from global warming is currently going into the ocean, not the air.  In fact, there was a study just yesterday–Justin Worland summarizes :

Temperatures have risen more slowly in the past decade than in the previous 50 years and will continue to rise at a somewhat slower rate in the next decade, according to a new study, even as climate change continues to raise temperatures to unprecedented levels worldwide.

The study, published in the journal Science, explained the temporary slowdown in rising temperatures as a potential consequence of the end of a 30-year current cycle in the Atlantic Ocean that pushes heat into the ocean.

The Economist looks at how the study credits the oceans for the pause:

Dr Chen and Dr Tung have shown where exactly in the sea the missing heat is lurking. … [O]ver the past decade and a bit the ocean depths have been warming faster than the surface. This period corresponds perfectly with the pause, and contrasts with the last two decades of the 20th century, when the surface was warming faster than the deep. The authors calculate that, between 1999 and 2012, 69 zettajoules of heat (that is, 69 x 1021 joules—a huge amount of energy) have been sequestered in the oceans between 300 metres and 1,500 metres down. If it had not been so sequestered, they think, there would have been no pause in warming at the surface.

Some of that heat may well be causing these methane formations to melt, in what would be yet another vicious feedback loop. But even if this turns out to (and oh one hopes) a red herring, the basic news that the oceans are heating quickly is quite bad enough. In part because we don’t notice it as much as we do heating of the air, which slows down our response.

As Jane Lee puts it:

It’s important to note that a pause in rising temperatures doesn’t mean global warming isn’t happening, writes Gerald Meehl, a senior scientist at NCAR, in an email. “Global warming hasn’t stopped, it has temporarily shifted to the subsurface ocean,” says Meehl, who first proposed that the Atlantic Ocean was storing some of the missing heat.

Indeed, it’s just a matter of time before this heat is reflected in atmospheric temperatures, says Tung. If this 30-year cycle holds, we’re starting to climb out of the current pause, he explains.

“The frightening part,” Tung says, is “it’s going to warm just as fast as the last three decades of the 20th century, which was the fastest warming we’ve seen.” Only now, we’ll be starting from a higher average surface temperature than before.

Oh, and by the way, to return to this problem with methane: it’s why scientists increasingly worry that fracking is a bad idea not just for local water supplies, but for the climate. As Naomi Oreskes pointed out recently, if more than a couple of percent of methane leaks, it’s possible that the Obama adminstration’s turn to natural gas hasn’t really cut our greenhouse gas emissions at all:

But how do we know what our emissions actually are? Most people would assume that we measure them, but they would be wrong.  Emissions are instead calculated based on energy data — how much coal, oil, and gas was bought and sold in the U.S. that year — multiplied by assumed rates of greenhouse gas production by those fuels. Here’s the rub: the gas calculation depends on the assumed leakage rate.  If we’ve been underestimating leakage, then we’ve underestimated the emissions.