Greenhouse gas concentrations spike — heating the atmosphere and the deep ocean after a period of glaciation during which vast stores of carbon accumulated. Massive volumes of this carbon lay dormant — trapped in frozen ground and in clathrates on the sea bed. As the ocean and airs warm, these carbon stores release causing a massive spike of additional greenhouse gasses to hit the atmosphere and setting off ever-more-rampant heating. The cycle continues until much of these carbon stores out-gas, pushing the Earth into a hothouse state.
Sound chillingly familiar?
What I’ve just described is the process that most scientists believe occurred during the worst mass extinction event in the geological past — the Permian Extinction. A hothouse event that killed 95% of life in the oceans and 70% of life on land. And what humans are now doing to the Earth’s airs and waters through CO2 and related greenhouse gas emissions may well be shockingly similar.
(Substantial methane release from the East Siberian Sea surface during early August likely in the range of 0.5 to 1 megatons points toward both atmospheric methane overburden and likely carbon store instability and large scale out-gassing in the Arctic. Image credit: Sam Carana and NOAA.)
From the Arctic tundra to the Arctic Ocean sea bed to the Atlantic Ocean, we have growing evidence of methane and CO2 releases from carbon stores that may well be at the start of just such a large scale feedback. Time and time again, we see evidence of significant (but not yet catastrophic) emissions from Arctic methane stores (see image above). With each passing year, the methane overburden in the Arctic air grows. And we have had increasing evidence of a growing volume of releases from the East Siberian Arctic Shelf sea bed, to the methane emitting melt lakes proliferating over the thawing permafrost, to the chilling and terrifying methane blow holes discovered this year in Siberia.
As of 2011, many Arctic scientists believed that human-caused heating could set off methane and CO2 emissions from that region equivalent to between 10 and 35 percent or more of current human fossil fuel burning by the end of this century. The lower boundary of this range is with rapid reductions in human greenhouse gas emissions, the upper boundary is under business as usual. Such a 35 percent equivalent emission, happening year on year for centuries, would be more than enough to push Earth into a runaway hothouse scenario without any further human greenhouse gas releases. And it is this scenario, or the even more chilling worse case of very rapidly ramping Arctic methane outbursts, that we should be very concerned about.
Atlantic Methane Hydrate Destabilization off US East Coast
Unfortunately, the vast carbon store in the Arctic is not the only potential source of heating feedback carbon release. For around the world, upon and beneath the ocean sea bed, billions of tons of methane lay stored in clathrate structures. These stores are separate from the large carbon deposits in the Arctic. But they are no less dangerous.
In 2012, Nature issued a study that found a store of clathrates composing billions of tons of methane was now destabilizing off the US East Coast. The study predicted large-scale releases in the multi-gigaton range from the southern region of the East Coast methane clathrate store due both to changes in the Gulf Stream circulation and to warming bottom waters — both impacts set off by human-caused climate change. The study was uncertain how fast such a release could occur, but noted that the eventual release was likely due to wide-scale clathrate degradation associated with ocean bottom warming.
(Methane Seep off US East Coast. Image source: Nature.)
This year, research vessels returned to the region and found 570 plumes of methane venting from destabilized clathrate stores there. This result was surprising due to the fact that only three methane seep sources had previously been identified. The plumes were discovered in 50 to 1,500 meters of water, with most of the seeps occurring at between 250 and 600 meters depth, along a zone stretching from Cape Hatteras to Georges Bank. The seeps ranged in age from recent to 100 or even 1000 or more years old. Overall, the prevalence of seeps was more widespread than expected.
“This is the first time anyone has systematically mapped an entire margin,” Christian Berndt, a marine geophysicist at GEOMAR in Kiel, Germany, who was not involved in the study, said in an interview to Science Magazine. “They found that there was much more methane coming out than was suspected beforehand.”
Currently, only a small amount of the methane being released from the sea bed off the US East Coast is likely hitting the atmosphere and is probably not contributing anywhere near the volume of known emission sources from the East Siberian Arctic Shelf. Most of the gas is just absorbed by the water column, increasing acidification in the region and contributing to anoxia. But the known clathrate store off the US East Coast is very significant and large scale releases could result in much more widespread anoxia, acidification, and provide a substantial atmospheric heating feedback to human-caused warming. Very large and catastrophic outbursts could also result in slope collapse and generate tsunamis along the US East Coast. A concern that researchers may also need to further investigate.
Overall, as much as 300 to 400 gigatons of methane could be at risk and even a fraction of this store hitting the atmosphere would cause serious and lasting harm.
Overall, it is estimated that at least 30,000 methane seeps like the ones recently discovered off the US East Coast may now be active with potentially 10,000 in the East Coast region now under investigation. The current study provides a good base line for further exploration of what may well be a rather significant problem going forward.
“It highlights a really key area where we can test some of the more radical hypotheses about climate change,” said John Kessler, a professor at the University of Rochester, in an interview with the New York Times. “How will those release rates accelerate as bottom temperature warms?”
The acceleration would indeed have to be substantial to add to the already significant and troubling Arctic methane and CO2 release. But the sea bed stores are vast and the rate of human warming is very rapid. So the global ocean clathrate store is something to keep under close watch and the discovery of yet one more source that is already emitting at faster than expected rates is not at all comforting.