Gas hydrate breakdown unlikely to cause massive greenhouse gas release

February 9, 2017
Summary of the locations where gas hydrate occurs beneath the seafloor, in permafrost areas, and beneath some ice sheets, along with the processes (shown in red) that destroy methane (sinks) in the sediments, ocean, and atmosphere. The differently colored circles denote different sources of methane. Gas hydrates are likely breaking down now on shallow continental shelves in the Arctic Ocean and at the feather edge of gas hydrate stability on continental margins (1000-1650 feet). Credit: Ruppel and Kessler (2017). (Public domain.)

The breakdown of methane hydrates due to warming climate is unlikely to lead to massive amounts of methane being released to the atmosphere, according to a recent interpretive review of scientific literature performed by the U.S. Geological Survey and the University of Rochester.

Methane hydrate, which is also referred to as gas hydrate, is a naturally-occurring, ice-like form of methane and water that is stable within a narrow range of pressure and temperature conditions. These conditions are mostly found in undersea sediments at water depths greater than 1000 to 1650 ft and in and beneath permafrost (permanently frozen ground) at high latitudes. Methane hydrates are distinct from conventional natural gas, shale gas, and coalbed methane reservoirs and are not currently exploited for energy production, either in the United States or the rest of the world.

On a global scale, gas hydrate deposits store enormous amounts of methane at relatively shallow depths, making them particularly susceptible to the changes in temperature that accompany climate change. Methane itself is also a potent greenhouse gas, and some researchers have suggested that methane released by the breakdown of gas hydrate during past climate events may have exacerbated global warming.

The new review concludes that current warming of ocean waters is likely causing gas hydrate deposits to break down at some locations. However, not only are the annual emissions of methane to the ocean from degrading far smaller than greenhouse gas emissions to the atmosphere from human activities, but most of the methane released by gas hydrates never reaches the atmosphere. Instead, the methane often remains in the undersea sediments, dissolves in the ocean, or is converted to carbon dioxide by microbes in the sediments or water column.

Gas hydrate (white, ice-like material) under authigenic carbonate rock that is encrusted with deep-sea chemosynthetic mussels and other organisms on the seafloor of the northern Gulf of Mexico at 966 m (~3170 ft) water depth. Although gas hydrate that forms on the seafloor is not an important component of the global gas hydrate inventory, deposits such as these demonstrate that methane and other gases cross the seafloor and enter the ocean. Credit: Photograph was taken by the Deep Discoverer remotely operated vehicle in April 2014 and is courtesy of the National Oceanic and Atmospheric Administration's Ocean Exploration and Research Program.

The review pays particular attention to gas hydrates beneath the Arctic Ocean, where some studies have observed elevated rates of methane transfer between the ocean and the atmosphere. As noted by the authors, the methane being emitted to the atmosphere in the Arctic Ocean has not been directly traced to the breakdown of gas hydrate in response to recent climate change, nor as a consequence of longer-term warming since the end of the last Ice Age.

"Our review is the culmination of nearly a decade of original research by the USGS, my coauthor Professor John Kessler at the University of Rochester, and many other groups in the community," said USGS geophysicist Carolyn Ruppel, who is the paper's lead author and oversees the USGS Gas Hydrates Project. "After so many years spent determining where gas hydrates are breaking down and measuring methane flux at the sea-air interface, we suggest that conclusive evidence for release of hydrate-related methane to the atmosphere is lacking."

Professor Kessler explains that, "Even where we do see slightly elevated emissions of methane at the sea-air interface, our research shows that this methane is rarely attributable to gas hydrate degradation."

A sample of gas hydrate from the Mallik Test Well in Canada. Credit: Credit: USGS.

The review summarizes how much gas hydrate exists and where it occurs; identifies the technical challenges associated with determining whether atmospheric methane originates with gas hydrate breakdown; and examines the assumptions of the Intergovernmental Panels on Climate Change, which have typically attributed a small amount of annual atmospheric methane emissions to gas hydrate sources.

The review also systematically evaluates different environments to assess the susceptibility of gas hydrates at each location to warming climate and addresses the potential environmental impact of an accidental gas release associated with a hypothetical well producing methane from gas hydrate deposits.

Virginia Burkett, USGS Associate Director for Climate and Land Use Change, noted, "This review paper provides a truly comprehensive synthesis of the knowledge on the interaction of gas hydrates and climate during the contemporary period. The authors' sober, data-driven analyses and conclusions challenge the popular perception that warming climate will lead to a catastrophic release of to the atmosphere as a result of gas hydrate breakdown."

A sample of gas hydrate from sediments under the Indian Ocean. Credit: USGS.(Public domain.)

Explore further: Can melting of frozen methane explain rapid climate change 56 million years ago?

More information: Carolyn D. Ruppel et al, The interaction of climate change and methane hydrates, Reviews of Geophysics (2017). DOI: 10.1002/2016RG000534

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FactsReallyMatter
4 / 5 (4) Feb 10, 2017
Phew, well that is one panic averted. Plenty more still on the table.
brentnorring
5 / 5 (1) Feb 10, 2017
I would love to accept this explanation but there are several details that have not been looked at which would suggest that a massive release can and most likely will happen.
Methane plumes have been popping up everywhere where there weren't any before.
Please tell us that warmer waters are not causing these plumes to occur.
Evidence shows us otherwise.
Where is the consensus?
I noticed that you will not allow me to post the evidence of the plumes.
Look it up yourself. It will be from Scientific America "150,000 methane plumes as the Arctic Ice retreats".
antigoracle
1 / 5 (8) Feb 10, 2017
Methane plumes have been popping up everywhere...

Uh huh, stop sniffing the plume from your pants, it's effect is quite obvious.
https://phys.org/...ble.html
TheGhostofOtto1923
3 / 5 (2) Feb 11, 2017
"Estimates vary, but conservative figures place global reserves at roughly 3 trillion tons of previously untapped carbon -- more than is trapped in all the other known fossil fuel reserves put together, says Klaus Wallmann of the Leibniz Institute of Marine Science in Kiel, Germany"

-We keep finding more and more hydrocarbons on this planet that we never imagined existed, as well as throughout the solar system, and people keep insisting that the stuff on earth alone comes from dead plants and animals.

This makes no sense to me.

Its the same with water. You would have to assume first that this material was present like everything else in the protoplanetary disk, and congealed out at the same time.
gkam
1 / 5 (6) Feb 11, 2017
When some greedy company starts mining these, we can probably expect a big disaster if an uncontrolled breakout occurs.

We are more clever than intelligent.
FactsReallyMatter
1 / 5 (2) Feb 14, 2017
I'd be more afraid of a gov't agency running the show, look how well they managed california's dams.

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