|"The ice that burns" -- frozen methane|
Two hundred and fifty million years ago, massive seafloor deposits of frozen methane destabilized, leading to the release of of thousands of gigatons of stored carbon and a global temperature spike of over +6C. Ninty-six percent of marine species and 70% of terrestrial vertebrates were wiped out. The trigger for this massive release of methyl hydrates was a more gradual global warming of a few degrees.
|Extinction events -- intensity|
Like any event 250 million years ago, details are hard to come by. But there is at least one reason to implicate methyl hydrate release in the Permian-Triassic extinction event: a hundred and ninety million years later, the same thing happened again. Gradual global warming, followed by a rapid release of massive amounts of carbon with a distinct isotope signature, followed by rapid global warming that ended with tropical fish swimming at the North Pole.
But don't worry. ThatMcGuire noted for the Royal Society in 2010:
definitely probably maybe couldn't happen again on a human timescale. As
While rising ocean temperatures will tend towards destabilizing hydrates, increasing load pressures as a result of rising sea levels will act in the opposite sense. Maslin et al. (2010) note that, even if marine hydrate dissociation is triggered on a large scale, it may be that all or much of the methane released will not reach the atmosphere because either (i) thermal penetration of marine sediments to the gas-hydrate interface could be sufficiently tardy as to allow a new equilibrium to become established without significant gas release or (ii) a fraction of any gas released may be oxidized in the ocean.
The paper McGuire alludes too, "Gas hydrates: past and future geohazard?" has been discussed here before. It is linked to on the right. It typifies the cautiously optimistic attitude of climate scientists towards the possibility of a rapid, catastrophic release of methyl hydrates, aka methyl clathrates, the "clathrate gun hypothesis."
It is still unknown whether future ocean warming could lead to significant methane release, as thermal penetration of marine sediments to the clathrate–gas interface could be slow enough to allow a new equilibrium to occur without any gas escaping. Even if methane gas does escape, it is still unclear how much of this could be oxidized in the overlying ocean. Models of the global inventory of hydrates and trapped methane bubbles suggest that a global 3°C warming could release between 35 and 940 GtC, which could add up to an additional 0.5°C to global warming. The destabilization of gas hydrate reserves in permafrost areas is more certain as climate models predict that high-latitude regions will be disproportionately affected by global warming with temperature increases of over 12°C predicted for much of North America and Northern Asia. Our current estimates of gas hydrate storage in the Arctic region are, however, extremely poor and non-existent for Antarctica. The shrinking of both the Greenland and Antarctic ice sheets in response to regional warming may also lead to destabilization of gas hydrates. As ice sheets shrink, the weight removed allows the coastal region and adjacent continental slope to rise through isostacy. This removal of hydrostatic pressure could destabilize gas hydrates, leading to massive slope failure, and may increase the risk of tsunamis.Hmmm. I have to say, even that article is not as reassuring as I remembered it being. But there has certainly been a period in recent years in which scientists have thrown cold water on some of the more lurid disaster scenarios. Take this very recent paper, focusing on the Arctic, where, Maslin notes, destabilization of methyl hydrates is "more certain":
Vast amounts of methane hydrates are potentially stored in sediments along the continental margins, owing their stability to low temperature - high pressure conditions. Global warming could destabilize these hydrates and cause a release of methane (CH4) into the water column and possibly the atmosphere. Since the Arctic has and will be warmed considerably, Arctic bottom water temperatures and their future evolution projected by a climate model were analyzed. The resulting warming is spatially inhomogeneous, with the strongest impact on shallow regions affected by Atlantic inflow. Within the next 100 years, the warming affects 25% of shallow and mid-depth regions containing methane hydrates. Release of methane from melting hydrates in these areas could enhance ocean acidification and oxygen depletion in the water column. The impact of methane release on global warming, however, would not be significant within the considered time span.There may be reasons for concern outside the Arctic as well. The best recent review article on the subject and the inspiration for my revisiting the issue is (full text): "Methane release from gas hydrate systems during the Paleocene-Eocene thermal maximum and other past hyperthermal events: setting appropriate parameters for discussion" (Biastoch et al, GRL, 2011). He cites Zeebe (2009) (which I can't access) for the following: "the Atlantic reservoir . . . is the most likely location of an oceanic carbon release."
And in another of those funny little quirks of the actual vs the model climate, the Atlantic Ocean is warming far faster than expected, likely due to the "leaking" of warm water from the Indian Ocean caused by the weakening of the mighty Agulhas Current.
Weakening of the Agulhas Current means more of the hot subtropical water you see in the figure above remains behind in the cold Atlantic.
Skeptical Science has more on the disturbing implications of Biastoch (2011):
Carozza et al (2011) find that natural global warming occurred in 2 stages: First, global warming of 3° to 9° C accompanied by a large bolus of organic carbon released to the atmosphere through the burning of terrestrial biomass (Kurtz et al, 2003) over approximately a 50-year period; second, a catastrophic release of methane hydrate from sediment, followed by the oxidation of a part of this methane gas in the water column and the escape of the remaining CH4 to the atmosphere over a 50-year period.Remember, this is not the methyl hydrate release that wiped out 96% of marine life and 70% of terrestrial vertebrates. That was 250 million years ago. This one was 60 million years ago -- relatively mild by comparison.
The description of Stage 2: Very rapid and massive release of carbon deficient in ∂13C, does put one in mind of the Methane Gun hypothesis. It postulates that methane clathrate at shallow depth begins melting and through the feed-back process accelerate atmospheric and oceanic warming, melting even larger and deeper clathrate deposits. The result: A relatively sudden massive venting of methane - the firing of the Methane Gun. Recent discovery by Davy et al (2010) of kilometer-wide (ten 8-11 kilometer and about 1,000 1-kilometer-wide features) eruption craters on the Chatham Rise seafloor off New Zealand adds further ammunition to the Methane Gun hypothesis.
Just like we used to with ice loss, we comfort ourselves with the notion that warm air takes a long time to melt anything:
Significant methane release can occur when on-shore permafrost is thawed by a warmer atmosphere (unlikely to occur in significance on less than a century timescale) and undersea clathrate at relatively shallow depths is melted by warming water. This is now occurring. In both cases, methane gas bubbles to the surface with little or no oxidation, entering the atmosphere as CH4 – a powerful greenhouse gas which increases local, then Arctic atmospheric and ocean temperature, resulting in progressively deeper and larger deposits of clathrate melting.However you have the same problem with that projection as befell the reassuring forecasts for ice mass loss: these deposits are surrounded by water. Warm water carries heat far more efficiently than warm air. Increased rainfall and changes in groundwater, ocean currents, and freshwater streams already shows some indications of accelerating permafrost melting, and water dynamics may, by implication, affect shallow methyl hydrates as well.
Skeptical Science continues with these heavily qualified reassurances:
Methane released from deeper deposits such as those found off Svalbard has to pass through a much higher water column (>300 meters) before reaching the surface. As it does so, it oxidises to CO2, dissolving in seawater or reaching the atmosphere as CO2 which causes far slower warming, but can nevertheless contribute to ocean acidification.Since the carbon mass of methyl hydrates dwarfs known fossil fuel reserves, the prospect of their release as CO2 is cold comfort. But consider how (again, just like our old, falsely reassuring, ice models) this scenario presumes a gradual, linear process. What if methyl hydrates disassociate rapidly, and produce a local anoxic event? No oxygen in the water, no oxidation of methane. What isf the methane starts to escape in discreet events, producing a column of gas, like this:
Would a large plume of gas shield the methane at the center from oxidization? Would a column of bubbles reduce friction on the individual bubbles, allowing them to rise faster and have less time to oxidize? Stupid questions, maybe. I hope smarter people than me have considered such possibilities and found them unlikely.
Is there a clathrate gun pointed at our heads? Scientists are conservative. They don't like to paint doomsday scenarios. We've all seen interviews with journalists that flounder on the shoals of their rightful, sound reticence:
So let's give the last word to somebody determined to be as conservative as possible, titling their article "'Arctic Armageddon' Needs More Science, Less Hype":
Methane is a powerful greenhouse gas 25 times more potent than carbon dioxide, and the ongoing global warming driven by carbon dioxide will inevitably force it out of its frozen reservoirs and into the atmosphere to amplify the warming. Such an amplifying feedback may have operated in the past, with devastating effects. If the modern version is anything like past episodes, two scientists warned earlier this year, it could mean that "far from the Arctic, crops could fail and nations crumble." Yet, with bubbles of methane streaming from the warming Arctic sea floor and deteriorating permafrost, many scientists are trying to send a more balanced message. The threat of global warming amplifying itself by triggering massive methane releases is real and may already be under way, providing plenty of fodder for scary headlines. But what researchers understand about the threat points to a less malevolent, more protracted process.I love how reassuring and level-headed the author is trying to be while still being honest about the not-very-reassuring facts. Well, yes, he says, release of methyl hydrates is going to happen. And yes, in the past, when this happened, the results have been "devastating." Yes, this could rapidly accelerate global warming: we know that because there's evidence it's already happening. But there's no reason to panic. Everyone should remain calm. If you don't remain calm you will waste our precious shotgun shells as your trembling hands cause you to miss the looters.
There seems to be cause for concern. No hype needed.
UPDATE: This morning Ari Jokimäki at AGW Observer posted his usual weekly climate news roundup, and, low and behold, there's a methyl hydrates study. Ari's a phlegmatic fellow who highlights middle-of-the-road, non-sensationalist, workaday climate research. Surely this study will talk me down from the clathrate-gun ledge.
Methane release from hydrates may already be occurringShit, Ari. What are you doing to me here? I guess we need to read on. After all "'Arctic Armageddon' Needs More Science, Less Hype" turned out to be fairly scary; maybe this one, with a scary headline, will turn out to be soothing. Let's see:
Contribution of Oceanic Gas Hydrate Dissociation to the Formation of Arctic Ocean Methane Plumes – Reagan et al. (2011) “Vast quantities of methane are trapped in oceanic hydrate deposits, and there is concern that a rise in the ocean temperature will induce dissociation of these hydrate accumulations, potentially releasing large amounts of carbon into the atmosphere. Because methane is a powerful greenhouse gas, such a release could have dramatic climatic consequences. The recent discovery of active methane gas venting along the landward limit of the gas hydrate stability zone (GHSZ) on the shallow continental slope (150 m – 400 m) west of Svalbard suggests that this process may already have begun, but the source of the methane has not yet been determined. This study performs 2-D simulations of hydrate dissociation in conditions representative of the Arctic Ocean margin to assess whether such hydrates could contribute to the observed gas release. The results show that shallow, low-saturation hydrate deposits, if subjected to recently observed or future predicted temperature changes at the seafloor, can release quantities of methane at the magnitudes similar to what has been observed, and that the releases will be localized near the landward limit of the GHSZ. Both gradual and rapid warming is simulated, along with a parametric sensitivity analysis, and localized gas release is observed for most of the cases. These results resemble the recently published observations and strongly suggest that hydrate dissociation and methane release as a result of climate change may be a real phenomenon, that it could occur on decadal timescales, and that it already may be occurring.” Reagan, M. T., G. J. Moridis, S. Elliott, and M. E. Maltrud (2011), J. Geophys. Res., doi:10.1029/2011JC007189, in press.