[ Articles skeptical of the clathrate gun theory:
Mooney, C. 2013. How Much Should You Worry About an Arctic Methane Bomb? Mother Jones.
While researching the Permian extinction, I came across all sorts of doubts about methane hydrates as a major killer.
A popular theory of a giant methane burp as the killer is known as the “clathrate gun” hypothesis posits a sudden and massive release of methane hydrates from the land, on ocean shelves, and the depths of the ocean. There are many reasons to question this though:
- Majorowicz (2014) found methane hydrate reservoirs would have melted over 100 to 400 thousand years in the hothouse Permean world, long before the first extinction pulse
- Hydrates only form in cool oceans, like those of today, and there isn’t much carbon in them, somewhere between 500 and 2500 GtC (Milkov 2004). Yet this is far more than what would have existed in Permean oceans, and just a small fraction of the overall 24,000 to 46,000 GtC Siberian Trap emissions.
- Ocean hydrates would have also been far less extensive than they are today because supercontinent Pangea had far fewer miles of hydrate-containing continental shelves than the shelf length of our multiple continents today (Wignall 2017).
- Methane is a far more powerful greenhouse gas than carbon dioxide, but doesn’t last long in the air because it oxidizes to CO2 and water vapor in about 9 years
- It is not likely deep water methane hydrates would reach the atmosphere since they’d be oxidized in the water column (Rupple 2011).
Even if there were a methane hydrate burp in the first killer pulse, a new suspect has to be found for the second killing pulse, since there was no cooling in the 200,000 year interval between them. It takes millions of years of cold water for methane hydrates to form again after they’ve melted.
Milkov (2004) concludes “A significantly smaller global gas hydrate inventory implies that the role of gas hydrates in the global carbon cycle may not be as significant as speculated previously. Gas hydrate may be considered a future energy source not because the global volume of hydrate-bound gas is large, but because some individual gas hydrate accumulations may contain significant and concentrated resources that may be profitably recovered in the future”.
- Majorowicz, J., et al. 2014. Gas hydrate contribution to Late Permian global warming. Earth and Planetary Science Letters 393:243-253.
- Milkov, A. 2004. Global estimates of hydrate-bound gas in marine sediments: How much is really out there? Earth-Science Reviews 66: 183-197.
- Rupple, C. D. 2011. Methane Hydrates and Contemporary Climate Change. Nature Education Knowledge.
- Wignall, P. B. 2017. The Worst of Times: How Life on Earth Survived Eighty Million Years of Extinctions. Princeton University Press.
In addition, here are some posts by SJ at Fractal Planet debunking Guy McPherson:
Alice Friedemann www.energyskeptic.com author of “When Trucks Stop Running: Energy and the Future of Transportation, 2015, Springer]
SBC. June 2015. Gas Hydrates. Taking the heat out of the burning-ice debate. Potential and future of Gas Hydrates. SBC energy institute.
Recent studies (e.g. Whiteman et al) have raised the alarm that methane emissions could occur in the Arctic, especially over the East Siberian Shelf and in Siberian Lakes (e.g. Shakhova et al). However, there is a vigorous academic debate on the origin and potential impact of these emissions. As acknowledged by the IPCC: “How much of this CH 4 originates from decomposing organic carbon or from destabilizing hydrates is not known. There is also no evidence available to determine whether these sources have been stimulated by recent regional warming, or whether they have always existed
…since the last deglaciation. More research is therefore urgently needed.
The response of gas hydrates to climate change has only been investigated recently. Modeling in this field remains in its infancy. As a consequence, the likelihood, and impact, of gas-hydrate dissociation due to climate change is still poorly understood and more research is needed.
The first uncertainty is the amount of gas hydrates stored on Earth. Global gas-in-place estimates range over an order of magnitude 1,000-20,000 tcm, with most estimates around 3,000 tcm. Estimates are even more uncertain at the regional level. For instance, there are no models for Antarctic reservoirs, and estimates for Arctic permafrost have only been done recently.
In the permafrost, additional uncertainty arises from the origin of methane emissions, whereas in the case of ocean sediments, the mechanisms by which methane is released and its ability to reach the atmosphere are also disputed. So are the biochemical and chemical consequences that gas-hydrate releases would have on oxidation mechanisms e.g. there may be resource limitations hindering methane oxidation in the ocean.
Since gas hydrates are only stable under high pressures and at low temperatures, there have been concerns that climate change could result in gas-hydrate dissociation and the release of methane into the atmosphere. The response of gas hydrates to climate change has only been investigated recently. Modelling in this field is in its infancy and faces major uncertainties. Nevertheless, it is generally agreed that gas-hydrate dissociation is likely to be a regional phenomenon, rather than a global one, and more likely to occur in subsea permafrost and upper continental shelves than in deep-water reservoirs, which make up the majority of gas hydrates. Indeed,the later are relatively well insulated from climate change because of the slow propagation of warming and the long ventilation time of the ocean. Moreover, the release of methane from gas-hydrate dissociation should be chronic rather than explosive, as was once assumed;and emissions to the atmosphere caused by hydrate dissociation should be in the form of CO2 because of the oxidation of methane in the water column.
1 Graphs adapted from Archer (2007), “Methane hydrate stability and anthropogenic climate change”. In the graph on the right, ventilation timescale corresponds to the timescale required by temperature (heat), pressure and solutes such as methane to diffuse through the sediments
Ocean thermal response varies according to depth, as highlighted in the graph above (left), but also from place to place, especially in deep-water locations, due to ocean currents. In sediments, the diffusion of heat towards deeper layers takes time and varies primarily according to depth, but also according to the composition of the sediment and to the geothermal gradient. Heat can diffuse approximately 100 meters in about 300 years (point A). Solutes such as dissolved methane diffuse even more slowly (100 meters in about 30,000 years), point B), while pressure perturbation (e.g. following a sea-level rise) diffuses more quickly (100 meters in about 3 years), point C.
As a result of thermal inertia, heat diffusion and the melting of permafrost take time, and should be slow enough to insulate most hydrate deposits from expected anthropogenic warming over a 100-year timescale. Nevertheless, temperature increases in high latitudes, such as the Arctic, are expected to be much higher than increases in the mean global temperature, and are therefore more likely to affect gas-hydrates reservoirs. Rises in sea level would result in pressure increases at the seafloor that may mitigate further dissociation of offshore gas-hydrate deposits. However, it is likely to be insufficient to negate the warming.
Even if warming were to reach the gas hydrate stability zone, the fate of any methane released would be uncertain.Gas could escape if the pressure exceeded the sediment’s lithostatic pressure, but it might also remain in place. In addition, since gas-hydrate dissociation will start at the edge of the stability zone, even if gas were able to migrate, it might subsequently be trapped in newly formed hydrates.
Finally, even if methane were able to migrate towards the seafloor, it would probably not reach the atmosphere. Most methane is expected to be oxidized in the water column rather than released by bubble plumes or other “transport pathways” directly into the atmosphere as methane. Nevertheless, the oxidation of methane produces CO2, which will have an impact on ocean acidification and will remain in the atmosphere.
The risk of climate change causing gas-hydrate dissociation and methane leaks varies significantly by location.This can be explained by depth differentials, the existence of mitigation mechanisms such as water-column oxidation, or by the exposure of gas-hydrate deposits to varying regional warming phenomena. High-latitude warming is expected to be much greater than global-mean-temperature warming.
As a rule-of-thumb, gas hydrates held within subsea permafrost on the circum-Arctic ocean shelves and on upper continental slopes are the most prone to dissociation. Subsea permafrost, which were flooded under relatively warm waters due to sea level rises thousands of years ago, have been exposed to dramatic rises in temperature that have led to a significant degradation both of subsea permafrost and t he gas hydrates within it.The latter are believed to store a greater quantity of gas hydrates than the former, but methane releases are less likely to reach directly the atmosphere because of oxidation in the water column.
However, it is very unlikely that climate warming will disturb gas-hydrate deposits that are held in deep-water reservoirs around 95% of all deposits on a millennial timescale. Finally,
gas hydrates in seafloor mounds may also dissociate as a result of warming, overlying water or pressure perturbation, but these account for a very limited share of gas hydrates in place.
The sensitivity of gas-hydrate deposits in onshore permafrost,especially at the top of the hydrate stability zone, is more uncertain and subject to greater debate
Archer et al. calculated that between 35 and 940 GtC of methane could escape as a result of global warming of 3° C, with maximum consequences of adding a further 0.5° C to global warming. On top of the uncertainty reflected in the range above, there are other considerable uncertainties, notably concerning the effectiveness of mitigation mechanisms and the long-term outlook, since methane will continue to be released, even if warming stops.
Reagan and Moridis (2007), “Oceanic gas hydrate instability and dissociation under climate change scenarios”;
Maslin et al. (2010), “Gas hydrates: past and future geohazard?”;
Shakhova et al. (2010), “Predicted Methane Emission on the East Siberian Shelf”;
Whitemann et al. (2013), “Climate science: Vast costs of Arctic change”
Ananthaswamy, A. May 20, 2015 Methane apocalypse? Defusing the Arctic’s time bomb. NewScientist.
Do the huge craters pockmarking Siberia herald a release of underground methane that could exceed our worst climate change fears? They look like massive bomb craters. So far 7 of these gaping chasms have been discovered in Siberia, apparently caused by pockets of methane exploding out of the melting permafrost. Has the Arctic methane time bomb begun to detonate in a more literal way than anyone imagined?
The “methane time bomb” is the popular shorthand for the idea that the thawing of the Arctic could at any moment trigger the sudden release of massive amounts of the potent greenhouse gas methane, rapidly accelerating the warming of the planet. Some refer to it in more dramatic terms: the Arctic methane catastrophe or methane apocalypse.
Some scientists have been issuing dire warnings about this. There is even an Arctic Methane Emergency Group. Others, though, think that while we are on course for catastrophic warming, the one thing we don’t need to worry about is the so-called methane time bomb. The possibility of an imminent release massive enough to accelerate warming can be ruled out, they say. So who is right?
Few scientists think there is any chance of limiting warming to 2 °C, even though many still publicly support this goal. Our carbon dioxide emissions are the main cause of the warming, but methane is a significant player.
Methane is a highly potent greenhouse gas – causing 86 times as much warming per molecule as CO2 over a 20-year period. Fortunately, there’s very little of it in the atmosphere. Before humans arrived on the scene there was less than 1000 parts per billion. Levels started rising very slowly around 5000 years ago, possibly to due to rice farming. They’ve gone up more since the industrial age began: the fossil fuel industry is by far the single biggest source, followed by farting farm animals, leaking landfills and so on. Only a tiny percentage comes from melting Arctic permafrost.
The level in the atmosphere is now nearing 1900 ppb, but that’s still low. CO2 levels were much higher to start with, around 270,000 ppb before the industrial age. They have now shot up to 400,000 ppb today. The main reason is that CO2 persists for hundreds of years, so even small increases in emissions lead to its buildup in the atmosphere, just as water dripping into a bath with the plug left in can fill the bath eventually.
Methane, by contrast, breaks down after just 12 years, so its level in the atmosphere can only increase if there are big ongoing emissions.
So for methane to cause a big jump in global warming there not only has to be a massive source, it has to be released very rapidly. Is there such a source?
Yes, claim a few scientists. They point to the Arctic permafrost, and specifically to the East Siberian Arctic shelf. This vast submerged shelf underlies a huge area of the Arctic Ocean, which is less than 100 meters deep in most places. During past ice ages, when sea level dropped 120 meters, the land froze solid.
This permafrost was covered by rising seas as the ice age ended around 15,000 years ago. The upper layer has been slowly melting as the relative warmth of the seawater penetrates down. But the frozen layer is still hundreds of meters thick. No one doubts that there is plenty of carbon locked away in and under it. The questions are, how much is there, how much will come out in the form of methane, and how fast?
Natalia Shakhova of the International Arctic Research Center at the University of Alaska Fairbanks, has been studying the East Siberian Arctic shelf for more than two decades. Her team has made more than 30 expeditions to the region, in winter and in summer, collected thousands of water samples and tons of seabed cores during four drilling campaigns and made millions of measurements of ambient levels of methane in the air.
Her team has estimated that there is a whopping 1750 gigatons of methane buried in and below the subsea permafrost, some of it in the form of methane hydrates – an ice-like substance that forms when methane and water combine under the right temperature and pressure. What’s more, they say that the permafrost is already beginning to thaw in places. “Our results show that… [the] subsea permafrost is perforating and opening gas migration paths for methane from the seabed to be released to the water column,” says Shakhova.
Her team’s work hit the headlines in 2010, when in a letter in the journal Science they reported finding more than 100 hot spots where methane was bubbling out from the seabed. But as others pointed out, it was not clear whether these emissions were something new or had been going on for thousands of years.
More sensational stuff was to follow. In another 2010 paper, the team explored the consequences of 50 gigatons of methane – 3% of their estimated total – entering the atmosphere (Doklady Earth Sciences, vol 430, p 190). If this happened over five years methane levels could soar to 20,000 ppb, albeit briefly. Using a simple model, the team calculated that if the world was on course to warm 2 °C by 2100, the extra methane would lead to additional warming of 1.3 °C, so temperatures would hit 3.3 °C by 2100.
This study appeared in an obscure journal and did not get much attention at the time. But then Peter Wadhams of the University of Cambridge and colleagues decided to see how much difference a huge methane release between 2015 and 2025 would make when added to an existing model of the economic costs of global warming. “A 50-gigaton reservoir of methane, stored in the form of hydrates, exists on the East Siberian Arctic shelf,” they stated in Nature, citing Shakhova’s paper as evidence. “It is likely to be emitted as the seabed warms, either steadily over 50 years or suddenly. Understandably, this was big news.
But in reality the idea that 50 gigatons could suddenly be released, or that there’s a store of 1750 gigatons in total, is very far from being accepted fact. On the contrary, Patrick Crill, a biogeochemist at Stockholm University in Sweden who studies methane release from the Arctic, says it is simply untenable. He wants Shakhova’s team to be more open about how they came up with these figures. “The data aren’t available,” says Crill. “It’s not very clear how those extrapolations are made, what the geophysics are that lead to those kinds of claims.
Shakhova now says, “We never stated that 50 gigatons is likely to be released in near or distant future.” It is true that the 2010 study explores the consequences of the release of 50 gigatons rather than explicitly claiming that this will happen. However, it has certainly been widely misunderstood both by other scientists and the media. And her team’s papers continue to fuel the idea that we should be worried about dramatic and damaging releases of methane from the Arctic.
But other researchers disagree. “The Arctic methane catastrophe hypothesis mostly works if you believe that there is a lot of methane hydrate,” says Carolyn Ruppel, who heads the gas hydrates project for the US Geological Survey in Woods Hole, Massachusetts. And her team estimates that there are only 20 gigatons of permafrost-associated hydrates in the Arctic (Journal of Chemical and Engineering Data, vol 60, p 429). If this is right, there’s little reason for concern.
The issue is not just how much methane hydrate there is, but whether it could be released rapidly enough to build up to high levels.
This could happen soon only if the hydrates are shallow enough to be destabilized by heat from the warming Arctic Ocean.
But David Archer of the University of Chicago says that hydrates could only exist hundreds of meters below the sea floor. That’s far too deep for any surface warming to have a rapid impact. The heat will take thousands of years to work its way down to that depth, he calculated last year, and only then will the hydrates respond (Biogeosciences Discussions, vol 12, p 1). “There is no way to get it all out on a short timescale,” says Archer. “That’s the crux of my position.
This concerted push back against the idea of an impending methane bomb has led to something of a feud. Commenting on Archer’s paper, for instance, Shakhova said he clearly knew nothing about the topic. She has repeatedly pointed out that her team has actual experience of collecting data in the East Siberian Ice shelf, unlike her detractors.
But there is skepticism about Shakhova’s actual measurements, too. For instance, her team has reported that methane levels above some hotspots in the East Siberian shelf were as high as 8000 ppb. Last summer, Crill was aboard the Swedish icebreaker Oden, measuring levels of methane over the East Siberian shelf. Nowhere did he find levels this high. Even when the Oden ventured near the hotspots identified by Shakhova’s team, he never saw levels much beyond 2000 ppb. “There was no indication of any large-scale rapid degassing,” says Crill.
It’s not clear why other teams are finding lower levels than Shakhova’s. But to find out if a catastrophic release of methane is imminent, there is another line of evidence we can turn to. Thanks to ice cores from places like Greenland, we have a record of past methane levels going back hundreds of thousands of years. If there are lots of shallow hydrates in the Arctic poised to release methane as soon it warms up a little, they should have done so in the past, and this should show up in the ice cores, says Gavin Schmidt of the NASA Goddard Institute for Space Studies in New York.
Around 6000 years ago, although the world as a whole was not warmer, Arctic summers were much warmer thanks to the peculiarities of Earth’s orbit. There is no sign of any short-term spikes in methane at this time. “There’s absolutely nothing,” says Schmidt. “If those methane hydrates were there, they were there 6000 years ago. They weren’t triggered 6000 years ago, so it’s unlikely they’d be triggered imminently.
During the last interglacial period, 125,000 years ago, when temperatures in the Arctic were about 3 °C warmer than now, methane levels rose a little, as expected in warmer periods, but never exceeded 750 ppb. Again, there’s no sign of the kind of spike a large release would produce.
There is, then, no solid evidence to back the idea of a methane bomb and past climate records suggest there is no cause for alarm. Extraordinary claims require extraordinary proof, otherwise it’s going to undermine credibility and slow down our ability to actually make the decisions that we are going to have to make as a society.
No one is saying methane is not a concern. Levels are now the highest they’ve been for at least 800,000 years and climbing. The Intergovernmental Panel on Climate Change’s worst-case emissions scenario assumes a big rise in methane, to as much as 4000 ppb by 2100.
What about the gaping craters? They are certainly spectacular and scary-looking. The latest idea is that they are caused by the release of pockets of compressed methane as ice seals melt. But the amount of methane released per crater is minuscule in global terms. Around 20 million craters would have to form within a few years to release 50 gigatons of the gas.