(Image source: Nature)
The methane monster is an enormous, tricky beast of a thing. A number of past sudden climate change and mass extinction events are tied to methane pulses that appear to have happened over very brief geological spans. Massive carbon stores at risk of emitting methane in response to human warming have piled up over 2.5 million years of ice ages and 30 million years of glaciation. Now, a rapid human warming resulting from raging greenhouse gas emissions is starting to unlock these immense frozen carbon stores, prodding the methane monster and causing it to stir.
Not much is clearly known about natural methane releases during rapid warming events — both past or current. Tracking of human and Earth Systems methane emission has been far less detailed than direct CO2 forcing research and, due to the complex nature of methane in the atmosphere, far more difficult to put into context. So it is entirely understandable that a recent article in the scientific journal Nature, authored by Gail Whiteman, Chris Hope, and Peter Wadhams, has caused what can best be called a media implosion. Climate change deniers have buried their heads ever deeper into the sand, doomers are predicting the end of the world tomorrow no matter what we do, and finger pointing has erupted among members of the journalistic and scientific community who have deep professional knowledge but differing opinions as to how the methane problem will ultimately manifest.
It is important that we do our best to side-step the fuss and drill down to the critically important issues at hand: risks, costs, and the potential for mitigation.
At issue is the Nature article’s warning that 50 gigatons of methane could rapidly release from a vulnerable region called the East Siberian Arctic Shelf. This area contains only a fraction of a massive Arctic carbon store. But its location in a thawing, shallow sea put it at risk of an extreme sudden release.
In the absolute worst case, the article notes that the entire 50 gigatons could emit within one year. In an intermediate worst case, the article shows that about 5 gigatons of methane could emit each year during a period from 2015 to 2025. And in the low-end worst case, the Nature article warns that the 50 gigaton volume in the East Siberian Arctic Shelf could all emit by 2035. The article also considers potential costs from a lesser, but still enormously damaging, 25 gigaton release from the East Siberian Arctic Shelf over similar time periods.
The article states that such events would cause massive economic damage, on the order of 30 trillion to 70 trillion dollars over a period from now to 2100, adding substantially to the approximately $400 trillion in damage already projected from human caused global warming through 2100 (without rapid mitigation).
The article notes that such large emissions would result in a temperature increase of around 3 degrees Celsius by 2050, about a degree higher than predicted under base case emissions scenarios. Such a rapid increase in so short a period would, indeed, have devastating economic consequences (It is important to note that the only ‘slow feedbacks’ added to this model run include a methane pulse along with a portion of added Arctic carbon dioxide, but no related albedo change. So numbers here are likely lower than they would be under such circumstances.).
There is some reason to believe, due to a current lack of scientific consensus, that the large releases explored in the study are a low risk potential. But the lack of concerted and coordinated research on the subject creates an infuriating uncertainty over an issue critical to long-term human survival and prosperity.
A closer look at the East Siberian Arctic Shelf and the larger Arctic
The 50 gigatons in question rests in a submerged section of frozen tundra beneath the shallow waters of the East Siberian Arctic Shelf. At the end of the last ice age, this tundra, locking in the 50 gigatons of methane along with other carbon stores was flooded due to sea level rise as glaciers melted. The Arctic sea ice covered this submerged, frozen tundra for most of this period, keeping water temperatures close to or below 0 degrees Celsius.
In recent years, summer ice cover has increasingly receded from the East Siberian Arctic Shelf as Arctic sea ice extent has rapidly declined. From 1979 to 2012, ice extent had shrunk by as much as 55%. From 2005 to 2013, this region of the Arctic Ocean lost the majority of its sea ice for as long 1-2 months at a time. During these periods, the shallow sea warmed by as much a 7 degrees Celsius above average — all the way to the sea floor — creating perforations in the submerged tundra through which the methane could bubble up. Due to the fact that this ocean region was so shallow, a majority of these methane emissions hit the atmosphere.
Expeditions to the East Siberian Arctic Shelf during the late 2000s and during 2011 found large plumes of methane venting from the warming tundra beneath the shallow sea. In 2011, plumes as large as 1 kilometer across were discovered. Scientific papers during this time announced findings that this region of the Arctic was emitting about 14 megatons of methane each year.
As time moves forward, continuing erosion of sea ice will result in longer warm periods that transfer more of the surface heat energy through the water column and down to the frozen methane stores, almost certainly causing a rising volume of emissions. Under current trends, sea ice may be mostly gone from Arctic waters year round by as early as 2040. Such an event would likely result in a number of severe consequences, just one of which is rising and potentially catastrophic ESAS emissions. (And the only event likely to provide enough negative feedback to shut down such a deadly occurrence is an equally dangerous large melt pulse from Greenland and Antarctica.)
The 50 gigatons of methane frozen in this section of tundra is likely trapped in ice and frozen sea bed representing between 100 and 500 cubic kilometers of total volume. The large volume of this frozen material makes it far less likely that stores will immediately release within a single summer and emit all 50 gigatons of the trapped methane. Nor is it highly likely that all 50 gigatons will release in 10 or even 40 years. A more probable range for total ESAS release is between 50 and 300 years. Even then, effects from the emission of this major store into the atmosphere would constitute a terrible event.
Around the Arctic, a much larger store of carbon will also likely contribute increasing methane emissions. As the Arctic Ocean warms, some of the estimated 1,000 gigatons of methane locked in sea bed deposits will almost certainly reach the surface. In addition, a portion of the estimated 1,500 gigatons of carbon trapped in tundra deposits will certainly release as methane as the Arctic warms. So the ESAS is just one, rather unstable, part of a larger methane beast. Instead of 30-50 megatons of annual methane emission coming from the Earth System (excluding typical wetlands emissions), it is entirely plausible that we could see emissions rising to 100, 200, 300 megatons or more (effectively doubling the human emission). Further, to entirely ignore the potential for catastrophic events of the kind Wadhams and Shakhova warn about, where yearly emission pulses of 1 gigaton or higher hit the atmosphere as a result of radically amplifying Earth System feedbacks, would be deeply irresponsible.
To these, rather stark, points, it is important to note that it is almost certain that releases from the East Siberian Arctic Shelf and other Arctic locations will rise by less if we rapidly reduce human forcings and by more if we continue to do little or nothing to reduce global human carbon emissions. The current human emission of methane is at least 350-400 megatons per year. This massive release is equivalent to a long-term natural methane pulse of devastating proportion and it is one key reason why we are in so much trouble. Even more damaging is a CO2 emission near 32 gigatons per year. There is no corollary for a CO2 emission of this yearly rate in all of the geological record and atmospheric concentrations of 400 parts per million CO2 are the highest level since major ice ages began about 2.5 million years ago. Instances where annual methane emissions have been this high are also very difficult to locate, with past rapid pulses being measured over the 1,000 to 10,000 year time-scale. To reduce and eliminate these vast and extraordinarily dangerous human emissions would be to take out a huge part of the problem before us. We are directly in control of these emissions, but it will be impossible for us to control Earth System emissions as they spontaneously emerge. Though some damage will likely still be in store due to our past dumping of greenhouse gasses into the atmosphere, it will be far less than if we continue to, immorally and insanely, add to what is already a very difficult problem.
In context of this major and damaging human emission on the order of a major geological event, it is also worth re-examining the broad disagreement among scientists about the potential rate of future Arctic methane emissions. Many have pointed to evidence in paleoclimate data that shows methane response generally occurs on the 1,000s to 10,000s of years time-frame. But paleoclimate seems to also indicate a slower sea ice, tundra, and ice sheet response than what we are currently seeing as a result of the very rapid human greenhouse gas forcing. Further, recent expeditions and monitoring studies have found anomalous and large methane emissions throughout the Earth System that are consistent to the initiation of a feedback response to human warming. That Dr. Wadhams, Shakhova and a handful of other Arctic experts have warned of the potential for single year emissions (somewhat remote, but great enough to be cause for worry) as large as 50 gigatons should serve as a chilling message best heeded. The still unlikely, but almost equally catastrophic, potential for emissions of 1-5 gigatons per year from the East Siberian Arctic Shelf are also cause for a high degree of concern. And though such large, single events remain less likely than slower releases, it is highly likely that Arctic methane emissions, in total, will greatly increase as polar amplification continues, resulting in a powerful feedback to human-caused warming.
Our best indications are that total Earth Systems responses will result in at least double the amount of warming shown in Equilibrium Climate Sensitivity models. What the Nature paper explores is just one instance of such a response. So even if Arctic methane release estimates are lower than the ‘catastrophic cases’ provided in the article, they will add to other global methane and CO2 release feedbacks, loss of albedo and Earth System changes to produce this likely doubling or more. So the sense of urgency for effective responses should be great, indeed.
More mitigation, adaptation, and monitoring necessary
The Nature Article is, therefore, an important warning. One that should be considered and discussed. More important than the scientific and media debate surrounding this article is its demonstration of a dire need for increased knowledge of Arctic methane systems to gain a better handle on potential risks. The clarity of science, right now between 50 gigaton potential emissions in one year and far, far slower emissions over the course of thousands of years, is too murky given the current state of overall climate risk in the context of break-neck human greenhouse gas emissions.
In addition, the most important finding of this study has been mostly ignored by almost all media responses to it. The study found that mitigation, through the drastic reduction of human carbon emissions, was extraordinarily valuable in even the worst case scenarios.
The Nature article notes:
The WEF should also encourage innovative adaptation and mitigation plans. It will be difficult — perhaps impossible — to avoid large methane releases in the East Siberian Sea without major reductions in global emissions of CO2. Given that the methane originates in local seabed warming, then reducing black carbon deposits on snow and ice might [also] buy some precious time.
Model runs conducted in conjunction with the article showed that physical damage was halved when human emissions drastically fell in even the most dire of circumstances. This study, therefore, should come as a clear signal to any who would call for continued reliance on fossil fuels — either through the failed and anti-human arguments of denial that human climate change exists, through the equally mentally and morally bankrupt doomer calculus that falsely claims no response is effective, or through a continued intransigence by entrenched industries that have built their business models so as to profit from a vast harm to humankind.
If one believes that the very high damage events presented by these scientists are possible, they must also consider their findings that drastically cutting carbon emissions vastly enhances human prospects as we enter an age of fossil fuel inflicted climate crisis.