|The Author in the field|
My terrestrial interest has long been palaeoenvironmental – what the rock record can tell us about past environments and climates. The Lyellian notion of Uniformity, that 'the Present is the key to the Past', is needlessly contrasted with catastrophism in planetary science (e.g., Baker, 1978; 1993; 1996; 1998; 2002; 2014), and was never a principle to be applied beyond Earth. Yet, it gains an extra dimension with the multiple geological examples that study of multiple planets affords, and can be made to work both ways in that context – i.e., not only can the Present be the key to the Past, but that Past can also be key to the Future.
Let me explain.
Fifty years of orbital observation has resulted in the consensus view that the northern lowlands of Mars are covered in lava. The most cursory geological examination shows this model-based view to be wrong, but study of the heavens is the province of the physicist and the astronomer and so this view prevails. Of the many geological anomalies with this story, the standout is that the ostensibly 'volcanic cones' that populate this terrain are demonstrably post-depositional in origin and thus more likely to be intrusive permafrost mounds. Look at this terrain stratigraphically and that likelihood becomes a certainty, the mounds presenting striking parallels to a new phenomenon in Arctic permafrost.
The dramatic explosion of Siberian permafrost mounds over the last four years has received worldwide media attention, igniting speculations of a methane "time-bomb" and a climatic threshold crossed. Absent any precedent in the geological past, we do not know whether these blasts are random events related to local permafrost instabilities, or the first sign of cascading methane release under climatic warming. Prior to the Arctic explosions the possibility that Mars' mounds might also explode could never be anticipated. Yet explode they do, synchronously, and in their thousands, presenting a scaleable vision of this process run to completion on Earth.
The parallel between this mass-explosion on Mars and the Yamal explosions vis-à-vis methane is described in the paper 'A candidate methane-clathrate destabilisation event on Mars: a model for sub-millennial-scale climatic change on Earth' published last week in the journal 'Gondwana Research'. This link – https://authors.elsevier.com/a/1WtNh,UYEnN-Xs – allows the readers of Arctic-news to freely download the full text of the paper without limitation or registration (until June 9th). I've been asked to extract my paper for that readership and have chosen to précis that aspect that I believe will be of the most interest to them: what the geology says about the rate of devolatilisation on Mars.
It is typically not possible to constrain the rate of past geological events with any accuracy (e.g., was the methane-expulsion of the PETM a geologically instantaneous event, occurring over decades, or did it play out over 10s to 100s of 1000s of years?). Uncharacteristically for a past such event (and uniquely so for a non-terrestrial one), two aspects of the Mars observations allow both the frequency and the scale of the explosions there to be calculated.
Secondly, as neither the Earth nor Mars mounds are explosion 'craters' but positive-relief constructional landforms (whose explosion plays no part in their formation), this explosion of pre-existing landforms allows assessment of the degree of degassing on Mars to be made (i.e., "how many have exploded out of how many"). Observation shows over 99% of the exposed mounds to have exploded.
These explosions on Mars and Earth, both new-to-science, offer a unique opportunity for climatic inquiry across two worlds, having already occurred on Mars and now underway on Earth. Can this 'snapshot' of an abrupt, mass-devolatilisation event in-progress tell us anything about current events in Siberia? There is reason to believe that the Siberian explosions are only just beginning as neither the 1000s of onshore lake depressions across the Yamal-Pangody region nor the methane-venting 'pockmarks' of the various Arctic sea-floors show any evidence of explosive genesis, having thermokarstic- and subsidence-origins, respectively. What Mars shows is that once a certain permafrost stability threshold is passed, either through increasing temperature or decreasing pressure, the explosive 'reaction' appears to cascade.
It is important to place this statement in observational context, as those who set store by the solutions of numerical models will say that such cascading devolatilisation is not likely (and perhaps even irresponsible to voice) in regard to the Earth. Yet the martian observations are quite unambiguous, so let us list those elements that are factual:
- Thousands of mounds have exploded on a regional scale at a single geological horizon on Mars and with a significant degree of synchrony;
- This synchrony has operated, certainly partially and potentially completely, on a human timescale;
- The devolatilisation was effectively complete, with > 99% of mounds exploded, the entire reservoir (at least as expressed at the surface) depleting in non-linear fashion.
Climate-change studies have long struggled with the “impossible” task (Stassen, 2016) of predicting the consequences of sub-millennial-scale climatic change on Earth absent any example from our past. Mars provides one such example, the first, and a sobering one. If such cascade can occur on a permafrozen body such as Mars without the added drivers of annually-forced temperature increase or inundation by a warming transgressive ocean, then the scope for the same on Earth – where the shallow-marine clathrates of the East Siberian Arctic Shelf (ESAS), the largest near-surface reservoir of labile carbon on the planet, are rapidly warmed to the permafrost thaw-point – would appear straightforward. As a planet (probably) devoid of life and geologically inactive, the amount of methane on Mars will be both small and finite – were this degassing to occur on the same scale and frequency in a region of massive methane concentration on Earth, such as ESAS, then the beyond-worst-case scenario would follow: unstoppable runaway warming.
I don't think that it's 'alarmist' to be alarmed about events in the Yamal when seen in this new martian context – Siberian news reports last year described mapping of 7000 methane-venting mounds across the Yamal-Gydan (The Siberian Times, 27/03/2017), a number far in excess of the global frost mound population (~ 5000 [Mackay, 1998]) as of 1998. If confirmed, these 1000s of 'new' mounds must have formed within the last 20 years by a disequilibrium process unrelated to progressive ice-intrusion (Page, 2018). A University of Alaska permafrost decay expert quoted on the same day (The Washington Post, 27/03/2017) said that this mapping is likely to be an underestimate, and that the new mounds may number as many as 100,000. Should even the smaller of these numbers be correct and disequilibrium methanogenesis the cause, then Mars' explosions may only hint at the near future for a methane-rich Earth of rapidly rising temperatures if Arctic permafrost-explosion follows suit.
A seemingly compelling counterargument, often reused in the media, is that none of the glacial-interglacial transitions of the past 400 kyr shows a sudden, large methane-spike, suggesting that abrupt, large-scale methane outbursts are unlikely. One might appeal to such abrupt events being below the temporal resolution of the rock record in explanation, but absent such spikes the safest answer is to say that large-scale interglacial outbursts did not occur during that time. This time, however, is different. Anthropogenic warming has interrupted the Glacial-Interglacial cycle of the Quaternary (Ganopolski et al., 2016; Haqq-Misra, 2014) and there will be no coming Ice-Age n-1000 years from now to reseal all of this volatile Carbon, as happened at the end of each previous interglacial. This now-broken cyclicity is one reason why catastrophic reservoir-collapse has never occurred in the past and we should not take any comfort from that lack of precedent as never before has an Interglacial period been combined with annual, planetary-scale thermal forcing.
While high CO₂ levels have been present in Earth's atmosphere before (e.g., during the Cambrian and Archaean) without initiating either the moist or runaway greenhouse state, never has the rate of warming been annual in scale as today. The question is not whether anthropogenic emissions could initiate these greenhouse states, but whether Arctic clathrate release could. The IPCC 3rd Assessment Report (2001) concluded that rapid increase in atmospheric methane from the release of buried clathrate reservoirs would be "exceptionally unlikely", at < 1% chance, a figure revised up to 10% by the following report in 2008. Yet the Mars observations show that abrupt, cascading devolatilisation occurs readily in nature, and there is nothing about these observations to suggest that this process is not portable or scalable to Earth. That ESAS lacks Mars' mound-density makes the scaling no less valid, the methane-supersaturation of 80% of ESAS bottom waters (Shakhova et al., 2010) showing that frost mounds are not the sole venting pathway, gas migration pathways growing in capacity annually in the areas of greatest emissions (Shakhova et al., 2017). Destabilisation of the shallow-marine clathrates of ESAS continues to be excluded from every global climate model, the only (regional-scale) model to consider this being that of Archer (2015). The reader is referred to that paper for detail (https://www.biogeosciences.net/12/2953/2015/bg-12-2953-2015.pdf), but I would like to consider one element of that model here.
As a geologist, it is not clear to me how a model can have "...lessons to teach us about the real Siberian continental margin" (Archer, 2015) when "...many of the model variables are not well known", "...meaning that in some aspects the model results are not a strong constraint on reality". When this model "...neglects many of the mechanisms that could come into play in transporting methane quickly to the atmosphere, such as faults, channels, and blowouts of the sediment column" then one must ask what bearing or predictive-value it has for abrupt methane release. In ignoring faults and thaw-taliks, this model – "...the first simulation of the full methane cycle on the Siberian continental margin" – neglects those surface, subsurface, subaqueous, and subaerial pathways through which methane moves rapidly through permafrost, as observed in ESAS (e.g., Shakhova et al., 2010, 2017). Little wonder that "...No mechanism has been proposed whereby a significant fraction of the Siberian permafrost hydrates could release their methane catastrophically" (Archer, 2007) when every method of rapid release is neglected by the only 'full' model. The importance of such thaw-discontinuities cannot be underplayed in a model of catastrophic devolatilisation (Shakhova, 2014), as illustrated by Mars where violent degassing equivalent to 20 Yamal explosions per km² occurs through sub-mound palaeo-taliks alone (e.g., Figure above). The stated lack of constraint between model and reality is reflected in its most important Prediction, i.e., that atmospheric methane flux from anthropogenic warming of ESAS permafrost will never exceed 0.04 Tg C-CH₄ yr⁻¹ over 100-kyr of global warming (see Figure 15 of Archer, 2015). In Actuality, air sampling surveys over ESAS yield a calculated annual flux to the atmosphere of 8 Tg C-CH₄ (Shakhova et al., 2010), a figure 200 x higher than the model estimate (at Year-1 of this 100-kyr-scale warming) and equivalent to the methane emissions of the entire world's oceans.
In questioning the abrupt 50 Gt Arctic-methane release proposed by Shakhova et al. (2010), Archer says that "...A complex model is not really required to conclude that methane hydrate will probably not produce a methane eruption of this scale so quickly". Yet models (particularly the complex ones) are only as good as their base assumptions, and that regarding the methane flux in this region shows little correspondence with reality. There is thus no support for the Conclusion that "...The model results give no indication of a mechanism by which methane emissions from the Siberian continental shelf could have a significant impact on the near-term evolution of Earth’s climate" as the geological discontinuities that should be foremost in that mechanism are omitted from the model and the long-term CH₄-flux predictions of that model have no bearing to current, observed methane flux.
Knowing whether reservoir degassing follows a linear or cascading path makes all of the difference to whether such a system can be dynamically modelled. The 'plan-view' of the martian event exposed at the surface shows one explosion communicated to another and another, with mutual interference of blast-waves evident throughout. In this explosive degassing over 100s-of-km, Mars shows that once explosion begins it spreads, with local- to regional-scale synchrony. Thus, whether this is the explosion of 1000s of discrete volatile caches confined to the mounds, or 1000s of explosions that depleted a greater reservoir at-depth doesn't really matter, as devolatilisation appears to be limited only by volatile availability and to run to completion once initiated. As such, the proposed < 5% (50 Gt) release from ESAS may be highly conservative. It could also be extremely rapid if the isochroneity of explosion on Mars is valid, the brief dune-remobilisation there consistent with mass-emission of a warming volatile of decadal atmospheric lifetime. If a mechanism be required before mass-degassing of ESAS is considered possible, then Mars provides one in the thermal disequilibrium of progressive deposit unroofing – a thermophysical process that will operate just as readily in submerged permafrost as subaerial, having already occurred on Mars and now underway in ESAS.
Unsurprisingly, argument in the scientific press between those who place their faith in numerical models and those who prefer the empiricism of "boots on the ground" (or ice, in this case) is heated in regard to possible ESAS degassing (e.g., http://www.biogeosciencesdiscuss.net/11/C6800/2014/bgd-11-C6800-2014-print.pdf). Ultimately, the 'watchful waiting' of ongoing, in situ documentation and the under-parameterised, low-dimensional abstractions of the modeller will both fail to capture the complexity and timescale of change in this most Open climate system as we must wait for the outcome to arrive before we can fully understand it, and that will be too late. Let us have no more 'scientific reticence' about Arctic methane. Earth at 1 AU is forever on the 0.97-0.99 AU margin of runaway warming (Kopparapu et al., 2013). To see what that's like, we need only look to our other nearest planetary neighbour and carry on with 'Business-As-Usual'. For the $3-trillion that was spent a decade ago bailing-out the shareholders of two corrupt mortgage lenders and a failing bank we could have built enough offshore wind turbines to power the entire planet, fixing dangerous climate-change globally and permanently.
If we're lucky, we may have a decade remaining to fix it now.
A Question and an Answer
Q: Why should the reader pay any heed to the words of an 'off-world' geologist when it comes to Arctic methane, particularly one who mentions Uniformitarianism? A: Because the methodology employed is not his own but one grounded in the geometrical principles of that science, honed over 200 years of inquiry¹. Using that methodology, the volatile-hypothesis for genesis of the martian mounds has been testing its own predictions observationally for over a decade now and has yet to falter, leaving others to explain-away the resulting inconsistencies in the established model (e.g., Jaeger et al., 2008; Dundas et al., 2010). In 2007, I suggested that the methane detected over this region was related to decadal-scale thaw-destabilisation of permafrost mounds, providing a mechanism for clathrate dissociation, and that "...unless thaw and the local methane enhancement over this region are unrelated, release of methane from within the permafrost is a consistent explanation" (Page, 2007). Ten-years on, and this destabilisation-geology and -chronology have been borne out in the discovery of widespread explosive mass-devolatilisation of frost mounds in that same region, paralleling the identical but otherwise new-to-science explosive phenomena in the Yamal (Page, 2018).
This successful prediction is not self-advertisement, and is stated here for one reason alone² – in providing the only analogue for what is beginning in Siberian permafrost now, this past event on Mars provides a unique guide to how such degassing plays-out for real. It is one that we must not ignore – scaling this event to Earth yields 10s-of-millions of explosions in the Arctic and a terminal mass-emission of methane that will make 50 Gt look modest.
It is said that the greatest contribution that Geology has made to human knowledge is the discovery of 'Deep Time'. More significant Today is its unique capacity to reconstruct the Past, and to apply that understanding to anticipating the Future.
¹ When I consider the landforms and surfaces of other planets I do not do so in terms of models, morphology, or hypotheses of origin, but their geometrical relations with one-another vis-à-vis relative-age, a method of inquiry that goes back two centuries to the very inception of geology as a science. In a traverse across the Scottish Highlands, James Hutton (1788) was able to piece together the history of the various plutonic, metamorphic, and sedimentary rocks based on the geometry of their intersections. He inferred that the Caledonian granites were younger than the “Primitive” (metamorphic) basement that they intrude, with the numerous faults and intrusive dykes younger than the Old Red Sandstone that they cut. By determining the age of one rock relative to another, Hutton produced a geological “history of events” for rocks whose origins he did not know, a history that remains unchanged to this day (Page, 2015). This directional, temporal logic is practiced by all geologists as a matter of course, whether they be determining the crystallization history of minerals under the microscope, the stratigraphy of an outcrop in the field, or the order of undefined events on a distant planetary surface. These relative-age relations are all defined geometrically, a straightforward reductio, such as Euclid's proof that two intersecting circles cannot share their centres, being the basis for much stratigraphical reasoning. By the same reasoning, two spatially coincident events (mound-formation and -explosion, in this case) cannot share the same point in time if they are separated by a third, intervening event of significant duration (e.g., dune-formation). This simple deposit geometry is what shows accepted explanation of the geology of mound-bearing terrain on Mars to be deficient, and something entirely different, the propositions of planar geometry matters of neither opinion nor interpretation.
² As stated by Hansen (2017) after losing funding for publishing research that pointed out the consequences of findings with no other consideration, "...Funding decisions for other researchers, I noted, sent a clear message: funding prospects were brighter if one emphasized that the science was very uncertain and that much more research was needed before it might be possible to draw inferences related to policy". If emphasising 'uncertainty' is the path to healthy funding, then this Contribution makes it clear that my work is not scientific careerism pitching for funds – the Author's post-doctoral research is entirely self-funded, as detailed in my Funding Statements for papers going back to 2010. It took 15 months to get this paper through peer-review in two Elsevier journals, the majority of which time was taken, after 13 reviewers refused to look at it, by a single, gainsaying reviewer who did not wish to see the MS published and resorted to foot-dragging and non-physical pseudo-geology to try to block its progress. These observations, if not necessarily my treatment of them, should not be blocked simply to protect the previous intellectual contributions of others.
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