Methane Bombs and Massive Sinkholes in Arctic Tundra
The future of permafrost and a tipping point that was passed decades ago
Background
There are still mysteries in the Earth system, and places not fully explored, and some novel events that can change how we view our climate future.
We might think to look for those mysteries hidden in the vast and impenetrable tropical forests of the Amazon and Congo basins, but some are, as mystery writers love to say, hidden in plain sight. Here’s one that has been discovered relatively recently in the wide open but sparsely populated tundra systems of the far north.
So what are methane bombs and how can sinkholes form in a region so cold that soils can be perpetually frozen? Let’s start by setting the stage.
The Setting
The arctic tundra circles the globe in the far north between the boreal forest (or taiga) to the south and the Arctic Ocean. With the harsh climate, limited numbers of plant and animal species, low growing vegetation, and very short growing season, it is as different from tropical forests in biology, geography and climate as can be imagined.
“Soils” are frozen most of the year and often waterlogged when thawed. At the end of the very short growing season, plants die back onto wet and then frozen ground where decomposition is limited. The result is a continual, vast accumulation of partially decomposed organic matter that contains a tremendous amount of carbon.
It is one of the ironies of the arctic that tundra ecosystems that support the lowest rates of plant growth contain the largest amounts of stored, undecomposed organic matter and carbon. Basically, plant growth, though slow, stays ahead of decomposition, which is slower still.
The result is huge deposits of “peat” – the same kind of partially decayed organic matter harvested from wetlands in more temperate regions for use in gardens or fireplaces.
Tundra ecosystems have been a net sink for carbon for thousands of years.
But the arctic is warming 2-4 times faster than the world at large. How does this affect all that frozen ground and all the carbon it contains?
A key player here is permafrost - locations and depths where the ground remains frozen year round. Biology operates slowly in the shallow, thawed summer soils above deeper, permanently frozen layers in the tundra. It happens not at all in the ice.
The Mystery
Most of the tundra region is flat, with wide vistas - not a great place to hide a mystery. But it is also one of the most sparsely populated biomes on the planet, so human reconnaissance is still limited.
And in 2014, a Russian helicopter pilot stumbled across something not seen before in undisturbed tundra: A huge sinkhole in that flat, limitless Siberian landscape.
There are apparently no good images of this phenomenon in the public domain, so I can’t include one here, but there is an excellent PBS NOVA show that tells the story. Directing you to a video on another site is something akin to showing a video in class, which I’ve never done, but this is a good one and includes images I can’t show directly.
I tend to get impatient watching these programs and find myself trying to sift through the dramatic footage of researchers in the field, etc. to nab the relevant facts. If you feel the same way, I will summarize the science presented and why it might be so important.
Spoiler alert – there is a usage of the term “tipping point” at the end of the video that needs correcting.
The first minute of the show includes a reconstructed scene of that Russian helicopter flying over Siberian tundra and discovering that very large sinkhole in the usually flat and frozen ground. It is indeed huge - 15 stories deep and 80 feet wide.
Scientists visiting the site discover that the rim of this crater is not flat but is surrounded by a raised berm that looks like fallout from an explosion - not a real burning explosion, but the bursting of a huge bubble of methane that had accumulated beneath the spot. They conclude that melting of the permafrost above this bubble weakened the surface materials until the bubble could burst through. There are some graphic visualizations of how this might have looked in that first minute as well!
Less dramatic scenes also highlight increased emissions of methane from thawing tundra ecosystems. Most tundra sinkholes form as permafrost melts and the now-thawed peat collapses in on itself. These can fill with water forming “Thermokarst” lakes. The PBS video shows one lake where bubbles of methane burst at the surface continually (minute 12). Methane emissions from these lakes can be 10 times higher than pre-existing lakes in the region.
In one scene (minute 31), researchers punch a hole through a thin layer of ice over such a lake and then light the gas stream that erupts from the hole. Methane is natural gas and highly flammable. It’s another dramatic scene!
There are uncertainties around the future of the permafrost and what will happen to the organic matter being exposed by the ongoing thaw. As microbes begin to attack the once unavailable material, they convert that organic carbon to carbon dioxide or perhaps to the more potent greenhouse gas, methane.
But some of the most dramatic images in the PBS video are about the potential for thawing permafrost to release already-existing methane trapped beneath the permafrost, some of it far underground and very, very old.
In one recently formed lake, a deep tunnel or “chimney” is found going down hundreds of feet and penetrating below permafrost to tap old to very old methane. This raises the specter of very large increases in methane release if more of these chimneys are formed. The 3-D rendering of the chimneys is excellent.
A less dramatic video on this topic has been produced by NASA, and we can put this story into the larger context of a thawing tundra in a minute, but first…
A Tipping Point Long Since Past
Near the end of the PBS video (minute 45) the interviewer asks if the tundra has passed a tipping point – a point of no return. One scientist notes that it took thousands of years to produce all the peat that is now starting to decay, and it would take thousands more to put it back.
But that misrepresents the situation in the arctic tundra because there is no going back. In terms of a human lifetime, there are no climate scenarios or pathways that will reverse the progressive thawing of the tundra. There are no models that predict the refreezing of the missing permafrost.
That tipping point happened decades ago.
Thawing Permafrost and Methane Emissions
Even the most professional presentations on a subject like this tend to emphasize the dramatic expeditions and the adventures of the field scientists who explore these remote sites. And kudos to those field scientists who brave extreme conditions (and possibly bears as well) to bring us the evidence we need.
But what is the larger context for this story? How fast is permafrost receding? How much carbon is being released as ancient organic matter is exposed to oxygen and active microbes? Is it being released as carbon dioxide or methane, and why does that matter?
Taking that last question first, methane as a gas is about 120 times as effective as carbon dioxide in trapping longwave or heat radiation. It is chemically a much more potent greenhouse gas.
However, methane does not persist in the atmosphere as long as carbon dioxide, so its impact on temperature over time is reduced, but still about 28 times the impact of carbon dioxide when calculated over a 100 year time frame.
The Future of Permafrost
Regardless of which methane impact number your use, there is no question that the arctic is warming faster than the rest of the planet, and the tremendous inertia given to the global climate system by the slow, continuous melting or retreat of permafrost portends a long and continuous release of carbon from all that ancient organic matter – even if “chimneys” into deeper and even more ancient methane do not become an important part of the story.
There is a lot of scientific literature on this subject and the numbers still contain uncertainties because of the vast and remote nature of the tundra system and the importance of small, hard to survey “hot spots” where very high rates of methane release occur. How many are there (one survey spotted 150,000 methane seeps)? What are their rates of emissions? How much do they contribute to the regional total? This could well be one of the largest unknowns in our climate future.
But this is a question of quantity, not direction – how fast, but not which way.
Here are three summaries of measured and predicted rates of change.
A satellite-based method developed to determine the extent of permafrost demonstrates a fairly dramatic reduction between 2003 and 2017.
Measurements of change in temperature in peat that still remains permanently frozen show, again, a continuous increase that will eventually approach the melting point. All measured temperatures are increasing, none are decreasing.
A recent summary paper by a large group of scientists links the rate of thaw to the rate of global warming.
This complex figure maps the predicted spatial extent of permafrost loss as a function of realized increases in global average temperature, and also graphs that continuous loss.
The lower part of the figure describes a sequence of events where an initial thaw leads to a collapse (formation of a sinkhole) as the support previously provided by frozen water is lost. The sinkhole fills with water and a “thermokarst” lake is formed. Low oxygen content in the underlying peat results in increased losses of methane (CH4). An eventual increase in new peat production is included in this scenario, but note that a return to net carbon dioxide (CO2) gain (the green arrow) only happens in the 50-150 year time period, and increased losses of methane continue throughout the 300+ year scenario.
To Sum Up
All existing measurements show that air, soil and permafrost temperatures in the arctic are increasing. There are no models that suggest that, in the absence of a very dramatic decreases in greenhouse gas emissions, these trends will be reversed.
The future of permafrost and the role of the arctic tundra in global climate change repeats a story you have seen before in these essays. Ice represents a huge source of inertia in the climate system. The increasing temperatures measured within existing permafrost included in the figure above show where permafrost is headed and the final figure above tells us how much permafrost we will lose as global temperatures increase.
As with “Zombie Ice” in Greenland, arctic permafrost is not in balance with the current climate regime, and will be even further out of balance as the climate warms. The details of how far and how fast thawing and methane emissions change are still a subject for intense research, but the direction is clear.
Inertia in ice (and in the oceans) again turns into momentum for directional change in the climate system.
There are remaining mysteries in the Arctic, but the direction is clear – less ice, more thawed soil, more lakes, more carbon dioxide, more methane.
Sources
The tundra image is from:
https://commons.wikimedia.org/wiki/File:Vontut_National_Park.jpg
Creative Commons Attribution-Share Alike 3.0 Unported license.
And the map with it is from
https://nsidc.org/learn/parts-cryosphere/frozen-ground-permafrost
The image of peat is from:
https://commons.wikimedia.org/wiki/File:Peat_(49302157252).jpg
Creative Commons Attribution 2.0 Generic license.
And the harvesting peat is from:
https://commons.wikimedia.org/wiki/File:Peat_Lewis.jpg
Creative Commons Attribution 3.0 Generic license.
Methane being 120 times as efficient at absorbing longwave or heat radiation is from:
https://climate.mit.edu/ask-mit/what-makes-methane-more-potent-greenhouse-gas-carbon-dioxide
and the value of 28 times over a 100 year period is from:
https://www.epa.gov/ghgemissions/overview-greenhouse-gases
The number of identified methane seeps (150,000) is from
https://www.nature.com/articles/ngeo1480
The double satellite image of retreating permafrost is from:
The image of changing permafrost temperatures is from:
https://www.epa.gov/climate-indicators/climate-change-indicators-permafrost
The image of change in carbon balance and peat formation in thawing permafrost is from:
https://commons.wikimedia.org/wiki/File:Hugelius_2020_peatland_projections.jpg
https://www.pnas.org/doi/full/10.1073/pnas.1916387117
Licensed under creative commons 4.0 international