Context - Tipping Points– Permafrost Thaw

Overview
Mechanisms
Impacts
Reference Articles
Recent Articles

(Article Note – All references used in the Article are listed at the end of the article. Direct quotations are indicated in italics with emphasis highlighted in maroon.)

1. Overview – Permafrost Thresholds

(from McKay et al, Science (2022)

Type – Principal and supplemental feedbacks leading to potential major tipping point of runaway GHG releases
Temperature Threshold (estimated) +4 degrees C (min 3C – max 6C)
Abrupt Change Possible – Yes (high confidence)
Reversibility – Irreversible – over multiple centuries (high confidence)
Timeframe (estimated) to threshold – 200 years (minimum – 100 years, maximum – 300 years) assuming no change in current emissions pathways
Impact Scale – Global and Regional

2. Mechanisms

Basic Feedback and Tipping Point Summary

– The basic mechanism is simple and intuitive – Permafrost is long-term frozen ground which in the arctic region reaches several meters in depth. Climate change causes atmospheric heating which thaws the permafrost (leaving ‘thermokrast’ lakes pock marking the landscape resulting from the thaw). As the frozen ground begins to thaw bacteria are activated and work to break down organic matter that has accumulated over for hundreds and thousands of years. The breakdown of this organic material releases potentially vast amounts of greenhouse gases (GHG); either carbon dioxide (CO2) or methane (CH4) where oxygen isn’t present, which is primarily in waterlogged conditions.

Thermokrast – Featured Image from ClimateTippingPoint.Info : Permafrost thaw ponds in Hudson Bay Canada near Greenland. By Steve Jurvetson http://www.flickr.com/photos/44124348109@N01/2661598702 en:Flicker.com, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=34436593

The release of these GHGs contribute to the further warming of the atmosphere which in turn drives deeper thaw and further releases of GHGs in further cycles of this positive, reinforcing feedback. The feedback can work slowly over decades and centuries as the ground is gradually warmed by the warmer air conditions overhead or it can be significantly accelerated by other indirect, additional warming related feedbacks.

The other factors accelerating permafrost are several climate change drivers including: increased wildfires, increased precipitation and widespread accumulation and penetration of water into the frozen ground, loss of snow cover(approximately 800,000km2 or 13.4% per decade according to IPCC’s Special Report on the Ocean and Cryosphere (SROCC) and related loss of heat reflectivity (albedo) all combing to result in ‘abrupt thawing’ and the faster cycling of the feedback.

A second direct form of feedback is the heat that is directly generated by the bacteria as they breakdown the organic matter, separate to the greenhouse gases that are released. This local heat generation in the frozen soil is doubly significant as it directly drives further thaw, further heat generation and release of greenhouse gases in what has been described in the Carbon Brief article a ‘compost bomb’.

Further Details:

Area Affected

Permafrost covers approximately one quarter of non-glacial land of the northern hemisphere as well as shall parts of the Arctic and the Arctic as reported by NOAA is warming up to three times faster than the rest of the world.

The SROCC indicates that record high temperatures at soil depths of between 10-20m have been reported at many long term monitoring sites in the polar regions and in some cases up to 3C higher than 30 years ago. The SORCC Technical Support states:

d ‘By 2100, near-surface permafrost area will decrease by 2–66% for RCP2.6 and 30–99% for RCP8.5. This is projected to release 10s to 100s of billions of tons (Gt C), up to as much as 240 Gt C, of permafrost carbon stored as carbon dioxide and methane to the atmosphere with the potential to accelerate climate change’.

The following diagram presented in TippingPoint.info shows the regions currently impacted, extent and rates of thawing.

A map showing the major permafrost regions bordering the Arctic ocean, and where the thaw is happening fastest. Source: Turetsky et al. (2019), Nature; data from Refs. 1 & 2

Rapid/Abrupt Thaw

The SROCC Technical Summary indicates that about 20% of the Arctic permafrost is vulnerable to abrupt permafrost thaw. Because of the acceleration of the feedback cycle described earlier, large scale abrupt thawing would represent a type of tipping point as a threshold where small further amounts of thawing results in the unleashing of large scale non-linear greenhouse gases emission response.

SROCC describes abrupt permafrost thaw in the following terms: ‘Abrupt permafrost thaw occurs when changing environmental and ecological conditions interact with geomorphological processes. Melting ground ice causes the ground surface to subside. Pooling or flowing water causes localised permafrost thaw and sometimes mass erosion. Together, these localised feedbacks can thaw through meters of permafrost within a short time, much more rapidly than would be caused by increasing air temperature alone. This process is a pulse disturbance to permafrost that can occur in response to climate, such as an extreme precipitation event (Balser et al., 2014)’

However the SROCC, Carbon Brief and ClimateTipping Point all agree that the actual tipping point is unclear and the climate modelling is not sufficiently defined to accurately predict timescales of such an event. The consensus from the reporting in SROCC, Carbon Brief and ClimateTippingPoint.info is that while abrupt thaw may occur in certain localised regions, in words of Dr David Armstrong McKay (lead on the ClimateTippingPoint.Info site) the permafrost thaw “will act as more of a continuous positive feedback on climate change rather than an abrupt tipping point” (Carbon Brief)

However the consensus is also clear that the thawing will be irreversible over timeframes relevant to humans. As noted in Carbon Brief from Dr Andy Wiltshire, Met Office Hadley Centre, ‘the carbon contained in the soils has built up over an incredibly long periods of time. Once it is lost to the atmosphere, there is no getting it back.’

Methane Hydrates

A related major concern has arisen in recent years as documented in Climatetippingpoint.info related to the potential for massive leakage of methane hydrates under warming ocean conditions from the seabed, particularly in an area in Northern Russia, the East Siberian Arctic Shelf. The site reports in particular three reports on the issue which suggested that the event could be imminent and discharge an enormous amount of Greenhouse Gases in as little as 1 – 5 years in what would be catastrophic relative to the amount of greenhouse gases currently in the atmosphere. However Climatetippingpoint.info analyses the details of the reports and finds that the actual report findings have been exaggerated in the retelling and that the growth in emissions has not been exponential, the sources of the increased methane is not mostly from other sources (not permafrost, from isotope analysis) and that satellite monitoring has significantly improved the accurate estimation of methane release in the region. It concludes:

‘The most likely situation then is one of a gradually growing chronic leakage of additional methane and CO2 from the Arctic over the coming decades and centuries, rather than an abrupt “methane bomb”. This will act as a gradual amplifier of human-driven global warming, making staying within the Paris Targets of 1.5-2°C even more challenging and urgent.’

3. Impacts

Quantities

Current SROCC reports that permafrost temperatures have increased to record high levels driving increased permafrost thaws as seen above and both SROCC and the latest NOAA 2024 Arctic Report Card indicate that there is 1.4 to 1.6 trillion tonnes of carbon accumulated in the frozen soils across the region. While the ClimateTippingPoint.info indicates that there is widespread alarm of the affect that the release of just 1% would have on the climate and global warming. However whilst 1.5 trillion tonnes sounds like a lot of carbon, 1 per cent would be approximately equivalent to the amount of carbon discharged annually by humans into the atmosphere ( 1% of 1.5 trillion tonnes = 15 Giga tonnes of Carbon = 55 Giga tonnes of CO2). Nevertheless it is still a lot of carbon and the estimations are very rough and a hoping for the best approach!

Carbon Dioxide or Methane

It also matters in what form that carbon is released; either as carbon dioxide (CO2) or methane (CH4) as methane has x85 times the warming impact of carbon dioxide over a 20 year period but also decays much more rapidly in the atmosphere than CO2 (which remains for several hundred years before gradually declining). So if 15GtC (ie 1% of the estimated stored Carbon in Permafrost) was to be discharged as Methane it would quickly lead to additional warming of 1.1C which would indeed have devastating consequences for the climate and all other systems on earth in both the size and speed of the temperature increase.

However, in a critical estimation, ClimateTippingPoint.Info reports that most of the bacteria driving the decay release CO2 instead of methane (which is confined to waterlogged soils where anaerobic bacteria operate) and that Overall, ‘the proportion of carbon released as methane has been estimated at ~2% of future emissions’. But that would itself be enough to boost the impact of the carbon emitted by 40% over the next century, illustrating the powerful difference the type of emission can make.

Future Emissions

ClimateTippingPoint.Info goes onto to consider what sort of emissions we can expect in the future and what the warming impact would be. It indicates under the most severe emissions pathway (RCP8.5) 71–92 Gt Carbon could be released by gradual thawing by 2100 which, incidentally, is much higher than the 1% release considered earlier.

A second study indicated that 10% of permafrost carbon could be released by 2100 which would be 130-160Gt Carbon resulting in an additional 0.3-0.4C, under the lowest emission scenario, limited to 20-58 GtC (+~0.1°C). In the same vein, it reports the IPCC indication that permafrost emissions could reduce the available carbon budget by 27GtC ~27 GtC (=100 GtCO₂) which considering that that 1.5 degree warming budget is now is estimated to about 250 GtCO2 (50% chance) or 1,200GtCO2 for the 2.0 degrees warming, the release would have an enormous impact on remaining carbon budgets, to remain within relatively safe heating boundaries, from permafrost source alone.

Conclusion

From the above figures, it doesn’t really matter whether we characterize permafrost carbon as a tipping point in terms of abrupt emissions or more gradual, what is clear is that the impact will be significant even on the lowest warming scenario (aligned to Paris Agreement goals) and potentially devastating on current or higher emission pathways over the next hundred year, with heating of up to an additional 0.5C conservatively estimated from this one source.

The second important point is that we are dealing with rough estimations and fine margins – the estimate that only 2% of the gases emitted when permafrost thaws is methane as noted earlier is a critical estimation. But it is only an estimate of how a very complex systems will behave – if it is incorrect by small fractions, say 1% or 2%; this would more than double the amount of Methane being released which because of the much greater warming potential of Methane compared to Carbon would have immense consequences for the temperature increases on Earth.

As will be seen in another Context article on paleoclimatology, it was the runaway release of Methane and large temperature rises in a reinforcing feedback loop approximately55 million years ago during the ‘Paleocene-Eocene Thermal Maximum’ (PETM) that made the earth within in a geologically short space of time largely uninhabitable. Being out by marginal amounts could have significant consequences, even if not on the total life devestation scale of the PETM.

[technical note –1 tonne Carbon (1tC) = 3.67 tonnes Carbon Dioxide (1tCO2) some sources describe in terms of Carbon and others in Carbon Dioxide – the conversion factor of x 3.7 is applied to Carbon to describe the global warming potential (GWP) in terms of CO2 which has by definition a GWP of 1 and the warming potentials of all other GHGs are measured against that standard ]