Fear Not for Permafrosty

 

The Permafrost Bogeyman is Back!

The Climate Scare of this Week is apparently melting permafrost.The Met Office warning on April 10:

Increased climate change risk to permafrost. Global warming will thaw about 20% more permafrost than previously thought, scientists have warned – potentially releasing significant amounts of greenhouse gases into the Earth’s atmosphere.

The researchers, from Sweden and Norway as well as the UK, suggest that the huge permafrost losses could be averted if ambitious global climate targets are met.

Lead-author Dr Sarah Chadburn of the University of Leeds said: “A lower stabilisation target of 1.5ºC would save approximately two million square kilometres of permafrost.

“Achieving the ambitious Paris Agreement climate targets could limit permafrost loss. For the first time we have calculated how much could be saved.”

The permafrost bogeyman has been reported before, been debunked, but will likely return again like a zombie that never dies. I have likened the climate false alarm system to a Climate Whack-A-Mole game because the scary notions keep popping up no matter how often you beat them down with reason and facts. So once again into the breach, this time on the subject of Permafrost.

Permafrost basics

I Travelled to the Arctic to Plunge a Probe Into the Melting Permafrost is a Motherboard article that aims to alarm but also provides some useful information.

The ground above the permafrost that freezes and thaws on an annual cycle is called the active layer. The uppermost segment is organic soil, because it contains all the roots and decomposing vegetation from the surface. Beneath the organic layer is the moist, clay-like mineral soil, which sits directly on top of the permafrost. The types of vegetation will influence the contents of the soil—but in return, the soil determines what can grow there.

Kholodov inserted probes into the layers of soil and the permafrost to measure its temperature, moisture content, and thermal conductivity. The air-filled organic layer is a much better insulator than the waterlogged mineral soil. So an ecosystem with a thicker organic layer, where there’s more vegetation, should provide better protection for the permafrost below.

On a warm morning in the boreal forests around Fairbanks, Loranty squeezed between two black spruce trees and motioned to all the woody debris scattered on the ground. “Here, where we have more trees and denser forests, we have shallower permafrost thaw depths.”

He grabbed a T-shaped depth probe and shoved it into the ground. It only sank about a handspan before it struck permafrost. “When you have trees, they provide shade,” he said, “and that prevents the ground from getting too warm in the summer.” So here, the permafrost is shallow, right beneath the surface.

Other vegetation, like moss, can also protect permafrost. “It’s fluffy, with lots of airspace, like a down coat,” Loranty explained, “and heat can’t move through it well, so it’s a good insulator.”

But 800km north on the tundra, close to the Arctic Ocean, there are no trees. It’s a less productive ecosystem than the forest and provides little insulation to the frozen ground. Here, low-lying shrubs, grasses, and lichens dominate underfoot. When I grabbed the depth probe and pushed it in, it sunk down a meter before it bottomed out because the permafrost was much deeper.

Permafrost Nittty Gritty

To really understand permafrost, it helps to listen to people dealing with Arctic infrastructure like roads. A thorough discussion and analysis is presented in Impacts of permafrost degradation on a road embankment at Umiujaq in Nunavik (Quebec), Canada By Richard Fortier, Anne-Marie LeBlanc, and Wenbing Yu

Fig. 1. Permafrost distribution and marine transgression in Nunavik (modified after Allard and Seguin 1987). Location of the 14 Inuit communities in Nunavik.

Following the retreat of the Wisconsin Ice Sheet about 7600–7300 years B.P. on the east coast of Hudson Bay (Hillaire–Marcel 1976; Allard and Seguin 1985) and about 7500– 7000 years B.P. in Ungava (Gray et al. 1980; Allard et al. 1989), the sea flooded a large band of coastline in Nunavik (Fig. 1). Glaciomarine sediments were then deposited in deep water in the Tyrrell and D’Iberville Seas (Fig. 1). Due to the isostatic rebound, once exposed to the cold atmosphere, the raised marine deposits were subsequently eroded and colonized by vegetation, and permafrost aggraded from sporadic permafrost to continuous permafrost with increasing latitude (Fig. 1).

A case study is presented herein on recent thaw subsidence observed along the access road to the Umiujaq Airport in Nunavik (Quebec). In addition to the measurement of the subsidence, a geotechnical and geophysical investigation including a piezocone test, ground-penetrating radar (GPR) profiling, and electrical resistivity tomography (ERT) was carried out to characterize the underlying stratigraphy and permafrost conditions. In the absence of available ground temperature data for assessing the causes of permafrost degradation, numerical modeling of the thermal regime of the road embankment and subgrade was also undertaken to simulate the impacts of (i) an increase in air temperature observed recently in Nunavik and (ii) the thermal insulation effect of snow accumulating on the embankment shoulders and toes. The causes and effects of permafrost degradation on the road embankment are also discussed.

Fig. 11. (a) GPR reflection profile carried out on 14 July 2006 in the field with the 100 MHz antennas at a fixed offset of 1 m. (b) Major reflectors identified on the GPR reflection profile. (c) Cross section of the ground based on the combined interpretation of the GPR reflection profile and model of electrical resistivity (Fig. 12c). Note the vertical exaggeration (1:5).

Values of thawing and freezing n-factors according to the surface conditions (Figs. 4 and 13) are given in Table 1. The gray road surface absorbs solar radiation in summer, inducing a higher surface temperature than air temperature and a higher thawing n-factor than the ones for the natural ground surface. The thawing n-factor is close to unity and the surface temperature is close to the air temperature in summer for the natural ground surface (ground surface boundaries Nos. 2, 3, and 4). Due to the absence of snow cover on the road surface, the freezing n-factor is close to unity. However, an increase in snow thickness leads to a decrease in the freezing n-factor (Fig. 13 and Table 1). We make the assumption that from one year to another there is no change in surface conditions due to climate variability and the thawing and freezing n-factors are constant.

Fig. 13. Cross section of the road embankment and subgrade showing the stratigraphy and boundary conditions used for the numerical modeling. The numbers between arrows refer to the ground surface boundaries (Table 1)

Only the governing equation of heat transfer by conduction taking into account the phase change problem was considered to simulate the permafrost warming and thawing underneath the road embankment. However, complex processes of heat transfer, groundwater flow, and thaw consolidation can take place in degrading permafrost. The development of a two dimensional numerical model of these coupled processes is needed to accurately predict the thaw subsidence based on the thaw consolidation properties of permafrost and to compare this prediction with the performance of the access road to Umiujaq Airport.

As expected from the design of thick road embankments in cold regions,the permafrost table has moved upward 0.9 m underneath the road embankment, preventing permafrost degradation (Fig. 14a). However, the permafrost is slightly warmer by a few tenths of degree Celsius underneath the road embankment than away from the road (Fig. 15). This increase in permafrost temperature due to the thermal effect of the road embankment makes the permafrost more vulnerable to any potential climate warming. The permafrost base in the bedrock has also moved upward 3.9 m for a permafrost thinning of 3 m (Fig. 15). This thawing taking place at the permafrost base does not induce any thaw settlement because the bedrock is thaw stable.

The subsidence is due to thaw consolidation taking place in a layer of ice-rich silt underneath a superficial sand layer. While the seasonal freeze–thaw cycles were initially restricted to the sand layer, the thawing front has now reached the thaw-unstable ice-rich silt layer. According to our numerical modeling, the increase in air temperature recently observed in Nunavik cannot be the sole cause of the observed subsidence affecting this engineering structure. The thick embankment also acts as a snow fence favoring the accumulation of snow on the embankment shoulders. The permafrost degradation is also due to the thermal insulation of the snow cover reducing heat loss in the embankment shoulders and toes.

Permafrost in Russia

Yakutsk Permafrost Institute Underground Lab

The Russians are seasoned permafrost scientists with Siberia as their preserve, and their observations are balanced by their long experience. The latest Russia report is from 2010.

We conclude the following based on initial analysis and interpretation of the data obtained in this project:

  • Most of the permafrost observatories in Russia show substantial warming of permafrost during the last 20 to 30 years. The magnitude of warming varied with location, but was typically from 0.5C to 2C at the depth of zero annual amplitude. This warming occurred predominantly between the 1970s and 1990s. There was no significant observed warming in permafrost temperatures in the 2000s in most of the research areas; some sites even show a slight cooling during the late 1990s and early 2000s.
  • Warming has resumed during the last two to three years at many locations predominantly near the coasts of the Arctic Ocean. Much less or no warming was observed during the 1980s and 1990s in the north of East Siberia. However, the last three years show significant permafrost warming in the eastern part of this region.
  • Permafrost is thawing in specific landscape settings within the southern part of the permafrost domain in the European North and in northwest Siberia. Formation of new closed taliks and an increase in the depth of preexisting taliks have been observed in this area during the last 20 to 30 years.

Methane Realism

An article in Scientific American raises several concerns about permafrost, but does add some realism:

First, while most of the methane is believed to be buried roughly 200 meters below the sea bed, only the top 25 meters or so of sea-bed are currently thawed, and thawing seems to have only progressed by about one meter in the last 25 years – a pace that suggests that the large bulk of the buried methane will stay in place for centuries to come.

Second, several thousand years ago, when orbital mechanics maximized Arctic warmth, the area around the North Pole is believed to have been roughly 4 degrees Celsius warmer than it is today and covered in less sea ice than today. Yet there’s no evidence of a massive amount of methane release in this time.

Third, the last time methane was released in vast quantities into the atmosphere – during the Paleocene-Eocene Thermal Maximum 56 million years ago – the process didn’t happen overnight. It took thousands of years.

Put those facts together, and we are probably not in danger of a methane time bomb going off any time soon.

Summary

The active layer of permafrost does vary from time to time and place to place. There was warming and some permafrost melting end of last century, but lately not so much. Any specific permafrost layer is influenced by many factors, including air temperatures, snow cover and vegetation, as well as the structure of the land, combining fill, sand, silt, ice and salinity mixtures on top of bedrock.

And nature includes negative feedbacks to permafrost melt. Any vegetation, even moss, growing in unfrozen soil provides insulation limiting further melting, as well as absorbing additional CO2. Reduced snowcover aids freezing and constrains later melting.

Rather than a permafrost bogeyman, we need a more people-friendly mascot. Consider our traditional nature friends loved by children and adults.

For example, Smokey the Bear

Rudolph the Reindeer

And the ever-popular Cola Bear

Introducing Permafrosty



Permafrosty is here!  Love him tender, and he’ll never let you down.

Additional Background on Permafrost in an earlier post The Permafrost Bogeyman

 

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