In areas where temperatures rarely rise above the freezing point of water and the summer warmth cannot penetrate the ground to thaw the soil, a frozen layer of rock, soil or organic material remains locked in the ground. The geological term for these layers is permafrost, a term coined by the American geologist Siemon W. Muller in 1943 (Page et al, 1970). The conditions that are conducive to the formation of permafrost prevail in high-latitude or high altitude mountainous areas that cover roughly a quarter of the earth’s surface —Alaska, Canada or Siberia, Antarctica etc. For a layer of frozen soil to be defined as permafrost, it has to remain at or below 0oC for two consecutive years (IPA, 2006). In the Southern Hemisphere, permafrost occurs in the Andes Mountain in South America, the Southern Alps in New Zealand, Tasmania, and almost the whole of the Antarctic. Permafrost occurrence is lower in the Southern Hemisphere as the land area is much less then that of the Northern Hemisphere (National Snow and Ice Data Centre, 2008).
Permafrost acts a giant freezer, keeping buried large quantities of organic carbon, microbes, mercury and methane, the release of which can potentially accelerate global warming and climate change (Grosse et al, 2016). With global temperatures rising, the thawing accelerates microbial breakdown of organic carbon and consecutively, the release of greenhouse gases in the form of carbon dioxide (CO2) and methane (CH4). A highly potent greenhouse gas, methane’s potential for warming the climate is five times than that of carbon dioxide. The loop is as simple as it is dangerous – the more the increase in global warming, the higher the permafrost thaw and so on (ibid). While the immediate effects of permafrost thaw are local and visible — such as roads warping in Alaska and craters opening up in regions of Siberia and Canada — it is difficult to ascertain the magnitude and timing of the greenhouse gas emissions from these regions and their long term impact on climate change (Moskvitch, 2014).
The Disruptions from Permafrost Thaw
As noted by the International Permafrost Association (IPA), headquarted in the Norwegian archipelago of Svalbard, permafrost formation began in the cold glacial periods, persisting through the Holocene (a geological epoch that began about 11,700 years ago). Shallow permafrost, at a depth of about 30 to 70 m was formed during the second part of the Holocene i.e., during the last 6,000 years and during the Little Ice Age that lasted 400 to 150 years ago (IPA, 2006). While by definition, permafrost is ground that has remained below a temperature of 0oC for more than two consecutive years, as a geological phenomenon, permafrost has existed for millions of years and occupies about 25 per cent of land area (Fig. 1) in the Northern Hemisphere; the land area in Southern Hemisphere being lesser, the occurrence of permafrost is lower.
Currently as much as 1,400 to 1,850 billion metric tonnes of carbon from plant matter and animal fossil are trapped in permafrost. This amount is about half of all the estimated organic carbon stored in the earth’s soils (National Aeronautics and Space Administration, 2013). As the permafrost thaws, microbial activity begins to decompose the locked organic matter, releasing carbon dioxide when the digestion is aerobic and methane when the digestion is anaerobic (Schaefer, 2018). The release of these gases further speeds up the rate of permafrost thaw (Fig 2).
Thawing permafrost could potentially release into the atmosphere around 120 gigatons of carbon by 2100, resulting in 0.29oC of additional warming (Schaefer et al, 2014). As we move further, in time, by 2300, the feedback loop from melting permafrost will result in an additional warming of about 1.69oC (MacDougall et al, 2012).
“Permafrost is ground that remains at sub-zero temperature for two consecutive years, although a large amount of it has existed for centuries. In some regions, cities are located on or close to permafrost. So in the short run, infrastructural damage in areas close to permafrost is likely to occur,” Dr Shin’ichi Kuramoto, Director General at Center for Deep Earth Exploration, Japan, noted while speaking with G’nY. “Residential areas will face a crisis as sea levels rise, both from permafrost thaw and increased global warming, threatening to submerge land surface close to the seas.”
The studies that have predicted the rate of thaw, emission of greenhouse gases and increase in global warming are as per present estimates. Much debate exists over the rates at which permafrost thaw can affect global temperatures. While some scientists have pointed towards a sudden upsurge in carbon breakdown and emissions in the form of ‘carbon bombs’ (Treat and Frolking, 2013), others (Schurr et al, 2015) have countered this idea, instead stating that while the thaw and consequent emissions are persistent, they are more likely to be gradual, spread over decades and centuries (Rosen, 2016).
At the same time, the study (Schurr et al, 2015) that countered the concept of carbon bombs was restricted to permafrost on land alone. Scientists who undertook the study have also pointed out that subsea permafrost and methane pose an entirely different set of questions and challenges (Rosen, 2016). In places like the East Siberian Arctic Shelf, assessment is much more difficult. A 2014 study (Shakhova et al, 2014) found that significant quantities of methane were escaping from this area as a result of the degradation of submarine permafrost over thousands of years.
Speaking with G’nY, Dr Parmanand Sharma, scientist at National Centre for Antarctic and Ocean Research, Goa, notes, “The rate of permafrost thaw and the extent to which it will contribute to an increase of carbon in the atmosphere will differ in different areas. In some regions it may contribute to slight increase in water flow. But there is no doubt that carbon dioxide emissions are likely to increase if thawing speeds up. Even a 0.1oC increase in global temperatures will result in a significant amount of permafrost melt and release of carbon dioxide.”
Mercury release from permafrost
It is not just carbon that lies trapped inside the layers of permafrost. In the Alaskan region, scientists recently discovered that besides carbon, permafrost soils also contain the largest reservoirs of mercury — a neurotoxin — on the planet, storing twice as much as of the chemical as all other soils, the ocean and the atmosphere combined. While carbon in permafrost is formed by the deposition and freezing of organic matter, in the case of mercury, natural mercury in the atmosphere binds with organic material in the soil, gets buried by sediment and becomes frozen into permafrost (Schuster et al, 2018). The study estimated more than 15 million gallons of mercury in the northern permafrost soil.
The major threat that mercury poses is through its potential to leach out of the soil into surrounding waterways. In this case it could be absorbed by microorganisms and transformed into methyl mercury, a toxin that can travel up the food chain and cause neurological effects ranging from motor impairment to birth defects (American Geophysical Union, 2018).
Permafrost and the Carbon Budget
Carbon budget is the estimated amount of carbon dioxide humans can emit while still having a likely chance of limiting global temperature rise to 2oC above pre-industrial levels. This is the target that the Paris Agreement intends to achieve (Harvey, 2018). If, on the other hand, we exceed our carbon budget through unabated emissions, sea levels could be nearly 1 m higher by 2100, fires in the Amazon rainforest could almost double by 2050 and annual runoff in the Nile and the Ganga river basins will increase by roughly 20 per cent, causing significant flooding (World Resources Institute, 2014).
However, calculations for the carbon budget – which at the rate of current emissions is likely to be exhausted in the next 18 years — do not factor in permafrost thaw. The carbon budget is likely to be much smaller than previously thought. The United Nations Emissions Gap Report 2017 has already recorded that the cuts in emissions pledged by different nations cover merely one-third of the actual emission cuts needed and that if the gap is left unchecked by 2030, it is highly unlikely that the goal of containing global warming to below 2oC will be achieved.
If the permafrost thaw is factored in, the projected carbon and methane emissions are likely to add to the current emissions, further lowering the chances of keeping the carbon budget in check (Chaudhary, 2015).
Permafrost occurrence in the Himalayan Regions
A considerable area of the Himalaya is underlain by frozen ground and is sensitive to climate change. Besides the risk of long term emission of greenhouse gases, significant thawing poses risks of landslides and avalanches, which will drastically affect an already altering landscape (Ali et al, 2018). While glaciers have been substantially studied in the northwestern Himalaya, permafrost is not observable spatially and as such the data available on its conditions in the Himalayan region is sparse (Gruber et al, 2017). Some studies (ibid) have used the experiences and findings made in the Arctic regions to infer what the features of permafrost in these regions are and what the effects from thawing will be. While the Himalayan region is diverse and conditions therefore vary, there is increasing evidence that the impacts will be greatly felt on vegetation, water quality, and livelihoods (Ali et al, 2018). In the past two years progress has however been made in estimating the impact of global warming on the permafrost regimes of the Himalayan realm with scientists from the National Institute of Hydrology and Indo-Swiss Indian Climate Adaptation Programme undertaking field measurements and modeling (Mullick, 2017).
As mentioned earlier, the scientific community is divided on whether the carbon emissions from permafrost thaw will have a drastic impact on global temperatures, largely owing to the fact that there is no defined method of calculating on how much of permafrost can melt and the quantity of carbon that can thereby be released.
A July 2018 study conducted in permafrost zones in Sweden extracted over 1,500 microbial genomes from intact, thawing and thawed sites to study the genetic composition of the microbes that cause the decomposition of carbon. By understanding the activities and capabilities of the microbes that cause decomposition, a better estimate of the speed of emissions and therefore, climate change, may be calculated, which will in turn help us develop a clearer timetable for response (Woodcroft et al 2018).
While permafrost thaw and the rates at which they can emit greenhouse gases are debated subjects, one thing is clear — anthropogenic interventions and the consequent rise in global temperatures are drastically affecting the fragile environment of permafrost regions. If the thawing speeds up, it is highly unlikely that the goals for containing carbon emissions and rising global temperatures will be achieved.
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