Permafrost

Since the ocean floor in the Arctic is insulated by water and sea ice, one might assume there was no permafrost there. But guess again: at the bottom of certain shallow coastal seas, the ground is permanently frozen. This type of permafrost formed during the last ice age. Back then, there was so much water frozen in the massive inland ice sheets of Scandinavia and North America that in some places, the sea level was 120 metres lower than today. Where now we see ocean waves, there was solid and glacier-free land, which meant there was nothing to stop the cold from transforming broad expanses into permafrost. When the inland ice sheets ultimately melted and the sea level rose again, these areas were covered in water. Although the comparatively warm seawater and heat from Earth’s core have since gnawed away at this submarine permafrost from above and below, in some places it has survived to the present. However, it covers only a tenth as much area as land-based permafrost. The majority lies below the shallow coastal seas of the Siberian Arctic.

During the ice age 100,000 to 10,000 years ago, Northeast Siberia experienced particularly long and harsh winters. At the same time, the soil wasn’t protected by glaciers, allowing extreme and unhindered cooling. As a result, it froze to remarkable depths – and in some places, the permafrost still extends to a depth of 1.6 kilometres today.

Depending on the region and type of ground, the top 15 to 200 centimetres thaw in summer. Since this is also where the majority of biological and biochemical activity takes place, it is also referred to as the “active layer”, which, as the thawing layer, is not considered to be part of the permafrost. The layer below it remains frozen year-round. Scientists record the temperatures in both layers, together with the thawing depth, on a regular basis. While the thawing depth offers insights into short-term climate fluctuations, the temperature of the frozen layer can help identify longer-term climatic changes. For example, it can give us an overview of how global warming is affecting the polar regions and alpine regions. The outcomes of such investigations are published in the database Global Terrestrial Network for Permafrost, which is partly coordinated by the AWI. The data reveals a clearly recognisable trend: in many regions, the ground is thawing deeper and deeper in summer. This aspect is most important in the top ten metres – where the greatest risks for the global climate and the infrastructure of affected regions are.

The permafrost has a major influence on the climate; its soils are enormous deep freezes containing the remains of long-dead plants and animals, and therefore huge quantities of carbonaceous organic matter. This matter has been preserved by the cold for millennia. But when the permafrost thaws, bacteria and other microorganisms set to work breaking it down. In the process, they transform the carbon compounds in the organic matter into greenhouse gases: under dry conditions, into carbon dioxide; under wet, low-oxygen conditions, into carbon dioxide and methane. Although the latter only makes up two percent of the greenhouse gases released, it is extremely potent: over a 100-year timeframe, the global warming potential (GWP) of methane is 28 to 36 times as high as the GWP of carbon dioxide.

Experts surmise that the total permafrost regions on land alone contain between 1460 and 1600 gigatons (billions of metric tons) of organic carbon. Of that number, roughly 1024 gigatons are currently still frozen. Much of this carbon is in the upper soil layers. There’s also the carbon contained in submarine permafrost, which is very difficult to quantify. By comparison: the entire atmosphere currently contains approximately 882 gigatons of carbon.

To find out, researchers measure the permafrost’s temperature at depths below roughly 6 to 20 metres – in other words, at depths where the temperature no longer varies from year to year. Data gathered by the international monitoring programme “Global Terrestrial Network for Permafrost” (GTN-P) indicates that the permafrost warmed by 0.20 degrees Celsius from 2007 to 2016 – that was the global mean value; there were major differences from region to region. In this regard, the largest temperature increases took place in the coldest regions, e.g. Northern Canada, Northern Greenland, and Eastern Siberia, where the permafrost warmed by 0.39 degrees Celsius from 2007 to 2016. And the Antarctic shows a similar picture, with a temperature rise of 0.37 degrees Celsius in the same period.  In contrast, in the permafrost underlying mountains outside the polar regions, the GTN-P has “only” observed an increase of 0.19 degrees Celsius. But that hardly means the developments there are less critical – on the contrary: since the soils there are already warmer than in the high latitudes of the Arctic and Antarctic, a minor rise is enough to set off thawing.

Coastal erosion has worsened in the Arctic over the past few decades – due to the reduced sea-ice cover on the Arctic Ocean in summer, to higher water and air temperatures, and to rising sea levels. Less sea ice means e.g. that winds produce larger waves, which batter Arctic coasts. On average, the Arctic’s coastline is retreating by half a metre per year. However, certain stretches of coastline, which consist of particularly ice-rich permafrost, are losing up to 50 metres per year to erosion. These rapid changes have major consequences for the Arctic’s coastal ecosystem and the people living there.

The permafrost regions of the Arctic are hardly an uninhabited no man’s land: in 2017, an estimated 2.3 million people lived there. More than half of all Arctic communities are built on permafrost. They are connected by 22,000 kilometres of roads and 235 airports. But life there is changing. According to estimates prepared by AWI experts, by 2050 half of the communities built on permafrost will no longer rest atop frozen soil, and the 860,000 people now living in them will have to adjust to the fact that, by then, the ground beneath their feet will have thawed.

Above all, the thawing will make the ice-rich permafrost unstable; once the ice is gone, the surrounding soil collapses. This can have massive effects on buildings: damage to their facades can make them unstable, while cracks in the walls can lead to structural damage that makes buildings unsafe, or to compromised insulation, which can promote the formation of mildew and associated health risks. For example, in Qaanaaq, a town on the western coast of Greenland, 40 percent of the buildings are now in a state that would be classified as uninhabitable elsewhere. In addition, due to intense erosion on the coasts, entire houses are being washed away, while many cemeteries and other cultural sites are at risk. Damage to pipelines and fuel tanks can produce environmental spills on a supra-regional scale in the Arctic’s fragile ecosystems. And in the mountains, thawing permafrost is making avalanches more common.

Oil, natural gas, and other resources are mined in the Arctic, which is only possible with an intact infrastructure. But when the ground is unstable, it can do massive damage to roads, train tracks, airports, and oil and gas pipelines. According to AWI estimates, roughly a third of the Arctic’s total infrastructure and 45 percent of Russia’s oil and gas fields are located in areas at a high risk of damage. As a result, maintaining this infrastructure will likely become a much more expensive and dangerous undertaking in the future: by 2060 the maintenance and repair costs for roads and rail tracks, harbours and airports could rise by more than 40 percent, and by more than 60 percent for pipelines.

The processes at work in the world’s complex and diverse permafrost landscapes are difficult to model. Consequently, we currently only have a general idea of how much carbon these landscapes could release. A rough estimate can be found in a report issued by the IPCC in 2021, according to which, for every degree of global warming, greenhouse gases equivalent to between 14 and 177 gigatons of CO2 are released into the atmosphere. And it could be even worse if, in certain regions, the permafrost thawed abruptly – for every additional degree Celsius, between 50 and 240 gigatons of CO2 equivalent could be released by the permanently frozen soils.

As such, the warmer our planet becomes, the more greenhouse gases these regions will release into the atmosphere, and the harder it will be to prevent further warming. According to computer models, by the end of the 21st century, the thawing permafrost could produce an additional temperature rise of up to 0.29 degrees Celsius. And by 2300, warming of 0.4 degrees Celsius would be possible due to this process alone. Bearing these aspects in mind, reaching the climate protection targets defined in the Paris Agreement will be even harder than previously assumed.

It’s questionable whether (or not) humanity will be able to implement climate protection fast enough to limit global warming to 1.5 degrees Celsius. To compensate for temporarily larger temperature increases, which are accepted in some models, we would need to use technological innovations that haven’t even been invented yet, let alone refined or scaled up, to remove sufficient greenhouse gases from the atmosphere and dial back the temperature rise to 1.5 degrees Celsius. But the thawing of permafrost at higher temperatures could torpedo this strategy – firstly, because temperatures could exceed the target limit even more than feared, and secondly, because the permafrost and the carbon it stored (in some cases for millennia) can’t simply be magically restored once lost. Even if humanity managed to stop all greenhouse-gas emissions today, it would take decades for the permafrost to stop shrinking. And the enormous areas already thawed would continue to release the greenhouse gases carbon dioxide and methane for centuries. As such, it may not be possible to quickly solve the problem that anthropogenic climate change has created, especially when irreversible changes take place in the permafrost regions. In other words, once the old permafrost is thawed and the coasts eroded, it can’t be undone using restoration processes. These are issues we’ll be facing for generations to come.

In a warmer Arctic, more plants will thrive – and need CO2 in order to grow. Consequently, these green climate protectors will remove more carbon from the atmosphere and store it in their leaves, stems and roots. Initially, this could offset the greenhouse-gas emissions from the permafrost. But over extended periods and if temperatures continue to rise, microorganisms and their decomposition processes will release more greenhouse gases than the plants can absorb.

In the Alps, some small permafrost zones are already being covered with white sheets in summer to protect them from thawing. In the Arctic, experiments are also being conducted with large herbivores, which could also become climate protectors. In theory, large herds of bison, horses and reindeer could gradually transform the comparatively dark taiga into a brighter grassland that reflected more sunlight and didn’t grow so warm. And in the long winter, their hooves would churn up the snow cover, reducing the ground’s insulation. Then more cold could penetrate the soil, helping prevent thawing. However, it’s hard to imagine that the global permafrost retreat could be effectively mitigated Arctic-wide using this local approach alone: the at-risk regions are simply too large, the climate change too rapid, and the number of animals needed too unrealistic. To date, there is only one practicable way to slow the great thaw: human beings have to radically reduce greenhouse-gas emissions.