The collapse of permafrost accelerates the release of carbon

This is clear: the Arctic is warming rapidly and frozen soils are beginning to melt, often for the first time in thousands of years. But the way it happens is as cloudy as the mud that comes out of the permafrost when the ice melts.

When the soil temperature exceeds the freezing point, the microorganisms break down the organic matter in the soil. Greenhouse gases, including carbon dioxide, methane and nitrous oxide, are released into the atmosphere, accelerating global warming. Soils in the permafrost region contain twice as much carbon as the atmosphere – nearly 1,600 billion tonnes¹.

What fraction of this will break down? Will it suddenly be released or will it escape slowly? We must discover.

Current models of greenhouse gas emissions and climate assume that permafrost is gradually thawing from the surface downwards. Deeper layers of organic matter are exposed over decades or even centuries, and some models are beginning to follow these slow changes.

But the models ignore an even more troubling problem. Frozen soils not only block carbon – they keep the landscape together. In the Arctic and Boreal regions, permafrost collapses suddenly as pockets of ice melt into it. Instead of a few centimeters of soil thawed each year, several meters of soil can become destabilized in a few days or weeks. The land can sink and be flooded by the multiplication of lakes and wetlands.

The steep thawing of the permafrost is spectacular. Returning to field sites in Alaska, for example, we often find that the lands that were forested a year ago are now covered with lakes². Rivers that once flowed are thick with sediment. Hillsides can liquefy, sometimes carrying with them sensitive scientific material.

This type of thaw is a serious problem for communities living around the Arctic (see 'Arctic permafrost'). Roads give way, houses become unstable. Access to traditional foods is changing as it becomes dangerous to roam the country to hunt. Families can not reach the game traps that have sustained them for generations.

In short, permafrost thaws much faster than predicted by models, with unknown consequences for greenhouse gas emissions. Researchers urgently need to learn more about this. Here we describe how.

Twice the problem

Permafrost is a permanently frozen ground. It is composed of soil, rocks or sediments, often mixed with large chunks of ice. About a quarter of the land in the northern hemisphere is frozen. Carbon has accumulated in these frozen soils for millennia because organic matter from plants, animals and dead microbes has not degraded.

Modelers are trying to predict how much carbon will be released during permafrost melting. This is complicated: for example, they need to understand how much carbon in the air will be absorbed by the plants and returned to the soil, restoring some of what has been lost. It is forecast that a slow and steady thaw would release about 200 billion tonnes of carbon over the next 300 years under a business-as-usual scenario.³. This equates to about 15% of all soil carbon currently stored in the frozen north.

But this could be a vast underestimate. About 20% of frozen land has features that increase the risk of sudden thaw, such as large amounts of ice in the ground or unstable slopes.². Permafrost thaws rapidly and irregularly, causing landslides and rapid erosion. Forests can be flooded, killing large areas of trees. Lakes that have existed for generations may disappear or their waters may be diverted.

Even worse, the more unstable regions also tend to be the most carbon-rich². For example, 1 million square kilometers of Siberia, Canada, and Alaska contain pockets of Yedoma – thick deposits of permafrost dating back to the last ice age.⁴. These deposits are often made up of 90% ice, which makes them extremely vulnerable to warming. In addition, due to the glacial dusts and meadows that were folded when the deposits formed, Yedoma contains 130 billion tonnes of organic carbon, the equivalent of more than a decade of rain. greenhouse gas emissions around the world.

How much permafrost carbon could be released during a sudden thaw? As a first step, this year, we synthesized the results of published studies on the sudden thawing in the permafrost zone. We asked how this type of thaw affected plants, soils and soil moisture. Studies have revealed patterns of collapse and recovery. This international project was funded by the Permafrost Carbon Network (www.permafrostcarbon.org), part of the multi-million dollar global study on environmental change in the Arctic (SEARCH).

Lakes and wetlands are an important part of the problem because they release large amounts of methane, a much more potent greenhouse gas than CO₂⁵. Erosion by hills and mountains is also problematic: when the hillsides melt and dissolve, many CO₂ is released when materials are destabilized, decomposed or carried into streams or rivers⁶.

We estimate that the rapid melting of permafrost thaw in lakes and lowland wetlands, as well as in the upland hills, could release between 60 and 100 billion tonnes of carbon by 2300. This figure s adds to the 200 billion tons of carbon that should be released in other regions. regions that will gradually thaw. Although less than 20% of the frozen lands undergo a sudden permafrost thaw, they increase the permafrost carbon release projections by approximately 50%. Gradual thawing affects the frozen ground surface and slowly penetrates downward. A sudden collapse frees up more carbon per square meter because it disrupts stocks deep in frozen layers.

In addition, since the steep thaw releases more methane than the progressive thaw, the impacts of both processes on the climate will be similar.⁷. Thus, together, the effects of melting permafrost on the Earth's climate could be twice as large as those expected by current models.

Stabilize the climate at 1.5 ° C warming⁸ demands massive reductions in carbon emissions from human activities; The additional carbon emissions from melting the Arctic make this situation even more urgent.

Research Gaps

Our estimates are approximate and need to be refined. However, they show that the understanding of brutal thaw must be a research priority.

First, climate and soil scientists need to determine the most important sources of methane and CO₂ will come from. Although we have a good idea of ​​the current number of lakes and wetlands thawing⁹and how many existed in the past^tenwe must be able to project where new ones will appear. We also need to know how fast they will drain as the climate warms up.

Second, the erosion of thawed soils on the hills is poorly understood. Since it is difficult to detect collapsed slopes with satellites, only a few large-scale studies have been conducted, often using data from petroleum exploration or road surveys. Researchers need to determine how much carbon in the permafrost is displaced and what happens after thawing. For example, it is unknown how much will remain in the soil or will be buried and how much will enter the atmosphere as a greenhouse gas^11,12. And what happens to this material as it pours into rivers, lakes and estuaries?

Third, we need to determine how much plant growth will offset the carbon released by permafrost.³. Over time, lakes are invaded by wetland plants and eventually drain and reconvert to tundra. Eroded areas are colonized by plants, helping to stabilize soils and speed up their recovery. Researchers need to monitor the evolution of thawed ecosystems, the rate at which vegetation stabilizes, and how these plants accumulate biomass. Vegetation also responds to rising CO₂ and nutrients, longer growing seasons and varying levels of soil moisture. Modellers will need to anticipate the evolution of responses between ecological communities and geomorphology as the permafrost landscape changes.

Fourth, the distribution of ice in the soil is the main factor affecting the carbon fate of permafrost. However, ground ice observations are rare. More widespread geophysical measurements could map ice pockets below the surface, revealing where it is concentrated and how fast it melts. Machine learning techniques could even be developed to predict where most of the ice is buried, by analyzing soils and topography on the surface.

Next steps

To fill these gaps in knowledge, we have five recommendations.

Extend measurement technology. There should be better monitoring of permafrost and carbon in the Arctic, especially in regions with steep thawing. It is important to establish baselines of permafrost and the evolution of the ecosystem with which future measurements can be compared. This will require an aircraft-based lidar (light detection and telemetry, survey technique using pulsed laser light), drone surveys and better algorithms for image analysis.

Site Monitoring Fund. River chemistry can be a sensitive indicator of rapid melting, but many monitoring stations are being abandoned.¹³. Instead, national and international investments in long-term sites that link terrestrial observations to aquatic and marine measurements should be increased. Better records of organic matter and nutrients in rivers would provide a better understanding of how plant and microbial communities of permafrost respond to progressive melting and thawing.

Collect more data. Regions vulnerable to abrupt thaw need more drilling, long-term observatories and experiments. Field measurements should quantify the amount of CO₂ and methane is released into the atmosphere when frozen soils are disturbed and recovered. It is important to note that researchers and groups in the permafrost sector must deposit all soil ice data, even qualitative data, in public archives.

Build holistic models. Terrestrial system models should include key processes affecting permafrost carbon release, including the influence of temperature and moisture on carbon release for various climate and vegetation scenarios. Since abrupt thawing occurs at small spatial scales, detailed process models of this dynamic may not be directly exploitable in Earth system models. Frameworks need to be developed to understand and quantify the effect of these fine-scale processes at the global level.

Improve relationships. Policymakers need the best current estimates of the implications of the sudden thaw on climate change. It must be taken into account in the whole of the unresolved climate reactions, as has the Intergovernmental Panel on Climate Change (IPCC) in its special report. 2018 for gradual thawing.⁸. The Permafrost carbon network contributes to these efforts, for example by ensuring that the sudden thaw is characterized Special report on the ocean and the cryosphere in a changing climatewhich will be published later this year.

We can not stop thawing permafrost. But we can try to predict where and when this will happen, to enable decision-makers and communities to protect people and resources. Reducing global emissions could be the surest way to slow carbon emissions from permafrost into the atmosphere³. Let's keep that carbon where it belongs – frozen safely in the beautiful northern soils.