A thawing, rotting Arctic?

Permafrost thaw causes the ground to become unstable as the soil collapses. This can damage building and roads built on permafrost. Cracks also expose the carbon stored within to sunlight, which may speed the release of carbon dioxide, a greenhouse gas. Photo credit: Dentren (http://upload.wikimedia.org/wikipedia/commons/a/ac/Storflaket.JPG)

Permafrost thaw causes the ground to become unstable as the soil collapses. This can damage building and roads built on permafrost. Cracks also expose the carbon stored within to sunlight, which may speed the release of carbon dioxide, a greenhouse gas.
Photo credit: Dentren (http://upload.wikimedia.org/wikipedia/commons/a/ac/Storflaket.JPG)

As greenhouse gas emissions continue to rise, researchers are looking at a source of even more carbon emissions: thawing permafrost. A warming Arctic may cause significant amounts of dead, organic material currently frozen in permafrost to thaw out and decay, releasing more carbon into the atmosphere. How exactly does permafrost store carbon? And what are the consequences if the permafrost thaws?

Carbon and permafrost

Permafrost is soil with temperatures at or below 0 degrees Celsius for at least two or more  years in a row.  Some areas of permafrost absorb enough heat  in the summer time to let the topmost layer of soil, called the active layer, to temporarily thaw, allowing plants to grow and animals to find food. Underneath this layer, the soil remains frozen, preventing decay and preserving plant matter and organic material for thousands of years.

If temperatures rise and permafrost thaws, the organic material decays, and the soil becomes wet and marshy. As the organic material rots, most of the carbon is released into the atmosphere as carbon dioxide, but in this moist environment, a significant fraction of the carbon is released as methane, a potent greenhouse gas.  When the frozen ground thaws, the soil may also collapse and creates holes in the tundra, exposing the old carbon directly to the atmosphere and accelerating its decay.

This airport in Greenland was built on formerly frozen ground. As the permafrost thaws, the runways sink and crack as do the roads around it, impairing aircraft travel to the area. In fact, airport managers have already repaired part of a runway that sank into melting permafrost.  Photograph credit: Jamie McIntyre (http://www.flickr.com/photos/obstreperously/3793709435/)

This airport in Iqaluit, Nunavut, was built on formerly frozen ground. As the permafrost thaws, the runways sink and crack as do the roads around it, impairing aircraft travel to the area. In fact, airport managers have already repaired part of a runway that sank into melting permafrost.
Photograph credit: Jamie McIntyre (http://www.flickr.com/photos/obstreperously/3793709435/)

Local consequences

On a local scale, permafrost thaw has direct and immediate impacts for people and animals living in the Arctic. As the ice in the permafrost  melts, the ground becomes unstable. Houses and buildings that previously rested on solid frozen soil sink and structural foundations crack. Thawing permafrost  also causes roads to heave and crack, making travel difficult.

When temperatures rise and the active layer becomes thicker, the Arctic is also likely to become greener as more plants are able to survive the terrain and climate. Arctic tundra vegetation and needle-leaf forests are advancing northward, as deciduous shrubs and other nonnative vegetation edge to higher latitudes. The encroaching shrubs replace the tundra vegetation, which feeds caribou, hares, and marmots. In turn, these animals are vital food sources for Arctic predators. Thawing permafrost may lead to a decline in biodiversity for both vegetation and wildlife.

Uneven settling due to permafrost thaw destroyed this apartment building in Cherski, Siberia. The settling occurred only days after the first cracks appeared. Photo credit: Vladimir Romanovsky

Uneven settling due to permafrost thaw destroyed this apartment building in Cherski, Siberia. The settling occurred only days after the first cracks appeared. Photo credit: Vladimir Romanovsky

Global impacts

While local effects of thawing permafrost are worrisome, the sheer amount of carbon that could be released in the future concerns everyone. Scientists estimate that Arctic permafrost contains nearly 1,700 billion tons of carbon, about twice  the carbon  currently in the atmosphere. Methane is over twenty-five times more potent at retaining heat than its carbon dioxide counterpart. In addition, carbon dioxide released due to thawing permafrost is a phenomenon only recently discovered and could convert Arctic carbon into carbon dioxide much more quickly than previously thought.

As the Arctic continues to thaw, scientists continue to study its impact on local and global systems, as well as raise awareness about increased greenhouse gas emissions in the atmosphere. The carbon released into the atmosphere from permafrost, either as methane or carbon dioxide, accelerates the increase global temperatures, which may thaw  more frozen ground. At this rate, permafrost may be not only a consequence of global climate change, but a contributor to it as well.

References

Cory, R. M., R. C. Crump, J. A. Dobkowski, and G. W. Kling. 2013. Surface exposure to sunlight stimulates CO2 release from permafrost soil carbon in the Arctic. Proceedings of the National Academy of Sciences of the United States of America 110(9), doi:10.1073/pnas.1214104110.

Schaefer, K., T. Zhang, L. Bruhwiler, and A. P. Barrett. 2011. Amount and timing of permafrost carbon release in response to climate warming. Tellus 63B: 165-180.

Links to previous Icelights posts and sources for more information

What does seeping methane mean for the thawing Arctic?

NSIDC’s All About Frozen Ground

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