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.
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.
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.
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.
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