Permafrost melt causes dramatic greenhouse gas emissions

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Regions at high latitudes have seen a 0.6°C rise in temperature over the last 30 years: almost twice as fast as the average rate of global warming. This especially fast rate of warming produces increased ice melt, rising sea level and loss of Arctic species. One particular consequence that has been largely overlooked is the gradual melting of permafrost in the Arctic.

Permafrost is soil that is permanently maintained at 0°C or lower. Such conditions are possible only in the high latitude environments that cover roughly a quarter of Earth’s surface, including Alaska, Canada and Greenland. Large amounts of organic matter accumulated over thousands of years are stored in permafrost. It is estimated that permafrost soils contain approximately 1,700 gigatonnes of carbon nearly twice the amount of carbon in atmospheric reserves. The melting of permafrost, due to rising temperatures, threatens to release this sequestered carbon.

Permafrost soil is only found in the northernmost regions of the Earth.
Permafrost soil is only found in the northernmost regions of the Earth

Melting permafrost has many short-term implications such as damaging infrastructure and threatening ecosystems. Most important, however, is the looming threat of releasing trapped carbon. When the permafrost is frozen, carbon is shielded from decomposition. The melting permafrost subjects sequestered organic matter to microbial decomposition, which releases large amounts of carbon into the atmosphere. This emitted carbon will work to enhance the effects of global warming, indirectly leading to additional melting of the permafrost and greater release of carbon. In this way, a vicious cycle can settle in. There may be a tipping point at which this feedback loop becomes uncontrollable.

Long-term monitoring of permafrost in high latitude environments indicates a gradual warming trend combined with thinning of the permafrost. Recent research has found that up to 120 gigatonnes of carbon may be released from thawing permafrost equivalent to one tenth of the total permafrost pool. The released carbon could result in up to 0.5°C of additional warming. To further complicate the matter, carbon released from permafrost can take one of two forms: carbon dioxide (CO­2) or methane (CH4). The form it takes depends on the conditions of decomposition: where abundant oxygen is available for decomposition, carbon dioxide will be released, but where there is little to no oxygen, methane is emitted instead. While methane is currently not as important as carbon dioxide in contributing to the greenhouse effect, it is a dormant danger. Methane has the ability to trap 25 times more heat than carbon dioxide, depending on the time scale considered. Unlike carbon dioxide, methane is not released through fossil fuel emissions, but there is a large natural source of methane and thawing of permafrost will increase its emissions.

The predicted one tenth of permafrost carbon that may be released is effectively equal to twenty years of present human-induced carbon emissions, but thawing of permafrost is not currently considered in emission scenarios produced by the Intergovernmental Panel on Climate Change (IPCC). This may be a mistake as it renders the global target of limiting warming to 2°C unrealistic. This body of data strengthens the case for cutting human-induced carbon emissions to ensure carbon stored in permafrost soils remains frozen.

Photograph: William Troyer, U.S. Fish and Wildlife Service via Wikimedia Commons

Illustration: NASA via Wikimedia Commons

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