気候変動：永久凍土の融解がもたらす影響の評価

Approximately 30–50％ of critical circumpolar infrastructure in the Arctic could be at high risk of damage as a result of permafrost thawing owing to anthropogenic warming, suggests an article published in Nature Reviews Earth & Environment. The findings form part of a collection, which examines the physical, biogeochemical and ecosystem changes related to permafrost thaw and the associated impacts.

Arctic permafrost regions store nearly 1,700 billion metric tons of frozen and thawing carbon. Anthropogenic warming threatens to release an unknown quantity of this carbon into the atmosphere, influencing the climate in processes collectively known as the permafrost carbon feedback. Permafrost thaw also poses a considerable threat to the integrity of polar and high-altitude infrastructure.

Jan Hjort and colleagues report that under anthropogenic warming, approximately 69％ of residential, transportation and industrial infrastructure in permafrost regions is located in areas with high potential for near-surface permafrost thaw by the middle of this century. Accordingly, permafrost degradation-related infrastructure costs could rise to tens of billions US dollars by the second half of the century. For example, in Russia, the total cost of support and maintenance of road infrastructure owing to permafrost degradation from 2020 to 2050 is estimated to reach approximately US $7 billion (422 billion RUB) for the existing network, with no additional development. The authors note that a number of techniques exist to alleviate these impacts, such as air convection embankments (which uses a porous stone layer to generate convection within embankments and improve heat extraction). However, a better understanding of the regions at high risk are needed for mitigation methods to be effective, they conclude.

In a second review in the collection, Sharon Smith and colleagues note that increases in permafrost temperature vary spatially owing to interactions between climate, vegetation, snow cover, organic-layer thickness and ground ice content. In warmer permafrost (temperatures close to 0 °C), rates of warming are typically less than 0.3 °C per decade, as seen in sub-Arctic regions. However, in colder permafrost (temperatures less than −2 °C) as seen in the high-latitude Arctic, warming of up to about 1 °C per decade is apparent. Smith and co-authors conclude that a greater understanding of longer-term interactions between permafrost and the surrounding environment is needed to reduce the uncertainty regarding the thermal state of permafrost and its future response.

The articles in this collection outline the progress made in understanding permafrost and its role in the Earth System, but also the vast uncertainties and continued unknowns. Cooperation will be key to predicting and mitigating the impacts of permafrost thaw.