Statistical modelling of circumpolar permafrost: thermal and geomorphic sensitivities to climate change and societal implications

One-fourth of the land area in the Northern Hemisphere is affected by perennially frozen ground, known as permafrost. The thermal conditions of permafrost govern complex geo- and ecosystems and provide support for Arctic cities and transportation infrastructure. Permafrost, however, is not permanent. Rather it is sensitive to the warming climate and human-induced disturbances. Recently, rapid degradation of permafrost landscapes has been observed across the Arctic. In addition to the local implications for the hydro-ecology, geo- and biodiversity and ground stability, permafrost degradation can affect the global climate through biogeochemical feedbacks. Ongoing changes to Arctic permafrost systems may have environmental and socio-economic repercussions on national and international scales. The main aims of this thesis were to first examine how environmental conditions control the thermal and geomorphic permafrost characteristics on a circumpolar scale. Next, the sensitivity of permafrost to 21st century climate change was assessed. Lastly, high-resolution geohazard maps were produced and used to quantify the amount of infrastructure potentially at risk from thawing near-surface permafrost across the Northern Hemisphere. The thesis utilized statistical ensemble modelling techniques and geospatial datasets combined with comprehensive circumpolar observational datasets. Based on the results, the studied permafrost characteristics were strongly controlled by and sensitive to current and future climatic conditions. The air temperature and rainfall had the most prominent contributions, while the effects of local terrain properties on a circumpolar scale were often found to be small. By the mid-century, the extent of near-surface permafrost may decrease by 34–47% depending on human-induced greenhouse gas emissions. Suitable areas for permafrost landform occurrence will similarly shrink, including regions of cold continuous permafrost. Quantifications of the infrastructure at risk indicated that around 70% of the studied engineering elements and four million people were located in areas of projected near-surface permafrost thaw. Moreover, one-third of all the infrastructure elements and nearly a million people situated in regions with high potential for permafrost degradation-related damage to the built environment. In conclusion, circumpolar permafrost was projected to show extensive regionally distinct sensitivities to the ongoing climate change. Although most of the thermal and geomorphic impacts were projected to occur by the mid-century regardless of the climate-change scenario, it is argued that mitigating climate change could reduce the potential consequences for natural and human systems. In order to achieve a higher applicability of circumpolar-scale analyses on local scales, further developments in the availability and quality of global observational and geospatial data are required. Moreover, it is proposed that the pronounced nonlinearity found between climatic conditions and the studied permafrost characteristics should be carefully considered in future assessments.