As a consequence of global warming and human-induced climate change, the thawing of permafrost not only contributes to global greenhouse gas (GHG) emissions and warming, but also poses substantial risks to both local ecosystems and human communities in affected regions (Figure 2.2.4). Permafrost thaw interacts with various climatic and human factors at a regional level, leading to significant alterations in geomorphology, hydrology and ecosystems (due to thermokarst and hillslope failures), thaw dynamic succession, biomes (e.g. plant communities influencing carbon balance), biogeochemical fluxes, tundra plant and animal ecology, and the functioning of lake, river and coastal marine ecosystems (Schuur and Mack, 2018; Vincent et al., 2017, Knapp & Trainor, 2015). The hydrological dynamics of affected areas are also disrupted, impacting water availability and quality. These alterations, in turn, have cascading effects on the frequency and magnitude of natural disasters such as floods, landslides and coastal erosion.

Figure: 2.2.4
Figure 2.2.4: Permafrost changes under climate change and subsequent effects on environment and society (https://www.grida.no/resources/13348). Credit to Riccardo Pravettoni and Philippe Rekacewicz.

Regions with boreal forests and tundra biomes located above permafrost areas are experiencing pronounced changes in vegetation and ecosystems. While the tundra is showing signs of overall greening, boreal forests are facing regional browning, indicating significant shifts in plant and animal communities (Higgins et al., 2023, Myers-Smith et al., 2020). Such changes may affect the range and abundance of ecologically important species, including those in freshwater ecosystems. The consequences of these ecological transformations extend to the wellbeing of local communities, whose livelihoods and cultural heritage are intimately tied to the health of the surrounding environment. Further, the presence of vegetation above permafrost employs various mechanisms to protect permafrost from the effects of atmospheric conditions, serving as insulation for permafrost that has not adjusted to the present climate (Nitzbon et al., 2023). Alterations in this vegetation can impact the thermal conditions of permafrost (Loranty et al., 2011). Specifically, warming in northern regions can alter vegetation patterns, leading to an expansion of taller shrubs and trees. This increased vegetation cover can insulate underlying permafrost and cause it to warm. The resulting thaw and subsidence of permafrost promotes further shrub growth, creating a positive feedback loop, opening the door to potential self-sustaining and tipping point dynamics in response to a warming climate.

Considering the cold winters and short, cool summers, the presence of permafrost affects the availability of arable land and the growing season for crops, making agriculture challenging. While climate-driven northward expansion of agriculture increasingly provides new food sources, little is known about the effectiveness, feasibility and risks in cultivation-permafrost interactions (Ward Jones et al., 2022). Indigenous communities in permafrost regions therefore often rely on traditional knowledge and practices that are deeply rooted in their culture and are essential for their food security. They depend on the availability of natural resources such as fish and plants. Access to these resources and the ability to store them long-term in permanently frozen cellars may be impacted by environmental changes in permafrost regions (Maslakov et al., 2022). Increasingly, traditional diets transition to a diet from industrial store-bought food, which can significantly impact human health (Loring and Gerlach, 2009). Thawing permafrost also releases contaminants, including mercury, into the environment (Schäfer et al., 2020). This negatively impacts water quality in Arctic rivers and lakes, leading to potential risks to human health through contaminated food chains and drinking water sources.

Beyond its ecological consequences, permafrost thaw has significant implications for the infrastructure built on permafrost soil. As the ground becomes unstable, buildings, roads, pipelines, water facilities, and communication systems are damaged (Hjort et al., 2022; Hjort et al., 2018) and hazardous substances mobilised (Langer et al., 2023; Miner et al., 2021). Up to 80 per cent of infrastructure elements show substantial infrastructure damage and 70 per cent of current infrastructure in the permafrost domain is in areas with high potential for thaw by 2050 (Hjort et al., 2022).

Thus, permafrost thaw is a complex and multifaceted issue with global, regional and local ramifications. It not only contributes to global climate change but also poses considerable risks to ecosystems, human health and infrastructure in affected areas, posing substantial challenges for economic development and human activities and necessitating adaptation strategies and long-term planning. However, there is hope that mitigating global warming and limiting temperature rise to below 2°C would significantly reduce the impacts of permafrost thaw on infrastructure in permafrost areas. This highlights the urgency of adopting comprehensive climate change mitigation measures to protect both the environment and human communities in vulnerable regions.

The permafrost-carbon feedback, as a major part of the global carbon cycle, has long been proposed as a feedback loop that accelerates climate change. The potential for permafrost carbon emissions to alter the rate and magnitude of global warming is still uncertain (due to missing model representation and lack of observations) and likely to be too small to be self-perpetuating (Deutloff et al., 2023; Nitzbon et al., 2023; Wang et al., 2023; Schäfer et al., 2014) (see Chapter 1.2). Therefore, large-scale carbon release from permafrost thaw can be considered a threshold-free process (Nitzbon et al., 2023; Hugelius et al., 2020; Chadburn et al., 2017; Schuur et al., 2015). However, permafrost carbon can significantly contribute to the carbon budget of specific warming targets or scenarios, specifically those aiming for low warming levels, such as those more likely to prevent tipping of other elements (Schuur et al., 2022; Natali et al., 2021; Gasser et al., 2018). Thus, biogeochemical feedback of permafrost has the potential to influence socioeconomic conditions. More importantly, any changes today commit us to long-term impacts (McGuire et al., 2018). At the local scale, rapid permafrost thaw can have severe consequences on a number of services to humans as well as to global society across four domains of ecosystem services: provisioning, regulating, supporting, and cultural (Schuur and Mack, 2018).

Communicating a ‘threshold’ for permafrost that indicates a ‘safe zone’ is misleading, as every tenth of a degree of global warming leads to significant impacts in permafrost-dominated landscapes.

Schuur et al., 2022
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