Permafrost Loss

Primary reference(s)

IPCC, 2019 . Annex I: Glossary [Weyer, N.M. (ed.)]. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. Intergovernmental Panel on Climate Change (IPCC). Accessed 21 October 2020.

Additional scientific description

Permafrost includes the mineral part of the ground (rocks) as well as any organic matter and ice if it is present (IPCC, 2019). The active layer is the uppermost part of permafrost, which thaws during summer and re-freezes during winter.

Permafrost currently covers around 15 million km2, or approximately 24% of the land in the Northern Hemisphere, mostly in the Arctic region, and is very sensitive to climate change (Chadburn et al., 2017).

• Gradual permafrost loss or thaw is related to a general increase in the temperature of the ground. Ground temperatures are monitored by the Global Terrestrial Network for Permafrost at over 150 borehole sites across the permafrost regions (Biskaborn et al., 2019). During 2007–2016, continuous-zone permafrost temperatures in the Arctic and Antarctic increased by 0.39 ± 0.15°C and 0.37 ± 0.10°C respectively and at some locations, the temperature is 2–3°C higher than 30 years ago (Biskaborn et al., 2019).
• Abrupt thaw happens mainly in regions with excess ice and occurs when the land surface collapses resulting in, for example, thaw slumps, active layer detachments or thermokarst lakes. This can affect many metres of permafrost soil in the period of a few days to years and will impact the hydrological state of the permafrost (Turetsky et al., 2020). Olefeldt et al. (2016) estimated that 20% of the northern permafrost region is covered by ice-rich thermokarst landscapes. Abrupt thaw is not currently well represented by models (Turetsky et al., 2020).

Under future climate change scenarios, the Coupled Model Intercomparison Project Phase 6 (CMIP6) models project a gradual loss of permafrost of between 0.3 and 3.4 million km2 per °C increase in global surface air temperature (5th to 95th percentile; Burke et al., 2020). This is equivalent to a reduction of between 10% and 40% per °C in the annual mean frozen volume in the top 2 m of soil. These estimates are slightly lower than the 4.0 [-1.1; +1.0] million km2 per °C equilibrium sensitivity projected by Chadburn et al. (2017) who derived this using an observational-based relationship.

The permafrost region represents a large, climate sensitive reservoir of organic carbon with approximately twice as much carbon in the soil as is currently contained in the Earth’s atmosphere. The top 3 m of permafrost soils contain 1035 ± 150 Pg C (Tarnocai et al., 2009; Hugelius et al., 2014) and could become vulnerable to decomposition under climate change. Schuur et al. (2015) suggested that between 5% and 15% of this permafrost carbon pool may be decayed and released as either carbon dioxide or methane during the 21st century, contributing to further global warming. This feedback could cause an additional warming of between 0.2% and 12% of the change in global temperature by 2100 (Burke et al., 2017). About half of below-ground carbon is stored in thermokarst landscapes vulnerable to abrupt thaw (Olefeldt et al., 2016) and has not been considered in these estimates. Therefore, these estimates may well be a substantial underestimation of carbon emissions from thawing permafrost (Turetsky et al., 2020).

Metrics and numeric limits

The Global Terrestrial Network for Permafrost (GTN-P, Streletskiy et al., 2017) coordinates long-term monitoring of the thermal state of permafrost via an extensive borehole network used to measure ground temperatures at a range of depths from the surface to up to 100 m in depth. It also coordinates the monitoring of the maximum active layer thickness via the Circumpolar Active Layer Monitoring program (CALM, no date). Typically, this is done at the end of the summer on a grid arrangement via mechanical probing of the soil. Currently it is not possible to use Earth Observation data for routine monitoring of permafrost.

Examples of drivers, outcomes and risk management

Permafrost thaw is one of the leading factors increasing climate-related vulnerability (Murray et al., 2012).

Changes in temperature and precipitation typically act as gradual (i.e., continuous) disturbances that directly affect permafrost by modifying the ground thermal regime. Climate change can also modify the occurrence and magnitude of abrupt physical disturbances such as fire (e.g., Wotton et al., 2017), and soil subsidence and erosion resulting from ice rich permafrost thaw (e.g., Lewkowicz and Way, 2019). These ‘pulse’ (i.e., discrete) disturbances often are part of the ongoing disturbance and successional cycle in Arctic and boreal ecosystems (Grosse et al., 2011) but changing rates of occurrence have recently been observed altering the landscape distribution of successional ecosystem states (Farquharson et al., 2019).

Recent climate warming has been linked to increased wildfire activity in the boreal forest regions in Alaska and western Canada where this has been studied (Gillett et al., 2004; Veraverbeke et al., 2017). Based on satellite imagery, an estimated 80,000 km2 of boreal area was burned globally per year from 1997 to 2011 (Giglio et al., 2013). There is high confidence that fire will accelerate change in permafrost relative to climate effects alone, if the rates of these disturbances increase. The observed trend of increasing fire is projected to continue for the rest of the 21st century across most of the tundra and boreal region for many climate scenarios (Meredith et al., 2019).

Permafrost thaw causes serious damage to infrastructure (e.g., roads, runways, buildings) and affects different types of infrastructure in radically different ways. The impacts of permafrost thaw on infrastructure have implications for the health, economic livelihood, and safety of affected communities. For example, in Northern Canada, the costs of adapting and/or repairing existing infrastructure can range from several million to many billions of dollars, depending on the extent of the damage and the type of infrastructure that is at risk. The Tibbitt to Contwoyto winter road (Northwest Territories, Canada) experienced climate-related closures in 2006, remaining open for only 42 days compared to 76 in 2005 (Bastedo, 2007). This resulted in residents and businesses having to airlift materials to their communities, costing them millions of dollars.

In the Northwest Territories, 10% of public access buildings have been retrofitted since 2004 to address critical structural malfunctions. In Inuvik, Northwest Territories, a local school suffered a complete roof collapse under a particularly heavy snowfall. As permafrost continues to thaw, resulting in a loss of overall structural integrity, greater impacts will be linked to the increase in snow loads as structures previously weakened by permafrost thaw topple under larger or heavier snowfalls (Bastedo, 2007; Murray et al., 2012).

The rapid changes permafrost is undergoing create challenges for planners, decision makers and engineers by threatening the structural stability and functional capacities of infrastructure (Meredith et al., 2019). Projections of changes in climate and permafrost suggest that a wide range of current infrastructure will be impacted by the changing conditions (Melvin et al., 2017; Schneider von Deimling et al., 2020). For example, a circumpolar study found that approximately 70% of infrastructure (residential, transportation and industrial facilities), including over 1200 settlements (about 40 with a population of more than 5000), is located in areas where permafrost is projected to thaw by 2050 under RCP4.5 (Hjort et al., 2018).

Reducing and avoiding the impacts of climate change on infrastructure will require special attention to engineering, land use planning, maintenance operations, local culture and private and public budgeting. In some cases, relocation of human settlements will be required (Meredith et al., 2019). Subsidence due to thawing permafrost and river and delta erosion makes coastal and rural communities of Alaska and Russia particularly vulnerable, potentially requiring relocation in the future (Bronen, 2015; Romero Manrique et al., 2018).

Permafrost loss also alters ecosystems, for example, the ecology of thaw-impacted lakes and streams is also likely to change with microbiological communities adapting to changes in sediment, dissolved organic matter, and nutrient levels (Vonk et al., 2015).