Indicator of global warming
The permafrost regions occupy approximately 24% of the terrestrial surface of the Northern Hemisphere (9). Permafrost is also extensive in such mid-latitude mountain ranges as the Rockies, Andes, Alps, and Himalayas. Two classes of frozen ground are generally distinguished: seasonally frozen ground, which freezes and thaws on an annual basis, and perennially frozen ground (permafrost), defined as any subsurface material that remains at or below 0ºC continuously for at least two consecutive years (10).
Permafrost thicknesses range from very thin layers only a few centimeters thick to about 1500 m in unglaciated areas of Siberia (11).
Because permafrost is highly susceptible to long-term warming, it has been designated a “geoindicator,” to be used as a primary tool for monitoring and assessing environmental change (12). Empirical evidence strongly indicates that impacts related to climate warming are well underway in the polar regions (13). Permafrost at many Arctic locations has experienced temperature increases in recent decades (10).
A significant reduction in the area of near-surface permafrost could occur during the next century. The hypothesis and existing evidence that warming will increase the thickness of the active layer, resulting in thawing of ice-rich permafrost, ground instability, and surface subsidence, require further investigation under a variety of contemporary environmental settings (10).
Permafrost degradation and ground settlement under 2 °C global warming
Global warming of 2°C above preindustrial levels has been considered to be the threshold that should not be exceeded to avoid dangerous interference with the climate system. What will a 2°C rise of global mean temperature lead to with respect to the degradation of permafrost, covering 1/4 of the Northern Hemisphere? This was studied by estimating permafrost soil temperature increase under 2°C global warming with ten climate models (GCMs), and quantifying the resulting thaw and settlement of the soil (22).
Permafrost is defined as the ground where soil temperature remains at or below 0°C for at least two consecutive years. Approximately 1/4 of the Northern Hemisphere land area is permafrost. Melting of permafrost under global warming will affect hydrology and water resources, because of the water that flows out of the melting soil (23). It will affect ecosystems, because the heating of the soil and its changing hydrology changes the biogeochemical cycles in the soil (24). It will affect human infrastructures, because the soil gets less stable and buildings, roads, oil and gas pipelines, etc., settle differently from one point to another (25). In fact, melting permafrost affects climate change itself, because of the release of carbon from the degrading soil (26).
According to these climate models, global warming of 2°C above preindustrial levels will be reached in the first half of the 22nd century (2037 / 2045 under the RCP4.5 / RCP8.5 scenario). Global warming at northern latitudes will exceed the global mean (27). When the global mean temperature rise reaches 2°C, air temperature in the permafrost region increases by at least 2.9-4.4°C and 3.0-4.1°C under the RCP4.5 and RCP8.5 scenario, respectively. As a result, the Northern Hemisphere’s permafrost soil temperature will increase by 2.34-2.67°C at 6 m depth relative to the period 1990-2000 (22).
Under 2°C global warming the permafrost extent will obviously retreat north and decrease by about 25%. The thickness of the so-called active soil layer, the layer that thaws and freezes in turn, will increase by 0.42-0.45 m on average. Locally the increase may be much higher though, up to 5 metres. Ground settlement owing to permafrost thaw is estimated at 3.8-15 cm on average for the Northern Hemisphere permafrost land area, but may reach several metres locally (22).
Cause of global warming
Permafrost plays three important roles in the context of climatic change (14):
- as a record keeper by functioning as a temperature archive,
- as a translator of climate change through subsidence and related impacts, and
- as a facilitator of further change through its impact on the global carbon cycle.
If organic material is present in the newly thawed layer, it again becomes subject to decomposition by soil microbes, ultimately releasing CO2 and CH4 to the atmosphere. CH4 (methane) is 27 times more effective at absorbing thermal radiation than CO2. Release of large quantities of CO2 and CH4 to the atmosphere would create a positive feedback mechanism that can amplify regional and global warming (10).
Vulnerabilities - Lowland permafrost
In northern Europe, lowland permafrost will eventually disappear (1), and it will become necessary to factor in the dissipation and eventual disappearance of permafrost in infrastructure planning (2) and building techniques (3).
Thawing of ground permafrost will disrupt access through shorter ice road seasons and cause damage to existing infrastructure (4). On the other hand, reduced sea ice and thawing ground in the Arctic will increase marine access and navigable periods for the Northern Sea Route (5).
The irregular surface created by thawing of ice-rich permafrost is known as thermokarst terrain. Global warming is likely to trigger a new episode of widespread thermokarst development, with serious consequences for a large proportion of the engineered works constructed in the permafrost regions during the twentieth century. Thawing of ice-rich permafrost is presently creating thermokarst terrain in the Alaskan interior and is having significant effects on subarctic ecosystems and infrastructure (15). Recent geographic overviews indicate that the hazard potential associated with ice-rich permafrost is high in many parts of the Arctic (16).
The accelerated thawing of permafrost not only disrupts vegetation and essential infrastructure, such as roads and pipelines, but could eventually release into the atmosphere vast amounts of methane. The maximum permafrost area has already shrunk by 7% since 1900 (6).
Warming will also accelerate the erosion of shorelines and riverbanks, threatening the infrastructure located on eroding shorelines. Increased storminess and higher waves are eroding arctic coasts at greater rates than in the past (18). The combination of increased wave action and warming permafrost especially threatens lowlying coastal villages (19). Several villages in Alaska have lost buildings to the sea (20).
Vulnerabilities - Mountain permafrost
On slopes, particularly in mountainous regions, thawing of ice-rich, near-surface permafrost layers can create mechanical discontinuities in the substrate, leading to active-layer detachment slides and retrogressive thaw slumps (17).
Systematic measurements have been carried out of European mountain permafrost temperatures from a latitudinal transect of six boreholes extending from the Alps, through Scandinavia to Svalbard. Boreholes were drilled in bedrock to depths of at least 100 m between May 1998 and September 2000. Geothermal profiles provide evidence for regional-scale secular warming, since all are nonlinear, with near-surface warm-side temperature deviations from the deeper thermal gradient (7).
Topographic effects lead to variability between Alpine sites. First approximation estimates, based on curvature within the borehole thermal profiles, indicate a maximum ground surface warming of +1°C in Svalbard, considered to relate to thermal changes in the last 100 years. In addition, a 15-year time series of thermal data from the 58 meter deep Murtèl–Corvatsch permafrost borehole in Switzerland, drilled in creeping frozen ice-rich rock debris, shows an overall warming trend, but with high-amplitude interannual fluctuations that reflect early winter snow cover more strongly than air temperatures (7).
Vulnerabilities - Palsa mires
Palsa mires, which contain peat with permanently frozen ice, are located at the outer margin of the permafrost zone and are expected to undergo rapid changes under global warming. These changes are expected to have a significant influence on the biodiversity of sub-arctic mires and could also potentially affect the regional carbon budget (8).
For the spatial distribution of palsa mires in Fennoscandia it was estimated as very likely (>90% probability) that a loss of area suitable for palsa mires to less than half of the baseline distribution will occur by the 2030s and very likely or likely (>66%) that all suitable areas will disappear by the end of the 21st century under the A1B and A2 emissions scenarios. For the B1 scenario, it was more likely than not (>50%) that a small proportion of the current palsa mire distribution would remain until the end of the 21st century (8).
One rare plant community, highland permafrost string bogs (palsamires), is already under threat from the recent climate warming. The string bogs and their discontinuous permafrost areas might even disappear with further warming. Then their function as important habitats for plants and as breeding ground for birds would disappear as well. The permafrost string bogs hold much soil organic matter that currently is unavailable to decomposition. The thawing of these soils could therefore result in more emissions of GHGs (21).
During new construction, if ice-rich permafrost cannot be avoided, it can be addressed with proper design and construction techniques. Methods include digging out the permafrost if it is relatively shallow and thin, raising the structure on piles, or otherwise assuring that the substrate remains frozen through active or passive refrigeration (10).
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Iceland.
- Haeberli and Burns (2002), in: Alcamo et al. (2007)
- Nelson (2003), in: Alcamo et al. (2007)
- Mazhitova et al. (2004), in: Alcamo et al. (2007)
- ACIA (2004)
- Alcamo et al. (2007)
- Commission of the European Communities (2007)
- Harris et al. (2003)
- Fronzek and Carter (2009)
- Brown et al. (1997); Zhang et al. (1999, 2003), all in: U.S. Arctic Research Commission (2003)
- U.S. Arctic Research Commission (2003)
- Washburn (1980), in: U.S. Arctic Research Commission (2003)
- Berger and Lams (1996), in: U.S. Arctic Research Commission (2003)
- Hansen et al. (1998); Morison et al. (2000); Serreze et al. (2000); Smith et al. (2002), all in: U.S. Arctic Research Commission (2003)
- Nelson et al. (1993); Anisimov et al. (2001), both in: U.S. Arctic Research Commission (2003)
- Jorgenson et al. (2001); Instanes (2003), both in: U.S. Arctic Research Commission (2003)
- Nelson et al. (2001, 2002), in: U.S. Arctic Research Commission (2003)
- Lewkowicz (1992); French (1996), both in: U.S. Arctic Research Commission (2003)
- Brown et al. (2003), in: U.S. Arctic Research Commission (2003)
- Walker (2001), in: U.S. Arctic Research Commission (2003)
- Callaway et al. (1999), in: U.S. Arctic Research Commission (2003)
- Ministry for the Environment of Iceland (2010)
- Guo and Wang (2017)
- Guo et al. (2012); Lan et al. (2015); Liljedahl et al. (2016), all in: Guo and Wang (2017)
- Yang et al. (2010, 2014); Guo et al. (2011a, b); Li and Chen (2013); Yi et al. (2014); Qin et al. (2014), all in: Guo and Wang (2017)
- Guo and Sun (2015), in: Guo and Wang (2017)
- Schuur et al. (2009, 2015); Koven et al. (2011); Burke et al. (2013), all in: Guo and Wang (2017)
- Hartmann et al. (2013), in: Guo and Wang (2017)