Climate change, impacts and vulnerability in Europe ... - MemoFin.fr

Changes in the climate system2.3.5 PermafrostRelevancePermafrost is permanently frozen ground andconsists of rock or soil that has remained at orbelow 0 °C continuously for more than 2 years.It is a widespread phenomenon in the Arctic aswell as in the alpine high mountain environments(Harris et al., 2009; Boeckli et al., 2012; Gruber, 2012).Climate change leads to changes in spatial extent,thickness and temperature of permafrost. Thechanges are not uniform across all permafrost areas,but depend on the geographical location and specificcharacteristics of the permafrost.Permafrost influences the evolution of landscapesand ecosystems and affects human infrastructureand safety. Permafrost warming or thaw increasesrisks of natural hazards, such as rock falls, debrisflows and ground subsidence (Huggel et al., 2012).Arctic permafrost thaw can also accelerate climatechange through the increased release of CO 2andCH 4which is a powerful GHG (Zimov et al., 2006;Schuur et al., 2009; Isaksen et al., 2011).Past trendsPermafrost data is collected through nationalnetworks as well as globally. This informationshows the regional and seasonal variation as wellas trends in permafrost temperatures. Changes inbelow-ground temperatures can be influenced asmuch by temporal variations of snow cover as bychanges in the near-surface air temperature. It hasalso become evident that landform characteristicssuch as elevation, topography, surface cover and soiltype also influence the effects of climate change onpermafrost.Data from three boreholes, to a depth of 100 m ormore, extending from Svalbard to the Alps indicatea long-term regional warming of permafrost of0.5–1.0 °C during the recent decade (Harris et al.,2009). Continuous monitoring over 5–7 years showswarming down to 60 m depth and current warmingrates at the permafrost surface of 0.04–0.07 °C/year,with greatest warming in Svalbard and northernSweden (Isaksen et al., 2007). In Switzerland, somewarming and increasing active-layer depths (toplayer of the soil that thaws during the summer)have been observed (Noetzli and Vonder Muehll,2010), but results vary between borehole locationsand site characteristics such as different snow cover,surface cover, subsurface material, ice contentin the underground and temperature conditions(Figure 2.16).In Europe data series with a length of more than15 years are available from Greenland, Svalbard,northern Sweden and Switzerland. Active layerthickness has generally increased during the periodof observation, but there is also significant variationdue to site characteristics (Figure 2.17).ProjectionsPermafrost areas are affected by the rate of warmingand will very likely continue to thaw acrossEurope, with the possible exception of Svalbard,where permafrost thaw can mainly be expectedat low elevations close to the coast (Voigt et al.,2010; Etzelmüller et al., 2011). Projections havealso shown that the palsa mires in Fennoscandiarepresent a special case of arctic permafrost whererapid responses can be expected. The probability ofa complete loss of palsas in northern Fennoscandiaduring the 21st century is sensitive to the emissionsscenarios (see Box 2.5).Key messages: 2.3.5 Permafrost• In the past 10–20 years European permafrost has shown a general warming trend, with greatestwarming in Svalbard and Scandinavia. The active layer thickness has increased at some Europeanpermafrost sites. Several sites show great interannual variability which reflects the complex interactionbetween the atmospheric conditions and local snow and ground characteristics.• Present and projected atmospheric warming is projected to lead to widespread warming and thawing ofpermafrost.• Warming and thawing of permafrost is expected to increase the risk of landslides, ground subsidenceand flash floods from bursting glacial lakes. Thawing of permafrost also affects biodiversity and mayaccelerate climate change through release of CO 2and CH 4from arctic permafrost areas.Climate change, impacts and vulnerability in Europe 201283