Adaptation Actions for a Changing Arctic: Perspectives from the Barents Area

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Chapter 4 · Physical and socio-economic environment

4.4.3 Land ice Whereas tundra dominates the northern Siberian mainland, glaciers and ice caps are mainly located on the Arctic archipelagos of the Barents and Kara Seas (Figure 4.16). Some of the world’s largest continuous icefields are found there (see Chapter 2), and nowhere else in the Arctic does so much of the coastline constitute of ice-cliffed glacier fronts. These marine glaciers are almost entirely grounded on the sea floor, with only a few examples of floating tongues or ice shelves, mainly on Franz Josef Land (Dowdeswell et al., 1994). Most glacier cover occurs on the Svalbard archipelago (33,800 km 2 ), followed by Novaya Zemlya (22,100 km 2 ), Severnaya Zemlya (16,700 km 2 ), and Franz Josef Land (12,700 km 2 ). Glaciers on the mainland are limited to a few mountain areas in northern Scandinavia (Lyngen and Øksfjord region, 230 km 2 ; Sweden/Sarek, 240 km 2 ) and Siberia (Polar Urals, 15 km 2 ; Putorana, 9 km 2 ; Taymir, 35 km 2 ) (Pfeffer et al., 2014; Arendt et al., 2015). Most glaciers in the region have been in retreat since the end of the Little Ice Age about 100 years ago (Vaughan et al., 2013). The longest observational record of surface mass balance is from two small mountain glaciers near Ny-Ålesund (Svalbard), and this shows a relatively stable trend of glacier wastage over the last half century (Hagen et al., 2003). Shorter-term records from the larger glaciers and ice caps on Svalbard and the Russian archipelagos show these ice masses are shrinking more slowly, which has also been confirmed by satellite remote sensing over the past decade (Moholdt et al., 2010, 2012b). The first reliable estimates of regional mass balance were obtained from satellite altimetry and gravimetry, and show a negative mass balance of 5–10 Gt/y for Svalbard and about 10 Gt/y for the Russian archipelagos (Gardner et al., 2013). This is unlikely to differ much from the longer-term trend, which contrasts with the situation in the CanadianArctic and Greenland where glacier mass losses over the past decade have been much larger than in previous decades (Gardner et al., 2011; Kjeldsen et al., 2015). Climate reanalysis and modelling indicate that these regional patterns could change in the future, and surface melting is predicted to increase substantially this century under current climate scenarios (Lang et al., 2015). The effects of oceanic and climatic change on glacier dynamics are unclear. Two of the largest ice caps in the region, Austfonna on Svalbard and the Academy of Sciences ice cap on Severnaya Zemlya are currently experiencing surging or accelerated glacier flow in several drainage basins, causing rapid dynamic thinning and increased ice discharge into the ocean (Moholdt et al., 2012a; Dunse et al., 2015; see also icebergs in Section 4.3.6). Although these are cyclical or transient effects, they do have a large impact on the regional mass balance and the frequency and size of such events might change under a future climate. No widespread changes in ice flow have been observed, but the retreat of marine glaciers on Novaya Zemlya has increased substantially since about 2000 (Carr et al., 2014) and this might affect their future flow rates. The largest ice shelf in the region (the Matusevich Ice Shelf on Severnaya Zemlya) collapsed in summer 2012 and satellites have observed accelerated flow and increased thinning in the tributary glacier basins in response to the reduced buttressing (Willis et al., 2015).

Although there is a general decrease in permafrost temperature with increasing latitude, this relationship varies between regions. Permafrost is warmer in Scandinavia, Svalbard and northwestern Russia than in other Arctic regions, due to the influence of warm ocean currents and prevailing winds on climate, while elevation is a modifying factor in the Nordic countries (Romanovsky et al., 2010; Sato et al., 2014). Temporal trends in historical permafrost temperature below the depth of seasonal variation (the top layer of soil that thaws during summer and refreezes in autumn, known as the ‘active layer) in Svalbard and Scandinavia were analyzed by Isaksen et al. (2007b). Updated records from the Nordic monitoring sites show ground temperature at 20 m depth to have increased by 0.3–0.7°C per decade since the late 1990s at the colder mountain permafrost sites (Figure 4.15).A significant temperature increase is measurable to at least 80 m depth, reflecting multi-decadal warming of the permafrost surface. The high rate of warming on Svalbard since 1998 coincided with a period of higher air temperature. In addition, several extreme and long-lasting warm spells were superimposed on a significant warming trend (Isaksen et al., 2007a; Hansen et al., 2014). Less warming has been observed at warm permafrost sites that have been affected by latent heat exchange close to 0°C.Ground temperature observations at some Nordic sites also confirm permafrost degradation over this period: 1999–2009 (Isaksen et al., 2011) and 2002–2012 (Farbrot et al., 2013). Active layer thickness (ALT) is more sensitive to short-term variations in climate than deeper ground. ALT records thus exhibit greater interannual variability, mainly in response to variations in summer temperature (e.g. Smith et al., 2009). Most regions where long-termALT observations are available show an increase over the past five years (Romanovsky et al., 2015). The Russian European North has been characterized by almost monotonic thickening of the active layer over the past 15 years, reaching a maximum in 2012, but decreasing between 2012 and 2014. In the Nordic countries, records (1996–2013) indicate a general increase in ALT since 1999. Summer 2014 was particularly warm in the Nordic countries and contributed to the deepest active layer measured to date at some sites (Romanovsky et al., 2017). McGuire et al. (2016) analyzed uncertainties in the permafrost response to climate change within the permafrost region since 1960 for 15 model simulations. Although all models showed a loss in permafrost area (ALT <3 m) from 1960 to 2009 over the study area (Romanovsky et al.,2017),there were large differences in loss rates among the models. Slater and Lawrence (2013) and Koven et al. (2013) analyzed Earth SystemModel projections of soil temperature from the CMIP5 database to assess the models’ representation of current-climate soil thermal dynamics.Despite large differences in the extent and rate of change in the permafrost, all models agree that the projected warming and increased snow thickness will result in near-surface permafrost degradation over large areas. In the northern hemisphere, the sensitivity of permafrost to climate change is 0.8–2.3 million km 2 per 1°C of warming. This range in sensitivity results in a wide range of projections for permafrost loss: 15–87% under the RCP4.5 scenario and 30–99% under RCP8.5. Collectively, the CMIP5 models project that permafrost will have largely disappeared from the present-day discontinuous zone by 2100 under RCP4.5.