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

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

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NorESM

Change in SST, °C

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Figure 4.12 Change in sea surface temperature in March for downscaled GISS (left), NCAR (middle) and NorESM (right).The left and middle plots are from Sandø et al. (2014a) and show change between present (1981–2000, data from the 20C3M control run) and future (2046–2065,A1B scenario).The right plots shows change between 2010–2019 and 2060–2069 using the RCP4.5 scenario (Bentsen et al., 2013).

biota. Oceanographic conditions are strongly determined by advection (horizontal movement of mass, heat and salt) and by exchange with the atmosphere (precipitation, evaporation, air-ocean energy fluxes). Observed trends are likely to continue or strengthen in the future, and recent climate model simulations (CMIP5; IPCC, 2013) suggest the Barents Sea will be the first Arctic region ice- free all year round. An evaluation of how well the most recent GCMs capture past trends suggests there is a tendency for models to slightly overestimate sea-ice extent in the Arctic (by about 10%) in winter and spring (Flato et al., 2013). Projections indicate that surface air temperature in the Barents Sea and Arctic Ocean will increase by about twice as much as the global mean, with accompanying decreases in sea-ice extent (IPCC, 2013). The air-ocean heat fluxes will thus show considerable change, principally in response to a warmer ocean due to increased uptake of solar heat following the decline in ice cover and increased heat transport into the region. The Barents Sea will be ice-free all year round by mid-century according to many climate models, and recent analyses of future projections suggest that increased oceanic heat transport will be a major contributory factor to sea-ice decline in this area (Koenigk and Brodeau, 2014). The latest assessment by the Intergovernmental Panel on Climate Change (AR5) confirms the findings of its previous assessment (IPCC, 2007) in terms of change in Arctic sea-ice extent to the end of the century, despite a wide spread in model results.The rate of decrease in mean sea-ice cover is greatest in September, but there are major differences in the multi-model averages depending on RCP used. The projected decline in sea-ice extent ranges from 8% (RCP2.6) to 34% (RCP8.5) in February and 43% (RCP2.6) to 94% (RCP8.5) in September (Collins et al., 2013). Due to a substantial reduction in sea- ice thickness, the corresponding losses in sea ice volume are expected to be much higher. Regional effects of climate change can be heavily modulated by internal variability andmay eithermitigate or worsen the impacts of global warming. Interannual variability in sea-ice extent is largely determined by the inflow of relatively warm Atlantic Water through the Barents Sea Opening (Sandø et al., 2010; Årthun et al., 2012, Smedsrud et al., 2013, Nakanowatari et al.,

temperature and snowfall extremes over parts of Europe andAsia (Petoukhov and Semenov, 2010; Hopsch et al., 2012; Yang and Christensen, 2012; Liptak and Strong, 2014; Mori et al., 2014). Observations provide clear evidence of change in Arctic sea ice. First-year sea ice extent decreased by 3.5–4.1% per decade over the period 1979–2012, with the most pronounced reduction occurring during summer at 9.4–13.6% per decade (equivalent to a loss of 0.73–1.07 million km 2 per decade), and was 11–16% per decade for multi-year sea ice (Vaughan et al., 2013). In the Barents Sea, observations reveal that ice extent in the‘cold’ 1965–1975 period reached on average 180,000 km 2 in August, while in the ‘warm’ 2001–2012 period ice extent was considerably less at 46,000 km 2 (Roshydromet, 2014). The monthly ice cover anomaly in the Barents Sea reveals a linear decrease of ~7% per decade over the period 1979–2007, but significant interannual variability (Comiso and Nishio, 2008). Submarine data and satellite measurements showmean Arctic sea ice thickness decreased from 3.64 to 1.89 m over the period 1980–2008 (Rothrock et al., 2008; Kwok and Rothrock, 2009). Observations over recent decades show a strong reduction in sea ice volume in the Arctic (Döscher andVihma, 2014), attributed to increased greenhouse gas concentrations and increased northward ocean heat transport into the Barents Sea (Skagseth et al., 2008; Levitus et al., 2009). Sea-ice loss has many consequences in the underlying ocean and the overlaying atmosphere. For example, ice decline in winter increases the exposure of relatively warm open water to cold air outbreaks, which in turn leads to stronger turbulent convection in the atmospheric boundary layer. Sea ice may provide a link between changes in the ocean and in atmospheric circulation (Nakanowatari et al., 2014; Sato et al., 2014), and stronger convection will increase boundary layer thickness and cloudiness,whichmay generate extreme snowfall and unusually strong winds (Tetzlaff et al., 2014). The physical environment of the Barents Sea is influenced by climate change in terms of changes in sea level, salinity, temperature, and thereby also changes in sea-ice extent and thickness. Changes in temperature and salinity are likely to cause changes in vertical stratification, which has implications for vertical exchange, water chemistry and the