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

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Chapter 4 · Physical and socio-economic environment

area, which suggested an annual mean rate of 8.75% per 1°C temperature rise (Benestad et al., 2016). This estimate is not necessarily inconsistent with the value of 4.5% per 1°C temperature rise for total precipitation . Changes in large-scale circulation are expected to influence the frequency of wet days, but a shift in the storm track implies precipitation may increase in some regions and decrease in others. There was little indication that mean wet or dry spell lengths (number of consecutive wet or dry days) will change dramatically. The Arctic Climate Impact Assessment reported that total precipitation had increased by 8% through the 20th century and gave a projected increase of 20% for 2100 (1981–2000 baseline to 2090; Juday et al., 2005).While increasing precipitation in the Arctic is consistent with model results and past observations, there is conflicting evidence about its cause.Førland andHanssen- Bauer (2003) found an increase of more than 2.5% per decade in the historical annual precipitation measured in the Svalbard region and at JanMayenover the 20th century.They observed that the annual fraction of solid precipitationdecreased at all sites with precipitation measurement during recent decades at the Arctic islands monitored by the Norwegian Meteorological Institute. This was suggested to have affected the total precipitation value through a reduction in undercatch at the precipitation gauges, and thus a larger fraction of ‘true’ precipitation being caught by the gauges.Which means much of the‘increase’may actually be due to more precipitation falling as rain. 4.2.3 Natural variability Ecosystems and society are both exposed to a combination of natural variability and anthropogenic change. Arctic climate and weather exhibit considerable temporal variability, often associated with changes in mean sea-level pressure, sea- ice cover, wind patterns, and the distribution of air masses and temperature. The natural variations are associated with different weather phenomena and are linked to the position and strength of the polar jet (polar vortex), storm tracks, the Arctic Oscillation (AO), and ocean currents (especially the Atlantic Meridional Overturning Circulation). Some of these phenomena are expected to change over the coming decades and in so doing affect the nature of the short-term fluctuations, but how they are likely to change under a warmer climate is currently unclear. This is examined in the following sections. 4.2.3.1 Feedback mechanisms The various components of the climate system interact in different ways, often with a change in one causing a change in another, which then leads back to cause additional change in the first. This is known as a feedback, and it is these feedback mechanisms that are responsible for natural variability in the climate system and make predictions so challenging. Although many feedbacks are well understood, the possibility of additional feedbackmechanisms that are currently unknown cannot be excluded. One type of inter-connection is between sea-ice or snow and temperature, through their reflecting properties and the ability of the surface to absorb sunlight (the albedo effect ). Clouds and atmospheric humidity also play a role by influencing the way light and heat are transferred.Air temperature itself also involves feedbacks to heat loss.

substantially more for the Barents Sea (up to 50 mm per month) bymid-century,and the increase is expected to continue until the end of the century (Koenigk et al., 2015).The projected increase is strongest in late autumn and winter and primarily attributed to increased evaporation from the local surface, with poleward moisture transport from lower latitudes a secondary factor.The increased surface evaporation associated with declining sea ice can be described as an amplifier for theArctic hydrological cycle, and the Barents Sea region has been identified as an important source regionwhere summer sea-ice anomalies feed back strongly to the atmosphere in autumn and winter (Rinke et al., 2013). Other researchers have also suggested a link between sea-ice decline and precipitation increase in summer,autumn andwinter (e.g. Vihma, 2014). The increase in Arctic mean annual-average precipitation sensitivity has been estimated at 4.5% per 1°C temperature rise, compared to a global average of 1.6–1.9% per 1°C temperature rise (Bintanja and Selten, 2014). This global estimate was based on many GCM runs, whereas Koenigk et al. (2015) used a single RCM driven by four GCMs to compute climate change over theArctic.They found different precipitation sensitivity in winter (0.8 mm per month per 1°C temperature rise) and summer (2 mm per month per 1°C temperature rise) and more pronounced summer precipitation changes in the regional model than the global models.The study byDobler et al. (2016) using a single RCM and GCM provides further support for high precipitation sensitivity for the projected temperature changes in the area (Figure 4.4).Relative and absolute sensitivities following the RCP8.5 scenario show the biggest increases along the Norwegian west coast in summer and autumn. Relative sensitivity is about 4% per 1°C temperature rise in the Barents area and a large increase can be found in summer in the more Arctic parts of the domain. However, it should be noted that Koenigk et al. (2015) used a far larger Arctic area to calculate precipitation sensitivity than Dobler et al. (2016). Stroeve et al. (2011) found a trend for increasing cyclone activity in the Atlantic sector of the Arctic, based on reanalysis data, and showed there is more precipitation associated with autumn cyclone activity and column water vapor during low ice-cover years than high ice-cover years. This has been supported by statistically significant responses in climate models (e.g. Strey et al., 2010; Porter et al., 2012; Rinke et al., 2013; Screen et al., 2014). Wegmann et al. (2015) presented observational evidence for increased snowfall over parts of Eurasia due to moisture transport in years of anomalous low sea-ice cover in the Barents/Kara seas region. Kusunoki et al. (2015) used a high-resolution global atmosphere model to project future changes in precipitation intensity over the Arctic. They reported a monotonic increase in annual mean precipitation, daily precipitation intensity, and the maximum 5-day precipitation total towards the end of the century, taking the average over theArctic.The increases were partly attributed to an increase inwater vapor connectedwith rising temperatures, but also to stronger horizontal transport of water vapor from low to high latitudes associated with transient cyclones. More recent projections for precipitation intensity suggest up to a 70% increase for the wettest years in the annual totals between 2015 and 2080 under the RCP4.5 scenario (Figure 4.2). These estimates were derived based on projected temperature increases and a comparison between past trends in the wet- day mean precipitation and temperatures over the Barents

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