Coastal flood risk Norway
Projected future sea level rise in Norway
A detailed analysis of twenty first century regional sea-level changes for Norway has been carried out by accounting for spatial variations in
- ocean density (due to variations in temperature and salinity) and circulation,
- ice and ocean mass changes and associated gravitational effects on sea level, and
- vertical land motion arising from past surface loading change and associated gravitational effects on sea level (1).
An important component of past and present sea-level change in Norway is glacial isostatic adjustment: the Earth’s viscous relaxation in response to ice mass loss over the past 10,000 years. Uplift rates along the Norwegian coast are between 1 and 5 mm/year (or between -0.1 and -0.5 m as a contribution to twenty-first century relative sea-level change) (1).
Projected twenty-first century sea-level changes in Norway are below the global mean: the projected relative sea-level changes in Norway for the period 2090–2099 relative to 1980–1999, based on the emission scenarios A2, A1B and B1, vary between -0.2 to 0.3 m (1-sigma ± 0.13 m). These changes are between -40 and 60 % of the projected global mean (0.47 m) (1).
The projected relative sea-level changes for Norway based on a high-end scenario of 6°C global warming and an emerging collapse for some areas of the Antarctic ice sheets vary between 0.25 and 0.85 m (min/max ± 0.45 m). These changes are between 25 and 95 % of the projected central estimate of the global mean (0.91 m). For this high-end scenario, ocean surface increases dominate over the land uplift signal across all of Norway. The pattern of relative sea-level changes, however, still largely reflects land motion due to glacial isostatic adjustment (1).
Global sea level rise
In their fourth assessment report the IPCC reported that there was high confidence that the rate of observed sea level rise increased from the 19th to the 20th century (3). They also reported that the global mean sea level rose at an average rate of 1.7 (1.2 to 2.2) mm yr-1 over the 20th century, 1.8 (1.3 to 2.3) mm yr-1 over 1961 to 2003, and at a rate of 3.1 (2.4 to 3.8) mm yr-1 over 1993 to 2003.
According to satellite altimetry-based data anthropogenic global warming has resulted in global mean sea-level rise of 3.3 ± 0.4 mm/year over the period 1994-2011 (9). According to a recent study, however, this previous estimate of global mean sea level rise is too high and global sea level rise over the period 1993 to mid-2014 has been between +2.6 ± 0.4 mm/year and +2.9 ± 0.4 mm/year (11). According to this same study sea-level rise is accelerating; this acceleration is in reasonable agreement with an accelerating contribution from the Greenland and West Antarctic ice sheets over this period (13,14), and the Intergovernmental Panel on Climate Change projections (13,15) of acceleration in sea-level rise during the early decades of the twenty-first century of about +0.07 mm/year. Sea-level rise varies from year to year, however, due to short-term natural climate variability (especially the effect of El Niño–Southern Oscillation) (9,12): the global mean sea level was reported to have dropped 5 mm due to the 2010/2011 La Niña and have recovered in 1 year (12).
Updated satellite data to 2010 show that satellite-measured sea levels continue to rise at a rate close to that of the upper range of the IPCC projections (4). Whether the faster rate of increase during the latter period reflects decadal variability or an increase in the longer-term trend is not clear. However, there is evidence that the contribution to sea level due to mass loss from Greenland and Antarctica is accelerating (5).
For 2081-2100 compared to 1986-2005, projected global mean sea level rises (metres) are in the range (10):
- 0.29-0.55 (for scenario RCP2.6)
- 0.36-0.63 (for scenario RCP4.5)
- 0.37-0.64 (for scenario RCP6.0) and
- 0.48-0.82 (for scenario RCP8.5)
Extreme water levels - Global trends
More recent studies provide additional evidence that trends in extreme coastal high water across the globe reflect the increases in mean sea level (6), suggesting that mean sea level rise rather than changes in storminess are largely contributing to this increase (although data are sparse in many regions and this lowers the confidence in this assessment). It is therefore considered likely that sea level rise has led to a change in extreme coastal high water levels. It is likely that there has been an anthropogenic influence on increasing extreme coastal high water levels via mean sea level contributions. While changes in storminess may contribute to changes in sea level extremes, the limited geographical coverage of studies to date and the uncertainties associated with storminess changes overall mean that a general assessment of the effects of storminess changes on storm surge is not possible at this time.
On the basis of studies of observed trends in extreme coastal high water levels it is very likely that mean sea level rise will contribute to upward trends in the future.
Extreme waves - Future trends along the western European coast
Recent regional studies provide evidence for positive projected future trends in significant wave height and extreme waves along the western European coast (7). However, considerable variation in projections can arise from the different climate models and scenarios used to force wave models, which lowers the confidence in the projections (8).
The large natural variability has a greater impact on the local North Sea wind field than potential anthropogenic-induced trends. For the North Sea region reliable predictions concerning strongly wind- influenced characteristics such as local sea level, storm surges, surface waves and thermocline depth are still impossible (18).
Vulnerabilities - Flood damage
Norway has an extensive coastline, along which more than 40% of the total population is settled, some in very small and isolated communities. Linked systems of roads, tunnels, bridges, ferries, electricity supply, and lines of communication are vital to these communities (2).
Although sea level rise is not considered a serious threat for Norway, it may have some negative impacts on infrastructure, particularly along the western and northern coastline. The possibility of an increase in the frequency and magnitude of storms, including storm surges, is indeed a concern along Norway’s coast. On the first of January 1992, the western part of the country was hit by the strongest storm on record in Norway, resulting in damages estimated at approximately 300 million US dollars. Most of these damages were covered by private and government insurance schemes (2).
The Norwegian Water Resources and Energy Directorate has developed a climate change adaptation strategy that includes monitoring, research and measures to prevent increased damage by floods and landslides in a future climate (17). Under the Planning and Building Act, municipalities are responsible for ensuring that natural hazards are assessed and taken into account in spatial planning and processing of building applications. Adaptation to climate change, including the implications of sea-level rise and the resulting higher tides, is an integral part of municipal responsibilities. To enable municipalities to ensure resilient and sustainable communities, the central government therefore draws up guidelines for the incorporation of climate change adaptation into the planning activities of municipalities and counties (16).
The premise of the Norwegian climate adaptation policy is that individuals, private companies, public bodies and local and central government authorities all have a responsibility to take steps to safeguard their own property. If appropriate steps are taken, public and private properties are protected from financial risk associated with extreme weather events by adequate national insurance schemes (16).
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Norway.
- Simpson et al. (2014)
- O’Brien (2006)
- Bindoff et al. (2007), in: IPCC (2012)
- Church and White (2011), in: IPCC (2012)
- Velicogna (2009); Rignot et al. (2011); Sørensen et al. (2011), all in: IPCC (2012)
- Marcos et al. (2009); Haigh et al. (2010); Menendez and Woodworth (2010), all in: IPCC (2012)
- Debernard and Roed (2008); Grabemann and Weisse (2008), both in: IPCC (2012)
- IPCC (2012)
- Cazenave et al. (2014)
- IPCC (2014)
- Watson et al. (2015)
- Yi et al. (2015)
- Church et al. (2013), in: Watson et al. (2015)
- Shepherd et al. (2012), in: Watson et al. (2015)
- Church et al. (2013), in: Watson et al. (2015)
- Dronkers and Stojanovic (2016)
- NME (2009), in: Dronkers and Stojanovic (2016)
- Schrum et al. (2016)