Global and European sea level

Indicator Assessment
Prod-ID: IND-193-en
Also known as: CSI 047 , CLIM 012
Created 08 Nov 2017 Published 27 Nov 2017 Last modified 27 Nov 2017
14 min read
Global mean sea level in 2016 was the highest yearly average since measurements started in the late 19 th century; it was about 20 cm higher than at the beginning of the 20 th century. Estimates for the average rate of global sea level rise over the 20 th century range from 1.2 to 1.7 mm/year, with significant decadal variation. The rate of sea level rise since 1993, when satellite measurements became available, has been significantly higher, at around 3 mm/year. Evidence showing the predominant role of anthropogenic climate change in observed global mean sea level rise and the acceleration of sea level rise during recent decades has strengthened since the publication of the IPCC Fifth Assessment Report (AR5). All coastal regions in Europe have experienced an increase in absolute sea level, but with significant regional variation. Most coastal regions have also experienced an increase in sea level relative to land, with the exception of the northern Baltic Sea and the northern Atlantic coast, which are experiencing considerable land rise as a consequence of post-glacial rebound. Extreme high coastal water levels have increased at most locations along the European coastline. This increase appears to be predominantly due to increases in mean local sea level rather than to changes in storm activity. Global mean sea level rise during the 21st century will very likely occur at a higher rate than during the period 1971–2010. Process-based models considered in the IPCC AR5 project a rise in sea level over the 21st century (2100 vs. 1986–2005 baseline) that is likely (i.e. 66 % probability) in the range of 0.28–0.61 m for a low emissions scenario (RCP2.6) and 0.52–0.98 m for a high emissions scenario (RCP8.5). However, substantially higher values of sea level rise cannot be ruled out. Several recent model-based studies, expert assessments and national assessments have suggested an upper bound for 21st century global mean sea level rise in the range of 1.5–2.5 m. A recent study extending the IPCC AR5 projections estimates global sea level rise by 2300 to be in the range of 0.8–1.4 m for a low emissions scenario (RCP2.6) and 3.4–6.8 m for a high emissions scenario (RCP8.5). These values would rise substantially if the largest estimates of sea level contributions from Antarctica over the coming centuries were included. The rise in sea level relative to land along most European coasts is projected to be similar to the global average, with the exception of the northern Baltic Sea and the northern Atlantic coast, which are experiencing considerable land rise as a consequence of post-glacial rebound. Projected increases in extreme high coastal water levels are likely to mostly be the result of increases in local relative mean sea level in most locations. However, several recent studies suggest that increases in the meteorologically driven surge component could also play a substantial role, in particular along the northern European coastline. All available studies project that the damages from coastal floods in Europe would increase many-fold in the absence of adaptation, whereby the specific projections depend on the assumptions of the particular study.

Key messages

  • Global mean sea level in 2016 was the highest yearly average since measurements started in the late 19th century; it was about 20 cm higher than at the beginning of the 20th century.
  • Estimates for the average rate of global sea level rise over the 20th century range from 1.2 to 1.7 mm/year, with significant decadal variation. The rate of sea level rise since 1993, when satellite measurements became available, has been significantly higher, at around 3 mm/year.
  • Evidence showing the predominant role of anthropogenic climate change in observed global mean sea level rise and the acceleration of sea level rise during recent decades has strengthened since the publication of the IPCC Fifth Assessment Report (AR5).
  • All coastal regions in Europe have experienced an increase in absolute sea level, but with significant regional variation. Most coastal regions have also experienced an increase in sea level relative to land, with the exception of the northern Baltic Sea and the northern Atlantic coast, which are experiencing considerable land rise as a consequence of post-glacial rebound.
  • Extreme high coastal water levels have increased at most locations along the European coastline. This increase appears to be predominantly due to increases in mean local sea level rather than to changes in storm activity.
  • Global mean sea level rise during the 21st century will very likely occur at a higher rate than during the period 1971–2010. Process-based models considered in the IPCC AR5 project a rise in sea level over the 21st century (2100 vs. 1986–2005 baseline) that is likely (i.e. 66 % probability) in the range of 0.28–0.61 m for a low emissions scenario (RCP2.6) and 0.52–0.98 m for a high emissions scenario (RCP8.5). However, substantially higher values of sea level rise cannot be ruled out. Several recent model-based studies, expert assessments and national assessments have suggested an upper bound for 21st century global mean sea level rise in the range of 1.5–2.5 m.
  • A recent study extending the IPCC AR5 projections estimates global sea level rise by 2300 to be in the range of 0.8–1.4 m for a low emissions scenario (RCP2.6) and 3.4–6.8 m for a high emissions scenario (RCP8.5). These values would rise substantially if the largest estimates of sea level contributions from Antarctica over the coming centuries were included.
  • The rise in sea level relative to land along most European coasts is projected to be similar to the global average, with the exception of the northern Baltic Sea and the northern Atlantic coast, which are experiencing considerable land rise as a consequence of post-glacial rebound.
  • Projected increases in extreme high coastal water levels are likely to mostly be the result of increases in local relative mean sea level in most locations. However, several recent studies suggest that increases in the meteorologically driven surge component could also play a substantial role, in particular along the northern European coastline.
  • All available studies project that the damages from coastal floods in Europe would increase many-fold in the absence of adaptation, whereby the specific projections depend on the assumptions of the particular study.

What is the trend in mean sea level globally and across European seas?

Observed change in global mean sea level

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Trend in absolute sea level across Europe based on satellite measurements

Note: Horizontal spatial distribution of mean sea level trend in European Seas (January 1993- December 2015)

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Trend in relative sea level at selected European tide gauge stations

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Projections for global mean sea level rise and its contributions

Note: Projections for global mean sea level rise and its contributions in 2081–2100 relative to 1986–2005 from process-based models for the four representative concentration pathways (RCPs) and emisions scenario SRES A1B used in the IPCC Fourth Assessment Report. The grey boxes show the median of the model projections (central bar) as well as the likely range, which comprises two thirds of the model projections. The coloured bars and boxes show estimates for the different contributions to global sea-level rise. For further information, see the source document.

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Projected change in relative sea level

Note: The map shows the projected change in relative sea level in 2081-2100 compared to 1986-2005 for the medium-low emission scenario RCP4.5 based on an ensemble of CMIP5 climate models. Projections consider land movement due to glacial isostatic adjustment but not land subsidence due to human activities. No projections are available for the Black Sea.

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Past trends: global mean sea level

Sea level changes can be measured using tide gauges and remotely from space using satellite altimeters. Many tide gauge measurements have long multi-decade time series, with some exceeding more than 100 years. However, the results can be distorted by various regional and local effects, such as vertical land motion processes. Satellite altimeters enable absolute sea level to be measured from space and provide much better spatial coverage (except at high latitudes). However, the length of the altimeter record is limited to about 25 years.

Reconstructions of global mean sea level (GMSL) based on tide gauge observations suggest a rise of about 20 cm in the period between 1901 and 2015 (Figure 1). Global mean sea level in 2016 was the highest yearly average over the record. Reconstructions considered in the IPCC Fifth Assessment Report (AR5) estimate the rate of 20th century sea level rise at 1.6 mm/year, with significant decadal variation (see green curve in Figure 1). This value is somewhat higher than the sum of the known contributions to sea level rise over this period. More recent reconstructions suggest a slightly lower rate of 20th century sea level rise, at about 1.2 mm/year (see red curve in Figure 1) [i].

Estimates for the rate of GMSL rise during the period since 1993, for which satellite-based measurements are available, are considerably higher than the 20th century trend, at 2.4–3.2 mm/year (see dark blue curve in Figure 1). Different statistical methods for assessing sea level trends and changes therein can come to somewhat different conclusions, but all available assessments agree that an acceleration in the rate of GMSL rise since the early 1990s is detectable [ii]. If the lower estimates regarding 20th century sea level rise (shown in the red curve in Figure 1) were confirmed, the acceleration since the 1990s would be even more pronounced.

The causes of GMSL rise over recent decades are now reasonably well understood. Thermal expansion and melting of glaciers account for around 75 % of the measured sea level rise since 1971. The contribution from melting of the Greenland and Antarctic ice sheets has increased since the early 1990s. Changes in land water storage have made only a small contribution, but the rate of groundwater extraction has increased recently and now exceeds the rate of storage in reservoirs [iii]. A recent study concludes that climate-driven variability in precipitation has resulted in increased water storage on land, and that global sea level rise in the period 2002–2014 would have been 15–20 % higher in the absence of this climate variability [iv].

Evidence from formal detection and attribution studies showing that most of the observed increase in GMSL since the 1950s can be attributed to anthropogenic climate change has increased since the publication of the IPCC AR5 [v].

Past trends: mean sea level along the European coastline

Sea level measurements for the European region are available from satellite altimeter observations (Figure 2) and from tide gauges (Figure 3). Satellite observations, which show changes in absolute sea level, are available from 1993. Tide gauge records can be more than 100 years long; they show changes in relative sea level considering also land changes, which is more relevant for coastal protection than absolute sea level. Most European coastal regions experience increases in both absolute and relative sea level, but there are sizeable differences between the rates of absolute and relative sea level change across Europe.

Figure 2 shows linear trends in absolute sea level from 1992 to 2015 as observed by satellites. The main differences between regional seas and basins are primarily the result of different physical processes being the dominant cause of sea level change at different locations. For instance, the Mediterranean Sea is a semi-closed, very deep basin, exchanging water with the Atlantic Ocean through only the narrow Gibraltar Strait. Salinity in the Mediterranean Sea may increase in the future and this will tend to offset rises in sea level due to thermal expansion from warming. The NAO, interannual wind variability, changes in ocean circulation patterns, and the location of large-scale gyres and small-scale eddies are further factors that can influence local sea level in the European seas. Obviously, sea level changes in coastal zones are most relevant for society.

Figure 3 shows linear trends in relative sea level from 1970 to 2015 as observed by tide gauge stations in Europe. These trends can differ from those measured by satellites because of the longer time period covered and because tide gauge measurements are influenced by vertical land movement whereas satellite measurements are not. In particular, since the last ice age, the lands around the northern Baltic Sea have been, and are still, rising owing to the post-glacial rebound [vi].

Projections: global mean sea level

The main approach to projecting future sea level are process-based models, which are rooted in state-of-the-art climate model simulations. A significant recent step forwards in projecting future sea levels is the improved understanding of the contributing factors to recently observed sea level rise, which has increased confidence in the use of process-based models for projecting the future.

 

The IPCC AR5 concluded that the rate of GMSL rise during the 21st century will very likely exceed the rate observed in the period 1971–2010 for all emissions scenarios. Process-based models estimate the rise in GMSL for the period 2081–2100, compared with 1986–2005, to be likely in the range of 0.26–0.54 m for RCP2.6, 0.32–0.62 m for RCP4.5, 0.33–0.62 m for RCP6.0 and 0.45–0.81 m for RCP8.5. For RCP8.5, the rise in GMSL by 2100 is projected to be in the range of 0.53–0.97 m, with a rate during 2081–2100 of 7–15 mm/year (Figure 4). A collapse of marine-based sectors of the Antarctic Ice Sheet (i.e. those areas where the bed lies well below sea level and the edges flow into floating ice shelves) could cause GMSL to rise substantially above the likely range projected for the 21st century, but the evidence is insufficient for estimating the likelihood of such a collapse [vii].

Some recent studies highlight the contributions to recent sea level rise from ice sheet mass loss that were not included in the process-based models underlying the AR5 estimates above [viii]. A broad expert assessment of future sea level rise resulted in higher estimates than those from the process-based models reviewed in the AR5. The best expert estimates for sea level rise during the 21st century were 0.4–0.6 m for the low forcing scenario (RCP2.6) and 0.7–1.2 m for the high forcing scenario (RCP8.5) [ix]. Similar results were derived in other recent studies [x]. A study that combined the model-based assessments from the AR5 with updated models and probabilistic expert assessment of the sea level contributions from the Greenland and Antarctic ice sheets suggests an upper limit for GMSL rise during the 21st century of 1.8 m, which has a 5 % probability of being exceeded under the RCP8.5 forcing scenario [xi]. Various national reports have used values in the range of 1.5–2.5 m as upper estimates for GMSL rise during the 21st century [xii]. One recent study suggests that ice sheet melting in Antarctica and Greenland could occur much faster than previously thought and may result in sea level rise of several metres during the 21st century [xiii], but these findings have been controversial. While these high-end scenarios are somewhat speculative, their consideration is nevertheless important for long-term coastal risk management, in particular in densely populated coastal zones [xiv].

Sea level rise will continue to rise far beyond 2100. A recent effort to synthesise process-based model projections using a physically-based emulator suggests global sea level rise at 2300 of 0.8–1.4 m for RCP2.6, 1.3–2.3 m for RCP4.5, 1.7–3.2 m for RCP6.0 and 3.4–6.8 m for RCP8.5 [xv]. However, a more recent modelling study suggests that ice loss from Antarctica could occur more rapidly than previously thought and lead to sea level rise of more than 15 m by 2500 under the RCP8.5 emissions scenario [xvi]. On a multi-millennial time scale, projections based on process-based models suggest a quasi-linear GMSL rise of 1–3 m per degree of global warming for sustained warming over a period of 2 000 years. Significantly higher estimates for GMSL rise on multi-millennial time scales, of up to 50 m over 10 000 years for a high emissions scenario, have been derived from the geological record [xvii].

Projections: mean sea level along the European coastline

Regional and local sea levels differ from the global mean owing to large-scale factors such as non-uniform changes in ocean density and changes in ocean circulation. Furthermore, disintegrating land-ice affects sea level differentially because of gravitational effects and the viscoelastic response of the lithosphere [xviii]. Sea level is also affected by local and regional factors, such as vertical land movement. While there remains considerable uncertainty in the spatial patterns of future sea level rise, around 70 % of the world’s coastlines are expected to experience a local mean sea level change within ±20 % of the projected GMSL change [xix].

Relative sea level change along most of the European coastline is projected to be reasonably similar to the global average. The main exceptions are the northern Baltic Sea and the northern Atlantic coast, which are experiencing considerable land rise as a consequence of post-glacial rebound and changes in the gravity field of the Greenland ice sheet. As a result, sea level relative to land is rising slower than elsewhere in these regions or may even decrease (Figure 5) [xx].

A probabilistic assessment of regional sea-level rise in northern and central Europe estimated relative sea level change during the 21st century for the high RCP8.5 emissions scenario from –14 cm (in Luleå, northern Sweden) to 84 cm in Den Helder (Netherlands); high estimates (with a 5 % probability to be exceeded) range from 52 cm to 181 cm, respectively [xxi]. Making regional projections for relatively small isolated and semi-closed ocean basins, such as the Mediterranean or the Baltic, is even more difficult than for the open ocean.

[i] J. A. Church et al., ‘Sea-Level Change’, inClimate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, ed. T. F. Stocker et al. (Cambridge; New York: Cambridge University Press, 2013), 1137–1216, http://www.climatechange2013.org/images/report/WG1AR5_Chapter13_FINAL.pdf; Carling C. Hay et al., ‘Probabilistic Reanalysis of Twentieth-Century Sea-Level Rise’,Nature 517, no. 7535 (22 January 2015): 481–84, https://doi.org/10.1038/nature14093; Sönke Dangendorf et al., ‘Reassessment of 20th Century Global Mean Sea Level Rise’,Proceedings of the National Academy of Sciences 114, no. 23 (6 June 2017): 5946–51, https://doi.org/10.1073/pnas.1616007114.

[ii] M. Rhein et al., ‘Observations: Ocean’, inClimate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, ed. T. F. Stocker et al. (Cambridge; New York: Cambridge University Press, 2013), 255–316, http://www.climatechange2013.org/images/report/WG1AR5_Chapter03_FINAL.pdf; S. Jevrejeva et al., ‘Trends and Acceleration in Global and Regional Sea Levels since 1807’,Global and Planetary Change 113 (February 2014): 11–22, https://doi.org/10.1016/j.gloplacha.2013.12.004; Peter U. Clark et al., ‘Recent Progress in Understanding and Projecting Regional and Global Mean Sea Level Change’,Current Climate Change Reports 1, no. 4 (10 October 2015): 224–46, https://doi.org/10.1007/s40641-015-0024-4; Hay et al., ‘Probabilistic Reanalysis of Twentieth-Century Sea-Level Rise’; Christopher S. Watson et al., ‘Unabated Global Mean Sea-Level Rise over the Satellite Altimeter Era’,Nature Climate Change 5, no. 6 (11 May 2015): 565–68, https://doi.org/10.1038/nclimate2635; Xianyao Chen et al., ‘The Increasing Rate of Global Mean Sea-Level Rise during 1993–2014’,Nature Climate Change 7, no. 7 (26 June 2017): 492–95, https://doi.org/10.1038/nclimate3325; Hans Visser, Sönke Dangendorf, and Arthur C. Petersen, ‘A Review of Trend Models Applied to Sea Level Data with Reference to the “Acceleration-Deceleration Debate”’,Journal of Geophysical Research: Oceans 120, no. 6 (1 June 2015): 3873–95, https://doi.org/10.1002/2015JC010716; J. Blunden and D. S. Arndt, ‘A Look at 2016: Takeaway Points from theState of the Climate Supplement’,Bulletin of the American Meteorological Society 98, no. 8 (August 2017): 1563–72, https://doi.org/10.1175/BAMS-D-17-0148.1.

[iii] John A. Church et al., ‘Revisiting the Earth’s Sea-Level and Energy Budgets from 1961 to 2008’,Geophysical Research Letters 38, no. 18 (28 September 2011): L18601, https://doi.org/10.1029/2011GL048794; Church et al., ‘Sea-Level Change’; Clark et al., ‘Recent Progress in Understanding and Projecting Regional and Global Mean Sea Level Change’.

[iv] J. T. Reager et al., ‘A Decade of Sea Level Rise Slowed by Climate-Driven Hydrology’,Science 351, no. 6274 (12 February 2016): 699–703, https://doi.org/10.1126/science.aad8386.

[v] G. Jordà, ‘Detection Time for Global and Regional Sea Level Trends and Accelerations’,Journal of Geophysical Research: Oceans 119, no. 10 (1 October 2014): 7164–74, https://doi.org/10.1002/2014JC010005; Aimée B. A. Slangen et al., ‘Detection and Attribution of Global Mean Thermosteric Sea Level Change’,Geophysical Research Letters 41, no. 16 (28 August 2014): 5951–59, https://doi.org/10.1002/2014GL061356; Clark et al., ‘Recent Progress in Understanding and Projecting Regional and Global Mean Sea Level Change’.

[vi] J. M. Johansson et al., ‘Continuous GPS Measurements of Postglacial Adjustment in Fennoscandia 1. Geodetic Results’,Journal of Geophysical Research 107, no. B8 (10 August 2002): 2157, https://doi.org/10.1029/2001JB000400.

[vii] Church et al., ‘Sea-Level Change’; ; J. A. Church et al., ‘Sea Level Change Supplementary Material’, in Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, ed. T. F. Stocker et al. (Cambridge; New York: Cambridge University Press, 2013), 13SM–1–13SM–8, http://www.climatechange2013.org/images/report/WG1AR5_Ch13SM_FINAL.pdf.

[viii] e.g. Shfaqat A. Khan et al., ‘Sustained Mass Loss of the Northeast Greenland Ice Sheet Triggered by Regional Warming’,Nature Climate Change 4, no. 4 (April 2014): 292–99, https://doi.org/10.1038/nclimate2161; Robert M. DeConto and David Pollard, ‘Contribution of Antarctica to Past and Future Sea-Level Rise’,Nature 531, no. 7596 (31 March 2016): 591–97, https://doi.org/10.1038/nature17145; Johannes Jakob Fürst et al., ‘The Safety Band of Antarctic Ice Shelves’,Nature Climate Change 6 (8 February 2016): 479–82, https://doi.org/10.1038/nclimate2912; James Hansen et al., ‘Ice Melt, Sea Level Rise and Superstorms: Evidence from Paleoclimate Data, Climate Modeling, and Modern Observations That 2 °C Global Warming Could Be Dangerous’,Atmospheric Chemistry and Physics 16, no. 6 (22 March 2016): 3761–3812, https://doi.org/10.5194/acp-16-3761-2016; A. B. A. Slangen et al., ‘A Review of Recent Updates of Sea-Level Projections at Global and Regional Scales’,Surveys in Geophysics 38, no. 1 (January 2017): 385–406, https://doi.org/10.1007/s10712-016-9374-2.

[ix] Benjamin P. Horton et al., ‘Expert Assessment of Sea-Level Rise by AD 2100 and AD 2300’,Quaternary Science Reviews 84 (15 January 2014): 1–6, https://doi.org/10.1016/j.quascirev.2013.11.002.

[x] Robert E. Kopp et al., ‘Probabilistic 21st and 22nd Century Sea-Level Projections at a Global Network of Tide-Gauge Sites’,Earth’s Future 2, no. 8 (1 August 2014): 383–406, https://doi.org/10.1002/2014EF000239; Milla M. Johansson et al., ‘Global Sea Level Rise Scenarios Adapted to the Finnish Coast’,Journal of Marine Systems 129 (January 2014): 35–46, https://doi.org/10.1016/j.jmarsys.2012.08.007.

[xi] S Jevrejeva, A Grinsted, and J C Moore, ‘Upper Limit for Sea Level Projections by 2100’,Environmental Research Letters 9, no. 10 (1 October 2014): 104008, https://doi.org/10.1088/1748-9326/9/10/104008.

[xii] KNMI, ‘KNMI’14: Climate Change Scenarios for the 21st Century — A Netherlands Perspective’, Scientific Report (De Bilt: KNMI, 2014), http://www.klimaatscenarios.nl/brochures/images/KNMI_WR_2014-01_version26May2014.pdf; W. V. Sweet et al., ‘Global and Regional Sea Level Rise Scenarios for the United States’, NOAA Technical Report (Silver Spring, MD, USA: NOAA/NOS Center for Operational Oceanographic Products and Services, 2017), https://tidesandcurrents.noaa.gov/publications/techrpt83_Global_and_Regional_SLR_Scenarios_for_the_US_final.pdf.

[xiii] Hansen et al., ‘Ice Melt, Sea Level Rise and Superstorms’.

[xiv] Jochen Hinkel et al., ‘Sea-Level Rise Scenarios and Coastal Risk Management’,Nature Climate Change 5, no. 3 (25 February 2015): 188–90, https://doi.org/10.1038/nclimate2505.

[xv] Alexander Nauels et al., ‘Synthesizing Long-Term Sea Level Rise Projections – the MAGICC Sea Level Model v2.0’,Geoscientific Model Development 10, no. 6 (30 June 2017): 2495–2524, https://doi.org/10.5194/gmd-10-2495-2017.

[xvi] DeConto and Pollard, ‘Contribution of Antarctica to Past and Future Sea-Level Rise’.

[xvii] Church et al., ‘Sea-Level Change’; Gavin L. Foster and Eelco J. Rohling, ‘Relationship between Sea Level and Climate Forcing by CO2 on Geological Timescales’,Proceedings of the National Academy of Sciences 110, no. 4 (22 January 2013): 1209–14, https://doi.org/10.1073/pnas.1216073110; Anders Levermann et al., ‘The Multimillennial Sea-Level Commitment of Global Warming’,Proceedings of the National Academy of Sciences 110, no. 34 (20 August 2013): 13745–50, https://doi.org/10.1073/pnas.1219414110; Peter U. Clark et al., ‘Consequences of Twenty-First-Century Policy for Multi-Millennial Climate and Sea-Level Change’,Nature Climate Change 6, no. 4 (April 2016): 360–69, https://doi.org/10.1038/nclimate2923; DeConto and Pollard, ‘Contribution of Antarctica to Past and Future Sea-Level Rise’; Hansen et al., ‘Ice Melt, Sea Level Rise and Superstorms’.

[xviii] Hannes Konrad et al., ‘The Deformational Response of a Viscoelastic Solid Earth Model Coupled to a Thermomechanical Ice Sheet Model’,Surveys in Geophysics 35, no. 6 (1 November 2013): 1441–58, https://doi.org/10.1007/s10712-013-9257-8.

[xix] Church et al., ‘Sea-Level Change’; Luke P. Jackson and Svetlana Jevrejeva, ‘A Probabilistic Approach to 21st Century Regional Sea-Level Projections Using RCP and High-End Scenarios’,Global and Planetary Change 146 (November 2016): 179–89, https://doi.org/10.1016/j.gloplacha.2016.10.006.

[xx] Church et al., ‘Sea-Level Change’; HELCOM, ‘Climate Change in the Baltic Sea Area — HELCOM Thematic Assessment in 2013’, Baltic Sea Environment Proceedings (Helsinki: HELCOM, 2013), http://helcom.fi/Lists/Publications/BSEP137.pdf; A. B. A. Slangen et al., ‘Projecting Twenty-First Century Regional Sea-Level Changes’,Climatic Change 124, no. 1–2 (2014): 317–32, https://doi.org/10.1007/s10584-014-1080-9; Johansson et al., ‘Global Sea Level Rise Scenarios Adapted to the Finnish Coast’.

[xxi] A Grinsted et al., ‘Sea Level Rise Projections for Northern Europe under RCP8.5’,Climate Research 64, no. 1 (17 June 2015): 15–23, https://doi.org/10.3354/cr01309.

What is the trend in extreme sea level along European coasts?

Change in the frequency of flooding events under projected sea level rise

Note: This map shows the estimated multiplication factor, by which the frequency of flooding events of a given height changes between 2010 and 2100 due to projected regional sea relative level rise under the RCP4.5 scenario. Values larger than 1 indicate an increase in flooding frequency

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Past trends: extreme sea level along the European coastline

Producing a clear picture of either past changes or future projections of extreme high water levels for the entire European coastline is a challenging task because of the impact of local topographical features on surge events. While there are numerous studies for the North Sea coastline, fewer are available for the Mediterranean Sea and the Baltic Sea, although this situation is starting to improve.

Extreme sea levels show pronounced short- and long-term variability. A recent review of extreme sea level trends along European coasts concluded that long-term trends are mostly associated with the corresponding mean sea level changes. Changes in wave and storm surge climate mostly contribute to interannual and decadal variability, but do not show substantial long-term trends [i]. When the contribution from local mean sea level changes and variations in tide are removed from the recent trends, the remaining effects of changes in storminess on extreme sea level are much smaller or even no longer detectable [ii]. Additional studies are available for some European coastal locations, but these typically focus on more limited spatial scales [iii]. The only region where significant increases in storm surge height were found during the 20th century is the Estonian coast of the Baltic Sea [iv].

In conclusion, while there have been detectable changes in extreme water levels around the European coastline, most of these are the result of changes in local mean sea level. The contribution from changes in storminess is currently small in most European locations and there is little evidence that any trends can be separated from long-term natural variability.

Projections: extreme sea level at the European coastline

Future projections of extreme sea level can be made using either process-based (dynamic) or empirical statistical modelling of storm surge behaviour driven by the output of global climate models [v]. Uncertainty in these projections for Europe remains high and is ultimately linked to the uncertainty in future mid-latitude storminess changes. This is an area where current scientific understanding is advancing quickly, as climate model representations of aspects of Northern Hemisphere storm track behaviour are showing improvements associated with, for instance, greater ocean and atmosphere resolution. However, the newest global climate models have not yet, typically, been downscaled to suitably fine scales and used in studies of future storm surges [vi].

The current research evidence suggests that projected increases in extreme sea level along the European coast during the upcoming decades will mostly be the result of mean sea level changes [vii]. However, several recent studies suggest that changes in wave and storm surge climate may also play a substantial role in sea level changes during the 21st century in some regions. These studies project an increase in storm surge level for most scenarios and return periods along the northern European coastline, which can exceed 30 % of the relative sea level rise under the RCP8.5 scenario. Storm surge levels along most European coastal areas south of 50 °N showed small changes and in some regions may decline to partly offset the effect of mean sea level rise on projected extreme water levels [viii]. Sea level rise may also change extreme water levels by altering the tidal range and local wave climate. Tidal behaviour is particularly responsive in resonant areas of the Bristol Channel and the Gulf of Saint-Malo and in the south-eastern German Bight and Dutch Wadden Sea [ix].

A 10 cm rise in sea level typically causes an increase by about a factor of three in the frequency of flooding to a given height. The frequency of flooding events is estimated to increase by more than a factor of 10 in many European locations, and by a factor of more than 100 in some locations (Figure 6) for the RCP4.5 scenario [x]. Large changes in flood frequency mean that what is an extreme event today may become the norm by the end of the century in some locations.

Sea level rise substantially increases the risk of coastal flooding, which affects people, communities and infrastructure. The ClimateCost and PESETA II projects have estimated that a 30 cm sea level rise by the end of the 21st century, in the absence of public adaptation, would more than triple annual damages from coastal floods in the EU from EUR 5 to 17 billion [xi]. Another recent study has estimated the economic damage risk from coastal flooding in the main coastal cities in Europe to increase by a factor of about 40 from 2030 and 2100 under the RCP8.5 scenario, in the absence of adaptation  [xii].

The potential impacts from coastal flooding can be substantially reduced by timely adaptation measures, but they are associated with significant costs [xiii]. For any particular location, it is important to look in detail at the change in the height of flood defences that might be required. Where the flood frequency curve is very flat, modest increases in flood defences might be sufficient. Where the flood frequency curve is steeper, larger increases in protection height or alternative adaptation, including managed retreat, might be needed.

[i] Ralf Weisse et al., ‘Changing Extreme Sea Levels along European Coasts’,Coastal Engineering, Coasts@Risks: THESEUS, a new wave in coastal protection, 87 (May 2014): 4–14, https://doi.org/10.1016/j.coastaleng.2013.10.017.

[ii] Melisa Menéndez and Philip L. Woodworth, ‘Changes in Extreme High Water Levels Based on a Quasi-Global Tide-Gauge Data Set’,Journal of Geophysical Research 115, no. C10 (8 October 2010): C10011, https://doi.org/10.1029/2009JC005997; Øystein Hov et al., ‘Extreme Weather Events in Europe: Preparing for Climate Change Adaptation’ (Oslo: Norwegian Meteorological Institute, 2013), http://www.dnva.no/binfil/download.php?tid=58783; Weisse et al., ‘Changing Extreme Sea Levels along European Coasts’.

[iii] Isabel B. Araújo and David T. Pugh, ‘Sea Levels at Newlyn 1915–2005: Analysis of Trends for Future Flooding Risks’,Journal of Coastal Research 24 (July 2008): 203–12, https://doi.org/10.2112/06-0785.1; Ivan Haigh, Robert Nicholls, and Neil Wells, ‘Assessing Changes in Extreme Sea Levels: Application to the English Channel, 1900–2006’,Continental Shelf Research 30, no. 9 (May 2010): 1042–55, https://doi.org/10.1016/j.csr.2010.02.002; Marta Marcos et al., ‘Changes in Storm Surges in Southern Europe from a Regional Model under Climate Change Scenarios’,Global and Planetary Change 77, no. 3–4 (June 2011): 116–28, https://doi.org/10.1016/j.gloplacha.2011.04.002; Sönke Dangendorf et al., ‘North Sea Storminess from a Novel Storm Surge Record since AD 1843’,Journal of Climate 27, no. 10 (30 January 2014): 3582–95, https://doi.org/10.1175/JCLI-D-13-00427.1.

[iv] Ü. Suursaar, T. Kullas, and R. Szava-Kovats, ‘Wind and Wave Storms, Storm Surges and Sea Level Rise along the Estonian Coast of the Baltic Sea’,WIT Transactions on Ecology and Environment 127 (17 November 2009): 149–60, https://doi.org/10.2495/RAV090131.

[v] Jason A. Lowe et al., ‘Past and Future Changes in Extreme Sea Levels and Waves’, inUnderstanding Sea-Level Rise and Variability, ed. John A. Church et al. (Oxford: Wiley-Blackwell, 2010), 326–75, http://doi.wiley.com/10.1002/9781444323276.ch11.

[vi] A. A. Scaife et al., ‘Skillful Long-Range Prediction of European and North American Winters’,Geophysical Research Letters 41, no. 7 (16 April 2014): 2514–2519, https://doi.org/10.1002/2014GL059637; T. A. Shaw et al., ‘Storm Track Processes and the Opposing Influences of Climate Change’,Nature Geoscience 9, no. 9 (29 August 2016): 656–64, https://doi.org/10.1038/ngeo2783.

[vii] Weisse et al., ‘Changing Extreme Sea Levels along European Coasts’; Michalis I. Vousdoukas et al., ‘Extreme Sea Levels on the Rise along Europe’s Coasts’,Earth’s Future 5, no. 3 (March 2017): 304–23, https://doi.org/10.1002/2016EF000505.

[viii] T. Howard et al., ‘Sources of 21st Century Regional Sea-Level Rise along the Coast of Northwest Europe’,Ocean Science 10, no. 3 (19 June 2014): 473–83, https://doi.org/10.5194/os-10-473-2014; Michalis I. Vousdoukas et al., ‘Projections of Extreme Storm Surge Levels along Europe’,Climate Dynamics, 20 February 2016, https://doi.org/10.1007/s00382-016-3019-5; Vousdoukas et al., ‘Extreme Sea Levels on the Rise along Europe’s Coasts’.

[ix] M.D. Pickering et al., ‘The Impact of Future Sea-Level Rise on the European Shelf Tides’,Continental Shelf Research 35 (March 2012): 1–15, https://doi.org/10.1016/j.csr.2011.11.011.

[x] John Hunter, ‘A Simple Technique for Estimating an Allowance for Uncertain Sea-Level Rise’,Climatic Change 113, no. 2 (1 July 2012): 239–52, https://doi.org/10.1007/s10584-011-0332-1; J. A. Church et al., ‘Sea-Level Change’, inClimate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, ed. T. F. Stocker et al. (Cambridge; New York: Cambridge University Press, 2013), 1137–1216, http://www.climatechange2013.org/images/report/WG1AR5_Chapter13_FINAL.pdf; J. R. Hunter et al., ‘Towards a Global Regionally Varying Allowance for Sea-Level Rise’,Ocean Engineering, Sea Level Rise and Impacts on Engineering Practice, 71 (Oktober 2013): 17–27, https://doi.org/10.1016/j.oceaneng.2012.12.041.

[xi] S. Brown et al.,The Impacts and Economic Costs of Sea-Level Rise in Europe and the Costs and Benefits of Adaptation. Summary of Results from the EC RTD ClimateCost Project, The ClimateCost Project, Technical Policy Briefing Note 2 (Stockholm: Stockholm Environment Institute, 2011), http://www.climatecost.cc/images/Policy_brief_2_Coastal_10_lowres.pdf; J. C. Ciscar et al., ‘Climate Impacts in Europe: The JRC PESETA II Project’, JRC Scientific and Policy Reports (Seville: European Commission — Joint Research Centre Institute for Prospective Technological Studies, Institute for Environment and Sustainability, 2014), http://ipts.jrc.ec.europa.eu/publications/pub.cfm?id=7181.

[xii] Luis M. Abadie, Elisa Sainz de Murieta, and Ibon Galarraga, ‘Climate Risk Assessment under Uncertainty: An Application to Main European Coastal Cities’,Frontiers in Marine Science 3 (16 December 2016), https://doi.org/10.3389/fmars.2016.00265.

[xiii] M. Mokrech et al., ‘An Integrated Approach for Assessing Flood Impacts Due to Future Climate and Socio-Economic Conditions and the Scope of Adaptation in Europe’,Climatic Change 128, no. 3–4 (4 December 2014): 245–60, https://doi.org/10.1007/s10584-014-1298-6.

Indicator specification and metadata

Indicator definition

This indicator comprises several metrics to describe past and future sea level rise globally and in European seas. Global sea level rise is reported because it is the second-most important metric of global climate change (after global mean surface temperature), and because it is a proxy of sea level rise in Europe. Past sea level trends across Europe are reported in two different ways: first, absolute sea level change based on satellite altimeter measurements that reflect primarily the contribution of global climate change to sea level rise in Europe; second, relative sea level change based on tide gauges that also include local land movement, which is more relevant for the development of regional adaptation strategies. The indicator also addresses changes in extreme sea level along the European coast.

The following aspects of sea level rise are included:

  • Observed change in global mean sea level, based on two reconstructions from tide gauge measurements (since 1880) and on satellite altimeter data (since 1993)
  • Spatial trends in absolute sea level across European seas, based on satellite measurements (since 1993)
  • Spatial trends in relative sea level across European seas, based on European tide gauge stations with long time series (since 1970)
  • Projected change in global sea level for different forcing scenarios, including contributions from different sources
  • Projected change in relative sea level across European seas
  • Projected change in the frequency of flooding events along European coasts

Units

  • Change in sea level (mm)
  • Rate of sea level change (mm/yr)
  • Increase in flooding events (unitless)

Policy context and targets

Context description

In April 2013, the European Commission (EC) presented the EU Adaptation Strategy Package. This package consists of the EU Strategy on adaptation to climate change (COM/2013/216 final) and a number of supporting documents. The overall aim of the EU Adaptation Strategy is to contribute to a more climate-resilient Europe.

One of the objectives of the EU Adaptation Strategy is Better informed decision-making, which will be achieved by bridging the knowledge gap and further developing the European climate adaptation platform (Climate-ADAPT) as the ‘one-stop shop’ for adaptation information in Europe. Climate-ADAPT has been developed jointly by the EC and the EEA to share knowledge on (1) observed and projected climate change and its impacts on environmental and social systems and on human health, (2) relevant research, (3) EU, transnational, national and subnational adaptation strategies and plans, and (4) adaptation case studies.

Further objectives include Promoting adaptation in key vulnerable sectors through climate-proofing EU sector policies and Promoting action by Member States. Most EU Member States have already adopted national adaptation strategies and many have also prepared action plans on climate change adaptation. The EC also supports adaptation in cities through the Covenant of Mayors for Climate and Energy initiative.

In September 2016, the EC presented an indicative roadmap for the evaluation of the EU Adaptation Strategy by 2018.

In November 2013, the European Parliament and the European Council adopted the 7th EU Environment Action Programme (7th EAP) to 2020, ‘Living well, within the limits of our planet’. The 7th EAP is intended to help guide EU action on environment and climate change up to and beyond 2020. It highlights that ‘Action to mitigate and adapt to climate change will increase the resilience of the Union’s economy and society, while stimulating innovation and protecting the Union’s natural resources.’ Consequently, several priority objectives of the 7th EAP refer to climate change adaptation.

Targets

No targets have been specified.

Related policy documents

  • 7th Environment Action Programme
    DECISION No 1386/2013/EU OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 20 November 2013 on a General Union Environment Action Programme to 2020 ‘Living well, within the limits of our planet’. In November 2013, the European Parliament and the European Council adopted the 7 th EU Environment Action Programme to 2020 ‘Living well, within the limits of our planet’. This programme is intended to help guide EU action on the environment and climate change up to and beyond 2020 based on the following vision: ‘In 2050, we live well, within the planet’s ecological limits. Our prosperity and healthy environment stem from an innovative, circular economy where nothing is wasted and where natural resources are managed sustainably, and biodiversity is protected, valued and restored in ways that enhance our society’s resilience. Our low-carbon growth has long been decoupled from resource use, setting the pace for a safe and sustainable global society.’
  • Climate-ADAPT: Mainstreaming adaptation in EU sector policies
    Overview of EU sector policies in which mainstreaming of adaptation to climate change is ongoing or explored
  • Climate-ADAPT: National adaptation strategies
    Overview of activities of EEA member countries in preparing, developing and implementing adaptation strategies
  • DG CLIMA: Adaptation to climate change
    Adaptation means anticipating the adverse effects of climate change and taking appropriate action to prevent or minimise the damage they can cause, or taking advantage of opportunities that may arise. It has been shown that well planned, early adaptation action saves money and lives in the future. This web portal provides information on all adaptation activities of the European Commission.
  • EU Adaptation Strategy Package
    In April 2013, the European Commission adopted an EU strategy on adaptation to climate change, which has been welcomed by the EU Member States. The strategy aims to make Europe more climate-resilient. By taking a coherent approach and providing for improved coordination, it enhances the preparedness and capacity of all governance levels to respond to the impacts of climate change.

Methodology

Methodology for indicator calculation

Sea level changes are measured using tide gauges and remotely from space using altimeters. Tide gauges provide direct measurements, but they are influenced by local processes such as land subsidence. Furthermore, there are significant gaps in the spatial coverage of tide gauges with long time series, including in Europe.

As far as the satellite altimetry derived indicator is concerned, the global and European sea level trends are calculated from a combination of nine partly overlapping satellite missions. The data are corrected for seasonal variations, the inverse barometer effects and post-glacial rebound.

Sea level projections are based on process-based models, which are rooted in state-of-the-art climate model simulations. Projections for relative mean sea level in Europe consider the gravitational and solid Earth response and land movement due to glacial isostatic adjustment, but not land subsidence as a result of human activities.

Future projections of extreme sea level can be made using either process-based (dynamic) or empirical statistical modelling of storm surge behaviour driven by the output of global climate models.

Methodology for gap filling

Model-based projections for changes in regional sea level rise included only grid cells that are covered at least half by sea. Data for other grid cells partly covered by land and by sea were extrapolated using the nearest-neighbour method.

Methodology references

  • Holgate et al. (2012): New Data Systems and Products at the Permanent Service for Mean Sea Level. Holgate, S. J., Matthews, A., Woodworth, P. L., Rickards, L. J., Tamisiea, M. E., Bradshaw, E., Foden, P. R., Gordon, K. M., Jevrejeva, S. and Pugh, J., 2012, 'New data systems and products at the permanent service for mean sea level', Journal of Coastal Research 29(3), 493–504 (DOI: 10.2112/JCOASTRES-D-12-00175.1).
  • Church et al. (2013): Sea level change. Church, J. A., Clark, P. U., Cazenave, A., Gregory, J. M., Jevrejeva, S., Levermann, A., Merrifield, M. A., Milne, G. A., Nerem, R. S., Nunn, P. D., Payne, A. J., Pfeffer, W. T., Stammer, D. and Unnikrishnan, A. S., 2013, 'Sea level change', in: Stocker, T. F., Qin, D., Plattner, G.-K., et al. (eds), Climate change 2013: The physical science basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge; New York, pp. 1137–1216.
  • Church and White (2011): Sea-level rise from the late 19th to the early 21st century. Church, J. A. and White, N. J., 2011, 'Sea-level rise from the late 19th to the early 21st century',Surveys in Geophysics 32(4–5), 585–602 (DOI: 10.1007/s10712-011-9119-1).
  • Dangendorf et al. (2017): Reassessment of 20th century global mean sea level rise Dangendorf, S., Marcos, M., Wöppelmann, G., Conrad, C. P., Frederikse, T. and Riva, R., 2017, 'Reassessment of 20th century global mean sea level rise', Proceedings of the National Academy of Sciences 114(23), 5946–5951 (DOI: 10.1073/pnas.1616007114).
  • Legeais et al. (2017): An Accurate and Homogeneous Altimeter Sea Level Record from the ESA Climate Change Initiative Legeais, J.-F., Ablain, M., Zawadzki, L., Zuo, H., Johannessen, J. A., Scharffenberg, M. G., Fenoglio-Marc, L., Fernandes, M. J., Andersen, O. B., Rudenko, S., Cipollini, P., Quartly, G. D., Passaro, M., Cazenave, A. and Benveniste, J., 2017, 'An Accurate and Homogeneous Altimeter Sea Level Record from the ESA Climate Change Initiative', Earth System Science Data Discussions, 1–35 (DOI: 10.5194/essd-2017-116).
  • Quartly et al. (2017): A new phase in the production of quality-controlled sea level data G. D., Legeais, J.-F., Ablain, M., Zawadzki, L., Fernandes, M. J., Rudenko, S., Carrère, L., García, P. N., Cipollini, P., Andersen, O. B., Poisson, J.-C., Mbajon Njiche, S., Cazenave, A. and Benveniste, J., 2017, 'A new phase in the production of quality-controlled sea level data', Earth System Science Data 9(2), 557–572 (DOI: 10.5194/essd-9-557-2017)

Uncertainties

Methodology uncertainty

See under "Methodology"

Data sets uncertainty

Changes in global average sea level result from a combination of several physical processes. Thermal expansion of the oceans occurs as a result of warming ocean water. Additional water is added to the ocean from a net mass loss of glaciers and small ice caps, and from the large Greenland and West Antarctic ice sheets. Further contributions may come from changes in the storage of liquid water on land, either in natural reservoirs such as groundwater or man-made reservoirs.

The locally experienced changes in sea level differ from global average changes for various reasons. Changes in water density are not expected to be spatially uniform, and changes in ocean circulation also have regionally different impacts. At any particular location there may also be a vertical movement of the land in either direction, for example due to the post-glacial rebound (in northern Europe) or to local groundwater extraction.

Projections from process-based models with likely ranges and median values for global-mean sea level rise and its contributions in 2081–2100 relative to 1986–2005 have been made for the four RCP scenarios and scenario SRES A1B used in the AR4. The contributions from ice sheets include the contributions from ice-sheet rapid dynamical change. The contributions from ice-sheet rapid dynamics and anthropogenic land water storage have been treated as having uniform probability distributions, and as independent of scenario (except that a higher rate of change is used for Greenland ice-sheet outflow under RCP8.5).

Uncertainty in future projections of extreme sea level for Europe remains high and is ultimately linked to the uncertainty in future mid-latitude storminess changes. This is an area where current scientific understanding is advancing quickly, as climate model representations of aspects of Northern Hemisphere storm track behaviour are showing improvements associated with, for instance, greater ocean and atmosphere resolution. However, the newest global climate models have not yet, typically, been downscaled to suitably fine scales and used in studies of future storm surges.

Rationale uncertainty

No uncertainty has been specified

Data sources

Generic metadata

Topics:

information.png Tags:
, , , , , , , , , ,
DPSIR: Impact
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)

Contacts and ownership

EEA Contact Info

Hans-Martin Füssel

EEA Management Plan

2017 1.4.1 (note: EEA internal system)

Dates

Frequency of updates

Updates are scheduled once per year
European Environment Agency (EEA)
Kongens Nytorv 6
1050 Copenhagen K
Denmark
Phone: +45 3336 7100