Global and European sea level
- Global mean sea level has risen by 19.5 cm from 1901 to 2015, at an average rate of 1.7 mm/year, but with significant decadal variation. The rate of sea level rise since 1993, when satellite measurements have been available, has been higher, at around 3 mm/year. Global mean sea level in 2015 was the highest yearly average over the record and ~70 mm higher than in 1993.
- Evidence for a predominant role of anthropogenic climate change in the observed global mean sea level rise and for an acceleration during recent decades has strengthened since the publication of the IPCC AR5.
- Most coastal regions in Europe have experienced an increase in absolute sea level and in sea level relative to land, but there is significant regional variation.
- 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 that is likely in the range of 0.26–0.54 m for a low emissions scenario (RCP2.6) and 0.45–0.81 m for a high emissions scenario (RCP8.5). However, several recent studies suggest substantially higher values. Several national assessments, expert assessments and recent model-based studies have suggested an upper bound for 21st century global mean sea level rise in the range of 1.5–2.0 m.
- Available process-based models project that global mean sea level rise by 2300 will be less than 1 m for greenhouse gas concentrations that peak and decline and do not exceed 500 ppm CO2-equivalent, but will be in the range of 1 m to more than 3 m for concentrations above 700 ppm CO2-equivalent. However, these models are likely to systematically underestimate the sea level contribution from Antarctica, and some recent studies suggest substantially higher rates of sea level rise in the coming centuries.
- 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, recent studies suggest that increases in the meteorologically driven surge component can also play a substantial role, in particular along the northern European coastline.
What is the trend in mean sea level globally and across European seas?
Trend in asbolute sea level across Europe based on satellite measurements
Note: Spatial distribution of mean sea level trend in European Seas (1992–2014).
- Mean Sea Level Trend from satellite altimetry (T/P-Jason-1-Jason-2 merged datasets) provided by Copernicus Marine Environment Monitoring Service
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.
- Climate Change 2013: The Physical Science Basis provided by Intergovernmental Panel on Climate Change (IPCC)
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.
- FRCP4.5 total sea level rise projections provided by Integrated Climate Data Centre (ICDC)
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 local effects. Satellite altimeters enable sea level to be measured from space and give much better spatial coverage (except at high latitudes). However, the length of the altimeter record is limited to only about two decades.
The IPCC AR5 estimated that GMSL rose by 19.5 cm in the period between 1901 and 2015, which corresponds to an average rate of around 1.7 mm/year (Figure 1). This rate is somewhat higher than the sum of the known contributions to sea level rise over this period [i]. This value has been confirmed by more recent studies [ii]. One reanalysis suggests that GMSL during the 20th century rose at a lower rate of 1.2 ± 0.2 mm/year [iii], but this reanalysis has been criticised for its non-representative selection of tide gauges [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].
All 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 2.6–3.2 mm/year [vi]. Different statistical methods for assessing sea level trends and changes therein can come to somewhat different conclusions [vii]. However, available assessments agree that an acceleration in the rate of GMSL rise since the early 1990s is detectable, despite significant decadal variation. Global mean sea level in 2015 was the highest yearly average over the record and ~70 mm higher than in 1993 [viii].
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 [ix]. 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 [x].
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 2014 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 2014 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 [xi].
Projections: global mean sea level
Currently, there are two main approaches to projecting future sea level. Process-based models represent the most important known physical processes explicitly, whereas empirical statistical models look at the relationship between temperature (or radiative forcing) and sea level that has been observed in the past and extrapolate it into the future. 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 [xii].
The IPCC AR5 concludes 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. Based on current understanding, only 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 (by up to several tenths of a metre) above the likely range projected for the 21st century, but the evidence is insufficient for estimating the likelihood of such a collapse (Figure 4). Projections of sea level rise from recent empirical statistical models calibrated with newly available sea level reconstructions align with those from current process-based models [xiii].
Some recent studies highlight the contributions to recent sea level rise from ice sheet melting that were not included in the process-based models underlying the AR5 estimates above [xiv]. 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) [xv]. Similar results were derived in other recent studies [xvi]. 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 180 cm, which has a 5 % probability of being exceeded under the RCP8.5 forcing scenario [xvii]. Various national reports have also used values in the range of 1.5–2.0 m as upper estimates for GMSL rise during the 21st century. One recent study suggests that ice sheet melting in Antarctica and Greenland could occur much faster than previously assumed, which would result in sea level rise of several metres during the 21st century [xviii], but these findings have been controversial. These high-end scenarios are somewhat speculative, but their consideration is nevertheless important for long-term coastal risk management, in particular in densely populated coastal zones [xix].
Sea level rise will continue far beyond 2100. Based on a limited number of available simulations with process-based models, the AR5 suggests that the GMSL rise by 2300 will be less than 1 m for greenhouse gas concentrations that do not exceed 500 ppm CO2-equivalent, but will be in the range of 1 m to more than 3 m for concentrations above 700 ppm CO2-equivalent. However, the AR5 also considered it likely that the underlying models systematically underestimate Antarctica’s future contribution to sea level rise [xx]. Estimates for GMSL rise beyond 2100 from the above-mentioned expert assessment are broadly comparable [xxi]. A more recent study suggests that melting of the Antarctic ice sheet alone could lead to sea level rise of more than 15 m by 2500 under a high emissions scenario [xxii].
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 [xxiii].
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 [xxiv]. Sea level is also affected by changes in atmospheric loading (the ‘inverse barometer’ effect) and 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 [xxv].
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. As a result, sea level relative to land in these regions is rising slower than elsewhere or may even decrease (Figure 5) [xxvi]. A probabilistic assessment of regional sea-level rise in northern Europe reported central estimates of relative sea level change during the 21st century for the RCP8.5 emissions scenario from –14 cm (in Luleå, northern Sweden) to 84 cm in Den Helders (Netherlands); high estimates (with a 5 % probability to be exceeded) range from 52 cm to 181 cm, respectively [xxvii].
A recent review study estimated that 21st century sea level rise along the Dutch coast would be in the range of 25 to 75 cm for a low warming scenario and 50 to 100 cm for a high warming scenario (year 2100, compared with the 1986–2005 baseline period) [xxviii]. 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.
Sea level rise substantially increases the risk of coastal flooding, which affects people, communities and infrastructure. For example, 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 [xxix]. These potential impacts can be substantially reduced by timely adaptation measures, but they are associated with significant costs [xxx].
[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.
[ii] S. Jevrejeva et al., ‘Trends and Acceleration in Global and Regional Sea Levels since 1807’,Global and Planetary Change 113 (February 2014): 11–22, doi:10.1016/j.gloplacha.2013.12.004; Manfred Wenzel and Jens Schröter, ‘Global and Regional Sea Level Change during the 20th Century’,Journal of Geophysical Research: Oceans 119, no. 11 (1 November 2014): 7493–7508, doi:10.1002/2014JC009900.
[iii] Carling C. Hay et al., ‘Probabilistic Reanalysis of Twentieth-Century Sea-Level Rise’,Nature 517, no. 7535 (22 January 2015): 481–84, doi:10.1038/nature14093.
[iv] B. D. Hamlington and P. R. Thompson, ‘Considerations for Estimating the 20th Century Trend in Global Mean Sea Level’,Geophysical Research Letters 42, no. 10 (28 May 2015): 4102–4109, doi:10.1002/2015GL064177.
[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, doi: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, doi:10.1002/2014GL061356; 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, doi:10.1007/s40641-015-0024-4.
[vi] John A. Church and Neil J. White, ‘Sea-Level Rise from the Late 19th to the Early 21st Century’,Surveys in Geophysics 32, no. 4–5 (30 March 2011): 585–602, doi:10.1007/s10712-011-9119-1; D. Masters et al., ‘Comparison of Global Mean Sea Level Time Series from TOPEX/Poseidon, Jason-1, and Jason-2’,Marine Geodesy 35, no. Suppl. 1 (December 2012): 20–41, doi:10.1080/01490419.2012.717862; Church et al., ‘Sea-Level Change’; 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; Jevrejeva et al., ‘Trends and Acceleration in Global and Regional Sea Levels since 1807’; Clark et al., ‘Recent Progress in Understanding and Projecting Regional and Global Mean Sea Level Change’; 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, doi:10.1038/nclimate2635.
[vii] 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, doi:10.1002/2015JC010716.
[viii] Jessica Blunden and Derek S. Arndt, ‘State of the Climate in 2015’,Bulletin of the American Meteorological Society 97, no. 8 (August 2016): Si-S275, doi:10.1175/2016BAMSStateoftheClimate.1.
[ix] 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, doi: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’.
[x] 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, doi:10.1126/science.aad8386.
[xi] 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, doi:10.1029/2001JB000400.
[xii] Church et al., ‘Sea-Level Change’.
[xiii] Robert E. Kopp et al., ‘Temperature-Driven Global Sea-Level Variability in the Common Era’,Proceedings of the National Academy of Sciences 113, no. 11 (15 March 2016): E1434–41, doi:10.1073/pnas.1517056113; Matthias Mengel et al., ‘Future Sea Level Rise Constrained by Observations and Long-Term Commitment’,Proceedings of the National Academy of Sciences 113, no. 10 (8 March 2016): 2597–2602, doi:10.1073/pnas.1500515113.
[xiv] 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, doi: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, doi:10.1038/nature17145; Johannes Jakob Fürst et al., ‘The Safety Band of Antarctic Ice Shelves’,Nature Climate Change 6 (8 February 2016): 479–82, doi: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, doi:10.5194/acp-16-3761-2016.
[xv] 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, doi:10.1016/j.quascirev.2013.11.002.
[xvi] 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, doi: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, doi:10.1016/j.jmarsys.2012.08.007.
[xvii] 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, doi:10.1088/1748-9326/9/10/104008.
[xviii] Hansen et al., ‘Ice Melt, Sea Level Rise and Superstorms’.
[xix] Jochen Hinkel et al., ‘Sea-Level Rise Scenarios and Coastal Risk Management’,Nature Climate Change 5, no. 3 (25 February 2015): 188–90, doi:10.1038/nclimate2505.
[xx] S. Jevrejeva, J. C. Moore, and A. Grinsted, ‘Sea Level Projections to AD2500 with a New Generation of Climate Change Scenarios’,Global and Planetary Change 80–81 (January 2012): 14–20, doi:10.1016/j.gloplacha.2011.09.006; Michiel Schaeffer et al., ‘Long-Term Sea-Level Rise Implied by 1.5 °C and 2 °C Warming Levels’,Nature Climate Change 2, no. 12 (Dezember 2012): 867–70, doi:10.1038/nclimate1584; Church et al., ‘Sea-Level Change’.
[xxi] Horton et al., ‘Expert Assessment of Sea-Level Rise by AD 2100 and AD 2300’; Kopp et al., ‘Probabilistic 21st and 22nd Century Sea-Level Projections at a Global Network of Tide-Gauge Sites’.
[xxii] DeConto and Pollard, ‘Contribution of Antarctica to Past and Future Sea-Level Rise’.
[xxiii] 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, doi: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, doi: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, doi: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’.
[xxiv] 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, doi:10.1007/s10712-013-9257-8.
[xxv] Church et al., ‘Sea-Level Change’.
[xxvi] 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, doi:10.1007/s10584-014-1080-9; Johansson et al., ‘Global Sea Level Rise Scenarios Adapted to the Finnish Coast’.
[xxvii] Johansson et al., ‘Global Sea Level Rise Scenarios Adapted to the Finnish Coast’.
[xxviii] 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.
[xxix] 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.
[xxx] 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, doi:10.1007/s10584-014-1298-6.
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
- Summary of AR5 regional projections and allowances provided by Antarctic Climate & Ecosystems Cooperative Research Centre
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].
It has generally been expected 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 rather than changes in wave and storm surge climate [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. One recent study based on a multi-model ensemble projects an increase in storm surge level for most scenarios and return periods along the northern European coastline, which is more prominent for RCP8.5 than for RCP 4.5, and which can exceed 30 % of the relative sea level rise. Storm surge levels along most European coastal areas south of 50 °N showed small changes [viii]. Similar results were obtained by another study, which found that increases in storm surges can contribute significantly to the projected increases of the 50-year flood height in north-western Europe, particularly along the European mainland coast [ix]. Sea level rise may also change extreme water levels by altering the tidal range. Tidal behaviour is particularly responsive in resonant areas of the Bristol Channel and the Gulf of Saint-Malo (with large amplitude decreases) and in the south-eastern German Bight and Dutch Wadden Sea (with large amplitude increases) [x].
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 [xi]. 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. 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. However, 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 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, doi: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, doi: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, doi: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, doi: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, doi: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, doi: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, doi: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] Hov et al., ‘Extreme Weather Events in Europe: Preparing for Climate Change Adaptation’; 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, doi:10.1002/2014GL059637.
[vii] Weisse et al., ‘Changing Extreme Sea Levels along European Coasts’.
[viii] Michalis I. Vousdoukas et al., ‘Projections of Extreme Storm Surge Levels along Europe’,Climate Dynamics, 20 February 2016, doi:10.1007/s00382-016-3019-5.
[ix] 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, doi:10.5194/os-10-473-2014.
[x] 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, doi:10.1016/j.csr.2011.11.011.
[xi] John Hunter, ‘A Simple Technique for Estimating an Allowance for Uncertain Sea-Level Rise’,Climatic Change 113, no. 2 (1 July 2012): 239–52, doi:10.1007/s10584-011-0332-1; Church et al., ‘Sea-Level Change’; 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, doi:10.1016/j.oceaneng.2012.12.041.
Indicator specification and metadata
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 following components on observed sea-level rise are included:
- Change in global mean sea level (time series starting in 1880, in mm), based on a reconstruction from various data sources (since 1880) and on satellite altimeter data (since 1993)
- Trend in absolute sea level across Europe (map, in mm/year), based on satellite measurements (since 1992)
- Trend in relative sea level across Europe (map, in mm/year), based on selected European tide gauge stations (since 1970)
Furthermore, this indicator presents projections for sea level rise in the 21st century, both globally and for the European seas. The indicator also presents the contributions to past and future global sea level rise from different sources.
Finally, the indicator presents information on observed and projected changes in extreme sea level along European coasts. However, due to insufficient data availability this information cannot be presented by means of figures or maps.
- Change in sea level (mm)
- Rate of sea level change (mm/yr)
- Increase in flooding events (unitless)
Policy context and targets
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.
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 for indicator calculation
Sea-level changes are measured using tide gauges and remotely from space using altimeters.
Currently, there are two main approaches to projecting future sea level. Process-based models represent the most important known physical processes explicitly, whereas empirical-statistical models look at the relationship between temperature (or radiative forcing) and sea level that has been observed in the past and extrapolate it into the future. 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.
As far as the satellite altimetry derived indicator is concerned, the global sea level trends are calculated from the along-track T/P Jason-1&2 series of sea level anomalies obtained. For the regional mean sea level, other altimetry missions (Envisat, ERS-1, ERS-2, Geosat-FollowOn) are also used after being adjusted on these reference missions in order to compute mean sea level at high latitudes (higher than 66°N and S), and also to improve spatial resolution by combining all these missions together. The data are corrected for seasonal variations and the inverse barometer effects. There is a correction for post-glacial rebound. For the global trend maps defined on a 1/3° Mercator-grid the maps combining all available altimeter data are used. Data are provided by CSIRO (Australia). For the Mediterranean and Black Seas, regional products defined on a 1/8° grid are used. Data are provided by the Copernicus Marine environment monitoring service.
Projections for relative mean sea level in Europe consider gravitational fingerprinting 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.
- 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.
- Ssalto/Duacs User Handbook (2016). Ssalto/Duacs User Handbook, 2016: (M)SLA and (M)ADT Near-Real Time and Delayed Time Products, SALP-MU-P-EA-21065-CLS, Edition 3.6.
- Masters et al. (2012): Comparison of Global Mean Sea Level Time Series from TOPEX/Poseidon, Jason-1, and Jason-2. D. Masters , R. S. Nerem , C. Choe , E. Leuliette , B. Beckley , N. White & M. Ablain (2012): Comparison of Global Mean Sea Level Time Series from TOPEX/Poseidon, Jason-1, and Jason-2, Marine Geodesy, 35:sup1, 20-41. (DOI: 10.1080/01490419.2012.717862).
- 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).
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 melting 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.
No uncertainty has been specified
Global mean sea level reconstruction (satellite and altimetre)
provided by Commonwealth Scientific and Industrial Research Organisation (CSIRO)
Mean Sea Level Trend from satellite altimetry (T/P-Jason-1-Jason-2 merged datasets)
provided by Copernicus Marine Environment Monitoring Service
Relative sea level trends (tide gauge data)
provided by Permanent service for mean sea level (PSMSL)
Coupled Model Intercomparison Project Phase 5 - CMIP5
provided by Lawrence Livermore National Laboratory (LLNL)
FRCP4.5 total sea level rise projections
provided by Integrated Climate Data Centre (ICDC)
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
- CSI 047
- CLIM 012
Contacts and ownership
EEA Contact InfoHans-Martin Füssel
EEA Management Plan2016 1.4.1 (note: EEA internal system)
Frequency of updates
For references, please go to http://www.eea.europa.eu/data-and-maps/indicators/sea-level-rise-4/assessment-2 or scan the QR code.
PDF generated on 23 Apr 2017, 04:20 AM