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Indicator Assessment
Trend in absolute sea level across Europe based on satellite measurements, 1993-2019
Note: Spatial distribution of trends in mean sea level in European seas (January 1993- February 2019).
Trend in relative sea level at selected European tide gauge stations, 1970-2016
Note:
Projected change in relative sea level, 2081-2100
Note: European sea level change for 2081–2100 for RCP2.6 and RCP8.5 in metres. Results are median values based on the values in SROCC Table 4.4 for Antarctica including GIA and the gravitational and rotational effects, and results by Church et al. (2013) for glaciers, LWS and Greenland.
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-decadal 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.
Figure 1 shows the change in global mean sea level (GMSL) since the early 20th century, based on different tide gauge reconstructions (green and red curves) and satellite altimeters (dark blue curve). GMSL in 2018, assessed by satellite altimetry, was the highest level over the entire record. GMSL reconstructions based on tide gauge observations suggest a rise of 16 (±4) cm over the period between 1902 and 2010.
GMSL rise has accelerated since the 1960s. The rate of GMSL rise during the period 1993-2018, for which satellite-based measurements are available, has been around 3.3 mm/year; this is more than twice as fast as the mean trend for 1901-1990, which was1.4 (±0.6) mm/year [i]. A further acceleration of sea level rise has also been detected within the satellite altimeter period [ii]. Over the five-year period 2014-2019, the rate of GMSL rise has amounted to 5 mm/year [iii].
The causes of GMSL rise over recent decades are now well understood. Multiple lines of evidence support the conclusion that the dominant cause of global mean sea level rise since 1970 is anthropogenic forcing. Thermal expansion and melting of glaciers account for around 75 % of the measured sea level rise since 1971. However, the contribution from melting of the Greenland and Antarctic ice sheets has increased since the early 1990s. Over the period 2006–2015, the sum of ice sheet and glacier contributions was the dominant source of sea level rise (1.8±0.1 mm/year), exceeding the effect of thermal expansion of ocean water (1.4±0.3 mm/year) [iv]. Changes in land water storage and groundwater extraction have made only a small contribution [v].
Past trends: mean sea level along the European coastline
Most European coastal regions experience increases in both absolute sea level (as measured by satellites) and relative sea level (as measured by tide gauges), but there are sizeable differences in the rates of absolute and relative sea level change across Europe.
Figure 2 shows linear trends in absolute sea level from 1993 to 2019 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 2016 as observed by tide gauge stations in Europe. These trends are more relevant for coastal protection than absolute sea level. They 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.
Projections: global mean sea level
The main approach to projecting future sea level are simulations with process-based climate models. 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. These models estimate the rise in GMSL during the 21st century (i.e. in 2100, compared with 1986–2005) to be likely in the range of 0.29-0.59 m for RCP2.6, 0.39-0.72 m for RCP4.5, and 0.61-1.10 m for RCP8.5 (Figure 4). The rate of GMSL rise in 2100 is estimated at 4-9 mm/year for RCP2.6 and 10–20 mm/year for RCP8.5 [vi].
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 currently insufficient for estimating the likelihood of such a collapse. A structured expert assessment suggests that a GMSL rise of 2 or more metres cannot be ruled out [vii]. 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 [viii]. Whilst high-end scenarios are somewhat speculative, their consideration is nevertheless important for long-term coastal risk management, in particular in densely populated coastal zones [ix].
Sea levels will continue to rise far beyond the year 2100 due to continued thermal expansion and further ice loss from the Greenland and Antarctic ice sheet. GMSL rise is projected to reach 0.6-1.1 m by 2300 under ambitious mitigation (RCP2.6 extended) and 2.3-5.4 m under high emissions (RCP8.5 extended). These GMSL projections would rise substantially if the largest estimates of sea level contributions from Antarctica over the coming centuries were included [x]. A recent study has suggested that each 5-year delay in peaking of global greenhouse gas emissions increases median sea-level rise estimates for 2300 by 0.2 m, and extreme sea-level rise estimates by up to 1 m [xi].
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, disintegrating land ice and post-glacial rebound, and local factors, such as vertical land movement [xii]. However, around 70 % of the world’s coastlines are expected to experience a local mean sea level change within ±20 % of the projected GMSL change [xiii].
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) [xiv].
A probabilistic assessment of regional sea-level rise in northern and central Europe estimated relative sea level changes 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 [xv].
[i] Michael Oppenheimer et al., ‘Chapter 4: Sea Level Rise and Implications for Low Lying Islands, Coasts and Communities’, inIPCC Special Report on the Ocean and Cryosphere in a Changing Climate, ed. H.-O. Pörtner et al. (Cambridge, UK: Cambridge University Press, 2019), https://www.ipcc.ch/srocc/download-report/; Sönke Dangendorf et al., ‘Persistent Acceleration in Global Sea-Level Rise since the 1960s’,Nature Climate Change 9, no. 9 (September 2019): 705–10, https://doi.org/10.1038/s41558-019-0531-8.
[ii] R. S. Nerem et al., ‘Climate-Change–Driven Accelerated Sea-Level Rise Detected in the Altimeter Era’,Proceedings of the National Academy of Sciences 115, no. 9 (27 February 2018): 2022–25, https://doi.org/10.1073/pnas.1717312115.
[iii] WMO, ‘The Global Climate in 2015–2019’ (Geneva: World Meteorological Organization, 2019), https://library.wmo.int/index.php?lvl=notice_display&id=21522#.XeesozJ7lpg.
[iv] WCRP Global Sea Level Budget Group, ‘Global Sea-Level Budget 1993–Present’,Earth System Science Data 10, no. 3 (28 August 2018): 1551–90, https://doi.org/10.5194/essd-10-1551-2018; Oppenheimer et al., ‘Chapter 4: Sea Level Rise and Implications for Low Lying Islands, Coasts and Communities’.
[v] Yoshihide Wada et al., ‘Recent Changes in Land Water Storage and Its Contribution to Sea Level Variations’,Surveys in Geophysics 38, no. 1 (January 2017): 131–52, https://doi.org/10.1007/s10712-016-9399-6.
[vi] Oppenheimer et al., ‘Chapter 4: Sea Level Rise and Implications for Low Lying Islands, Coasts and Communities’.
[vii] Jonathan L. Bamber et al., ‘Ice Sheet Contributions to Future Sea-Level Rise from Structured Expert Judgment’,Proceedings of the National Academy of Sciences 116, no. 23 (4 June 2019): 11195–200, https://doi.org/10.1073/pnas.1817205116.
[viii] 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.
[ix] For an example of the application of damage curves to European cities, see L M Abadie et al., ‘Risk Measures and the Distribution of Damage Curves for 600 European Coastal Cities’,Environmental Research Letters 14, no. 6 (21 June 2019): 064021, https://doi.org/10.1088/1748-9326/ab185c.
[x] Oppenheimer et al., ‘Chapter 4: Sea Level Rise and Implications for Low Lying Islands, Coasts and Communities’.
[xi] Matthias Mengel et al., ‘Committed Sea-Level Rise under the Paris Agreement and the Legacy of Delayed Mitigation Action’,Nature Communications 9, no. 1 (December 2018): 601, https://doi.org/10.1038/s41467-018-02985-8.
[xii] 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.
[xiii] 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; 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.
[xiv] 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; 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; Oppenheimer et al., ‘Chapter 4: Sea Level Rise and Implications for Low Lying Islands, Coasts and Communities’.
[xv] 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.
Change in the frequency of flooding events in Europe given projected sea level rise under two climate scenarios
Note: This maps show the estimated change in the frequency of flooding events of a given height between 2010 and 2100 due to projected regional sea relative level rise under the RCP2.6 and RCP8.5 scenarios. Values larger than 1 indicate an increase in flooding frequency. RCP, representative concentration pathway; RCP2.6: low emissions scenario; RCP8.5: high emissions scenario
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 characteristics 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 storm surges 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
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 [v]. 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 [vi]. 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 [vii].
The co-occurrence of high sea level and heavy precipitation resulting in large runoff may cause compound flooding in low-lying coastal areas. The Mediterranean coasts are at highest risk of compound flooding in the present. For example, compound flooding was the cause of the catastrophic floods in Venice in November 2019. A recent study found that climate change increases the risk of compound flooding along most parts of the European coast, including the eastern and southern coasts of the North Sea, the Norwegian coast, the west coast of Great Britain, the coast of northern France, and the eastern coast of the Black Sea [viii].
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. Figure 6 shows that 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 or even 1000 in some locations during the 21st century, depending on the emissions scenario [ix]. 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.
Coastal flooding affects people, communities and infrastructure. A recent study conducted within the ECONADAPT project has estimated the average annual losses from coastal flooding in the 17 main coastal cities in EEA member countries to increase from about EUR 1 billion in 2030 to EUR 31 billion in 2100 under the RCP8.5 scenario, in the absence of adaptation [x]. Much higher damages were identified in a recent study from the HELIX and PESETA III projects, which considers sea level rise in parallel with different scenarios of socio-economic development. In the absence of adaptation, this study projects an increase in the average annual damage from coastal flooding in Europe (EU28 and Norway) from currently EUR 1.25 billion to a range between EUR 93 billion and EUR 961 billion by the end of the century, depending on the scenario. The annual number of people exposed is projected to rise from 102 000 to 1.52-3.65 million over the same time horizon [xi].
The potential impacts from coastal flooding can be substantially reduced by timely adaptation measures, but they are associated with significant costs [xii]. 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. Damage and protection cost curves for coastal floods within the 600 largest European cities are available from the RAMSES project [xiii].
[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), https://easac.eu/publications/details/extreme-weather-events-in-europe/; 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] 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.
[vi] 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’.
[vii] 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; M.D. Pickering et al., ‘The Impact of Future Sea-Level Rise on the Global Tides’,Continental Shelf Research 142 (June 2017): 50–68, https://doi.org/10.1016/j.csr.2017.02.004.
[viii] E. Bevacqua et al., ‘Higher Probability of Compound Flooding from Precipitation and Storm Surge in Europe under Anthropogenic Climate Change’,Science Advances 5, no. 9 (September 2019): eaaw5531, https://doi.org/10.1126/sciadv.aaw5531.
[ix] D J Rasmussen et al., ‘Extreme Sea Level Implications of 1.5 °C, 2.0 °C, and 2.5 °C Temperature Stabilization Targets in the 21st and 22nd Centuries’,Environmental Research Letters 13, no. 3 (1 March 2018): 034040, https://doi.org/10.1088/1748-9326/aaac87; Michael Oppenheimer et al., ‘Chapter 4: Sea Level Rise and Implications for Low Lying Islands, Coasts and Communities’, inIPCC Special Report on the Ocean and Cryosphere in a Changing Climate, ed. H.-O. Pörtner et al. (Cambridge, UK: Cambridge University Press, 2019), https://www.ipcc.ch/srocc/download-report/.
[x] 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.
[xi] Michalis I. Vousdoukas et al., ‘Climatic and Socioeconomic Controls of Future Coastal Flood Risk in Europe’,Nature Climate Change 8, no. 9 (September 2018): 776–80, https://doi.org/10.1038/s41558-018-0260-4.
[xii] 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.
[xiii] Boris F. Prahl et al., ‘Damage and Protection Cost Curves for Coastal Floods within the 600 Largest European Cities’,Scientific Data 5 (20 March 2018): 180034, https://doi.org/10.1038/sdata.2018.34.
This indicator comprises several metrics to describe past and future sea level rises 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:
In April 2013, the European Commission 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’. This will be achieved by bridging knowledge gaps and further developing the European climate adaptation platform (Climate-ADAPT) as the ‘one-stop shop’ for adaptation information in Europe. Climate-ADAPT was developed jointly by the European Commission 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. It was relaunched in early 2019 with a new design and updated content. Further objectives include ‘Promoting adaptation in key vulnerable sectors through climate-proofing EU sector policies’ and ‘Promoting action by Member States’.
In November 2018, the Commission published its evaluation of the 2013 EU adaptation strategy. The evaluation package includes a report from the Commission, a Commission staff working document, adaptation preparedness scoreboard country fiches and reports from the JRC Peseta III project. This evaluation includes recommendations for the further development and implementation of adaptation policies at all levels.
In November 2013, the European Parliament and the Council of the European Union adopted the EU's Seventh 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.
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 indicator derived from satellite altimetry 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, 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.
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.
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.
See ‘Methodology’ section.
Changes in global average sea levels result from a combination of several physical processes. The 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, in either natural reservoirs such as groundwater or man-made reservoirs.
The changes in sea level experienced locally 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, due for example 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 GMSL rise up to 2100 (relative to 1986-2005) have been made for three RCP scenarios. The contributions from ice sheets include contributions from ice-sheet rapid dynamical change. The value of the Antarctic contribution is the individual component with the largest uncertainty.
The level of uncertainty in future projections of extreme sea level for Europe remains high and is ultimately linked to uncertainties related to future mid-latitude storminess changes. This is an area in which current scientific understanding is advancing quickly, as climate model representations of aspects of northern hemisphere storm track behaviour are improving, because of, 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
For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/sea-level-rise-6/assessment or scan the QR code.
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