Global and European sea level

Assessment versions

Published (reviewed and quality assured)

• No published assessments

Rationale

Justification for indicator selection

Sea level is an important indicator of climate change because it can have significant impacts on settlements, infrastructure, people and natural systems. It acts on time scales much longer than those of indicators that are closely related to near-surface temperature change. Even if greenhouse gas concentrations were stabilised immediately, sea level would continue to rise for many centuries.

Changes in global mean sea level (GMSL) 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 disintegration of the large Greenland and 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 locally experienced changes in sea level differ from global average changes for various reasons. First, changes in water density are not expected to be spatially uniform, and the spatial pattern also depends on changes in large-scale ocean circulation. Second, changes in the gravity field, for instance as water moves from melting ice on land to the ocean, also vary across regions. Finally, at any particular location, there may be a vertical movement of the land in either direction, for example due to the ongoing effects of post-glacial rebound (also known as glacial isostatic adjustment), which is particularly strong in northern Europe, to local groundwater extraction or to other processes, including tectonic activity.

In Europe, the potential impacts of sea level rise include flooding, coastal erosion and the submergence of flat regions along continental coastlines and on islands. Rising sea levels can also cause saltwater intrusion into low-lying aquifers, thus threatening water supplies and endangering coastal ecosystems and wetlands. Higher flood levels increase the risk to life and property, including to sea dikes and other infrastructure, with potential impacts on tourism, recreation and transportation functions. Low-lying coastlines with high population densities and small tidal ranges are most vulnerable to sea level rise, in particular where adaptation is hindered by a lack of economic resources or by other constraints.

Damage associated with sea level rise is mostly caused by extreme events, such as storm surges. Of most concern are events when the surge coincides with high tidal levels and increases the risk of coastal flooding owing to extreme water levels. Changes in the climatology of extreme water levels (i.e. the frequency and height of maximum water levels) may be caused by changes in local mean sea level (i.e. the local sea level relative to land averaged over a year or so), changes in tidal range, changes in the local wave climate or changes in storm surge characteristics. Climate change can both increase and decrease average wave height along the European coastline, depending on the location and season.

Changes in storm surge characteristics are linked to changes in the characteristics of atmospheric storms, including the frequency, track and intensity of the storms. The intensity of storm surges can also be strongly affected by regional and local-scale geographical features, such as the shape of the coastline. Typically, the highest water levels are found on the rising limb of the tide. The most intense surge events typically occur during the winter months in Europe.

The most obvious impact of extreme sea level is flooding. The best known coastal flooding event in Europe in living memory occurred in 1953 when a combination of a severe storm surge and a high spring tide caused in excess of 2 000 deaths in the Netherlands, Belgium and the United Kingdom, and damaged or destroyed more than 40 000 buildings. Currently, around 200 million people live in the coastal zone in Europe, as defined by Eurostat. Coastal storms and storm surges can also have considerable ecological impacts, such as seabird wrecks, disruption to seal mating and pupping, and increases in large mammal and turtle strandings.

Scientific references

• IPCC, 2013. Climate Change: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T. F., D. Qin, G.-K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P. M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp.
• IPCC, 2014: Climate Change 2014a: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1132 pp.
• IPCC, 2014b: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part B: Regional Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D. Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 688 pp.

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 7^th EU Environment Action Programme (7^th EAP) to 2020, ‘Living well, within the limits of our planet’. The 7^th 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 7^th 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: Adaptation in EU policy sectors
  Overview of EU sector policies in which mainstreaming of adaptation to climate change is ongoing or explored
• Climate-ADAPT: Country profiles
  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)

Data specifications

EEA data references

• No datasets have been specified here.

External data references

• Time series of gridded Sea Level Anomalies (SL_cci v2.0)
• Global mean sea level reconstruction (Uni Siegen)
• Global mean sea level reconstruction (satellite and altimetre, CSIRO)
• Relative sea level trends (tide gauge data)
• Coupled Model Intercomparison Project Phase 5 - CMIP5
• RCP4.5 total sea level rise projections

Data sources in latest figures

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