Difference between revisions of "Sea level rise"

Latest revision as of 15:08, 21 January 2024

Definition of Sea Level Rise:

The term sea-level rise generally designates the average long-term global rise of the ocean surface measured from the centre of the earth (or more precisely, from the earth reference ellipsoid), as derived from satellite observations. Relative sea-level rise refers to long-term average sea-level rise relative to the local land level, as derived from coastal tide gauges.

This is the common definition for Sea Level Rise, other definitions can be discussed in the article

1 Contributions to sea-level rise
2 Observed sea-level rise
3 Annual and decadal sea level fluctuations
4 Projections of future sea-level rise
- 4.1 Uncertainties related to melting of the polar ice sheets
- 4.2 Extreme sea levels
5 Impact of sea-level rise
6 The long term
7 Progress in geoengineering studies to mitigate sea level rise
8 See also
9 References

Contributions to sea-level rise

Sea levels are highly variable over periods ranging from seconds to decades. Sea-level rise is the rising trend averaged over longer periods, which is observed at many coastal stations since more than a century. Global warming due to human emissions of greenhouse gases is responsible for steepening this trend since at least a few decades. Projections for future sea-level rise up to the year 2030 are presented in the Special IPCC Report on the Ocean and Cryosphere in a Changing Climate (SROCC, 2019)^[1], see Fig. 1. Two scenarios for greenhouse gas emissions are considered in this figure: (1) a "low" scenario, called RCP2.6, with strong reduction of global greenhouse gas emission, such that global warming will probably not exceed 2 ^oC; (2) a "high" scenario, called RCP8.5, in which no measures are taken to limit greenhouse gas emissions ('business as usual'). The high scenario can lead to a rise of up to 5 m of the global average sea level in 2300, but with great uncertainty. The sea level projections of the 2021 IPCC climate report^[2] for the year 2100 are similar to the projections of the 2019 report^[1].

Figure 1. Projections of possible sea-level rise for the low and high emission scenarios, RCP2.6 (blue) and RCP8.5 (red), respectively. The shaded areas indicate the uncertainty in the projections. Figure from (SROCC, 2019)Cite error: Invalid <ref> tag; refs with no name must have content.

Several phenomena contribute to sea-level rise. On a global scale, sea-level rise is mainly due to an increase of the water mass and water volume of the oceans. This global sea-level rise has three components:

(1) Thermal expansion of ocean waters related to decrease of the density (also referred to as thermo-steric component of sea-level rise, related to increasing temperature).

(2) Water mass increase, which is mainly due to melting of mountain glaciers and shrinking of the Greenland and Antarctic ice sheets.

(3) Change in the storage of surface water and groundwater on land.

Other phenomena can substantially influence sea levels at regional scale, inducing either sea-level rise or sea-level fall ^[3]. Most important are:

(4) Change in the Earth's gravitational field, particularly related to the decline of the Greenland and Antarctic ice sheets. Because of the reduced gravitational pull, sea levels fall within areas up to about 2,000 km from zones of ice melt, despite the added volume of water. In contrast, more distant ocean areas experience up to 30-40% greater sea level rise^[4].

(5) Earth crust motions - in particular the solid Earth deformation in response to mass reduction of the polar ice caps and associated water loading of the seabed, the so-called glacial isostatic adjustment (GIA); the response time scale of GIA (from decades to millennia) strongly depends on the local viscoelasticity of the earth mantle^[5]. Reduction of the ice mass causes local uplift of the earth crest and subsidence at greater peripheral distance. The movement of water toward these zones of subsidence causes sea level fall in the more distant ocean basins^[6].

(6) Land surface subsidence related in particular to extraction of groundwater and oil/gas mining and compaction of soft deltaic soils^[7]. In many coastal locations, including many mega cities, land subsidence is currently the dominant driver of relative sea level rise.

(7) Regional atmospheric pressure anomalies and changes in the strength and distribution of ocean currents (so-called Dynamic Sea Level Change), related in particular to the coupled ocean-atmosphere dynamics.

(8) Regional sea-level change related to changes in seawater salinity.

Due to these phenomena, sea-level rise is not uniform around the globe, but differs from place to place. Relative sea-level rise is the locally observed rise of the average sea level with respect to the land level. It is the sum of the components (1-8).

Observed sea-level rise

Trends in sea-level from world-wide available tide gauge records and from satellite altimetry have been analyzed by Church and White (2011) ^[8]. The tide gauge data were corrected for vertical land surface motion, by using estimates for glacial isostatic adjustment (but ignoring other causes of vertical land motion). From these corrected tide gauge data, a linear trend of 1.7 ± 0.2 mm/year sea-level rise was found for the period 1900 to 1990 and a linear trend of 2.8 ± 0.8 mm/year for the period 1990 to 2009.

Trend analyses of regularly updated satellite data can be viewed at the NOAA site ^[9] for global and regional sea-level changes around the world. Satellite altimeter data cover all the ocean basins. However, they do not replace tide gauge data because altimeter data are less reliable close to the land^[10].

The satellite data display substantial regional differences in sea level rise. Important causes are^[11]:

Glacial Isostatic Adjustment (GIA, elastic solid Earth deformation) and self-gravitation related to changes in land ice mass.
Dynamic Sea Level Change (DSLC), which is related to medium and long-term changes in ocean circulation patterns and the atmospheric pressure distribution, including local anomalous changes in seawater density (mainly related to local fresh water input and local water temperature). The interannual variance of sea level related to DSLC exceeds 20% over 48% of the global ocean area^[12].

All observations show that the global sea level has risen faster during the past decades than in the past century. While sea-level rise is estimated at 1-2 mm/year during the past century^[1]^[13], the estimate of the present sea-level rise (2022) ranges between 3 and 4 mm/year, with an acceleration rate of 0.12±0.07 mm yr^-2 ^[1]^[14]^[15]^[16]. The estimated global sea-level rise for the past decades (1993-2022) is primarily based on satellite altimeter data and estimates of different contributions to the ocean water budget (especially the melting of the Greenland and Antarctic ice sheets). A much higher than average sea-level rise was observed in the Indian Ocean–Eastern Pacific region, especially for the period 1993-2005^[4]. This regional anomaly has a strong impact on the estimate for the global sea-level rise^[13]. However, uncertainties remain in the calibration of the satellite altimeter data^[17]. For example, a substantially lower acceleration rate was found by Kleinherenbrink et al. (2019^[18]), based on a reanalysis of calibration drifts in the satellite altimeter data. Fig. 2 shows the sea-level data of 6 tide gauge stations along the Dutch coast^[19]. No significant acceleration of sea-level rise is apparent in these data, although a recent increase in the rate of sea level rise could be masked by the strong annual variability (as suggested by studies using different data analysis methods^[20]^[21]). An acceleration of sea level rise did also not show up in the analysis of many other tide gauge stations in the North-Atlantic region^[22]. A possible (partial) explanation is provided by the decreasing gravitational attraction associated with the shrinking ice mass of Greenland^[4].

Figure 2. Sea level data of 6 tide gauge station along the Dutch coast (Vlissingen, Hoek van Holland, IJmuiden, Den Helder, Harlingen, Delfzijl)^[19]. The contribution of soil subsidence is estimated at 0.24-0.6 mm/year. The green line is the linear trend, the wavy/wiggling line takes into account the estimated influence of long-term fluctuations in the wind field and in the tide (the 18.6-year lunar nodal component, see Long-period lunar tides). The light green shaded area is the 95% prediction interval and the red and blue lines and corresponding shaded areas are the 2014 sea-level rise projections of the Dutch Meteorological Institute.

Annual and decadal sea level fluctuations

Table 1. Major coupled ocean-atmosphere oscillation modes^[23].
Region	Oscillation mode	Acronym	Main periodicity range [year]
Pacific	El Nino Southern Oscillation	ENSO	2-7
	Pacific Decadal Oscillation	PDO	15-75
	North Pacific Gyre Oscillation	NPGO	15-40
Indian Ocean	Indian Ocean Basin Mode	DIOB	2-20
Indian Ocean	Indian Ocean Dipole	IOD	8-25
Atlantic Ocean	North Atlantic Oscillation	NAO	2-8
Atlantic Ocean	Atlantic Multidecadal Oscillation	AMO	50-80
Arctic Ocean	Arctic Oscillation	AO	2-12
Antarctic Ocean	Southern Annular Mode	SAM	8-16

The data in Fig. 2, representing averages of the annual mean sea level at 6 stations in the southern part of the North Sea, exhibit differences between consecutive years which are often greater than 10 cm. The figure shows that long-term fluctuations in the annual mean wind field in the southern North Sea can explain part of the fluctuations. The remaining part should probably be attributed to the inverse barometer effect in response to fluctuations in the atmospheric pressure and to larger scale phenomena associated e.g. to the North Atlantic Oscillation (NAO) or other large-scale interaction phenomena between ocean and atmospheric dynamics^[24].

Large-scale ocean-atmosphere interactions occur in all oceans, for example the well-known El Nino Southern Oscillation (ENSO) in the Tropical Pacific. Some components of these large-scale oscillations involve timescales up to several decades, see Table 1. The origin of oscillations at multidecadal timescale (driven by ocean-atmosphere interaction or by external forcing such as volcanic activity) is debated^[25]; multidecadal variability is considered a more appropriate term than multidecadal oscillation^[2]. Multiannual variability in ocean surface levels associated with large-scale ocean circulations can be quite substantial, according to satellite observations and coupled ocean-atmosphere simulation models^[23]. However, transmission across the continental slope is largely inhibited for oscillations at sub-basin scales^[26], see also Shelf sea exchange with the ocean. Sea level fluctuations in the coastal zone are mainly related to fluctuations in local atmospheric conditions; this holds especially for coastal zones situated on a wide continental shelf^[24]. Observation records from coastal tide gauges or from satellite observations should cover at least several decades in order to determine long-term trends.

Projections of future sea-level rise

Many model studies have been conducted to predict future sea-levels. Different forecasts of future sea levels display a large spread. This is due to uncertainty regarding future emissions of greenhouse gases, to shortcomings in the present understanding of climate dynamics (including ocean-atmosphere interaction) and to restrictions imposed on model grid scales. All models predict an increase of the rate of sea-level rise. Projections for the main components of sea-level rise according to different scenarios and different models are presented in Table 2.

Sea-level rise lags behind global warming. Even if greenhouse gas emissions would stop today, sea levels will continue rising for at least a century and probably much longer^[27]^[2]. In the hypothetical case that there will be no greenhouse gas emissions from now on, sea levels will be 0.7-1.2 m higher in 2300 than in 2000 ^[28].

Uncertainties related to melting of the polar ice sheets

Table 2. Typical ranges of projected sea-level rise (SLR) by each of the main SLR components for the year 2100 compared to 1985-2005, according to IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC, 2019) ^[1]. The ranges of sea level rise given in the IPCC 2021 climate report^[2] for the various components are similar.
sea-level rise component	SLR range [m] low IPCC scenario (RCP2.6)	SLR range [m] high IPCC scenario (RCP8.5)
Thermal expansion	0.1 - 0.18	0.21 – 0.33
Mountain glaciers	0.07 - 0.12	0.15 - 0.25
Greenland ice sheet	0.04 - 0.12	0.08 – 0.27
Antarctic ice sheet	0.01 - 0.11	0.03 – 0.28
Total SLR	0.29 - 0.59	0.61 – 1.1

It has been suggested that the contributions from the Antarctic to sea-level rise could be much larger when considering structural collapse of the marine-terminated ice cliffs and disintegration of the West Antarctic ice sheet after removal of the ice shelves^[29]^[30]. This could contribute to an additional sea-level rise of 1 m in 2100 and up to 15 m in 2500. However, some doubts exist whether marine ice-cliff instability is a realistic scenario ^[31].

Studies by Hansen et al. (2016) ^[32] and Golledge et al. (2019)^[33] based on modelling and paleoclimate records point to a feedback process that can enhance melting of the Antarctic ice sheet and produce additional sea-level rise. This feedback process is triggered by increasing amounts of fresh meltwater from the polar ice sheets that strengthen ocean stratification, reduce the sinking of Antarctic cold water and decrease the ocean heat flux to the atmosphere. This results in sequestration of warm deep water and enhanced melting of the Antarctic ice sheets. These authors also predict a slowing of the Atlantic meridional overturning circulation (AMOC) due to increasing meltwater outflow from the Greenland ice sheet, with possibly important consequences for the North Atlantic Gulfstream and the climate of northwestern Europe. A more detailed discussion is presented in the articles Ocean circulation and Thermohaline circulation of the oceans.

Another issue is the observed retreat of the grounding line (boundary between grounded and floating ice) of the Antarctic ice sheet^[34]. Ongoing retreat of the grounding line will accelerate melting and destabilize the Antarctic ice sheet. However, decrease of the ice mass will induce feedback effects. Evidence from observations and model simulations suggests that ongoing retreat of the grounding line could be reduced or even reversed when considering the combined effects of sea level fall due to a decrease of gravitational attraction and rebound of the solid Earth^[35]^[36]. A fine-grid model that explicitly resolves ocean eddies yields a more realistic Southern Ocean temperature distribution and volume transport; the simulated Antarctic mass loss in this model is three times lower than with earlier coarse-grid models^[37]. These different results and hypotheses explain the great uncertainty margins in the sea level projections shown in Table 2.

Extreme sea levels

Most coastal zones are more vulnerable to extreme sea levels than to the mean sea level. This holds in particular for coasts situated on broad continental shelves (North Sea, East China Sea, for example) where extreme levels are much higher than the mean sea level, due to amplification of the ocean tides and water-level setup by strong winds (storm surges). Rise of the local mean sea level is always the major component of the projected rise of the local extreme sea level (for any given long return period), although climate-induced change in extreme wind and wave conditions can influence extreme sea levels significantly in some regions^[38]^[39]. Climate models predict, for example, that extreme wind and wave conditions will be less frequent along the eastern African coast, whereas in northern Europe (especially the Baltic region in the RCP8.5 scenario^[40]) extreme levels will increase more than the mean sea level.

Sea-level rise does not only affect extreme sea levels, but also the average return period. This will be the case in particular for coasts situated close to the deep ocean, where sea levels are less influenced by storm surges, and for coasts outside the zone of tropical cyclones. For these coasts the average return period of extreme sea levels will strongly decrease; in many cases a reduction of a factor greater than 100 is projected in the IPCC scenario RCP8.5 in 2100: a once in 100 year extreme sea level will become a yearly event. For coasts situated on broad continental shelves where extreme levels are much higher than the mean sea level, the average return period will be reduced by a factor 10 or more ^[38]^[1]. For uplifting coasts the reduction of the average return period will be less, because of a smaller relative mean sea-level rise.

Impact of sea-level rise

Sea-level rise will have a great impact, in particular on low-lying coastal regions, such as river deltas and coral islands^[41]^[42]. Delta coasts and coral islands are shaped under the influence of marine geomorphological and biotic processes; their natural elevation is therefore around the present high water level – not much higher and sometimes lower. Many low-lying coastal zones are densely populated and host large cities; a large number of coastal megacities are located in developing countries ^[43]. The number of people living below the annual high water level by 2020 is estimated at about 110 million globally; this number could rise by 2100 to 190 million in a low-emission scenario and to 630 million in a high-emission scenario^[44]. In densely populated coastal zones, sea-level rise is often exacerbated by soil compaction and land subsidence in connection with drainage works and the extraction of groundwater or oil / gas mining, see Coastal cities and sea level rise. The vulnerability is further enhanced by coastal erosion, because of sediment retention behind upstream dams, hard coastal structures and/or conversion of mangrove forests to aquacultures ^[45], see also Human causes of coastal erosion. Considerable investments are required for adapting these vulnerable coastal zones to sea-level rise, in particular to reduce flooding risks ^[46].

Sea-level rise enhances shoreline retreat (for retreating coasts) or reduces shoreline progradation (for accreting coasts), see Natural causes of coastal erosion. The influence of sea-level rise on the shoreline position of sandy barrier coasts can be estimated by means of the Bruun rule ^[47]. Sea-level rise also threatens coastal wetlands, which may not be capable to keep pace with sea level and be partly lost due to so-called coastal squeeze. This can be the case for mudflats and salt marshes in the Wadden Sea ^[48] and for mangrove forests in the tropics and subtropics, see Potential Impacts of Sea Level Rise on Mangroves.

Salt intrusion is another major impact of sea-level rise in low-lying river deltas around the world. This impact is compounded by soil subsidence and by reduced fresh water supply to the coastal zone due to upstream diversion of river water for irrigation and other uses. Salt intrusion threatens crucially important fresh groundwater reservoirs in arid regions, for example in the Nile Delta ^[49]. Relative sea-level rise also causes loss of fertile agricultural land in the coastal hinterland by increased salt seepage to surface waters ^[50], with great economic and social consequences^[51]. Salt intrusion further affects drinking water availability in densely urbanized coastal regions. For more detailed information, see Groundwater management in low-lying coastal zones.

Strategies for dealing with the impacts of sea-level rise depend on local conditions. Different strategies are reviewed in recent IPCC Assessment reports^[42] ^[52]^[1]. See also the article Climate adaptation measures for the coastal zone.

The long term

If the current global warming trend is not stopped, melting of glaciers and polar icecaps will continue. In this scenario the sea level will continue rising to unprecedented heights. The complete melting of all land glaciers can already occur during the next centuries, raising the sea level by about 30 cm^[53]. A much greater increase will come from the complete melting of the Greenland Ice Sheet, which holds enough water to raise the sea level by more than 7 m^[54]. This will mainly affect the southern ocean regions. The greatest increase of about 50 m will occur if the Antarctic Ice Sheet is completely melted^[55]. Northern ocean regions will experience a larger sea level rise. Complete melting of the Greenland and Antarctica ice sheets could take more than thousand years, but is possible without reversal of the global warming trend.

Progress in geoengineering studies to mitigate sea level rise

Geoengineering research is not widely considered an acceptable practice for climate response. However, the polar ice sheets are melting, and it is questionable whether current climate policies will be effective in timely curbing ongoing trends in ocean warming and decreasing albedo of our planet. Climate adaptation measures for the coastal zone are generally limited to sea level rise scenarios of no more than a few meters. If the melting of the polar ice sheets continues, the current coastlines of low-lying coastal areas will eventually recede for tens of kilometers. Geoengineering research aims to explore the possibilities of returning the Earth's climate system to the desired state and thus limiting sea level rise. An overview of the state of the art is presented in the open access article A systematic literature review considering the implementation of planetary geoengineering techniques for the mitigation of sea-level rise by R. Minunno, N. Andersson and G.M. Morrison that was recently published in Earth-Science Reviews.

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↑ Konrad, H., Shepherd, A., Gilbert, L., Hogg, A.E., McMillan, M., Muir, A. and Slater, T. 2018. Net retreat of Antarctic glacier grounding lines. Nature Geosci 11: 258–262
↑ de Boer, B., Stocchi, P., Whitehouse, P. L. and van de Wal, R.S.W. 2017. Current state and future perspectives on coupled icesheet – sea-level modelling, Quaternary Sci. Rev. 169: 13–28
↑ Kingslake, J., Scherer, R., Albrecht, T., Coenen, J., Powell, R., Reese, R., Stansell, N., Tulaczyk, S., Wearing, M. and Whitehouse, P. L. 2018. Extensive retreat and re-advance of the West Antarctic ice sheet during the Holocene. Nature 558: 430–434
↑ Van Westen, R.M. and Dijkstra, H.A. 2021. Ocean eddies strongly affect global mean sea-level projections. Science Advances 7 : eabf1674
↑ ^38.0 ^38.1 Vousdoukas, M.I., Mentaschi, L., Voukouvalas, E., Verlaan, M., Jevrejeva, S., Jackson, L.P. and Feyen, L. 2018. Global probabilistic projections of extreme sea levels show intensification of coastal flood hazard. Nature communications, 9 (1), 2360
↑ Mentaschi, L., Vousdoukas, M. I., Voukouvalas, E., Dosio, A., and Feyen, L. 2017. Global changes of extreme coastal wave energy fluxes triggered by intensified teleconnection patterns. Geophys. Res. Lett. 44: 2416–2426, doi:10.1002/2016GL072488
↑ Vousdoukas, M. I., Mentaschi, L., Voukouvalas, E., Verlaan, M., and Feyen, L. 2017. Extreme sea levels on the rise along Europe’s coasts. Earth’s Future, 5: 304–323, doi:10.1002/2016EF000505
↑ Overeem, I. and Syvitski, J.P.M. 2009. Dynamics and Vulnerability of Delta Systems. LOICZ Reports & Studies No. 35. GKSS Research Center, Geesthacht, 54 pages.
↑ ^42.0 ^42.1 Wong , P.P., I.J. Losada, J.-P. Gattuso, J. Hinkel, A. Khattabi, K.L. McInnes, Y. Saito, and A. Sallenger, 2014. Coastal systems and low-lying areas. In: Climate Change 2014: 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, pp. 361-409.
↑ Hanson, S., Nicholls, R., Ranger, N., Hallegatte, S., Corfee-Morlot, J., Herweijer, C. and Chateau, J. 2011. A global ranking of port cities with high exposure to climate extremes. Climatic Change 104: 89–111. DOI 10.1007/s10584-010-9977-4
↑ Kulp, S.A. and Strauss, B.H. 2019. New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding. Nature Communications 10: 4844
↑ Syvitski, J.P., Kettner, A.J., Overeem, L., Hutton, E.W., Hannon, M.T., Brakenridge, G.R., Day, J., Vörösmarty, C., Saito, Y. and Giosan, L. 2009. Sinking deltas due to human activities. Nature Geosci. 2: 681–686.
↑ Hinkel, J., D.P. van Vuuren, R.J. Nicholls, and Klein, R.J.T. 2013. The effects of mitigation and adaptation on coastal impacts in the 21st century. An application of the DIVA and IMAGE models. Climatic Change 117(4): 783-794.
↑ Atkinson, A.L., Baldock, T.E., Birrien, F., Callaghan, D.P., Nielsen, P., Beuzen, T., Turner, I.I., Blenkinsopp, C.E. and Ranasinghe, R. 2018. Laboratory investigation of the Bruun Rule and beach response to sea-level rise. Coastal Engineering 136: 183–202.
↑ Dissanayake, D.M.P.K., Ranasinghe, R. and Roelvink, J.A. 2012. The morphological response of large tidal inlet/basin systems to relative sea-level rise. Climatic Change 113: 253-276
↑ Sefelnasr, A. and Sherif, M. 2014. Impacts of Seawater Rise on Seawater Intrusion in the Nile Delta, Egypt. Groundwater 52: 264–276
↑ Oude Essink, G. H. P., van Baaren, E. S. and de Louw, P. G. B. 2010. Effects of climate change on coastal groundwater systems: A modeling study in the Netherlands. Water Resources Res. 46, W00F04, doi:10.1029/2009WR008719
↑ Anderson, D.J. 2017. Coastal Groundwater and Climate Change, WRL Technical Report 2017/04. A technical monograph prepared for the National Climate Change Adaptation Research Facility. Water Research Laboratory of the School of Civil and Environmental Engineering, UNSW, Sydney. https://coastadapt.com.au/sites/default/files/factsheets/Coastal%20groundwater%20and%20Climate%20change_final.pdf
↑ Noble, I.R., S. Huq, Y.A. Anokhin, J. Carmin, D. Goudou, F.P. Lansigan, B. Osman-Elasha, and A. Villamizar, 2014. Adaptation needs and options. In: Climate Change 2014: 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, pp. 833-868.
↑ Farinotti, D., Huss, M., Fürst, J. J., Landmann, J., Machguth, H., Maussion, F. and Pandit, A. 2019. A consensus estimate for the ice thickness distribution of all glaciers on Earth. Nature Geoscience 12(3), 168
↑ Morlighem, M., Williams, C. N., Rignot, E., An, L., Arndt, J. E., Bamber, J. L., et al. 2017. BedMachine v3: Complete bed topography and ocean bathymetry mapping of Greenland from multibeam echo sounding combined with mass conservation. Geophysical Research Letters 44: 11,051–11,061
↑ Fretwell, P., Pritchard, H. D., Vaughan, D. G., Bamber, J. L., Barrand, N. E., Bell, R., et al. 2013. Bedmap2: Improved ice bed, surface and thickness datasets for Antarctica. The Cryosphere 7(1): 375–393

The main author of this article is Job Dronkers
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Citation: Job Dronkers (2024): Sea level rise. Available from http://www.coastalwiki.org/wiki/Sea_level_rise [accessed on 21-11-2024]

For other articles by this author see Category:Articles by Job Dronkers
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[41] Overeem, I. and Syvitski, J.P.M. 2009. Dynamics and Vulnerability of Delta Systems. LOICZ Reports & Studies No. 35. GKSS Research Center, Geesthacht, 54 pages.

[W-42] 42.0 ^42.1 Wong , P.P., I.J. Losada, J.-P. Gattuso, J. Hinkel, A. Khattabi, K.L. McInnes, Y. Saito, and A. Sallenger, 2014. Coastal systems and low-lying areas. In: Climate Change 2014: 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, pp. 361-409.

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[51] Anderson, D.J. 2017. Coastal Groundwater and Climate Change, WRL Technical Report 2017/04. A technical monograph prepared for the National Climate Change Adaptation Research Facility. Water Research Laboratory of the School of Civil and Environmental Engineering, UNSW, Sydney. https://coastadapt.com.au/sites/default/files/factsheets/Coastal%20groundwater%20and%20Climate%20change_final.pdf

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[54] Morlighem, M., Williams, C. N., Rignot, E., An, L., Arndt, J. E., Bamber, J. L., et al. 2017. BedMachine v3: Complete bed topography and ocean bathymetry mapping of Greenland from multibeam echo sounding combined with mass conservation. Geophysical Research Letters 44: 11,051–11,061

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 ==Contributions to sea-level rise==
-Sea levels are highly variable over periods ranging from seconds to decades. Sea-level rise is the rising trend averaged over longer periods, which is observed at many coastal stations since a few centuries. It is almost certain that global warming due to human emissions of greenhouse gases is responsible for steepening this trend since at least a few decades. Projections for future sea-level rise up to the year 2030 are presented in the Special IPCC Report on the Ocean and Cryosphere in a Changing Climate (SROCC, 2019)<ref name=I>Oppenheimer, M., Glavovic, B.C., Hinkel,, J., van de Wal, R., Magnan, A.K., Abd-Elgawad, A., Cai, R., Cifuentes-Jara, M., DeConto, R.M.  , Ghosh, T., Hay, J., Isla, F., Marzeion, B., Meyssignac, B. and Sebesvari, Z. 2019: Sea Level Rise and Implications for Low-Lying Islands, Coasts and Communities. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. </ref>, see Fig. 1. Two scenarios for greenhouse gas emissions are considered in this figure: (1) a "low" scenario, called RCP2.6, with strong reduction of global greenhouse gas emission, such that global warming will probably not exceed 2 <sup>o</sup>C; (2) a "high" scenario, called RCP8.5, in which no measures are taken to limit greenhouse gas emissions ('business as usual'). The high scenario can lead to a rise of up to 5 m of the global average sea level in 2300,  but with great uncertainty. The sea level projections of the 2021 IPCC climate report<ref name=IPCC21>Fox-Kemper, B., Hewitt H. T., Xiao C., Aoalgeirsdottir G., Drijfhout S. S., Edwards T. L., Golledge N. R., Hemer M., Kopp R. E., Krinner G., Mix A., Notz D., Nowicki S., Nurhati I. S., Ruiz L., Sallée J-B., Slangen A. B. A. and Yu Y. 2021. Ocean, Cryosphere and Sea Level Change. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekci, R. Yu and B. Zhou (eds.)]. Cambridge University Press.</ref> for the year 2100 are similar to the projections of the 2019 report<ref name=I/>.
+Sea levels are highly variable over periods ranging from seconds to decades. Sea-level rise is the rising trend averaged over longer periods, which is observed at many coastal stations since more than a century. Global warming due to human emissions of greenhouse gases is responsible for steepening this trend since at least a few decades. Projections for future sea-level rise up to the year 2030 are presented in the Special IPCC Report on the Ocean and Cryosphere in a Changing Climate (SROCC, 2019)<ref name=I>Oppenheimer, M., Glavovic, B.C., Hinkel,, J., van de Wal, R., Magnan, A.K., Abd-Elgawad, A., Cai, R., Cifuentes-Jara, M., DeConto, R.M.  , Ghosh, T., Hay, J., Isla, F., Marzeion, B., Meyssignac, B. and Sebesvari, Z. 2019: Sea Level Rise and Implications for Low-Lying Islands, Coasts and Communities. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. </ref>, see Fig. 1. Two scenarios for greenhouse gas emissions are considered in this figure: (1) a "low" scenario, called RCP2.6, with strong reduction of global greenhouse gas emission, such that global warming will probably not exceed 2 <sup>o</sup>C; (2) a "high" scenario, called RCP8.5, in which no measures are taken to limit greenhouse gas emissions ('business as usual'). The high scenario can lead to a rise of up to 5 m of the global average sea level in 2300,  but with great uncertainty. The sea level projections of the 2021 IPCC climate report<ref name=IPCC21>Fox-Kemper, B., Hewitt H. T., Xiao C., Aoalgeirsdottir G., Drijfhout S. S., Edwards T. L., Golledge N. R., Hemer M., Kopp R. E., Krinner G., Mix A., Notz D., Nowicki S., Nurhati I. S., Ruiz L., Sallée J-B., Slangen A. B. A. and Yu Y. 2021. Ocean, Cryosphere and Sea Level Change. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekci, R. Yu and B. Zhou (eds.)]. Cambridge University Press.</ref> for the year 2100 are similar to the projections of the 2019 report<ref name=I/>.
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-Several phenomena contribute to sea-level rise. On a global scale, sea-level rise is mainly due to an increase of the water mass and water volume of the oceans. This global sea-level rise (often termed Eustatic sea-level rise) has three components:
+Several phenomena contribute to sea-level rise. On a global scale, sea-level rise is mainly due to an increase of the water mass and water volume of the oceans. This global sea-level rise has three components:
-(1) thermal expansion of ocean waters related to decrease of the density (also referred to as thermo-steric component of sea-level rise, related to increasing temperature),
+(1) Thermal expansion of ocean waters related to decrease of the density (also referred to as thermo-steric component of sea-level rise, related to increasing temperature).
-(2) water mass increase, which is mainly due to melting of mountain glaciers and decrease of the Greenland and Antarctic ice sheets, and
+(2) Water mass increase, which is mainly due to melting of mountain glaciers and shrinking of the Greenland and Antarctic ice sheets.
-(3) decreasing storage of surface water and groundwater on land.
+(3) Change in the storage of surface water and groundwater on land.
 Other phenomena can substantially influence sea levels at regional scale, inducing either sea-level rise or sea-level fall <ref name=C> Church, J.A., P.U. Clark, A. Cazenave, J.M. Gregory, S. Jevrejeva, A. Levermann, M.A. Merrifield, G.A. Milne, R.S. Nerem, P.D. Nunn, A.J. Payne, W.T. Pfeffer, D. Stammer and A.S. Unnikrishnan, 2013. Sea Level Change. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [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.</ref>. Most important are:
-(4) earth crust motions - in particular the solid Earth deformation in response to mass reduction of the polar ice caps and concomitant water loading of the seabed, the so-called glacial isostatic adjustment (GIA); the response time scale of GIA (from decades to millennia) strongly depends on the local viscoelasticity of the earth mantle<ref>Whitehouse, P.L. 2018. Glacial isostatic adjustment modelling: historical perspectives, recent advances, and future directions. Earth Surf. Dynam. 6: 401–429</ref>,
+(4) Change in the Earth's gravitational field, particularly related to the decline of the Greenland and Antarctic ice sheets. Because of the reduced gravitational pull, sea levels fall within areas up to about 2,000 km from zones of ice melt, despite the added volume of water. In contrast, more distant ocean areas experience up to 30-40% greater sea level rise<ref name=H20>Hamlington, B. D., Gardner, A. S., Ivins, E., Lenaerts, J. T. M., Reager, J. T., Trossman, D. S., et al. 2020. Understanding of contemporary regional sea‐level change and the implications for the future. Reviews of Geophysics, 58, e2019RG000672</ref>.
-(5) changes in the earth gravitational field, related in particular to decrease of the Greenland and Antarctic ice sheets,
+(5) Earth crust motions - in particular the solid Earth deformation in response to mass reduction of the polar ice caps and associated water loading of the seabed, the so-called glacial isostatic adjustment (GIA); the response time scale of GIA (from decades to millennia) strongly depends on the local viscoelasticity of the earth mantle<ref>Whitehouse, P.L. 2018. Glacial isostatic adjustment modelling: historical perspectives, recent advances, and future directions. Earth Surf. Dynam. 6: 401–429</ref>. Reduction of the ice mass causes local uplift of the earth crest and subsidence at greater peripheral distance. The movement of water toward these zones of subsidence causes sea level fall in the more distant ocean basins<ref>Mitrovica, J. X. and Milne, G. A. 2002. On the origin of late Holocene sea‐level highstands within equatorial ocean basins. Quaternary Science Reviews 21: 2179–2190</ref>.
-(6) ubiquitous land surface subsidence related in particular to extraction of groundwater and oil/gas mining and compaction of soft deltaic soils<ref>Wöppelmann, G. and Marcos, M. 2016. Vertical land motion as a key to understanding sea level change and variability. Rev. Geophys. 54: 64–92</ref>,
+(6) Land surface subsidence related in particular to extraction of groundwater and oil/gas mining and compaction of soft deltaic soils<ref>Wöppelmann, G. and Marcos, M. 2016. Vertical land motion as a key to understanding sea level change and variability. Rev. Geophys. 54: 64–92</ref>. In many coastal locations, including many [[Coastal cities and sea level rise|mega cities]], land subsidence is currently the dominant driver of relative sea level rise.
-(7) regional atmospheric pressure anomalies and changes in the strength and distribution of ocean currents (so-called Dynamic Sea Level Change), related in particular to the coupled ocean-atmosphere dynamics, and
+(7) Regional atmospheric pressure anomalies and changes in the strength and distribution of ocean currents (so-called Dynamic Sea Level Change), related in particular to the coupled ocean-atmosphere dynamics.
-(8) regional sea-level change related to changes in seawater salinity.
+(8) Regional sea-level change related to changes in seawater salinity.
 Due to these phenomena, sea-level rise is not uniform around the globe, but differs from place to place. [[Relative sea level|Relative sea-level]] rise is the locally observed rise of the average sea level with respect to the land level. It is the sum of the components (1-8).
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 Trends in sea-level from world-wide available tide gauge records and from satellite altimetry have been analyzed by Church and White (2011) <ref>Church J.A. and White N.J. 2011. Sea-Level Rise from the Late 19th to the Early 21st Century. Surv.Geophys 32: 585–602, DOI 10.1007/s10712-011-9119-1</ref>. The tide gauge data were corrected for  vertical land surface motion, by using estimates for glacial isostatic adjustment (but ignoring other causes of vertical land motion). From these corrected tide gauge data, a linear trend of 1.7 ± 0.2 mm/year sea-level rise was found for the period 1900 to 1990 and a linear trend of 2.8 ± 0.8 mm/year for the period 1990 to 2009.
-Trend analyses of regularly updated satellite data can be viewed at the NOAA site <ref> https://www.star.nesdis.noaa.gov/sod/lsa/SeaLevelRise/LSA_SLR_timeseries.php </ref> for global and regional sea-level changes around the world. Satellite altimeter data cover all the ocean basins. However, they do not replace tide gauge data because altimeter data are not reliable close to the land<ref>Benveniste, J., Cazenave, A., Vignudelli, S., Fenoglio-Marc, L., Shah, R., Alma,r R., Andersen, O., Birol, F., Bonnefond, P., Bouffard, J., Calafat, F., Cardellach, E., Cipollini, P., Le Cozannet, G., Dufau, C., Fernandes, M.J., Frappart, F., Garrison, J., Gommenginger, C., Han, G., Hoyer, J.L., Kourafalou, V., Leuliette, E., Li, Z., Loise,l H., Madsen, K.S., Marcos ,M., Melet, A., Meyssignac, B., Pascual, A., Passaro, M., Ribo, S., Scharroo, R., Song, Y.T., Speich, S., Wilkin, J., Woodworth, P. and Wöppelmann, G. 2019. Requirements for a Coastal Hazards Observing System. Front. Mar. Sci. 6: 348</ref>.
+Trend analyses of regularly updated satellite data can be viewed at the NOAA site <ref> https://www.star.nesdis.noaa.gov/sod/lsa/SeaLevelRise/LSA_SLR_timeseries.php </ref> for global and regional sea-level changes around the world. Satellite altimeter data cover all the ocean basins. However, they do not replace tide gauge data because altimeter data are less reliable close to the land<ref>Benveniste, J., Cazenave, A., Vignudelli, S., Fenoglio-Marc, L., Shah, R., Alma,r R., Andersen, O., Birol, F., Bonnefond, P., Bouffard, J., Calafat, F., Cardellach, E., Cipollini, P., Le Cozannet, G., Dufau, C., Fernandes, M.J., Frappart, F., Garrison, J., Gommenginger, C., Han, G., Hoyer, J.L., Kourafalou, V., Leuliette, E., Li, Z., Loise,l H., Madsen, K.S., Marcos ,M., Melet, A., Meyssignac, B., Pascual, A., Passaro, M., Ribo, S., Scharroo, R., Song, Y.T., Speich, S., Wilkin, J., Woodworth, P. and Wöppelmann, G. 2019. Requirements for a Coastal Hazards Observing System. Front. Mar. Sci. 6: 348</ref>.
 The satellite data display substantial regional differences in sea level rise. Important causes are<ref> Slangen A.B.A., Katsman C.A., van der Wal R.S.W., Vermeersen L.L.A. and Riva R.E.M. 2012. Towards regional projections of twenty-first century sea-level change using IPCC SRES scenarios. Clim. Dyn. 38 (5): 1191-1209, doi:10.1007/s00382-011-1057-6</ref>:
-* Glacial Isostatic adjustment (elastic solid Earth deformation) and self-gravitation related to changes in land ice mass;
+* Glacial Isostatic Adjustment (GIA, elastic solid Earth deformation) and self-gravitation related to changes in land ice mass.
-* Dynamic Sea Level Change, which is related to medium and long-term changes in ocean circulation patterns and the atmospheric pressure distribution, including local anomalous changes in seawater density (mainly related to local fresh water input and local water temperature).
+* Dynamic Sea Level Change (DSLC), which is related to medium and long-term changes in ocean circulation patterns and the atmospheric pressure distribution, including local anomalous changes in seawater density (mainly related to local fresh water input and local water temperature). The interannual variance of sea level related to DSLC exceeds 20% over 48% of the global ocean area<ref> Carret, A., Llovel, W., Penduff, T. and Molines, J.-M. 2021. Atmospherically forced and chaotic interannual variability of regional sea level and its components over 1993–2015. Journal of Geophysical Research: Oceans 126, e2020JC017123</ref>.
-There is overwhelming evidence that the global sea level has risen faster during the past decades than in the past century. While sea-level rise is estimated at 1-2 mm/year during the past century<ref name=I></ref><ref name=D> Dangendorf, S., Marcos, M., Wöppelmann, G., Conrad, C.P., Frederikse, T. and Riva, T. 2017. Reassessment of 20th century global mean sea level rise. PNAS 114: 5946–5951, www.pnas.org/cgi/doi/10.1073/pnas.1616007114 </ref>, the estimate of the present sea-level rise (2019) ranges between 3 and 4 mm/year, with an acceleration rate of 0.12±0.07 mm yr<sup>-2</sup> <ref name=I></ref><ref> Ablain, M., Meyssignac, B., Zawadzki, L., Jugier, R., Ribes, A., Spada, G., Benveniste, J., Cazenave, A. and Picot, N. 2019. Uncertainty in satellite estimates of global mean sea-level changes, trend and acceleration. Earth Syst. Sci. Data 11: 1189–1202, https://doi.org/10.5194/essd-11-1189-2019</ref><ref> WCRP Global Sea Level Budget Group, Anny Cazenave coordinating author. 2018. Global sea-level budget 1993–present. Earth Syst. Sci. Data 10: 1551–1590. https://doi.org/10.5194/essd-10-1551-2018 </ref><ref> Nerem, R. S., Beckley, B. D., Fasullo, J. T., Hamlington, B. D., Masters, D. and Mitchum, G. T. 2018. Climate-change–driven accelerated sea-level rise detected in the altimeter era. PNAS 115: 2022–2025, www.pnas.org/cgi/doi/10.1073/pnas.1717312115</ref>. The estimated global sea-level rise for the past decades (1993-2017) is primarily based on satellite altimeter data and estimates of different contributions to the ocean water budget (especially melt of the Greenland and Antarctic ice sheets). A much higher than average sea-level rise is observed in the Indian Ocean–Eastern Pacific region. This regional anomaly has a strong impact on the estimate for the global sea-level rise<ref name=D/>. However, uncertainties remain in the calibration of the satellite altimeter data. A much lower acceleration rate of 0.018 ± 0.016 mm yr<sup>-2</sup> has been found by Kleinherenbrink et al. (2019<ref> Kleinherenbrink, M., Riva, R. and Scharroo, R. 2019. A revised acceleration rate from the altimetry-derived global mean sea level record. Scientific Reports 9: 10908</ref>), based on a reanalysis of calibration drifts in the satellite altimeter data. Fig. 2 shows the sea-level data of 6 tide gauge stations along the Dutch coast, corrected for soil subsidence<ref name=B>Baart, F., Rongen, G., Hijma, M., Kooi, H., de Winter, R, Nicolai, R. 2019. Zeespiegelmonitor 2018: De stand van zaken rond de zeespiegelstijging langs de Nederlandse kust. Deltares.</ref>. No significant acceleration of sea-level rise is visible in these data. This can be partly due to changes in the gravitational field (the influence of the decreasing ice mass of Greenland may account for a 0.9 mm/year sea-level decrease along the Dutch coast), but the difference with the global 3-4 mm/year sea-level rise cannot be fully explained. An analysis of other tide gauge stations in the North-Atlantic region yields a similar picture<ref>Boretti, A. 2020. The pattern of sea-level rise across the North Atlantic from long-term-trend tide gauges. Ocean and Coastal Management 196, 105309</ref>.
+All observations show that the global sea level has risen faster during the past decades than in the past century. While sea-level rise is estimated at 1-2 mm/year during the past century<ref name=I></ref><ref name=D> Dangendorf, S., Marcos, M., Wöppelmann, G., Conrad, C.P., Frederikse, T. and Riva, T. 2017. Reassessment of 20th century global mean sea level rise. PNAS 114: 5946–5951, www.pnas.org/cgi/doi/10.1073/pnas.1616007114 </ref>, the estimate of the present sea-level rise (2022) ranges between 3 and 4 mm/year, with an acceleration rate of 0.12±0.07 mm yr<sup>-2</sup> <ref name=I></ref><ref> Ablain, M., Meyssignac, B., Zawadzki, L., Jugier, R., Ribes, A., Spada, G., Benveniste, J., Cazenave, A. and Picot, N. 2019. Uncertainty in satellite estimates of global mean sea-level changes, trend and acceleration. Earth Syst. Sci. Data 11: 1189–1202, https://doi.org/10.5194/essd-11-1189-2019</ref><ref> WCRP Global Sea Level Budget Group, Anny Cazenave coordinating author. 2018. Global sea-level budget 1993–present. Earth Syst. Sci. Data 10: 1551–1590. https://doi.org/10.5194/essd-10-1551-2018 </ref><ref> Nerem, R. S., Beckley, B. D., Fasullo, J. T., Hamlington, B. D., Masters, D. and Mitchum, G. T. 2018. Climate-change–driven accelerated sea-level rise detected in the altimeter era. PNAS 115: 2022–2025, www.pnas.org/cgi/doi/10.1073/pnas.1717312115</ref>. The estimated global sea-level rise for the past decades (1993-2022) is primarily based on satellite altimeter data and estimates of different contributions to the ocean water budget (especially the melting of the Greenland and Antarctic ice sheets). A much higher than average sea-level rise was observed in the Indian Ocean–Eastern Pacific region, especially for the period 1993-2005<ref name=H20/>. This regional anomaly has a strong impact on the estimate for the global sea-level rise<ref name=D/>. However, uncertainties remain in the calibration of the satellite altimeter data<ref>Barnoud, A., Picard, B., Meyssignac, B., Marti, F., Ablain, M. and Roca, R. 2023. Reducing the Uncertainty in the Satellite Altimetry Estimates of Global Mean Sea Level Trends Using Highly Stable Water Vapor Climate Data Records. J. Geophys. Res. Oceans 128, e2022JC019378</ref>. For example, a substantially lower acceleration rate was found by Kleinherenbrink et al. (2019<ref> Kleinherenbrink, M., Riva, R. and Scharroo, R. 2019. A revised acceleration rate from the altimetry-derived global mean sea level record. Scientific Reports 9: 10908</ref>), based on a reanalysis of calibration drifts in the satellite altimeter data. Fig. 2 shows the sea-level data of 6 tide gauge stations along the Dutch coast<ref name=B>Baart, F., Rongen, G., Hijma, M., Kooi, H., de Winter, R, Nicolai, R. 2019. Zeespiegelmonitor 2018: De stand van zaken rond de zeespiegelstijging langs de Nederlandse kust. Deltares.</ref>. No significant acceleration of sea-level rise is apparent in these data, although a recent increase in the rate of sea level rise could be masked by the strong annual variability (as suggested by studies using different data analysis methods<ref>Steffelbauer, D. B., Riva, R. E. M., Timmermans, J. S., Kwakkel, J. H. and Bakker, M. 2022. Evidence of regional sea-level rise acceleration for the North Sea. Environmental Research Letters 17, 074 002</ref><ref>Keizer, I., Le Bars, D., de Valk, C., Jüling, A., van de Wal, R. and Drijfhout, S. 2022. The acceleration of sea-level rise along the coast of the Netherlands started in the 1960s. Egu-sphere preprint 2022-935</ref>). An acceleration of sea level rise did also not show up in the analysis of many other tide gauge stations in the North-Atlantic region<ref>Boretti, A. 2020. The pattern of sea-level rise across the North Atlantic from long-term-trend tide gauges. Ocean and Coastal Management 196, 105309</ref>. A possible (partial) explanation is provided by the decreasing gravitational attraction associated with the shrinking ice mass of Greenland<ref name=H20/>.
-[[Image: SeaLevelRiseDutchCoast.jpg|thumb|600px|center|Figure 2. Sea level data of 6 tide gauge station along the Dutch coast (Vlissingen, Hoek van Holland, IJmuiden, Den Helder, Harlingen, Delfzijl)<ref name=B></ref>. For each station, the data are corrected for the known soil subsidence (0.24-0.6 mm/year). The green line is the linear trend, the wavy/wiggling line takes into account the estimated influence of long-term fluctuations in the wind field and in the tide (the 18.6-year lunar nodal component), the light green shaded area is the 95% prediction interval and the red and blue lines and corresponding shaded areas are the 2014 sea-level rise projections of the Dutch Meteorological Institute.]]
+[[File: SeaLevelRiseDutchCoast.jpg|thumb|600px|center|Figure 2. Sea level data of 6 tide gauge station along the Dutch coast (Vlissingen, Hoek van Holland, IJmuiden, Den Helder, Harlingen, Delfzijl)<ref name=B></ref>. The contribution of soil subsidence is estimated at 0.24-0.6 mm/year. The green line is the linear trend, the wavy/wiggling line takes into account the estimated influence of long-term fluctuations in the wind field and in the tide (the 18.6-year lunar nodal component, see [[Long-period lunar tides]]). The light green shaded area is the 95% prediction interval and the red and blue lines and corresponding shaded areas are the 2014 sea-level rise projections of the Dutch Meteorological Institute.]]
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 | style="border:2px solid lightblue; font-size: 11px; text-align:center"|	Atlantic Multidecadal Oscillation
 | style="border:2px solid lightblue; font-size: 11px; text-align:center"|	AMO
-| style="border:2px solid lightblue; font-size: 11px; text-align:center"|	60-80
+| style="border:2px solid lightblue; font-size: 11px; text-align:center"|	50-80
 |-
 | style="border:2px solid lightblue; font-size: 11px; text-align:center"| Arctic Ocean
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 The data in Fig. 2, representing averages of the annual mean sea level at 6 stations in the southern part of the North Sea, exhibit differences between consecutive years which are often greater than 10 cm. The figure shows that long-term fluctuations in the annual mean wind field in the southern North Sea can explain part of the fluctuations. The remaining part should probably be attributed to the inverse barometer effect in response to fluctuations in the atmospheric pressure and to larger scale phenomena associated e.g. to the [[North Atlantic Oscillation]] (NAO) or other large-scale interaction phenomena between ocean and atmospheric dynamics<ref name=H19>Han, W., Stammer, D., Thompson, P., Ezer, T., Palanisamy, H., Zhang, X., Domingues, C.M., Zhang, L. and Yuan, D. 2019. Impacts of Basin‑Scale Climate Modes on Coastal Sea Level: a Review. Surveys in Geophysics 40: 1493–1541</ref>.
-Large-scale ocean-atmosphere interactions occur in all oceans, for example the well-known El Nino Southern Oscillation (ENSO) in the Tropical Pacific. Some components of these large-scale interactions involve timescales up to several decades, see Table 1. Multiannual oscillations in ocean surface levels associated with large-scale ocean circulations can be quite substantial, according to satellite observations and coupled ocean-atmosphere simulation models<ref name=H17/>. However, transmission across the continental slope is largely inhibited for oscillations at sub-basin scales<ref>Hughes, C.W., Fukumori, I., Griffies, S.M., Huthnance, J.M., Minobe, S., Spence, P., Thompson, K.R. and Wise, A. 2019. Sea Level and the Role of Coastal Trapped Waves in Mediating the Influence of the Open Ocean on the Coast. Surveys in Geophysics 40: 1467–1492</ref>, see also [[Shelf sea exchange with the ocean]]. Sea level fluctuations in the coastal zone are mainly related to fluctuations in local atmospheric conditions; this holds especially for coastal zones situated on a wide continental shelf<ref name=H19/>. Observation records from coastal tide gauges or from satellite observations should cover at least several decades in order to determine long-term trends.
+Large-scale ocean-atmosphere interactions occur in all oceans, for example the well-known El Nino Southern Oscillation (ENSO) in the Tropical Pacific. Some components of these large-scale oscillations involve timescales up to several decades, see Table 1. The origin of oscillations at multidecadal timescale (driven by ocean-atmosphere interaction or by external forcing such as volcanic activity) is debated<ref>Mann, M.E., Steinman, B.A., Brouillette, D.J. and Miller, S.K. 2021. Multidecadal climate oscillations during the past millennium driven by volcanic forcing. Science 371 (6533): 1014–1019</ref>; multidecadal variability is considered a more appropriate term than multidecadal oscillation<ref name=IPCC21/>. Multiannual variability in ocean surface levels associated with large-scale ocean circulations can be quite substantial, according to satellite observations and coupled ocean-atmosphere simulation models<ref name=H17/>. However, transmission across the continental slope is largely inhibited for oscillations at sub-basin scales<ref>Hughes, C.W., Fukumori, I., Griffies, S.M., Huthnance, J.M., Minobe, S., Spence, P., Thompson, K.R. and Wise, A. 2019. Sea Level and the Role of Coastal Trapped Waves in Mediating the Influence of the Open Ocean on the Coast. Surveys in Geophysics 40: 1467–1492</ref>, see also [[Shelf sea exchange with the ocean]]. Sea level fluctuations in the coastal zone are mainly related to fluctuations in local atmospheric conditions; this holds especially for coastal zones situated on a wide continental shelf<ref name=H19/>. Observation records from coastal tide gauges or from satellite observations should cover at least several decades in order to determine long-term trends.
 <br clear=all>
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 ==Impact of sea-level rise==
-Sea-level rise will have a great impact, in particular on low-lying coastal regions, such as river deltas and coral islands<ref> Overeem, I. and Syvitski, J.P.M. 2009. Dynamics and Vulnerability of Delta Systems. LOICZ Reports & Studies No. 35. GKSS Research Center, Geesthacht, 54 pages.</ref><ref name=W> Wong , P.P., I.J. Losada, J.-P. Gattuso, J. Hinkel, A. Khattabi, K.L. McInnes, Y. Saito, and A. Sallenger, 2014. Coastal systems and low-lying areas. In:  Climate Change 2014: 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, pp. 361-409.</ref>. Delta coasts and coral islands are shaped under the influence of marine geomorphological and biotic processes; their natural elevation is therefore around the present high water level – not much higher and sometimes lower. Many low-lying coastal zones are densely populated and host large cities; a large number of coastal megacities are located in developing countries <ref>Hanson, S., Nicholls, R., Ranger, N., Hallegatte, S., Corfee-Morlot, J., Herweijer, C. and Chateau, J. 2011. A global ranking of port cities with high exposure to climate extremes. Climatic Change 104: 89–111. DOI 10.1007/s10584-010-9977-4</ref>. The number of people living below the annual high water level by 2020 is estimated at about 110 million globally; this number could rise by 2100 to 190 million in a low-emission scenario and to 630 million in a high-emission scenario<ref>Kulp, S.A. and Strauss, B.H. 2019. New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding. Nature Communications 10: 4844</ref>. In densely populated coastal zones, sea-level rise is often exacerbated by soil compaction and land subsidence in connection with drainage works and the extraction of groundwater or oil / gas mining, see [[Coastal cities and sea level rise]]. The vulnerability is further enhanced by coastal erosion, because of sediment retention behind upstream dams, hard coastal structures and/or conversion of mangrove forests to aquacultures <ref> Syvitski, J.P., Kettner, A.J., Overeem, L., Hutton, E.W., Hannon, M.T., Brakenridge, G.R., Day, J., Vörösmarty, C., Saito, Y. and Giosan, L. 2009. Sinking deltas due to human activities. Nature Geosci. 2: 681–686.</ref>, see also [[Human causes of coastal erosion]]. Considerable investments are required for adapting these vulnerable coastal zones to sea-level rise, in particular to reduce flooding risks <ref> Hinkel, J., D.P. van Vuuren, R.J. Nicholls, and Klein, R.J.T. 2013. The effects of mitigation and adaptation on coastal impacts in the 21st century. An application of the DIVA and IMAGE models. Climatic Change 117(4): 783-794.</ref>.
+Sea-level rise will have a great impact, in particular on low-lying coastal regions, such as [[Morphology of estuaries|river deltas]] and [[coral islands]]<ref> Overeem, I. and Syvitski, J.P.M. 2009. Dynamics and Vulnerability of Delta Systems. LOICZ Reports & Studies No. 35. GKSS Research Center, Geesthacht, 54 pages.</ref><ref name=W> Wong , P.P., I.J. Losada, J.-P. Gattuso, J. Hinkel, A. Khattabi, K.L. McInnes, Y. Saito, and A. Sallenger, 2014. Coastal systems and low-lying areas. In:  Climate Change 2014: 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, pp. 361-409.</ref>. Delta coasts and coral islands are shaped under the influence of marine geomorphological and biotic processes; their natural elevation is therefore around the present high water level – not much higher and sometimes lower. Many low-lying coastal zones are densely populated and host large cities; a large number of coastal megacities are located in developing countries <ref>Hanson, S., Nicholls, R., Ranger, N., Hallegatte, S., Corfee-Morlot, J., Herweijer, C. and Chateau, J. 2011. A global ranking of port cities with high exposure to climate extremes. Climatic Change 104: 89–111. DOI 10.1007/s10584-010-9977-4</ref>. The number of people living below the annual high water level by 2020 is estimated at about 110 million globally; this number could rise by 2100 to 190 million in a low-emission scenario and to 630 million in a high-emission scenario<ref>Kulp, S.A. and Strauss, B.H. 2019. New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding. Nature Communications 10: 4844</ref>. In densely populated coastal zones, sea-level rise is often exacerbated by soil compaction and land subsidence in connection with drainage works and the extraction of groundwater or oil / gas mining, see [[Coastal cities and sea level rise]]. The vulnerability is further enhanced by coastal erosion, because of sediment retention behind upstream dams, hard coastal structures and/or conversion of mangrove forests to aquacultures <ref> Syvitski, J.P., Kettner, A.J., Overeem, L., Hutton, E.W., Hannon, M.T., Brakenridge, G.R., Day, J., Vörösmarty, C., Saito, Y. and Giosan, L. 2009. Sinking deltas due to human activities. Nature Geosci. 2: 681–686.</ref>, see also [[Human causes of coastal erosion]]. Considerable investments are required for adapting these vulnerable coastal zones to sea-level rise, in particular to reduce flooding risks <ref> Hinkel, J., D.P. van Vuuren, R.J. Nicholls, and Klein, R.J.T. 2013. The effects of mitigation and adaptation on coastal impacts in the 21st century. An application of the DIVA and IMAGE models. Climatic Change 117(4): 783-794.</ref>.
 Sea-level rise enhances shoreline retreat (for retreating coasts) or reduces shoreline progradation (for accreting coasts), see [[Natural causes of coastal erosion]]. The influence of sea-level rise on the shoreline position of sandy barrier coasts can be estimated by means of the [[Bruun rule]] <ref> Atkinson, A.L., Baldock, T.E., Birrien, F., Callaghan, D.P., Nielsen, P., Beuzen, T., Turner, I.I., Blenkinsopp, C.E. and Ranasinghe, R. 2018. Laboratory investigation of the Bruun Rule and beach response to sea-level rise. Coastal Engineering 136: 183–202.</ref>. Sea-level rise also threatens coastal wetlands, which may not be capable to keep pace with sea level and be partly lost due to so-called [[coastal squeeze]]. This can be the case for mudflats and salt marshes in the Wadden Sea <ref>Dissanayake, D.M.P.K., Ranasinghe, R. and Roelvink, J.A. 2012. The morphological response of large tidal inlet/basin systems to relative sea-level rise. Climatic Change 113: 253-276</ref> and for mangrove forests in the tropics and subtropics, see [[Potential Impacts of Sea Level Rise on Mangroves]].
@@ Line 169: / Line 170: @@
 Strategies for dealing with the impacts of sea-level rise depend on local conditions. Different strategies are reviewed in recent IPCC Assessment reports<ref name=W></ref> <ref> Noble, I.R., S. Huq, Y.A. Anokhin, J. Carmin, D. Goudou, F.P. Lansigan, B. Osman-Elasha, and A. Villamizar, 2014. Adaptation needs and options. In:  Climate Change 2014: 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, pp. 833-868.</ref><ref name=I></ref>. See also the article [[Climate adaptation measures for the coastal zone]].
+==The long term==
+If the current global warming trend is not stopped, melting of glaciers and polar icecaps will continue. In this scenario the sea level will continue rising to unprecedented heights. The complete melting of all land glaciers can already occur during the next centuries, raising the sea level by about 30 cm<ref>Farinotti, D., Huss, M., Fürst, J. J., Landmann, J., Machguth, H., Maussion, F. and Pandit, A. 2019. A consensus estimate for the ice thickness distribution of all glaciers on Earth. Nature Geoscience 12(3), 168</ref>. A much greater increase will come from the complete melting of the Greenland Ice Sheet, which holds enough water to raise the sea level by more than 7 m<ref>Morlighem, M., Williams, C. N., Rignot, E., An, L., Arndt, J. E., Bamber, J. L., et al. 2017. BedMachine v3: Complete bed topography and ocean bathymetry mapping of Greenland from multibeam echo sounding combined with mass conservation. Geophysical Research Letters 44: 11,051–11,061</ref>. This will mainly affect the southern ocean regions. The greatest increase of about 50 m will occur if the Antarctic Ice Sheet is completely melted<ref>Fretwell, P., Pritchard, H. D., Vaughan, D. G., Bamber, J. L., Barrand, N. E., Bell, R., et al. 2013. Bedmap2: Improved ice bed, surface and thickness datasets for Antarctica. The Cryosphere 7(1): 375–393</ref>. Northern ocean regions will experience a larger sea level rise. Complete melting of the Greenland and Antarctica ice sheets could take more than thousand years, but is possible without reversal of the global warming trend.
+==Progress in geoengineering studies to mitigate sea level rise==
+Geoengineering research is not widely considered an acceptable practice for climate response. However, the polar ice sheets are melting, and it is questionable whether current climate policies will be effective in timely curbing ongoing trends in ocean warming and decreasing albedo of our planet. [[Climate adaptation measures for the coastal zone]] are generally limited to sea level rise scenarios of no more than a few meters. If the melting of the polar ice sheets continues, the current coastlines of low-lying coastal areas will eventually recede for tens of kilometers.
+Geoengineering research aims to explore the possibilities of returning the Earth's climate system to the desired state and thus limiting sea level rise. An overview of the state of the art is presented in the open access article [https://www.sciencedirect.com/science/article/pii/S0012825223001204 A systematic literature review considering the implementation of planetary geoengineering techniques for the mitigation of sea-level rise] by R. Minunno, N. Andersson and G.M. Morrison that was recently published in Earth-Science Reviews.

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