Difference between revisions of "Sea level rise"

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Revision as of 21:58, 28 June 2019


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


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 [1]. 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:

(1) thermal expansion of ocean waters related to decrease of the density (also referred to as 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

(3) decreasing 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 [1]. Most important are:


(4) vertical earth crust motions - in particular earth crust adjustment to melting of polar ice caps, the so-called isostatic rebound,

(5) land surface subsidence, related in particular to extraction of groundwater and oil/gas mining and compaction of drained soils,

(6) changes in the earth gravitational field, related in particular to decrease of the Greenland and Antarctic ice sheets,

(7) regional atmospheric pressure anomalies and changes in the strength and distribution of ocean currents, related in particular to ocean-atmosphere interaction, and

(8) water volume changes due 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 measurements have been analyzed by Church and White (2011) [2]. The tide gauge data were corrected for vertical land surface motion, by using estimates for glacial isostatic adjustment (assuming that this is the major cause of vertical land surface 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. From the satellite data a linear trend of 3.2 ± 0.4 mm/year was derived for the same period 1990 to 2009. The authors conclude from this analysis that we are being confronted with a significant acceleration of sea level rise during the last decades.

Trend analyses of regularly updated satellite data can be viewed at the NOAA site [3] for global and regional sea level changes around the world.

Even after correcting for the effect of glacial isostatic adjustment, substantial regional differences in sea-level rise occur [4]. Major causes are:

  • self-gravitation related to changes in land ice mass, and elastic solid Earth deformation;
  • changes in seawater density (mainly related to fresh water input), in ocean currents and in the atmospheric pressure distribution.


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. Figure 1 shows a compilation of model forecasts up till 2100 presented in the 5th IPCC Assessment Report[1]. All models predict an increase of the rate of sea-level rise[1]. Projections for the main components of sea-level rise according to different scenarios and different models are presented in Table 1.

Figure 1. Compilation of sea level data derived from observations up till 2010 and model projections up till 2100, relative to pre-industrial values. From IPCC 5th Assessment report [1].


Table 1. Typical ranges of projected sea-level rise (SLR) by each of the main SLR components for the period 2081-2100 compared to 1985-2005, according to IPCC report AR5 (2013) [1] and Mengel et al. (2016)[5].
sea-level rise component SLR range [m]

AR5 (2013)

SLR range [m]

Mengel et al. (2016)

Thermal expansion 0.15 - 0.28 0.06 - 0.3
Mountain glaciers 0.07 - 0.2 0.06 - 0.12
Greenland ice sheet 0.03 - 0.15 0.07 – 0.4
Antarctic ice sheet 0 - 0.15 0.04 - 0.13
Land water storage 0 - 0.09












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[6][7]. 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 [8].

Increasing meltwater outflow from Greenland will lead to substantial slowing of the Atlantic meridional overturning circulation. Meltwater form Antarctica will trap warm water from below the sea surface, creating a positive feedback that increases Antarctic ice loss. This can contribute an additional 25 cm to sea-level rise by 2100 [9][10]. For a more detailed discussion see the articles Ocean circulation and Thermohaline circulation of the oceans.

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 [11]. 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 today [12].


Impact of sea-level rise

Sea-level rise will impact in particular on low-lying coastal regions, such as river deltas and coral islands[13][14]. Delta coasts and coral islands are shaped under the influence of marine bio-geomorphological processes; their natural elevation is therefore around the high water level – not much higher and often lower. Many low-lying coastal zones are densely populated and host large cities; a large number of coastal megacities are located in developing countries [15]. 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. 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 [16], 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 [17].

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 [18]. 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 [19] 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 [20]. Relative sea-level rise also causes loss of fertile agricultural land in the coastal hinterland by increased salt seepage to surface waters [21], with great economic and social consequences. Salt intrusion further affects drinking water availability in densely urbanized coastal regions.

Strategies for dealing with the impacts of sea-level rise depend on local conditions. Different strategies are reviewed in the 5th IPCC Assessment report[14] [22]. See also the article Climate adaptation policies for the coastal zone.


See also

https://en.wikipedia.org/wiki/Sea_level_rise

Coastal Wiki articles in Category:Climate change


References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 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.
  2. ↑ 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
  3. ↑ https://www.star.nesdis.noaa.gov/sod/lsa/SeaLevelRise/LSA_SLR_timeseries.php
  4. ↑ 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.
  5. ↑ Mengel, M., Levermann, A., Frieler, K., Robinson, A., Marzeion, B., and Winkelmann, R. 2016. Future sea level rise constrained by observations and long-term commitment. www.pnas.org/cgi/doi/10.1073/pnas.1500515113
  6. ↑ Deconto, R.M. and Pollard, D. 2016. Contribution of Antarctica to past and future sea-level rise. Nature 531: 591-597
  7. ↑ Le Bars, D., Drijfhout, S. and de Vries, H. 2017. A high-end sea level rise probabilistic projection including rapid Antarctic ice sheet mass loss. Environ. Res. Lett. 12, 044013 https://doi.org/10.1088/1748–9326/aa6512
  8. ↑ Edwards, T.L., Brandon, M.A., Durand, G., Edwards, N.R., Golledge, N.R., Holden, P.B., Nias, I.J., Payne, A.J., Ritz, C. and Wernecke, A. 2019. Revisiting Antarctic ice loss due to marine ice-cliff instability. Nature 566: 58-64
  9. ↑ Hansen, J., Sato, M., Hearty, P., Ruedy, R., Kelley, M., Masson-Delmotte, V., Russell, G., Tselioudis, G., Cao, J., Rignot, E., Velicogna, I., Kandiano, E., von Schuckmann, K., Kharecha, P., Legrande, A.N., Bauer, M. and Lo, K.-W. 2015. Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2◦ C global warming is highly dangerous. Atmospheric Chemistry and Physics Discussions 15: 20059–20179
  10. ↑ Golledge, N.R., Keller, E.D., Gomez, N., Naughten, K.A., Bernales, J., Trusel, L.D. and Edwards, T.L. 2019. Global environmental consequences of twenty-first-century ice-sheet melt. Nature 566: 65-72
  11. ↑ Mengel, M., Levermann, A., Frieler, K., Robinson, A., Marzeion, B., and Winkelmann, R. 2016. Future sea level rise constrained by observations and long-term commitment. www.pnas.org/cgi/doi/10.1073/pnas.1500515113
  12. ↑ Mengel, M., Nauels, A., Rogelj, J. and Schleussner, C.-F. 2018. Committed sea-level rise under the Paris Agreement and the legacy of delayed mitigation action. Nature Communications 9, Article number 601
  13. ↑ 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.
  14. ↑ 14.0 14.1 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.
  15. ↑ 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
  16. ↑ 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.
  17. ↑ 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.
  18. ↑ 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.
  19. ↑ 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
  20. ↑ Sefelnasr, A. and Sherif, M. 2014. Impacts of Seawater Rise on Seawater Intrusion in the Nile Delta, Egypt. Groundwater 52: 264–276
  21. ↑ 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
  22. ↑ 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.


The main author of this article is Job Dronkers
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