Difference between revisions of "Sea level rise"

From Coastal Wiki
Jump to: navigation, search
Line 1: Line 1:
 
  
 
{{Definition|title=Sea Level Rise
 
{{Definition|title=Sea Level Rise
Line 7: Line 6:
 
==Contributions to sea-level rise==
 
==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 <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>. 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:  
+
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. The most recent projections for future sea-level rise are presented in the Special IPCC Report on the Ocean and Cryosphere in a Changing Climate (2019)<ref name=I>IPCC, 2019. Special Report on the Ocean and Cryosphere in a Changing Climate [Eds.: H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, M. Nicolai, A. Okem, J. Petzold, B. Rama and N. Weyer].</ref>. This report is an update of the previous IPCC AR5 report (2013) <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>, and includes newer insights in the response of the Greenland and Antarctic ice sheets to global warming. It also provides an estimation of the possible sea-level rise up to the year 2030, 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. 
 +
 
 +
 
 +
[[Image:SLRscenariosIPCC2019.jpg|thumb|600px|center|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 (IPCC, 2019)<ref name=I></ref>.]]
 +
 
 +
 
 +
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),
+
(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 decrease of the Greenland and Antarctic ice sheets, and  
Line 20: Line 25:
 
(4) vertical earth crust motions - in particular earth crust adjustment to melting of polar ice caps, the so-called isostatic rebound,  
 
(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,  
+
(5) land surface subsidence, related in particular to extraction of groundwater and oil/gas mining and compaction of soft deltaic soils,
  
 
(6) changes in the earth gravitational field, related in particular to decrease of the Greenland and Antarctic ice sheets,  
 
(6) changes in the earth gravitational field, related in particular to decrease of the Greenland and Antarctic ice sheets,  
Line 26: Line 31:
 
(7) regional atmospheric pressure anomalies and changes in the strength and distribution of ocean currents, related in particular to ocean-atmosphere interaction, and
 
(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.
+
(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).
 
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).
Line 33: Line 38:
 
==Observed sea-level rise==
 
==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) <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 (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.
+
Trends in sea-level from world-wide available tide gauge records and from satellite measurements 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 (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.  
  
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.  
+
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.  
  
 
Even after correcting for the effect of glacial isostatic adjustment, substantial regional differences in sea-level rise occur <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>.  Major causes are:
 
Even after correcting for the effect of glacial isostatic adjustment, substantial regional differences in sea-level rise occur <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>.  Major causes are:
 
* self-gravitation related to changes in land ice mass, and elastic solid Earth deformation;
 
* 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.       
+
* changes in seawater density (mainly related to fresh water input and water temperature), in ocean currents and in the atmospheric pressure distribution.       
 +
 
 +
There is hardly any doubt 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 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–Southern Pacific region. This regional feature has a strong impact on the estimate for the global sea-level rise<ref name=D></ref>. 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), 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 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.
 +
 
 +
 
 +
[[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.]]
 +
 
  
  
Line 45: Line 56:
  
  
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<ref name=C></ref>. All models predict an increase of the rate of sea-level rise<ref name=C></ref>. Projections for the main components of sea-level rise according to different scenarios and different models are presented in Table 1.  
+
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 1.  
  
[[Image: SeaLevelRise_IPCC_AR5.jpg|thumb|400px|right|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 <ref name=C></ref>.]]
+
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 <ref>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</ref>. 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 <ref>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</ref>.
  
 +
===Uncertainties related to melting of the polar ice sheets===
  
{|  style="border-collapse:collapse; font-size: 13px;  background:ivory;" cellpadding=5px align=left width=50%
+
{|  style="border-collapse:collapse; font-size: 12px;  background:ivory;" cellpadding=5px align=right width=50%
|+ 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) <ref name=C></ref> and Mengel et al. (2016)<ref> 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</ref>.
+
|+ Table 1. 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 (2019) <ref name=I></ref>.
 
|- style="font-weight:bold;  font-size: 13px; text-align:center; background:lightblue"
 
|- style="font-weight:bold;  font-size: 13px; text-align:center; background:lightblue"
 
! width="20% style=" border:1px solid blue;"| sea-level rise component
 
! width="20% style=" border:1px solid blue;"| sea-level rise component
 
! width="15% style=" border:1px solid bleu;"| SLR range [m]  
 
! width="15% style=" border:1px solid bleu;"| SLR range [m]  
AR5 (2013)  
+
low IPCC scenario (RCP2.6)
 
! width="15% style=" border:1px solid blue;"| SLR range [m]   
 
! width="15% style=" border:1px solid blue;"| SLR range [m]   
Mengel et al. (2016)  
+
high IPCC scenario (RCP8.5)  
 
|-
 
|-
 
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| Thermal expansion
 
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| Thermal expansion
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 0.15 - 0.28
+
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 0.1 - 0.18
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 0.06 - 0.3
+
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 0.21 – 0.33
 
|-
 
|-
 
| style="border:2px solid lightblue; font-size: 12px;  text-align:center"|  Mountain glaciers
 
| style="border:2px solid lightblue; font-size: 12px;  text-align:center"|  Mountain glaciers
| style="border:2px solid lightblue; font-size: 12px;  text-align:center"| 0.07 - 0.2
+
| style="border:2px solid lightblue; font-size: 12px;  text-align:center"| 0.07 - 0.12
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 0.06 - 0.12
+
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 0.15 - 0.25
 
|-
 
|-
 
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| Greenland ice sheet
 
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| Greenland ice sheet
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 0.03 - 0.15
+
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 0.04 - 0.12
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 0.07 – 0.4
+
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 0.08 – 0.27
 
|-
 
|-
 
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| Antarctic ice sheet
 
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| Antarctic ice sheet
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 0 - 0.15
+
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 0.01 - 0.11
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 0.04 - 0.13
+
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 0.03 – 0.28
 
|-
 
|-
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| Land water storage
+
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| Total SLR
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 0 - 0.09
+
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 0.29 - 0.59
| style="border:2px solid lightblue; font-size: 12px; text-align:center"|
+
| style="border:2px solid lightblue; font-size: 12px; text-align:center"| 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<ref>Deconto, R.M. and Pollard, D. 2016. Contribution of Antarctica to past and future sea-level rise. Nature 531: 591-597</ref><ref> 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</ref>. 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 <ref> 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</ref>.
  
 +
Hansen et al. (2016) <ref> 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</ref> and Golledge et al. <ref> 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</ref> provide evidence from modelling and paleoclimate records for 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 ([[Ocean circulation# Deep ocean 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]].
  
 +
===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). Nevertheless, 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). However, climate-induced change in extreme wind and wave conditions can influence extreme sea levels significantly in some regions<ref name=V>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</ref><ref>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</ref>. Along the eastern African coast extreme wind and wave conditions will be less frequent, whereas in northern Europe (especially the Baltic region in the RCP8.5 scenario<ref>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</ref>) 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 <ref name=V></ref><ref name=I></ref>. For uplifting coasts the reduction of the average return period will be less, because of a smaller relative mean sea-level rise.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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<ref>Deconto, R.M. and Pollard, D. 2016. Contribution of Antarctica to past and future sea-level rise. Nature 531: 591-597</ref><ref> 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</ref>. 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 <ref> 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</ref>.
 
 
 
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 <ref> 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</ref><ref> 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</ref>. 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 <ref>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</ref>. 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 <ref>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</ref>.
 
 
 
  
 
==Impact of sea-level rise==
 
==Impact of sea-level rise==
  
Sea-level rise will 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 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 <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>. 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 <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 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 bio-geomorphological 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>. 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 <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]].
+
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]].
  
 
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 <ref> Sefelnasr, A. and Sherif, M. 2014. Impacts of Seawater Rise on Seawater Intrusion in the Nile Delta, Egypt. Groundwater 52: 264–276</ref>. Relative sea-level rise also causes loss of fertile agricultural land in the coastal hinterland by increased salt seepage to surface waters <ref>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</ref>, with great economic and social consequences. Salt intrusion further affects drinking water availability in densely urbanized coastal regions.  
 
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 <ref> Sefelnasr, A. and Sherif, M. 2014. Impacts of Seawater Rise on Seawater Intrusion in the Nile Delta, Egypt. Groundwater 52: 264–276</ref>. Relative sea-level rise also causes loss of fertile agricultural land in the coastal hinterland by increased salt seepage to surface waters <ref>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</ref>, 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<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>. See also the article [[Climate adaptation policies for the coastal zone]].  
+
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 policies for the coastal zone]].  
  
  
Line 135: Line 129:
 
|AuthorName=Dronkers J}}
 
|AuthorName=Dronkers J}}
  
[[Category:Climate change, impacts and adaptation]]
+
[[Category:Climate Change in the ICZM Process]]
[[Category:Sea level rise]]
+
‏‎[[Category:Climate change]]‏‎
 +
[[Category:Coastal flooding management]]
 +
[[Category:Coastal risk management]]
 +
[[Category:Protection of coastal and marine zones‏‎]]
 +
[[Category:Land and ocean interactions‏‎]]
 +
[[Category:Geomorphological processes and natural coastal features‏‎]]

Revision as of 15:51, 9 October 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. The most recent projections for future sea-level rise are presented in the Special IPCC Report on the Ocean and Cryosphere in a Changing Climate (2019)[1]. This report is an update of the previous IPCC AR5 report (2013) [2], and includes newer insights in the response of the Greenland and Antarctic ice sheets to global warming. It also provides an estimation of the possible sea-level rise up to the year 2030, 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.


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 (IPCC, 2019)[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 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

(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 [2]. 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 soft deltaic 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) 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 measurements have been analyzed by Church and White (2011) [3]. 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.

Trend analyses of regularly updated satellite data can be viewed at the NOAA site [4] 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 [5]. 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 and water temperature), in ocean currents and in the atmospheric pressure distribution.

There is hardly any doubt 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][6], 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-2 [1] [7][8][9]. The estimated global sea-level rise for the past decades (1993-2017) is 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–Southern Pacific region. This regional feature has a strong impact on the estimate for the global sea-level rise[6]. However, uncertainties remain in the calibration of the satellite altimeter data. A much lower acceleration rate of 0.018 ± 0.016 mm yr-2 has been found by Kleinherenbrink et al. (2019), 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[10]. No 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.


Figure 2. Sea level data of 6 tide gauge station along the Dutch coast (Vlissingen, Hoek van Holland, IJmuiden, Den Helder, Harlingen, Delfzijl)[10]. 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.


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 1.

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 in 2000 [12].

Uncertainties related to melting of the polar ice sheets

Table 1. 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 (2019) [1].
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[13][14]. 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 [15].

Hansen et al. (2016) [16] and Golledge et al. [17] provide evidence from modelling and paleoclimate records for 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.

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). Nevertheless, 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). However, climate-induced change in extreme wind and wave conditions can influence extreme sea levels significantly in some regions[18][19]. Along the eastern African coast extreme wind and wave conditions will be less frequent, whereas in northern Europe (especially the Baltic region in the RCP8.5 scenario[20]) 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 [18][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[21][22]. Delta coasts and coral islands are shaped under the influence of marine bio-geomorphological 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 [23]. 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 [24], 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 [25].

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 [26]. 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 [27] 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 [28]. Relative sea-level rise also causes loss of fertile agricultural land in the coastal hinterland by increased salt seepage to surface waters [29], 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 recent IPCC Assessment reports[22] [30][1]. 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 1.6 IPCC, 2019. Special Report on the Ocean and Cryosphere in a Changing Climate [Eds.: H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, M. Nicolai, A. Okem, J. Petzold, B. Rama and N. Weyer].
  2. 2.0 2.1 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.
  3. 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
  4. https://www.star.nesdis.noaa.gov/sod/lsa/SeaLevelRise/LSA_SLR_timeseries.php
  5. 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.
  6. 6.0 6.1 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
  7. 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
  8. 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
  9. 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
  10. 10.0 10.1 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.
  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. Deconto, R.M. and Pollard, D. 2016. Contribution of Antarctica to past and future sea-level rise. Nature 531: 591-597
  14. 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
  15. 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
  16. 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
  17. 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
  18. 18.0 18.1 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
  19. 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
  20. 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
  21. 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.
  22. 22.0 22.1 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.
  23. 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
  24. 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.
  25. 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.
  26. 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.
  27. 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
  28. Sefelnasr, A. and Sherif, M. 2014. Impacts of Seawater Rise on Seawater Intrusion in the Nile Delta, Egypt. Groundwater 52: 264–276
  29. 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
  30. 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
Please note that others may also have edited the contents of this article.

Citation: Job Dronkers (2019): Sea level rise. Available from http://www.coastalwiki.org/wiki/Sea_level_rise [accessed on 19-10-2019]

‏‎‏‎