Between 1901 and 2018, the average global sea level rise was 15–25 cm (6–10 in), with an increase of 2.3 mm (0.091 in) per year since the 1970s.[4]: 1216 This is faster than the sea level has risen over the past 3,000 years, if not longer.[4]: 1216 The rate accelerated to 4.62 mm (0.182 in)/yr for the decade 2013–2022.[5]Climate change due to human activities is the main cause.[6]: 5, 8 Between 1993 and 2018, melting ice sheets and glaciers accounted for 44% of sea level rise, with another 42% resulting from thermal expansion of water.[7]: 1576
Sea level rise lags behind changes in the Earth's temperature, and sea level rise will therefore continue to accelerate between now and 2050 in response to warming that has already happened.[8] What happens after that depends on human greenhouse gas emissions. Sea level rise would slow between 2050 and 2100 if there are very deep cuts in emissions. It could then reach slightly over 30 cm (1 ft) from now by 2100. With high emissions it would accelerate. It could rise by 1.01 m (3+1⁄3 ft) or even 1.6 m (5+1⁄3 ft) by then.[6][4]: 1302 In the long run, sea level rise would amount to 2–3 m (7–10 ft) over the next 2000 years if warming amounts to 1.5 °C (2.7 °F). It would be 19–22 metres (62–72 ft) if warming peaks at 5 °C (9.0 °F).[6]: 21
Rising seas affect every coastal and island population on Earth.[9][10] This can be through flooding, higher storm surges, king tides, and tsunamis. There are many knock-on effects. They lead to loss of coastal ecosystems like mangroves. Crop yields may reduce because of increasing salt levels in irrigation water. Damage to ports disrupts sea trade.[11][12][13] The sea level rise projected by 2050 will expose places currently inhabited by tens of millions of people to annual flooding. Without a sharp reduction in greenhouse gas emissions, this may increase to hundreds of millions in the latter decades of the century.[14] Areas not directly exposed to rising sea levels could be vulnerable to large-scale migration and economic disruption.
Local factors like tidal range or land subsidence will greatly affect the severity of impacts. There is also the varying resilience and adaptive capacity of ecosystems and countries which will result in more or less pronounced impacts.[15] For instance, sea level rise in the United States (particularly along the US East Coast) is likely to be 2 to 3 times greater than the global average by the end of the century.[16][17] Yet, of the 20 countries with the greatest exposure to sea level rise, 12 are in Asia, including Indonesia, Bangladesh and the Philippines.[18] The greatest impact on human populations in the near term will occur in the low-lying Caribbean and Pacific islands. Sea level rise will make many of them uninhabitable later this century.[19]
Societies can adapt to sea level rise in multiple ways. Managed retreat, accommodating coastal change, or protecting against sea level rise through hard-construction practices like seawalls[20] are hard approaches. There are also soft approaches such as dune rehabilitation and beach nourishment. Sometimes these adaptation strategies go hand in hand. At other times choices must be made among different strategies.[21] A managed retreat strategy is difficult if an area's population is increasing rapidly. This is a particularly acute problem for Africa.[22] Poorer nations may also struggle to implement the same approaches to adapt to sea level rise as richer states. Sea level rise at some locations may be compounded by other environmental issues. One example is subsidence in sinking cities.[23]Coastal ecosystems typically adapt to rising sea levels by moving inland. Natural or artificial barriers may make that impossible.[24]
^National Academies of Sciences, Engineering, and Medicine (2011). "Synopsis". Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia. Washington, DC: The National Academies Press. p. 5. doi:10.17226/12877. ISBN978-0-309-15176-4. Box SYN-1: Sustained warming could lead to severe impacts
^Bindoff, N. L.; Willebrand, J.; Artale, V.; Cazenave, A.; Gregory, J.; Gulev, S.; Hanawa, K.; Le Quéré, C.; Levitus, S.; Nojiri, Y.; Shum, C. K.; Talley, L. D.; Unnikrishnan, A. (2007). "Observations: Ocean Climate Change and Sea Level: §5.5.1: Introductory Remarks". In Solomon, S.; Qin, D.; Manning, M.; Chen, Z.; Marquis, M.; Averyt, K. B.; Tignor, M.; Miller, H. L. (eds.). Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. ISBN978-0-521-88009-1. Archived from the original on 20 June 2017. Retrieved 25 January 2017.
^Cite error: The named reference IPCC-2001 was invoked but never defined (see the help page).
^Cite error: The named reference AR6_WGII_Chapter10 was invoked but never defined (see the help page).
^Mycoo, M., M. Wairiu, D. Campbell, V. Duvat, Y. Golbuu, S. Maharaj, J. Nalau, P. Nunn, J. Pinnegar, and O. Warrick, 2022: Chapter 15: Small islands. In Climate Change 2022: Impacts, Adaptation and Vulnerability [H.-O. Pörtner, D. C. Roberts, M. Tignor, E. S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, New York, US, pp. 2043–2121 |doi=10.1017/9781009325844.017.
^Trisos, C. H., I. O. Adelekan, E. Totin, A. Ayanlade, J. Efitre, A. Gemeda, K. Kalaba, C. Lennard, C. Masao, Y. Mgaya, G. Ngaruiya, D. Olago, N. P. Simpson, and S. Zakieldeen 2022: Chapter 9: Africa. In Climate Change 2022: Impacts, Adaptation and Vulnerability [H.-O. Pörtner, D.C. Roberts, M. Tignor, E. S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, New York, US, pp. 2043–2121 |doi=10.1017/9781009325844.011.