sea level rise

File:20210125 The Cryosphere - Floating and grounded ice - imbalance - climate change.pngBetween 1901 and 2018, the global mean sea level rose by about {{convert|20|cm|abbr=on}}. More precise data gathered from satellite radar measurements found an increase of {{convert|7.5|cm|abbr=on}} from 1993 to 2017 (average of {{convert|2.9|mm|abbr=on}}/yr). This accelerated to {{convert|4.62|mm|abbr=on}}/yr for 2013–2022.{{cite web |date=21 April 2023 |title=WMO annual report highlights continuous advance of climate change |url=https://wmo.int/news/media-centre/wmo-annual-report-highlights-continuous-advance-of-climate-change |publisher=World Meteorological Organization |quote=Press Release Number: 21042023. |access-date=18 December 2023 |archive-date=17 December 2023 |archive-url=https://web.archive.org/web/20231217002918/https://wmo.int/news/media-centre/wmo-annual-report-highlights-continuous-advance-of-climate-change |url-status=live }} Paleoclimate data shows that this rate of sea level rise is the fastest it had been over at least the past 3,000 years.{{rp|1216}}

While sea level rise is uniform around the globe, some land masses are moving up or down as a consequence of subsidence (land sinking or settling) or post-glacial rebound (land rising as melting ice reduces weight). Therefore, local relative sea level rise may be higher or lower than the global average. Changing ice masses also affect the distribution of sea water around the globe through gravity.{{Cite journal |last1=Katsman |first1=Caroline A. |last2=Sterl |first2=A. |last3=Beersma |first3=J. J. |last4=van den Brink |first4=H. W. |last5=Church |first5=J. A. |last6=Hazeleger |first6=W. |last7=Kopp |first7=R. E. |last8=Kroon |first8=D. |last9=Kwadijk |first9=J. |date=2011 |title=Exploring high-end scenarios for local sea level rise to develop flood protection strategies for a low-lying delta—the Netherlands as an example |journal=Climatic Change |volume=109 |issue=3–4 |pages=617–645 |doi=10.1007/s10584-011-0037-5 |issn=0165-0009 |s2cid=2242594 |doi-access=free|bibcode=2011ClCh..109..617K }}{{cite book |last1=Church |first1=J. A. |title=Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change |last2=Clark |first2=P. U. |publisher=Cambridge University Press |year=2013 |editor-last=Stocker |editor-first=T. F. |location=Cambridge, UK and New York, US |chapter=Sea Level Change |access-date=2018-08-12 |display-editors=etal |chapter-url=https://ipcc.ch/report/ar5/wg1/ |archive-url=https://web.archive.org/web/20200509055710/https://www.ipcc.ch/report/ar5/wg1/ |archive-date=2020-05-09 |url-status=live}}

File:Slangen 2022 8 SLRs.jpg

Several complementary approaches are used for sea level rise (SLR) projections. One is process-based modeling, where ice melting is computed through an ice-sheet model and rising sea temperature and expansion through a general circulation model, and then these contributions are added up.{{cite journal |last1=Moore |first1=John C. |last2=Grinsted |first2=Aslak |last3=Zwinger |first3=Thomas |last4=Jevrejeva |first4=Svetlana |date=10 June 2013 |title=Semiempirical and process-based global sea level projections |journal=Reviews of Geophysics |volume=51 |issue=3 |pages=484–522 |doi=10.1002/rog.20015 |bibcode=2013RvGeo..51..484M}} The so-called semi-empirical approach instead applies statistical techniques and basic physical modeling to the observed recent sea level rise and reconstructions from the older historical geological data (known as paleoclimate modeling). It was developed because process-based model projections in the past IPCC reports (such as the Fourth Assessment Report from 2007) were found to underestimate the already observed sea level rise.

By 2013, improvements in modeling had addressed this issue, and model and semi-empirical projections for the year 2100 are now very similar. Yet, semi-empirical estimates are reliant on the quality of available observations and struggle to represent non-linearities, while processes without enough available information about them cannot be modeled. Thus, another approach is to combine the opinions of a large number of scientists in what is known as a structured expert judgement (SEJ).

Variations of these primary approaches exist. For instance, large climate models are computationally expensive, so less complex models are often used in their place for simpler tasks like projecting flood risk in the specific regions. A structured expert judgement may be used in combination with modeling to determine which outcomes are more or less likely, which is known as "shifted SEJ". Semi-empirical techniques can be combined with the so-called "intermediate-complexity" models. After 2016, some ice sheet modeling exhibited the so-called ice cliff instability in Antarctica, which results in substantially faster disintegration and retreat than otherwise simulated.{{Cite journal |last1=DeConto |first1=Robert M. |last2=Pollard |first2=David |date=30 March 2016 |title=Contribution of Antarctica to past and future sea-level rise |journal=Nature |language=en |volume=531 |issue=7596 |pages=591–597 |doi=10.1038/nature17145 |pmid=27029274 |bibcode=2016Natur.531..591D |s2cid=205247890}}{{cite news |last=Gillis |first=Justin |date=30 March 2016 |title=Climate Model Predicts West Antarctic Ice Sheet Could Melt Rapidly |newspaper=The New York Times |url=https://www.nytimes.com/2016/03/31/science/global-warming-antarctica-ice-sheet-sea-level-rise.html |access-date=28 May 2024 |archive-date=9 June 2024 |archive-url=https://web.archive.org/web/20240609214842/https://www.nytimes.com/2016/03/31/science/global-warming-antarctica-ice-sheet-sea-level-rise.html |url-status=live }} The differences are limited with low warming, but at higher warming levels, ice cliff instability predicts far greater sea level rise than any other approach.{{cite journal |last1=Slangen |first1=A. B. A. |last2=Haasnoot |first2=M. |last3=Winter |first3=G. |date=30 March 2022 |title=Rethinking Sea-Level Projections Using Families and Timing Differences |journal=Earth's Future |volume=10 |issue=4 |page=e2021EF002576 |doi=10.1029/2021EF002576 |bibcode=2022EaFut..1002576S |url=https://www.vliz.be/imisdocs/publications/00/378000.pdf |access-date=28 May 2024 |archive-date=26 May 2024 |archive-url=https://web.archive.org/web/20240526230811/https://www.vliz.be/imisdocs/publications/00/378000.pdf |url-status=live }}

The study reports that sea level also is expected to grow by another 6.6 inches (169 millimeters) globally over the next 30 years if it follows this trend, which will lead to 16.63 inches (42.25 centimeters) under a 1.75 °C warming by 2100.{{Cite web |last=Huang |first=Ethan |date=February 25, 2025 |title=Rate of Sea Level Rise Doubled over 30 Years, New Study Shows |url=https://sealevel.nasa.gov/news/280/rate-of-sea-level-rise-doubled-over-30-years-new-study-shows/ |access-date=February 25, 2025 |website=NASA}}

File:Sea level history and projections.svg.{{Cite web|url=https://tidesandcurrents.noaa.gov/publications/techrpt83_Global_and_Regional_SLR_Scenarios_for_the_US_final.pdf|title=January 2017 analysis from NOAA: Global and Regional Sea Level Rise Scenarios for the United States|access-date=2017-02-06|archive-date=2017-12-18|archive-url=https://web.archive.org/web/20171218140625/https://tidesandcurrents.noaa.gov/publications/techrpt83_Global_and_Regional_SLR_Scenarios_for_the_US_final.pdf|url-status=live}} RCPs are different scenarios for future concentrations of greenhouse gases.]]

The Intergovernmental Panel on Climate Change is the largest and most influential scientific organization on climate change, and since 1990, it provides several plausible scenarios of 21st century sea level rise in each of its major reports. The differences between scenarios are mainly due to uncertainty about future greenhouse gas emissions. These depend on future economic developments, and also future political action which is hard to predict. Each scenario provides an estimate for sea level rise as a range with a lower and upper limit to reflect the unknowns. The scenarios in the 2013–2014 Fifth Assessment Report (AR5) were called Representative Concentration Pathways, or RCPs and the scenarios in the IPCC Sixth Assessment Report (AR6) are known as Shared Socioeconomic Pathways, or SSPs. A large difference between the two was the addition of SSP1-1.9 to AR6, which represents meeting the best Paris climate agreement goal of {{convert|1.5|C-change|F-change}}. In that case, the likely range of sea level rise by 2100 is {{cvt|28–55|cm|in|frac=2}}.{{Rp|page=1302}}

File:Kopp 2023 4 flows.png projections from 2020 (lower left), research modeling the possibility of ice cliff instability (upper right) and combined expert projections of sea level rise from Greenland and Antarctica (lower right) were all considered before settling on the projections. Note that projections on the right use a larger scale, which ends at {{cvt|2.5|m|ft|frac=3}} instead of {{cvt|1.5|m|ft|frac=3}} ]]

The lowest scenario in AR5, RCP2.6, would see greenhouse gas emissions low enough to meet the goal of limiting warming by 2100 to {{convert|2|C-change|F-change}}. It shows sea level rise in 2100 of about {{convert|44|cm|abbr=on}} with a range of {{convert|28|-|61|cm|abbr=on}}. The "moderate" scenario, where {{CO2}} emissions take a decade or two to peak and its atmospheric concentration does not plateau until the 2070s is called RCP 4.5. Its likely range of sea level rise is {{cvt|36–71|cm|in|frac=2}}. The highest scenario in RCP8.5 pathway sea level would rise between {{cvt|52 and 98|cm|in|frac=2}}.{{cite web |url=https://climateactiontracker.org/global/cat-thermometer/ |title=The CAT Thermometer |access-date=8 January 2023 |archive-date=14 April 2019 |archive-url=https://web.archive.org/web/20190414131223/https://climateactiontracker.org/global/cat-thermometer/ |url-status=live }} AR6 had equivalents for both scenarios, but it estimated larger sea level rise under both. In AR6, the SSP1-2.6 pathway results in a range of {{cvt|32–62|cm|in|frac=2}} by 2100. The "moderate" SSP2-4.5 results in a {{cvt|44–76|cm|in|frac=2}} range by 2100 and SSP5-8.5 led to {{cvt|65–101|cm|in|frac=2}}.{{Rp|page=1302}}

This general increase of projections in AR6 came after the improvements in ice-sheet modeling and the incorporation of structured expert judgements. These decisions came as the observed ice-sheet erosion in Greenland and Antarctica had matched the upper-end range of the AR5 projections by 2020,{{cite news |title=Ice sheet melt on track with 'worst-case climate scenario' |language=en |work=www.esa.int |url=https://www.esa.int/Applications/Observing_the_Earth/Space_for_our_climate/Ice_sheet_melt_on_track_with_worst-case_climate_scenario |access-date=8 September 2020 |archive-date=9 June 2023 |archive-url=https://web.archive.org/web/20230609213115/https://www.esa.int/Applications/Observing_the_Earth/Space_for_our_climate/Ice_sheet_melt_on_track_with_worst-case_climate_scenario |url-status=live }}{{cite journal |last1=Slater |first1=Thomas |last2=Hogg |first2=Anna E. |last3=Mottram |first3=Ruth |author-link3=Ruth Mottram |date=31 August 2020 |title=Ice-sheet losses track high-end sea-level rise projections |url=https://www.nature.com/articles/s41558-020-0893-y |journal=Nature Climate Change |language=en |volume=10 |issue=10 |pages=879–881 |bibcode=2020NatCC..10..879S |doi=10.1038/s41558-020-0893-y |issn=1758-6798 |archive-url=https://web.archive.org/web/20200902132539/https://www.nature.com/articles/s41558-020-0893-y |archive-date=2 September 2020 |access-date=8 September 2020 |s2cid=221381924}} and the finding that AR5 projections were likely too slow next to an extrapolation of observed sea level rise trends, while the subsequent reports had improved in this regard.{{Cite journal |last1=Grinsted |first1=Aslak |last2=Christensen |first2=Jens Hesselbjerg |date=2 February 2021 |title=The transient sensitivity of sea level rise |url=https://os.copernicus.org/articles/17/181/2021/ |journal=Ocean Science |volume=17 |issue=1 |pages=181–186 |bibcode=2021OcSci..17..181G |doi=10.5194/os-17-181-2021 |issn=1812-0784 |s2cid=234353584 |doi-access=free |hdl=11250/3135359 |hdl-access=free |access-date=3 February 2021 |archive-date=19 June 2022 |archive-url=https://web.archive.org/web/20220619123914/https://os.copernicus.org/articles/17/181/2021/ |url-status=live }} Further, AR5 was criticized by multiple researchers for excluding detailed estimates the impact of "low-confidence" processes like marine ice sheet and marine ice cliff instability,{{cite journal |last1=Hansen |first1=James |last2=Sato |first2=Makiko |last3=Hearty |first3=Paul |last4=Ruedy |first4=Reto |last5=Kelley |first5=Maxwell |last6=Masson-Delmotte |first6=Valerie |last7=Russell |first7=Gary |last8=Tselioudis |first8=George |last9=Cao |first9=Junji |last10=Rignot |first10=Eric |last11=Velicogna |first11=Isabella |date=22 March 2016 |title=Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous |journal=Atmospheric Chemistry and Physics |volume=16 |issue=6 |pages=3761–3812 |arxiv=1602.01393 |bibcode=2016ACP....16.3761H |doi=10.5194/acp-16-3761-2016 |first18=Michael |first19=Kwok-Wai |last19=Lo |first12=Blair |last18=Bauer |first17=Allegra N. |last17=Legrande |first16=Pushker |last16=Kharecha |first15=Karina |last15=von Schuckmann |first14=Evgeniya |last14=Kandiano |first13=Bailey |last13=Donovan |last12=Tormey |author-link11=Isabella Velicogna |s2cid=9410444 |doi-access=free}} which can substantially accelerate ice loss to potentially add "tens of centimeters" to sea level rise within this century. AR6 includes a version of SSP5-8.5 where these processes take place, and in that case, sea level rise of up to {{cvt|1.6|m|ft|frac=3}} by 2100 could not be ruled out.{{Cite journal |last1=Fox-Kemper |first1=B. |last2=Hewitt |first2=Helene T. |author2-link=Helene Hewitt |last3=Xiao |first3=C. |last4=Aðalgeirsdóttir |first4=G. |last5=Drijfhout |first5=S. S. |last6=Edwards |first6=T. L. |last7=Golledge |first7=N. R. |last8=Hemer |first8=M. |last9=Kopp |first9=R. E. |last10=Krinner |first10=G. |last11=Mix |first11=A. |date=2021 |editor-last=Masson-Delmotte |editor-first=V. |editor2-last=Zhai |editor2-first=P. |editor3-last=Pirani |editor3-first=A. |editor4-last=Connors |editor4-first=S. L. |editor5-last=Péan |editor5-first=C. |editor6-last=Berger |editor6-first=S. |editor7-last=Caud |editor7-first=N. |editor8-last=Chen |editor8-first=Y. |editor9-last=Goldfarb |editor9-first=L. |title=Chapter 9: Ocean, Cryosphere and Sea Level Change |url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter09.pdf |journal=Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change |publisher=Cambridge University Press, Cambridge, UK and New York, US |page= |access-date=2022-10-18 |archive-date=2022-10-24 |archive-url=https://web.archive.org/web/20221024162651/https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter09.pdf |url-status=live }}{{Rp|page=1302}}

File:Zhang 2022 MISI and MICI.png

The greatest uncertainty with sea level rise projections is associated with the so-called marine ice sheet instability (MISI), and, even more so, Marine Ice Cliff Instability (MICI).{{Rp|page=1302}} These processes are mainly associated with West Antarctic Ice Sheet, but may also apply to some of Greenland's glaciers. The former suggests that when glaciers are mostly underwater on retrograde (backwards-sloping) bedrock, the water melts more and more of their height as their retreat continues, thus accelerating their breakdown on its own. This is widely accepted, but is difficult to model.

The latter posits that coastal ice cliffs which exceed ~{{cvt|90|m|ft|frac=2}} in above-ground height and are ~{{cvt|800|m|ft|frac=2}} in basal (underground) height are likely to rapidly collapse under their own weight once the ice shelves propping them up are gone. The collapse then exposes the ice masses following them to the same instability, potentially resulting in a self-sustaining cycle of cliff collapse and rapid ice sheet retreat.{{Cite journal |last=Pattyn |first=Frank |author-link=Frank Pattyn |date=2018 |title=The paradigm shift in Antarctic ice sheet modelling |journal=Nature Communications |language=En |volume=9 |issue=1 |page=2728 |bibcode=2018NatCo...9.2728P |doi=10.1038/s41467-018-05003-z |issn=2041-1723 |pmc=6048022 |pmid=30013142}}{{Cite journal|last1=Dow|first1=Christine F.|last2=Lee|first2=Won Sang|last3=Greenbaum|first3=Jamin S.|last4=Greene|first4=Chad A.|last5=Blankenship|first5=Donald D.|last6=Poinar|first6=Kristin|last7=Forrest|first7=Alexander L.|last8=Young|first8=Duncan A.|last9=Zappa|first9=Christopher J.|date=2018-06-01|title=Basal channels drive active surface hydrology and transverse ice shelf fracture|journal=Science Advances|language=en|volume=4|issue=6|pages=eaao7212|doi=10.1126/sciadv.aao7212|issn=2375-2548|pmc=6007161|pmid=29928691|bibcode=2018SciA....4.7212D}} This theory had been highly influential – in a 2020 survey of 106 experts, the 2016 paper which suggested {{cvt|1|m|ft|frac=2}} or more of sea level rise by 2100 from Antarctica alone, was considered even more important than the 2014 IPCC Fifth Assessment Report.{{Cite journal |last1=Horton |first1=Benjamin P. |last2=Khan |first2=Nicole S. |last3=Cahill |first3=Niamh |last4=Lee |first4=Janice S. H. |last5=Shaw |first5=Timothy A. |last6=Garner |first6=Andra J. |last7=Kemp |first7=Andrew C. |last8=Engelhart |first8=Simon E. |last9=Rahmstorf |first9=Stefan |date=2020-05-08 |title=Estimating global mean sea-level rise and its uncertainties by 2100 and 2300 from an expert survey |journal=npj Climate and Atmospheric Science |volume=3 |issue=1 |page=18 |doi=10.1038/s41612-020-0121-5 |bibcode=2020npCAS...3...18H |s2cid=218541055 |hdl=10356/143900 |hdl-access=free}} Even more rapid sea level rise was proposed in a 2016 study led by Jim Hansen, which hypothesized multi-meter sea level rise in 50–100 years as a plausible outcome of high emissions, but it remains a minority view amongst the scientific community.{{cite news |year=2015 |title=James Hansen's controversial sea level rise paper has now been published online |newspaper=The Washington Post |url=https://www.washingtonpost.com/news/energy-environment/wp/2015/07/23/controversial-sea-level-rise-paper-is-now-published-online/ |quote="There is no doubt that the sea level rise, within the IPCC, is a very conservative number," says Greg Holland, a climate and hurricane researcher at the National Center for Atmospheric Research, who has also reviewed the Hansen study. "So the truth lies somewhere between IPCC and Jim." |access-date=2017-09-11 |archive-date=2019-11-26 |archive-url=https://web.archive.org/web/20191126005216/https://www.washingtonpost.com/news/energy-environment/wp/2015/07/23/controversial-sea-level-rise-paper-is-now-published-online/ |url-status=live }}

File:Schlemm 2022 MICI embayment.png (viewed from the top) would do a lot to determine how quickly it may proceed]]

Marine ice cliff instability had also been very controversial, since it was proposed as a modelling exercise,{{Cite conference |last=Zhang |first=Zhe |date=7 November 2021 |title=Reviewing the elements of marine ice cliff instability |conference=The International Conference on Materials Chemistry and Environmental Engineering (CONF-MCEE 2021) |location=California, United States |journal=Journal of Physics: Conference Series |volume=2152 |doi=10.1088/1742-6596/2152/1/012057 |doi-access=free }} and the observational evidence from both the past and the present is very limited and ambiguous. So far, only one episode of seabed gouging by ice from the Younger Dryas period appears truly consistent with this theory, but it had lasted for an estimated 900 years,{{Cite journal |last1=Wise |first1=Matthew G. |last2=Dowdeswell |first2=Julian A. |last3=Jakobsson |first3=Martin |last4=Larter |first4=Robert D. |date=October 2017 |title=Evidence of marine ice-cliff instability in Pine Island Bay from iceberg-keel plough marks |url=https://nora.nerc.ac.uk/id/eprint/514800/1/Nature_final_accepted_ms.pdf |journal=Nature |language=en |volume=550 |issue=7677 |pages=506–510 |doi=10.1038/nature24458 |pmid=29072274 |bibcode=2017Natur.550..506W |issn=0028-0836 |archive-url=https://web.archive.org/web/20200506155034/https://nora.nerc.ac.uk/id/eprint/514800/1/Nature_final_accepted_ms.pdf |archive-date=May 6, 2020}} so it is unclear if it supports rapid sea level rise in the present. Modelling which investigated the hypothesis after 2016 often suggested that the ice shelves in the real world may collapse too slowly to make this scenario relevant,{{cite journal |last1=Clerc |first1=Fiona |last2=Minchew |first2=Brent M. |last3=Behn |first3=Mark D. |date=21 October 2019 |title=Marine Ice Cliff Instability Mitigated by Slow Removal of Ice Shelves |url=https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1029/2019GL084183 |journal=Geophysical Research Letters |volume=50 |issue=4 |pages=e2022GL102400 |doi=10.1029/2019GL084183 |bibcode=2019GeoRL..4612108C |via=American Geophysical Union |hdl=1912/25343 |hdl-access=free |access-date=3 June 2024 |archive-date=3 June 2024 |archive-url=https://web.archive.org/web/20240603163939/https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1029/2019GL084183 |url-status=live }} or that ice mélange – debris produced as the glacier breaks down – would quickly build up in front of the glacier and significantly slow or even outright stop the instability soon after it began.{{cite news|url=https://www.sciencenews.org/article/climate-marine-ice-cliffs-sheets-collapse-not-inevitable-sea-level|title=Collapse may not always be inevitable for marine ice cliffs|last1=Perkins|first1=Sid|date=17 June 2021|access-date=9 January 2023|agency=ScienceNews|archive-date=23 March 2023|archive-url=https://web.archive.org/web/20230323154132/https://www.sciencenews.org/article/climate-marine-ice-cliffs-sheets-collapse-not-inevitable-sea-level|url-status=live}}{{Cite journal |last1=Bassis |first1=J. N. |last2=Berg |first2=B. |last3=Crawford |first3=A. J. |last4=Benn |first4=D. I. |date=18 June 2021 |title=Transition to marine ice cliff instability controlled by ice thickness gradients and velocity |url=https://www.science.org/doi/10.1126/science.abf6271 |journal=Science |language=en |volume=372 |issue=6548 |pages=1342–1344 |bibcode=2021Sci...372.1342B |doi=10.1126/science.abf6271 |issn=0036-8075 |pmid=34140387 |hdl-access=free |hdl=10023/23422 |access-date=3 June 2024 |archive-date=3 June 2024 |archive-url=https://web.archive.org/web/20240603163939/https://www.science.org/doi/10.1126/science.abf6271 |url-status=live }}{{Cite journal |last1=Crawford |first1=Anna J. |last2=Benn |first2=Douglas I. |last3=Todd |first3=Joe |last4=Åström |first4=Jan A. |last5=Bassis |first5=Jeremy N. |last6=Zwinger |first6=Thomas |date=11 May 2021 |title=Marine ice-cliff instability modeling shows mixed-mode ice-cliff failure and yields calving rate parameterization |journal=Nature Communications |volume=12 |issue=1 |page=2701 |doi=10.1038/s41467-021-23070-7 |pmid=33976208 |pmc=8113328 |bibcode=2021NatCo..12.2701C }}{{Cite journal |last1=Schlemm |first1=Tanja |last2=Feldmann |first2=Johannes |last3=Winkelmann |first3=Ricarda |last4=Levermann |first4=Anders |date=24 May 2022 |title=Stabilizing effect of mélange buttressing on the marine ice-cliff instability of the West Antarctic Ice Sheet |journal=The Cryosphere |volume=16 |issue=5 |pages=1979–1996 |doi=10.5194/tc-16-1979-2022 |doi-access=free|bibcode=2022TCry...16.1979S }}

Due to these uncertainties, some scientists – including the originators of the hypothesis, Robert DeConto and David Pollard – have suggested that the best way to resolve the question would be to precisely determine sea level rise during the Last Interglacial. MICI can be effectively ruled out if SLR at the time was lower than {{cvt|4|m|ft|frac=2}}, while it is very likely if the SLR was greater than {{cvt|6|m|ft|frac=2}}.{{cite journal |last1=Gilford |first1=Daniel M. |last2=Ashe |first2=Erica L. |last3=DeConto |first3=Robert M. |last4=Kopp |first4=Robert E. |last5=Pollard |first5=David |last6=Rovere |first6=Alessio |date=5 October 2020 |title=Could the Last Interglacial Constrain Projections of Future Antarctic Ice Mass Loss and Sea-Level Rise? |url=https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1029/2019JF005418 |journal=Journal of Geophysical Research: Earth Surface |volume=124 |issue=7 |pages=1899–1918 |doi=10.1029/2019JF005418 |bibcode=2020JGRF..12505418G |via=American Geophysical Union|hdl=10278/3749063 |hdl-access=free }} As of 2023, the most recent analysis indicates that the Last Interglacial SLR is unlikely to have been higher than {{cvt|2.7|m|ft|frac=2}}, as higher values in other research, such as {{cvt|5.7|m|ft|frac=2}},{{cite journal |last1=Barnett |first1=Robert L. |last2=Austermann |first2=Jacqueline |last3=Dyer |first3=Blake |last4=Telfer |first4=Matt W. |last5=Barlow |first5=Natasha L. M. |last6=Boulton |first6=Sarah J. |last7=Carr |first7=Andrew S. |last8=Creel |first8=Roger |date=15 September 2023 |title=Constraining the contribution of the Antarctic Ice Sheet to Last Interglacial sea level |journal=Science Advances |volume=9 |issue=27 |pages=eadf0198 |doi=10.1126/sciadv.adf0198 |pmid=37406130 |pmc=10321746 |bibcode=2023SciA....9F.198B }} appear inconsistent with the new paleoclimate data from The Bahamas and the known history of the Greenland Ice Sheet.{{cite journal |last1=Dumitru |first1=Oana A. |last2=Dyer |first2=Blake |last3=Austermann |first3=Jacqueline |last4=Sandstrom |first4=Michael R. |last5=Goldstein |first5=Steven L. |last6=D'Andrea |first6=William J. |last7=Cashman |first7=Miranda |last8=Creel |first8=Roger |last9=Bolge |first9=Louise |last10=Raymo |first10=Maureen E. |date=15 September 2023 |title=Last interglacial global mean sea level from high-precision U-series ages of Bahamian fossil coral reefs |journal=Quaternary Science Reviews |volume=318 |page=108287 |doi=10.1016/j.quascirev.2023.108287 |doi-access=free |bibcode=2023QSRv..31808287D }}

File:1900-2300 Long-term projections of sea level rise.svg

Even if the temperature stabilizes, significant sea-level rise (SLR) will continue for centuries,{{cite book |author=National Research Council |title=Advancing the Science of Climate Change |publisher=The National Academies Press |year=2010 |isbn=978-0-309-14588-6 |location=Washington, DC |page=245 |chapter=7 Sea Level Rise and the Coastal Environment |doi=10.17226/12782 |access-date=2011-06-17 |chapter-url=http://books.nap.edu/openbook.php?record_id=12782&page=245 |archive-date=2015-08-13 |archive-url=https://web.archive.org/web/20150813203235/http://books.nap.edu/openbook.php?record_id=12782 |url-status=live }} consistent with paleo records of sea level rise.{{rp|1189}} This is due to the high level of inertia in the carbon cycle and the climate system, owing to factors such as the slow diffusion of heat into the deep ocean, leading to a longer climate response time.{{Cite journal |last1=Hansen |first1=J. |last2=Russell |first2=G. |last3=Lacis |first3=A. |last4=Fung |first4=I. |last5=Rind |first5=D. |last6=Stone |first6=P. |date=1985-08-30 |title=Climate Response Times: Dependence on Climate Sensitivity and Ocean Mixing |url=https://pubs.giss.nasa.gov/docs/1985/1985_Hansen_ha09600g.pdf |journal=Science |language=en |volume=229 |issue=4716 |pages=857–859 |doi=10.1126/science.229.4716.857 |pmid=17777925 |bibcode=1985Sci...229..857H |issn=0036-8075 |archive-url=https://web.archive.org/web/20210327184018/https://pubs.giss.nasa.gov/docs/1985/1985_Hansen_ha09600g.pdf |archive-date=March 27, 2021 |via=NASA}} A 2018 paper estimated that sea level rise in 2300 would increase by a median of 20 cm (8 in) for every five years {{CO2}} emissions increase before peaking. It shows a 5% likelihood of a {{cvt|1|m|ft|frac=2}} increase due to the same. The same estimate found that if the temperature stabilized below {{convert|2|C-change|F-change}}, 2300 sea level rise would still exceed {{cvt|1.5|m|ft|frac=2}}. Early net zero and slowly falling temperatures could limit it to {{cvt|70–120|cm|in|frac=2}}.{{Cite journal |last1=Mengel |first1=Matthias |last2=Nauels |first2=Alexander |last3=Rogelj |first3=Joeri |last4=Schleussner |first4=Carl-Friedrich |date=20 February 2018 |title=Committed sea-level rise under the Paris Agreement and the legacy of delayed mitigation action |journal=Nature Communications |volume=9 |issue=1 |page=601 |doi=10.1038/s41467-018-02985-8 |pmid=29463787 |pmc=5820313 |bibcode=2018NatCo...9..601M}}

By 2021, the IPCC Sixth Assessment Report was able to provide estimates for sea level rise in 2150. Keeping warming to 1.5{{Nbsp}}°C under the SSP1-1.9 scenario would result in sea level rise in the 17–83% range of {{cvt|37–86|cm|in|frac=2}}. In the SSP1-2.6 pathway the range would be {{cvt|46–99|cm|in|frac=2}}, for SSP2-4.5 a {{cvt|66–133|cm|in|frac=2}} range by 2100 and for SSP5-8.5 a rise of {{cvt|98–188|cm|in|frac=2}}. It stated that the "low-confidence, high impact" projected {{cvt|0.63-1.60|m|ft|frac=2}} mean sea level rise by 2100, and that by 2150, the total sea level rise in his scenario would be in the range of {{cvt|0.98 - 4.82|m|ft|frac=2}} by 2150.{{Rp|page=1302}} AR6 also provided lower-confidence estimates for year 2300 sea level rise under SSP1-2.6 and SSP5-8.5 with various impact assumptions. In the best case scenario, under SSP1-2.6 with no ice sheet acceleration after 2100, the estimate was only {{Convert|0.8 - 2.0|m|ft}}. In the worst estimated scenario, SSP-8.5 with ice cliff instability, the projected range for total sea level rise was {{Convert|9.5 - 16.2|m|ft}} by the year 2300.{{Rp|page=1306}}

Projections for subsequent years are more difficult. In 2019, when 22 experts on ice sheets were asked to estimate 2200 and 2300 SLR under the 5{{Nbsp}}°C warming scenario, there were 90% confidence intervals of −{{cvt|10|cm|in|frac=2}} to {{cvt|740|cm|ft|frac=2}} and −{{cvt|9|cm|in|frac=2}} to {{cvt|970|cm|ft|frac=2}}, respectively. (Negative values represent the extremely low probability of large climate change-induced increases in precipitation greatly elevating ice sheet surface mass balance.){{cite journal |last1=Bamber |first1=Jonathan L. |last2=Oppenheimer |first2=Michael |last3=Kopp |first3=Robert E. |last4=Aspinall |first4=Willy P. |last5=Cooke |first5=Roger M. |date=May 2019 |title=Ice sheet contributions to future sea-level rise from structured expert judgment |journal=Proceedings of the National Academy of Sciences |volume=116 |issue=23 |pages=11195–11200 |bibcode=2019PNAS..11611195B |doi=10.1073/pnas.1817205116 |pmc=6561295 |pmid=31110015 |doi-access=free}} In 2020, 106 experts who contributed to 6 or more papers on sea level estimated median {{cvt|118|cm|in|frac=2}} SLR in the year 2300 for the low-warming RCP2.6 scenario and the median of {{cvt|329|cm|in|frac=2}} for the high-warming RCP8.5. The former scenario had the 5%–95% confidence range of {{cvt|24–311|cm|in|frac=2}}, and the latter of {{cvt|88–783|cm|in|frac=2}}.

File:6m Sea Level Rise.jpg will also have an effect on local sea levels).|alt=A map showing major SLR impact in south-east Asia, Northern Europe and the East Coast of the US]]

After 500 years, sea level rise from thermal expansion alone may have reached only half of its eventual level - likely within ranges of {{cvt|0.5-2|m|ft|frac=2}}.{{cite journal |last1=Solomon |first1=Susan |last2=Plattner |first2=Gian-Kasper |last3=Knutti |first3=Reto |last4=Friedlingstein |first4=Pierre |date=10 February 2009 |title=Irreversible climate change due to carbon dioxide emissions |journal=Proceedings of the National Academy of Sciences |volume=106 |issue=6 |pages=1704–1709 |bibcode=2009PNAS..106.1704S |doi=10.1073/pnas.0812721106 |pmc=2632717 |pmid=19179281 |doi-access=free}} Additionally, tipping points of Greenland and Antarctica ice sheets are likely to play a larger role over such timescales.{{cite journal |last1=Pattyn |first1=Frank |last2=Ritz |first2=Catherine |last3=Hanna |first3=Edward |last4=Asay-Davis |first4=Xylar |last5=DeConto |first5=Rob |last6=Durand |first6=Gaël |last7=Favier |first7=Lionel |last8=Fettweis |first8=Xavier |last9=Goelzer |first9=Heiko |last10=Golledge |first10=Nicholas R. |last11=Kuipers Munneke |first11=Peter |date=12 November 2018 |title=The Greenland and Antarctic ice sheets under 1.5 °C global warming |url=https://dipot.ulb.ac.be/dspace/bitstream/2013/278021/3/ReviewOnePointFive_v7.pdf |journal=Nature Climate Change |volume=8 |issue=12 |pages=1053–1061 |bibcode=2018NatCC...8.1053P |doi=10.1038/s41558-018-0305-8 |first13=Sophie |last13=Nowicki |s2cid=91886763 |last12=Lenaerts |first18=Michiel |last14=Payne |last18=van den Broeke |first17=Luke D. |last17=Trusel |first16=Hélène |last16=Seroussi |first15=Alexander |last15=Robinson |first14=Antony J. |first12=Jan T. M. |access-date=31 October 2019 |archive-date=7 March 2020 |archive-url=https://web.archive.org/web/20200307041816/https://dipot.ulb.ac.be/dspace/bitstream/2013/278021/3/ReviewOnePointFive_v7.pdf |url-status=live }} Ice loss from Antarctica is likely to dominate very long-term SLR, especially if the warming exceeds {{convert|2|C-change|F-change}}. Continued carbon dioxide emissions from fossil fuel sources could cause additional tens of metres of sea level rise, over the next millennia.{{Cite journal |last1=Clark |first1=Peter U. |last2=Shakun |first2=Jeremy D. |last3=Marcott |first3=Shaun A. |last4=Mix |first4=Alan C. |last5=Eby |first5=Michael |date=April 2016 |title=Consequences of twenty-first-century policy for multi-millennial climate and sea-level change |url=https://ir.library.oregonstate.edu/concern/articles/mk61rj62n |journal=Nature Climate Change |language=en |volume=6 |issue=4 |pages=360–369 |doi=10.1038/nclimate2923 |bibcode=2016NatCC...6..360C |issn=1758-6798 |archive-url=https://web.archive.org/web/20200711054610/https://ir.library.oregonstate.edu/downloads/5999n523k |archive-date=July 11, 2020 |via=Oregon State University}} Burning of all fossil fuels on Earth is sufficient to melt the entire Antarctic ice sheet, causing about {{Cvt|58|m|ft}} of sea level rise.{{cite journal |last1=Winkelmann |first1=Ricarda |author1-link=Ricarda Winkelmann |last2=Levermann |first2=Anders |last3=Ridgwell |first3=Andy |last4=Caldeira |first4=Ken |date=11 September 2015 |title=Combustion of available fossil fuel resources sufficient to eliminate the Antarctic Ice Sheet |journal=Science Advances |volume=1 |issue=8 |pages=e1500589 |bibcode=2015SciA....1E0589W |doi=10.1126/sciadv.1500589 |pmc=4643791 |pmid=26601273}}

Year 2021 IPCC estimates for the amount of sea level rise over the next 2,000 years project that:

• At a warming peak of {{convert|1.5|C-change|F-change}}, global sea levels would rise {{cvt|2-3|m|ft|frac=2}}
• At a warming peak of {{convert|2|C-change|F-change}}, sea levels would rise {{cvt|2-6|m|ft|frac=2}}
• At a warming peak of {{convert|5|C-change|F-change}}, sea levels would rise {{cvt|19-22|m|ft|frac=2}}{{rp|SPM-21}}

Sea levels would continue to rise for several thousand years after the ceasing of emissions, due to the slow nature of climate response to heat. The same estimates on a timescale of 10,000 years project that:

• At a warming peak of {{convert|1.5|C-change|F-change}}, global sea levels would rise {{cvt|6-7|m|ft|frac=2}}
• At a warming peak of {{convert|2|C-change|F-change}}, sea levels would rise {{cvt|8-13|m|ft|frac=2}}
• At a warming peak of {{convert|5|C-change|F-change}}, sea levels would rise {{cvt|28-37|m|ft|frac=2}}{{rp|1306}}

Variations in the amount of water in the oceans, changes in its volume, or varying land elevation compared to the sea surface can drive sea level changes. Over a consistent time period, assessments can attribute contributions to sea level rise and provide early indications of change in trajectory. This helps to inform adaptation plans.{{Cite web |title=2022 Sea Level Rise Technical Report |url=https://oceanservice.noaa.gov/hazards/sealevelrise/sealevelrise-tech-report.html#step4 |access-date=2022-02-22 |website=oceanservice.noaa.gov |language=EN-US |archive-date=2022-11-29 |archive-url=https://web.archive.org/web/20221129070303/https://oceanservice.noaa.gov/hazards/sealevelrise/sealevelrise-tech-report.html#step4 |url-status=live }} The different techniques used to measure changes in sea level do not measure exactly the same level. Tide gauges can only measure relative sea level. Satellites can also measure absolute sea level changes.{{cite journal |last1=Rovere |first1=Alessio |last2=Stocchi |first2=Paolo |last3=Vacchi |first3=Matteo |date=2 August 2016 |title=Eustatic and Relative Sea Level Changes |journal=Current Climate Change Reports |volume=2 |issue=4 |pages=221–231 |doi=10.1007/s40641-016-0045-7 |bibcode=2016CCCR....2..221R |s2cid=131866367 |doi-access=free}} To get precise measurements for sea level, researchers studying the ice and oceans factor in ongoing deformations of the solid Earth. They look in particular at landmasses still rising from past ice masses retreating, and the Earth's gravity and rotation.

File:TOPEX-JasonSeries2008.jpg continued the sea surface measurements started by TOPEX/Poseidon. It was followed by the Ocean Surface Topography Mission on Jason-2, and by Jason-3.]]

Since the launch of TOPEX/Poseidon in 1992, an overlapping series of altimetric satellites has been continuously recording the sea level and its changes.{{cite web |title=Ocean Surface Topography from Space |url=http://sealevel.jpl.nasa.gov/missions/topex/ |archive-url=https://web.archive.org/web/20110722010847/http://sealevel.jpl.nasa.gov/missions/topex/ |archive-date=2011-07-22 |publisher=NASA/JPL}} These satellites can measure the hills and valleys in the sea caused by currents and detect trends in their height. To measure the distance to the sea surface, the satellites send a microwave pulse towards Earth and record the time it takes to return after reflecting off the ocean's surface. Microwave radiometers correct the additional delay caused by water vapor in the atmosphere. Combining these data with the location of the spacecraft determines the sea-surface height to within a few centimetres.{{Cite web |title=Jason-3 Satellite – Mission |url=https://www.nesdis.noaa.gov/jason-3/mission.html |access-date=2018-08-22 |website=www.nesdis.noaa.gov |archive-date=2019-09-06 |archive-url=https://web.archive.org/web/20190906144644/https://www.nesdis.noaa.gov/jason-3/mission.html |url-status=live }} These satellite measurements have estimated rates of sea level rise for 1993–2017 at {{convert|3.0|±|0.4|mm|frac=64|in}} per year.{{cite journal |last1=Nerem |first1=R. S. |last2=Beckley |first2=B. D. |last3=Fasullo |first3=J. T. |last4=Hamlington |first4=B. D. |last5=Masters |first5=D. |last6=Mitchum |first6=G. T. |date=27 February 2018 |title=Climate-change–driven accelerated sea-level rise detected in the altimeter era |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=115 |issue=9 |pages=2022–2025 |bibcode=2018PNAS..115.2022N |doi=10.1073/pnas.1717312115 |pmc=5834701 |pmid=29440401 |doi-access=free}}

Satellites are useful for measuring regional variations in sea level. An example is the substantial rise between 1993 and 2012 in the western tropical Pacific. This sharp rise has been linked to increasing trade winds. These occur when the Pacific Decadal Oscillation (PDO) and the El Niño–Southern Oscillation (ENSO) change from one state to the other.{{cite journal |last1=Merrifield |first1=Mark A. |last2=Thompson |first2=Philip R. |last3=Lander |first3=Mark |date=July 2012 |title=Multidecadal sea level anomalies and trends in the western tropical Pacific |journal=Geophysical Research Letters |volume=39 |issue=13 |pages=n/a |bibcode=2012GeoRL..3913602M |doi=10.1029/2012gl052032 |s2cid=128907116}} The PDO is a basin-wide climate pattern consisting of two phases, each commonly lasting 10 to 30 years. The ENSO has a shorter period of 2 to 7 years.{{cite journal |last1=Mantua |first1=Nathan J. |last2=Hare |first2=Steven R. |last3=Zhang |first3=Yuan |last4=Wallace |first4=John M. |last5=Francis |first5=Robert C. |date=June 1997 |title=A Pacific Interdecadal Climate Oscillation with Impacts on Salmon Production |journal=Bulletin of the American Meteorological Society |volume=78 |issue=6 |pages=1069–1079 |bibcode=1997BAMS...78.1069M |doi=10.1175/1520-0477(1997)078<1069:APICOW>2.0.CO;2 |doi-access=free}}

File:Sea_level_change_1993_to_2018.jpg

The global network of tide gauges is the other important source of sea-level observations. Compared to the satellite record, this record has major spatial gaps but covers a much longer period.{{Cite book |last1=Rhein |first1=Monika |title=IPCC AR5 WGI |last2=Rintoul |first2=Stephan |publisher=Cambridge University Press |year=2013 |location=New York |page=285 |chapter=Observations: Ocean |author-link1=Monika Rhein |access-date=2018-08-26 |chapter-url=https://ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter03_FINAL.pdf |archive-url=https://web.archive.org/web/20180613012554/https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter03_FINAL.pdf |archive-date=2018-06-13}} Coverage of tide gauges started mainly in the Northern Hemisphere. Data for the Southern Hemisphere remained scarce up to the 1970s. The longest running sea-level measurements, NAP or Amsterdam Ordnance Datum were established in 1675, in Amsterdam.{{cite web |title=Other Long Records not in the PSMSL Data Set |url=http://www.psmsl.org/data/longrecords/ |access-date=11 May 2015 |publisher=PSMSL |archive-date=20 April 2020 |archive-url=https://web.archive.org/web/20200420160218/https://www.psmsl.org/data/longrecords/ |url-status=live }} Record collection is also extensive in Australia. They include measurements by Thomas Lempriere, an amateur meteorologist, beginning in 1837. Lempriere established a sea-level benchmark on a small cliff on the Isle of the Dead near the Port Arthur convict settlement in 1841.{{cite journal |last=Hunter |first=John |author2=R. Coleman |author3=D. Pugh |date=2003 |title=The Sea Level at Port Arthur, Tasmania, from 1841 to the Present |url=https://figshare.com/articles/journal_contribution/22846694 |journal=Geophysical Research Letters |volume=30 |issue=7 |page=1401 |bibcode=2003GeoRL..30.1401H |doi=10.1029/2002GL016813 |s2cid=55384210}}

Together with satellite data for the period after 1992, this network established that global mean sea level rose {{Convert|19.5|cm|in|abbr=on}} between 1870 and 2004 at an average rate of about 1.44 mm/yr. (For the 20th century the average is 1.7 mm/yr.){{cite journal |author=Church, J.A. |author2=White, N.J. |date=2006 |title=20th century acceleration in global sea-level rise |journal=Geophysical Research Letters |volume=33 |issue=1 |pages=L01602 |bibcode=2006GeoRL..33.1602C |citeseerx=10.1.1.192.1792 |doi=10.1029/2005GL024826 |s2cid=129887186}} By 2018, data collected by Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO) had shown that the global mean sea level was rising by {{Convert|3.2|mm|in|abbr=on|frac=32}} per year. This was double the average 20th century rate.{{Cite web |title=Historical sea level changes: Last decades |url=http://www.cmar.csiro.au/sealevel/sl_hist_last_decades.html |access-date=2018-08-26 |website=www.cmar.csiro.au |archive-date=2020-03-18 |archive-url=https://web.archive.org/web/20200318220615/http://www.cmar.csiro.au/sealevel/sl_hist_last_decades.html |url-status=live }}{{cite web |last=Neil |first=White |title=Historical Sea Level Changes |url=http://www.cmar.csiro.au/sealevel/sl_hist_few_hundred.html |access-date=25 April 2013 |publisher=CSIRO |archive-date=13 May 2020 |archive-url=https://web.archive.org/web/20200513230040/http://www.cmar.csiro.au/sealevel/sl_hist_few_hundred.html |url-status=live }} The 2023 World Meteorological Organization report found further acceleration to 4.62 mm/yr over the 2013–2022 period. These observations help to check and verify predictions from climate change simulations.

Regional differences are also visible in the tide gauge data. Some are caused by local sea level differences. Others are due to vertical land movements. In Europe, only some land areas are rising while the others are sinking. Since 1970, most tidal stations have measured higher seas. However sea levels along the northern Baltic Sea have dropped due to post-glacial rebound.{{cite web |date=18 November 2021 |title=Global and European sea level rise |url=https://www.eea.europa.eu/ims/global-and-european-sea-level-rise |website=European Environment Agency |access-date=10 October 2022 |archive-date=27 August 2023 |archive-url=https://web.archive.org/web/20230827001932/https://www.eea.europa.eu/ims/global-and-european-sea-level-rise |url-status=live }}

{{Main|Past sea level|Sea level#Change|Marine transgression}}

File:Post-Glacial Sea Level.png]]An understanding of past sea level is an important guide to where current changes in sea level will end up. In the recent geological past, thermal expansion from increased temperatures and changes in land ice are the dominant reasons of sea level rise. The last time that the Earth was {{convert|2|C-change|F-change}} warmer than pre-industrial temperatures was 120,000 years ago. This was when warming due to Milankovitch cycles (changes in the amount of sunlight due to slow changes in the Earth's orbit) caused the Eemian interglacial. Sea levels during that warmer interglacial were at least {{Convert|5|m|ft|abbr=on|}} higher than now.{{Cite web |date=2019-08-30 |title=Scientists discover evidence for past high-level sea rise |url=https://phys.org/news/2019-08-scientists-evidence-high-level-sea.html |access-date=2019-09-07 |website=phys.org |language=en-us |archive-date=2019-12-13 |archive-url=https://web.archive.org/web/20191213220151/https://phys.org/news/2019-08-scientists-evidence-high-level-sea.html |url-status=live }} The Eemian warming was sustained over a period of thousands of years. The size of the rise in sea level implies a large contribution from the Antarctic and Greenland ice sheets.{{rp|1139}} Levels of atmospheric carbon dioxide of around 400 parts per million (similar to 2000s) had increased temperature by over {{convert|2-3|C-change|F-change}} around three million years ago. This temperature increase eventually melted one third of Antarctica's ice sheet, causing sea levels to rise 20 meters above the preindustrial levels.{{Cite web |title=Present CO2 levels caused 20-metre-sea-level rise in the past |url=https://www.nioz.nl/en/news/present-co2-levels-caused-20-metre-sea-level-rise-in-the-past |publisher=Royal Netherlands Institute for Sea Research |access-date=2020-02-03 |archive-date=2020-08-01 |archive-url=https://web.archive.org/web/20200801030150/https://www.nioz.nl/en/news/present-co2-levels-caused-20-metre-sea-level-rise-in-the-past |url-status=live }}

Since the Last Glacial Maximum, about 20,000 years ago, sea level has risen by more than {{Convert|125|m|ft|-1}}. Rates vary from less than 1 mm/year during the pre-industrial era to 40+ mm/year when major ice sheets over Canada and Eurasia melted. Meltwater pulses are periods of fast sea level rise caused by the rapid disintegration of these ice sheets. The rate of sea level rise started to slow down about 8,200 years before today. Sea level was almost constant for the last 2,500 years. The recent trend of rising sea level started at the end of the 19th or beginning of the 20th century.{{cite journal |last1=Lambeck |first1=Kurt |last2=Rouby |first2=Hélène |last3=Purcell |first3=Anthony |last4=Sun |first4=Yiying |last5=Sambridge |first5=Malcolm |date=28 October 2014 |title=Sea level and global ice volumes from the Last Glacial Maximum to the Holocene |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=111 |issue=43 |pages=15296–15303 |bibcode=2014PNAS..11115296L |doi=10.1073/pnas.1411762111 |pmc=4217469 |pmid=25313072 |doi-access=free}}

File:Kopp 2023 4 contributions.png

{{See also|Effects of climate change}}

The three main reasons why global warming causes sea levels to rise are the expansion of oceans due to heating, water inflow from melting ice sheets and water inflow from glaciers. Other factors affecting sea level rise include changes in snow mass, and flow from terrestrial water storage, though the contribution from these is thought to be small. Glacier retreat and ocean expansion have dominated sea level rise since the start of the 20th century. Some of the losses from glaciers are offset when precipitation falls as snow, accumulates and over time forms glacial ice. If precipitation, surface processes and ice loss at the edge balance each other, sea level remains the same. Because of this precipitation began as water vapor evaporated from the ocean surface, effects of climate change on the water cycle can even increase ice build-up. However, this effect is not enough to fully offset ice losses, and sea level rise continues to accelerate.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: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter09.pdf Chapter 9: Africa] {{Webarchive|url=https://web.archive.org/web/20221206082533/https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter09.pdf|date=2022-12-06}}. In [https://www.ipcc.ch/report/ar6/wg2/ Climate Change 2022: Impacts, Adaptation and Vulnerability] {{Webarchive|url=https://web.archive.org/web/20220228114918/https://www.ipcc.ch/report/ar6/wg2/|date=2022-02-28}} [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, UK and New York, US, pp. 2043–2121 {{doi|10.1017/9781009325844.011}}.

The contributions of the two large ice sheets, in Greenland and Antarctica, are likely to increase in the 21st century.{{cite journal |last1=Mengel |first1=Matthias |last2=Levermann |first2=Anders |last3=Frieler |first3=Katja |last4=Robinson |first4=Alexander |last5=Marzeion |first5=Ben |last6=Winkelmann |first6=Ricarda |title=Future sea level rise constrained by observations and long-term commitment |journal=Proceedings of the National Academy of Sciences |date=8 March 2016 |volume=113 |issue=10 |pages=2597–2602 |doi=10.1073/pnas.1500515113 |pmc=4791025 |pmid=26903648 |bibcode=2016PNAS..113.2597M |doi-access=free}} They store most of the land ice (~99.5%) and have a sea-level equivalent (SLE) of {{Convert|7.4|m|ftin|abbr=on}} for Greenland and {{Convert|58.3|m|ftin|abbr=on}} for Antarctica. Thus, melting of all the ice on Earth would result in about {{Convert|70|m|ftin|abbr=on}} of sea level rise,{{cite web |title=How would sea level change if all glaciers melted? |url=https://www.usgs.gov/faqs/how-would-sea-level-change-if-all-glaciers-melted |website=United States Geological Survey |access-date=15 January 2024 |archive-date=31 July 2023 |archive-url=https://web.archive.org/web/20230731120648/https://www.usgs.gov/faqs/how-would-sea-level-change-if-all-glaciers-melted |url-status=live }} although this would require at least 10,000 years and up to {{convert|10|C-change|F-change}} of global warming.

{{Main|Ocean heat content}}

File:1955- Ocean heat content - NOAA.svg created by human-induced global warming.Top 700 meters: {{cite web |last1=Lindsey |first1=Rebecca |last2=Dahlman |first2=Luann |title=Climate Change: Ocean Heat Content |url=https://www.climate.gov/news-features/understanding-climate/climate-change-ocean-heat-content |website=climate.gov |publisher=National Oceanic and Atmospheric Administration (NOAA) |archive-url=https://archive.today/20231029171303/https://www.climate.gov/news-features/understanding-climate/climate-change-ocean-heat-content |archive-date=29 October 2023 |date=6 September 2023 |url-status=live}} ● Top 2000 meters: {{cite web |title=Ocean Warming / Latest Measurement: December 2022 / 345 (±2) zettajoules since 1955 |url=https://climate.nasa.gov/vital-signs/ocean-warming/ |website=NASA.gov |publisher=National Aeronautics and Space Administration |archive-url=https://web.archive.org/web/20231020033606/https://climate.nasa.gov/vital-signs/ocean-warming/ |archive-date=20 October 2023 |url-status=live}}]]

The oceans store more than 90% of the extra heat added to the climate system by Earth's energy imbalance and act as a buffer against its effects.{{Cite journal |last1=Cheng |first1=Lijing |last2=Foster |first2=Grant |last3=Hausfather |first3=Zeke |last4=Trenberth |first4=Kevin E. |last5=Abraham |first5=John |date=2022 |title=Improved Quantification of the Rate of Ocean Warming |journal=Journal of Climate |volume=35 |issue=14 |pages=4827–4840 |bibcode=2022JCli...35.4827C |doi=10.1175/JCLI-D-21-0895.1 |doi-access=free}} This means that the same amount of heat that would increase the average world ocean temperature by {{convert|0.01|C-change|F-change}} would increase atmospheric temperature by approximately {{convert|10|C-change|F-change}}.{{cite journal |author1=Levitus, S. |author2=Boyer, T. |author3=Antonov, J. |title=Warming of the world ocean: 1955–2003 |year=2005 |journal=Geophysical Research Letters |volume=32 |issue=2 |doi=10.1029/2004GL021592 |doi-access=free|bibcode=2005GeoRL..32.2604L}} So a small change in the mean temperature of the ocean represents a very large change in the total heat content of the climate system. Winds and currents move heat into deeper parts of the ocean. Some of it reaches depths of more than {{Convert|2000|m|ft|sigfig=2|abbr=on}}.{{Cite web|url=https://www.scientificamerican.com/article/deep-ocean-waters-are-trapping-vast-stores-of-heat/|title=Deep Ocean Waters Are Trapping Vast Stores of Heat|last=Upton|first=John|date=2016-01-19|website=Scientific American|access-date=2019-02-01|archive-date=2020-06-30|archive-url=https://web.archive.org/web/20200630010341/https://www.scientificamerican.com/article/deep-ocean-waters-are-trapping-vast-stores-of-heat/|url-status=live}}

When the ocean gains heat, the water expands and sea level rises. Warmer water and water under great pressure (due to depth) expand more than cooler water and water under less pressure.{{rp|1161}} Consequently, cold Arctic Ocean water will expand less than warm tropical water. Different climate models present slightly different patterns of ocean heating. So their projections do not agree fully on how much ocean heating contributes to sea level rise.{{Cite journal|last1=Kuhlbrodt|first1=T|last2=Gregory|first2=J.M.|date=2012|title=Ocean heat uptake and its consequences for the magnitude of sea level rise and climate change|journal=Geophysical Research Letters|volume=39|issue=18|pages=L18608|doi=10.1029/2012GL052952|bibcode=2012GeoRL..3918608K|s2cid=19120823|url=http://centaur.reading.ac.uk/28951/1/Kuhlbrodt_Gregory_GRL_2012.pdf|access-date=2019-10-31|archive-date=2020-07-31|archive-url=https://web.archive.org/web/20200731215122/http://centaur.reading.ac.uk/28951/1/Kuhlbrodt_Gregory_GRL_2012.pdf|url-status=live}}

File:Antarctic shelf ice hg.png

File:Corp2400 - Flickr - NOAA Photo Library.jpg is Antarctica's largest. It is about the size of France and up to several hundred metres thick.]]

The large volume of ice on the Antarctic continent stores around 60% of the world's fresh water. Excluding groundwater this is 90%.{{cite web |title=Antarctic Factsheet |url=https://www.bas.ac.uk/science/science-and-society/education/antarctic-factsheet-geographical-statistics/ |publisher=British Antarctic Survey |access-date=15 January 2024 |archive-date=15 January 2024 |archive-url=https://web.archive.org/web/20240115190903/https://www.bas.ac.uk/science/science-and-society/education/antarctic-factsheet-geographical-statistics/ |url-status=live }} Antarctica is experiencing ice loss from coastal glaciers in the West Antarctica and some glaciers of East Antarctica. However it is gaining mass from the increased snow build-up inland, particularly in the East. This leads to contradicting trends. There are different satellite methods for measuring ice mass and change. Combining them helps to reconcile the differences.{{Cite journal|last1=Shepherd|first1=Andrew|last2=Ivins|first2=Erik|date=2012|title=A Reconciled Estimate of Ice-Sheet Mass Balance|url=http://www.escholarship.org/uc/item/0vq404h7|journal=Science|volume=338|issue=6111|pages=1183–1189|bibcode=2012Sci...338.1183S|doi=10.1126/science.1228102|pmid=23197528|collaboration=IMBIE team|hdl=2060/20140006608|s2cid=32653236|access-date=2020-11-10|archive-date=2023-01-23|archive-url=https://web.archive.org/web/20230123141116/https://escholarship.org/uc/item/0vq404h7|url-status=live}} However, there can still be variations between the studies. In 2018, a systematic review estimated average annual ice loss of 43 billion tons (Gt) across the entire continent between 1992 and 2002. This tripled to an annual average of 220 Gt from 2012 to 2017.{{cite journal |title=Mass balance of the Antarctic Ice Sheet from 1992 to 2017 |journal=Nature |date=13 June 2018 |volume=558 |issue=7709 |pages=219–222 |doi=10.1038/s41586-018-0179-y |hdl=2268/225208 |pmid=29899482 |bibcode=2018Natur.558..219I |author1=IMBIE team |s2cid=49188002 |hdl-access=free}}{{cite news |author=Scott K. Johnson |date=2018-06-13 |title=Latest estimate shows how much Antarctic ice has fallen into the sea |work=Ars Technica |url=https://arstechnica.com/science/2018/06/latest-estimate-shows-how-much-antarctic-ice-has-fallen-into-the-sea |access-date=2018-06-15 |archive-date=2018-06-15 |archive-url=https://web.archive.org/web/20180615083459/https://arstechnica.com/science/2018/06/latest-estimate-shows-how-much-antarctic-ice-has-fallen-into-the-sea/ |url-status=live }} However, a 2021 analysis of data from four different research satellite systems (Envisat, European Remote-Sensing Satellite, GRACE and GRACE-FO and ICESat) indicated annual mass loss of only about 12 Gt from 2012 to 2016. This was due to greater ice gain in East Antarctica than estimated earlier.

In the future, it is known that West Antarctica at least will continue to lose mass, and the likely future losses of sea ice and ice shelves, which block warmer currents from direct contact with the ice sheet, can accelerate declines even in East Antarctica.{{cite web|work=CNN|url=https://edition.cnn.com/2019/01/14/world/climate-change-antarctica-ice-melt-twin-studies/index.html|title=Antarctica ice melt has accelerated by 280% in the last 4 decades|date=14 January 2019|access-date=January 14, 2019|quote=Melting is taking place in the most vulnerable parts of Antarctica ... parts that hold the potential for multiple metres of sea level rise in the coming century or two|archive-date=30 June 2020|archive-url=https://web.archive.org/web/20200630182349/https://edition.cnn.com/2019/01/14/world/climate-change-antarctica-ice-melt-twin-studies/index.html|url-status=live}} Altogether, Antarctica is the source of the largest uncertainty for future sea level projections.{{cite journal |last1=Edwards |first1=Tamsin L. |last2=Nowicki |first2=Sophie |last3=Marzeion |first3=Ben |last4=Hock |first4=Regine |last5=Goelzer |first5=Heiko |last6=Seroussi |first6=Hélène |display-authors=4 |date=5 May 2021 |title=Projected land ice contributions to twenty-first-century sea level rise |url=https://www.nature.com/articles/s41586-021-03302-y |journal=Nature |volume=593 |issue=7857 |pages=74–82 |bibcode=2021Natur.593...74E |doi=10.1038/s41586-021-03302-y |issn=0028-0836 |pmid=33953415 |hdl=1874/412157 |archive-url=https://web.archive.org/web/20210511000000/https://www.nature.com/articles/s41586-021-03302-y |archive-date=11 May 2021 |s2cid=233871029 |hdl-access=free }} Alt URL https://eprints.whiterose.ac.uk/173870/ {{Webarchive|url=https://web.archive.org/web/20230322230428/https://eprints.whiterose.ac.uk/173870/ |date=2023-03-22 }} In 2019, the SROCC assessed several studies attempting to estimate 2300 sea level rise caused by ice loss in Antarctica alone, arriving at projected estimates of {{Convert|0.07 - 0.37|m|ft}} for the low emission RCP2.6 scenario, and {{Convert|0.60 - 2.89|m|ft}} in the high emission RCP8.5 scenario.{{Rp|page=1272}} This wide range of estimates is mainly due to the uncertainties regarding marine ice sheet and marine ice cliff instabilities.

{{Further|East Antarctic Ice Sheet}}

The world's largest potential source of sea level rise is the East Antarctic Ice Sheet (EAIS). It is 2.2 km thick on average and holds enough ice to raise global sea levels by 53.3 m (174 ft 10 in){{cite journal |last1=Fretwell |first1=P. |last2=Pritchard |first2=H. D. |last3=Vaughan |first3=D. G. |last4=Bamber |first4=J. L. |last5=Barrand |first5=N. E. |last6=Bell |first6=R. |last7=Bianchi |first7=C. |last8=Bingham |first8=R. G. |last9=Blankenship |first9=D. D. |last10=Casassa |first10=G. |last11=Catania |first11=G. |last12=Callens |first12=D. |last13=Conway |first13=H. |last14=Cook |first14=A. J. |last15=Corr |first15=H. F. J. |last16=Damaske |first16=D. |last17=Damm |first17=V. |last18=Ferraccioli |first18=F. |last19=Forsberg |first19=R. |last20=Fujita |first20=S. |last21=Gim |first21=Y. |last22=Gogineni |first22=P. |last23=Griggs |first23=J. A. |last24=Hindmarsh |first24=R. C. A. |last25=Holmlund |first25=P. |last26=Holt |first26=J. W. |last27=Jacobel |first27=R. W. |last28=Jenkins |first28=A. |last29=Jokat |first29=W. |last30=Jordan |first30=T. |last31=King |first31=E. C. |last32=Kohler |first32=J. |last33=Krabill |first33=W. |last34=Riger-Kusk |first34=M. |last35=Langley |first35=K. A. |last36=Leitchenkov |first36=G. |last37=Leuschen |first37=C. |last38=Luyendyk |first38=B. P. |last39=Matsuoka |first39=K. |last40=Mouginot |first40=J. |last41=Nitsche |first41=F. O. |last42=Nogi |first42=Y. |last43=Nost |first43=O. A. |last44=Popov |first44=S. V. |last45=Rignot |first45=E. |last46=Rippin |first46=D. M. |last47=Rivera |first47=A. |last48=Roberts |first48=J. |last49=Ross |first49=N. |last50=Siegert |first50=M. J. |last51=Smith |first51=A. M. |last52=Steinhage |first52=D. |last53=Studinger |first53=M. |last54=Sun |first54=B. |last55=Tinto |first55=B. K. |last56=Welch |first56=B. C. |last57=Wilson |first57=D. |last58=Young |first58=D. A. |last59=Xiangbin |first59=C. |last60=Zirizzotti |first60=A. |title=Bedmap2: improved ice bed, surface and thickness datasets for Antarctica |journal=The Cryosphere |date=28 February 2013 |volume=7 |issue=1 |pages=375–393 |doi=10.5194/tc-7-375-2013 |bibcode=2013TCry....7..375F |doi-access=free|hdl=1808/18763 |hdl-access=free }} Its great thickness and high elevation make it more stable than the other ice sheets.{{Cite journal |last1=Singh |first1=Hansi A. |last2=Polvani |first2=Lorenzo M. |date=10 January 2020 |title=Low Antarctic continental climate sensitivity due to high ice sheet orography |journal=npj Climate and Atmospheric Science |language=en |volume=3 |issue=1 |page=39 |doi=10.1038/s41612-020-00143-w |s2cid=222179485 |doi-access=free |bibcode=2020npCAS...3...39S}} As of the early 2020s, most studies show that it is still gaining mass.{{Cite journal|last1 = King|first1 = M. A.|last2 = Bingham|first2 = R. J.|last3 = Moore|first3 = P.|last4 = Whitehouse|first4 = P. L.|last5 = Bentley|first5 = M. J.|last6 = Milne|first6 = G. A.|doi = 10.1038/nature11621|title = Lower satellite-gravimetry estimates of Antarctic sea-level contribution|journal = Nature|volume = 491|issue = 7425|pages = 586–589|year = 2012|pmid = 23086145|bibcode = 2012Natur.491..586K|s2cid = 4414976}}{{cite web |title=Antarctic Ice Mass Loss 2002–2023 |url=https://svs.gsfc.nasa.gov/31158 |author=NASA |date=7 July 2023 |access-date=15 January 2024 |archive-date=18 January 2024 |archive-url=https://web.archive.org/web/20240118033629/https://svs.gsfc.nasa.gov/31158 |url-status=live }} Some analyses have suggested it began to lose mass in the 2000s.{{cite journal |last1=Chen |first1=J. L. |last2=Wilson |first2=C. R. |last3=Blankenship |first3=D. |last4=Tapley |first4=B. D. |year=2009 |title=Accelerated Antarctic ice loss from satellite gravity measurements |journal=Nature Geoscience |volume=2 |issue=12 |pages=859 |doi=10.1038/ngeo694 |bibcode=2009NatGe...2..859C |s2cid=130927366}}{{cite journal |last1=Rignot |first1=Eric |last2=Mouginot |first2=Jérémie |last3=Scheuchl |first3=Bernd |last4=van den Broeke |first4=Michiel |last5=van Wessem |first5=Melchior J. |last6=Morlighem |first6=Mathieu |title=Four decades of Antarctic Ice Sheet mass balance from 1979–2017 |journal=Proceedings of the National Academy of Sciences |date=22 January 2019 |volume=116 |issue=4 |pages=1095–1103 |doi=10.1073/pnas.1812883116 |pmid=30642972 |pmc=6347714 |bibcode=2019PNAS..116.1095R |doi-access=free}} However they over-extrapolated some observed losses on to the poorly observed areas. A more complete observational record shows continued mass gain.{{Cite journal |last1=Zwally |first1=H. Jay |last2=Robbins |first2=John W. |last3=Luthcke |first3=Scott B. |last4=Loomis |first4=Bryant D. |last5=Rémy |first5=Frédérique |date=29 March 2021 |title=Mass balance of the Antarctic ice sheet 1992–2016: reconciling results from GRACE gravimetry with ICESat, ERS1/2 and Envisat altimetry |journal=Journal of Glaciology |language=en |volume=67 |issue=263 |pages=533–559 |doi=10.1017/jog.2021.8 |bibcode=2021JGlac..67..533Z |quote=Although their methods of interpolation or extrapolation for areas with unobserved output velocities have an insufficient description for the evaluation of associated errors, such errors in previous results (Rignot and others, 2008) caused large overestimates of the mass losses as detailed in Zwally and Giovinetto (Zwally and Giovinetto, 2011).|doi-access=free }}

File:Denman oli 2020-057-059 lrg-labeled.svg

In spite of the net mass gain, some East Antarctica glaciers have lost ice in recent decades due to ocean warming and declining structural support from the local sea ice,{{cite journal |last1=Greene |first1=Chad A. |last2=Young |first2=Duncan A. |last3=Gwyther |first3=David E. |last4=Galton-Fenzi |first4=Benjamin K. |last5=Blankenship |first5=Donald D. |title=Seasonal dynamics of Totten Ice Shelf controlled by sea ice buttressing |journal=The Cryosphere |date=6 September 2018 |volume=12 |issue=9 |pages=2869–2882 |doi=10.5194/tc-12-2869-2018 |bibcode=2018TCry...12.2869G |doi-access=free}} such as Denman Glacier,{{cite journal|last1=Brancato |first1=V. |last2=Rignot |first2=E. |last3=Milillo |first3=P. |last4=Morlighem |first4=M. |last5=Mouginot |first5=J. |last6=An |first6=L. |last7=Scheuchl |first7=B. |last8=Jeong |first8=S. |last9=Rizzoli |first9=P. |last10=Bueso Bello |first10=J.L. |last11=Prats-Iraola |first11=P. |title=Grounding line retreat of Denman Glacier, East Antarctica, measured with COSMO-SkyMed radar interferometry data |journal=Geophysical Research Letters |year=2020 |volume=47 |issue=7 |pages=e2019GL086291|issn=0094-8276 |doi=10.1029/2019GL086291 |bibcode=2020GeoRL..4786291B |doi-access=free}}{{cite news|newspaper=BBC|url=https://www.bbc.com/news/science-environment-52007637|title=Climate change: Earth's deepest ice canyon vulnerable to melting|last=Amos|first=Jonathan|date=2020-03-23|access-date=2024-01-13|archive-date=2024-01-13|archive-url=https://web.archive.org/web/20240113200523/https://www.bbc.com/news/science-environment-52007637|url-status=live}} and Totten Glacier.{{cite journal |last1=Greene |first1=Chad A. |last2=Blankenship |first2=Donald D. |last3=Gwyther |first3=David E. |last4=Silvano |first4=Alessandro |last5=van Wijk |first5=Esmee |title=Wind causes Totten Ice Shelf melt and acceleration |journal=Science Advances |date=1 November 2017 |volume=3 |issue=11 |pages=e1701681 |doi=10.1126/sciadv.1701681 |pmid=29109976 |pmc=5665591 |bibcode=2017SciA....3E1681G}}{{cite journal |last1=Roberts |first1=Jason |last2=Galton-Fenzi |first2=Benjamin K. |last3=Paolo |first3=Fernando S. |last4=Donnelly |first4=Claire |last5=Gwyther |first5=David E. |last6=Padman |first6=Laurie |last7=Young |first7=Duncan |last8=Warner |first8=Roland |last9=Greenbaum |first9=Jamin |last10=Fricker |first10=Helen A. |last11=Payne |first11=Antony J. |last12=Cornford |first12=Stephen |last13=Le Brocq |first13=Anne |last14=van Ommen |first14=Tas |last15=Blankenship |first15=Don |last16=Siegert |first16=Martin J. |title=Ocean forced variability of Totten Glacier mass loss |journal=Geological Society, London, Special Publications |date=2018 |volume=461 |issue=1 |pages=175–186 |doi=10.1144/sp461.6 |bibcode=2018GSLSP.461..175R |s2cid=55567382 |url=https://research-information.bristol.ac.uk/en/publications/ocean-forced-variability-of-totten-glacier-mass-loss(27694a07-b3c7-45fd-bdfb-74eb6b09c3e0).html |doi-access=free|hdl=10871/28918 |hdl-access=free }} Totten Glacier is particularly important because it stabilizes the Aurora Subglacial Basin. Subglacial basins like Aurora and Wilkes Basin are major ice reservoirs together holding as much ice as all of West Antarctica.{{cite journal |last1=Greenbaum |first1=J. S. |last2=Blankenship |first2=D. D. |last3=Young |first3=D. A. |last4=Richter |first4=T. G. |last5=Roberts |first5=J. L. |last6=Aitken |first6=A. R. A. |last7=Legresy |first7=B. |last8=Schroeder |first8=D. M. |last9=Warner |first9=R. C. |last10=van Ommen |first10=T. D. |last11=Siegert |first11=M. J. |title=Ocean access to a cavity beneath Totten Glacier in East Antarctica |journal=Nature Geoscience |date=16 March 2015 |volume=8 |issue=4 |pages=294–298 |doi=10.1038/ngeo2388 |bibcode=2015NatGe...8..294G}} They are more vulnerable than the rest of East Antarctica.{{cite journal |last1=Pollard |first1=David |last2=DeConto |first2=Robert M. |last3=Alley |first3=Richard B. |title=Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure |journal=Earth and Planetary Science Letters |date=February 2015 |volume=412 |pages=112–121 |doi=10.1016/j.epsl.2014.12.035 |bibcode=2015E&PSL.412..112P |doi-access=free}} Their collective tipping point probably lies at around {{convert|3|C-change|F-change}} of global warming. It may be as high as {{convert|6|C-change|F-change}} or as low as {{convert|2|C-change|F-change}}. Once this tipping point is crossed, the collapse of these subglacial basins could take place over as little as 500 or as much as 10,000 years. The median timeline is 2000 years. Depending on how many subglacial basins are vulnerable, this causes sea level rise of between {{convert|1.4|m|ftin|abbr=on}} and {{convert|6.4|m|ftin|abbr=on}}.{{Cite journal|last1=Pan |first1=Linda |last2=Powell |first2=Evelyn M. |last3=Latychev |first3=Konstantin |last4=Mitrovica |first4=Jerry X. |last5=Creveling |first5=Jessica R. |last6=Gomez |first6=Natalya |last7=Hoggard |first7=Mark J. |last8=Clark |first8=Peter U. |date=30 April 2021 |title=Rapid postglacial rebound amplifies global sea level rise following West Antarctic Ice Sheet collapse |journal=Science Advances |volume=7 |issue=18 |doi=10.1126/sciadv.abf7787 |pmid=33931453 |pmc=8087405 |bibcode=2021SciA....7.7787P}}

On the other hand, the whole EAIS would not definitely collapse until global warming reaches {{convert|7.5|C-change|F-change}}, with a range between {{convert|5|C-change|F-change}} and {{convert|10|C-change|F-change}}. It would take at least 10,000 years to disappear. Some scientists have estimated that warming would have to reach at least {{convert|6|C-change|F-change}} to melt two thirds of its volume.{{Cite journal |last1=Garbe |first1=Julius |last2=Albrecht |first2=Torsten |last3=Levermann |first3=Anders |last4=Donges |first4=Jonathan F. |last5=Winkelmann |first5=Ricarda |date=2020 |title=The hysteresis of the Antarctic Ice Sheet |url=https://www.nature.com/articles/s41586-020-2727-5 |journal=Nature |volume=585 |issue=7826 |pages=538–544 |doi=10.1038/s41586-020-2727-5 |pmid=32968257 |bibcode=2020Natur.585..538G |s2cid=221885420 |access-date=2022-10-23 |archive-date=2023-08-19 |archive-url=https://web.archive.org/web/20230819234302/https://www.nature.com/articles/s41586-020-2727-5 |url-status=live }}

{{Further|West Antarctic Ice Sheet}}

File:Thwaites Glacier.jpg

East Antarctica contains the largest potential source of sea level rise. However the West Antarctic ice sheet (WAIS) is substantially more vulnerable. Temperatures on West Antarctica have increased significantly, unlike East Antarctica and the Antarctic Peninsula. The trend is between {{convert|0.08|C-change|F-change}} and {{convert|0.96|C-change|F-change}} per decade between 1976 and 2012.{{cite journal |last1=Ludescher |first1=Josef |last2=Bunde |first2=Armin |last3=Franzke |first3=Christian L. E. |last4=Schellnhuber |first4=Hans Joachim |title=Long-term persistence enhances uncertainty about anthropogenic warming of Antarctica |journal=Climate Dynamics |date=16 April 2015 |volume=46 |issue=1–2 |pages=263–271 |doi=10.1007/s00382-015-2582-5 |bibcode=2016ClDy...46..263L |s2cid=131723421}} Satellite observations recorded a substantial increase in WAIS melting from 1992 to 2017. This resulted in {{Convert|7.6 ± 3.9|mm|in|frac=64|abbr=on}} of Antarctica sea level rise. Outflow glaciers in the Amundsen Sea Embayment played a disproportionate role.{{cite journal |last1=Rignot |first1=Eric |last2=Bamber |first2=Jonathan L. |last3=van den Broeke |first3=Michiel R. |last4=Davis |first4=Curt |last5=Li |first5=Yonghong |last6=van de Berg |first6=Willem Jan |last7=van Meijgaard |first7=Erik |title=Recent Antarctic ice mass loss from radar interferometry and regional climate modelling |journal=Nature Geoscience |date=13 January 2008 |volume=1 |issue=2 |pages=106–110 |doi=10.1038/ngeo102 |bibcode=2008NatGe...1..106R |s2cid=784105 |url=http://www.escholarship.org/uc/item/26f4j9vv |access-date=11 December 2019 |archive-date=2 March 2020 |archive-url=https://web.archive.org/web/20200302093403/https://escholarship.org/uc/item/26f4j9vv |url-status=live }}

File:West Antarctic Collapse.ogv

The median estimated increase in sea level rise from Antarctica by 2100 is ~{{convert|11|cm|in|round=5|abbr=on}}. There is no difference between scenarios, because the increased warming would intensify the water cycle and increase snowfall accumulation over the EAIS at about the same rate as it would increase ice loss from WAIS. However, most of the bedrock underlying the WAIS lies well below sea level, and it has to be buttressed by the Thwaites and Pine Island glaciers. If these glaciers were to collapse, the entire ice sheet would as well. Their disappearance would take at least several centuries, but is considered almost inevitable, as their bedrock topography deepens inland and becomes more vulnerable to meltwater, in what is known as marine ice sheet instability.{{cite journal |last1=Robel |first1=Alexander A. |last2=Seroussi |first2=Hélène |last3=Roe |first3=Gerard H. |title=Marine ice sheet instability amplifies and skews uncertainty in projections of future sea-level rise |journal=Proceedings of the National Academy of Sciences |date=23 July 2019 |volume=116 |issue=30 |pages=14887–14892 |doi=10.1073/pnas.1904822116 |pmid=31285345 |pmc=6660720 |bibcode=2019PNAS..11614887R |doi-access=free}}{{Cite web|last1=Voosen|first1=Paul|date=13 December 2021|title=Ice shelf holding back keystone Antarctic glacier within years of failure|url=https://www.science.org/content/article/ice-shelf-holding-back-keystone-antarctic-glacier-within-years-failure|access-date=2022-10-22|website=Science Magazine|language=en|quote=Because Thwaites sits below sea level on ground that dips away from the coast, the warm water is likely to melt its way inland, beneath the glacier itself, freeing its underbelly from bedrock. A collapse of the entire glacier, which some researchers think is only centuries away, would raise global sea level by 65 centimeters.|archive-date=2023-04-18|archive-url=https://web.archive.org/web/20230418221429/https://www.science.org/content/article/ice-shelf-holding-back-keystone-antarctic-glacier-within-years-failure|url-status=live}}{{cite news |last=Amos |first=Jonathan |date=13 December 2021 |title=Thwaites: Antarctic glacier heading for dramatic change |url=https://www.bbc.com/news/science-environment-59644494 |work=BBC News |location=London |access-date=December 14, 2021 |archive-date=22 January 2022 |archive-url=https://web.archive.org/web/20220122115541/https://www.bbc.com/news/science-environment-59644494 |url-status=live }}

The contribution of these glaciers to global sea levels has already accelerated since the year 2000. The Thwaites Glacier now accounts for 4% of global sea level rise.{{cite web|url=https://www.theatlantic.com/science/archive/2018/06/after-decades-of-ice-loss-antarctica-is-now-hemorrhaging-mass/562748/|work=The Atlantic|year=2018|title=After Decades of Losing Ice, Antarctica Is Now Hemorrhaging It|access-date=2018-08-29|archive-date=2020-03-19|archive-url=https://web.archive.org/web/20200319000046/https://www.theatlantic.com/science/archive/2018/06/after-decades-of-ice-loss-antarctica-is-now-hemorrhaging-mass/562748/|url-status=live}}{{cite web|url=http://www.antarcticglaciers.org/glaciers-and-climate/ice-ocean-interactions/marine-ice-sheets/|work=AntarcticGlaciers.org|year=2014|title=Marine ice sheet instability|access-date=2018-08-29|archive-date=2020-05-03|archive-url=https://web.archive.org/web/20200503235803/http://www.antarcticglaciers.org/glaciers-and-climate/ice-ocean-interactions/marine-ice-sheets/|url-status=live}} It could start to lose even more ice if the Thwaites Ice Shelf fails and would no longer stabilize it, which could potentially occur in mid-2020s.{{cite news |last=Kaplan |first=Sarah |date=December 13, 2021 |title=Crucial Antarctic ice shelf could fail within five years, scientists say |url=https://www.washingtonpost.com/climate-environment/2021/12/13/thwaites-glacier-melt-antarctica/ |newspaper=The Washington Post |location=Washington DC |access-date=December 14, 2021 |archive-date=August 19, 2023 |archive-url=https://web.archive.org/web/20230819193033/https://www.washingtonpost.com/climate-environment/2021/12/13/thwaites-glacier-melt-antarctica/ |url-status=live }} A combination of ice sheet instability with other important but hard-to-model processes like hydrofracturing (meltwater collects atop the ice sheet, pools into fractures and forces them open){{cite journal |last1=Pattyn |first1=Frank |author-link=Frank Pattyn |date=16 July 2018 |title=The paradigm shift in Antarctic ice sheet modelling |journal=Nature Communications |volume=9 |issue=1 |page=2728 |bibcode=2018NatCo...9.2728P |doi=10.1038/s41467-018-05003-z |pmc=6048022 |pmid=30013142}} or smaller-scale changes in ocean circulation{{Cite journal |last1=Golledge |first1=Nicholas R. |last2=Keller |first2=Elizabeth D. |last3=Gomez |first3=Natalya |last4=Naughten |first4=Kaitlin A. |last5=Bernales |first5=Jorge |last6=Trusel |first6=Luke D. |last7=Edwards |first7=Tamsin L. |date=2019 |title=Global environmental consequences of twenty-first-century ice-sheet melt |journal=Nature |language=en |volume=566 |issue=7742 |pages=65–72 |doi=10.1038/s41586-019-0889-9 |pmid=30728520 |bibcode=2019Natur.566...65G |s2cid=59606358 |issn=1476-4687}}{{Cite journal |last1=Moorman |first1=Ruth |last2=Morrison |first2=Adele K. |last3=Hogg |first3=Andrew McC |date=2020-08-01 |title=Thermal Responses to Antarctic Ice Shelf Melt in an Eddy-Rich Global Ocean–Sea Ice Model |journal=Journal of Climate |language=EN |volume=33 |issue=15 |pages=6599–6620 |doi=10.1175/JCLI-D-19-0846.1 |bibcode=2020JCli...33.6599M |s2cid=219487981 |issn=0894-8755}}{{cite journal |last1=A. Naughten |first1=Kaitlin |last2=R. Holland |first2=Paul |last3=De Rydt |first3=Jan |date=23 October 2023 |title=Unavoidable future increase in West Antarctic ice-shelf melting over the twenty-first century |journal=Nature Climate Change |volume=13 |issue=11 |pages=1222–1228 |bibcode=2023NatCC..13.1222N |doi=10.1038/s41558-023-01818-x |s2cid=264476246 |doi-access=free}} could cause the WAIS to contribute up to {{convert|41|cm|in|0|abbr=on}} by 2100 under the low-emission scenario and up to {{convert|57|cm|in|0|abbr=on}} under the highest-emission one. Ice cliff instability would cause a contribution of {{cvt|1|m|ft|frac=2}} or more if it were applicable.

The melting of all the ice in West Antarctica would increase the total sea level rise to {{convert|4.3|m|ftin|abbr=on}}.{{cite journal |last1=Fretwell |first1=P. |display-authors=et al |title=Bedmap2: improved ice bed, surface and thickness datasets for Antarctica |journal=The Cryosphere |volume=7 |issue=1 |page=390 |date=28 February 2013 |url=http://www.the-cryosphere.net/7/375/2013/tc-7-375-2013.pdf |access-date=6 January 2014 |doi=10.5194/tc-7-375-2013 |bibcode=2013TCry....7..375F |s2cid=13129041 |doi-access=free |archive-date=16 February 2020 |archive-url=https://web.archive.org/web/20200216072841/https://www.the-cryosphere.net/7/375/2013/tc-7-375-2013.pdf |url-status=live}} However, mountain ice caps not in contact with water are less vulnerable than the majority of the ice sheet, which is located below the sea level.{{Cite journal |last1=Hein |first1=Andrew S. |last2=Woodward |first2=John |last3=Marrero |first3=Shasta M. |last4=Dunning |first4=Stuart A. |last5=Steig |first5=Eric J. |last6=Freeman |first6=Stewart P. H. T. |last7=Stuart |first7=Finlay M. |last8=Winter |first8=Kate |last9=Westoby |first9=Matthew J. |last10=Sugden |first10=David E. |date=3 February 2016 |title=Evidence for the stability of the West Antarctic Ice Sheet divide for 1.4 million years |journal=Nature Communications |volume=7 |page=10325 |doi=10.1038/ncomms10325 |pmid=26838462 |pmc=4742792 |bibcode=2016NatCo...710325H}} Its collapse would cause ~{{convert|3.3|m|ftin|abbr=on}} of sea level rise.{{cite journal |last1=Bamber |first1=J.L. |last2=Riva |first2=R.E.M. |last3=Vermeersen |first3=B.L.A. |last4=LeBrocq |first4=A.M. |title=Reassessment of the Potential Sea-Level Rise from a Collapse of the West Antarctic Ice Sheet |journal=Science |date=14 May 2009 |volume=324 |issue=5929 |pages=901–903 |doi=10.1126/science.1169335 |pmid=19443778 |bibcode=2009Sci...324..901B |s2cid=11083712}} This disappearance would take an estimated 2000 years. The absolute minimum for the loss of West Antarctica ice is 500 years, and the potential maximum is 13,000 years.{{Cite journal |last1=Armstrong McKay |first1=David |last2=Abrams |first2=Jesse |last3=Winkelmann |first3=Ricarda |last4=Sakschewski |first4=Boris |last5=Loriani |first5=Sina |last6=Fetzer |first6=Ingo |last7=Cornell |first7=Sarah |last8=Rockström |first8=Johan |last9=Staal |first9=Arie |last10=Lenton |first10=Timothy |date=9 September 2022 |title=Exceeding 1.5°C global warming could trigger multiple climate tipping points |url=https://www.science.org/doi/10.1126/science.abn7950 |journal=Science |language=en |volume=377 |issue=6611 |pages=eabn7950 |doi=10.1126/science.abn7950 |pmid=36074831 |hdl=10871/131584 |s2cid=252161375 |issn=0036-8075 |access-date=23 October 2022 |archive-date=14 November 2022 |archive-url=https://web.archive.org/web/20221114143835/https://www.science.org/doi/10.1126/science.abn7950 |url-status=live |hdl-access=free }}{{Cite web |last=Armstrong McKay |first=David |date=9 September 2022 |title=Exceeding 1.5°C global warming could trigger multiple climate tipping points – paper explainer |url=https://climatetippingpoints.info/2022/09/09/climate-tipping-points-reassessment-explainer/ |access-date=2 October 2022 |website=climatetippingpoints.info |language=en |archive-date=18 July 2023 |archive-url=https://web.archive.org/web/20230718085705/https://climatetippingpoints.info/2022/09/09/climate-tipping-points-reassessment-explainer/ |url-status=live }}

Once ice loss from the West Antarctica is triggered, the only way to restore it to near-present values is by lowering the global temperature to {{convert|1|C-change|F-change}} below the preindustrial level. This would be {{convert|2|C-change|F-change}} below the temperature of 2020. Other researchers suggested that a climate engineering intervention to stabilize the ice sheet's glaciers may delay its loss by centuries and give more time to adapt. However this is an uncertain proposal, and would end up as one of the most expensive projects ever attempted.{{Cite journal |last1=Wolovick |first1=Michael |last2=Moore |first2=John |last3=Keefer |first3=Bowie |date=27 March 2023 |title=Feasibility of ice sheet conservation using seabed anchored curtains |url=https://academic.oup.com/pnasnexus/article/2/4/pgad103/7087219 |journal=PNAS Nexus |volume=2 |issue=3 |pages=pgad053 |language=en |doi=10.1093/pnasnexus/pgad053 |pmid=37007716 |pmc=10062297 |access-date=27 October 2023 |archive-date=6 January 2024 |archive-url=https://web.archive.org/web/20240106123807/https://academic.oup.com/pnasnexus/article/2/4/pgad103/7087219 |url-status=live }}{{Cite journal |last1=Wolovick |first1=Michael |last2=Moore |first2=John |last3=Keefer |first3=Bowie |date=27 March 2023 |title=The potential for stabilizing Amundsen Sea glaciers via underwater curtains |url=https://academic.oup.com/pnasnexus/article/2/4/pgad103/7087219 |journal=PNAS Nexus |volume=2 |issue=4 |pages=pgad103 |language=en |doi=10.1093/pnasnexus/pgad103 |pmid=37091546 |pmc=10118300 |access-date=27 October 2023 |archive-date=6 January 2024 |archive-url=https://web.archive.org/web/20240106123807/https://academic.oup.com/pnasnexus/article/2/4/pgad103/7087219 |url-status=live }}

File:Mass changes of the Greenland Ice Sheet between 2002 and 2019.webp Text and images are available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License] {{Webarchive|url=https://web.archive.org/web/20171016050101/https://creativecommons.org/licenses/by/4.0/ |date=2017-10-16 }}.]]

Most ice on Greenland is in the Greenland ice sheet which is {{Convert|3|km|ft|abbr=on|sigfig=1}} at its thickest. The rest of Greenland ice forms isolated glaciers and ice caps. The average annual ice loss in Greenland more than doubled in the early 21st century compared to the 20th century.{{cite journal |last1=Kjeldsen |first1=Kristian K. |last2=Korsgaard |first2=Niels J. |last3=Bjørk |first3=Anders A. |last4=Khan |first4=Shfaqat A. |last5=Box |first5=Jason E. |last6=Funder |first6=Svend |last7=Larsen |first7=Nicolaj K. |last8=Bamber |first8=Jonathan L. |last9=Colgan |first9=William |last10=van den Broeke |first10=Michiel |last11=Siggaard-Andersen |first11=Marie-Louise |last12=Nuth |first12=Christopher |last13=Schomacker |first13=Anders |last14=Andresen |first14=Camilla S. |last15=Willerslev |first15=Eske |last16=Kjær |first16=Kurt H. |title=Spatial and temporal distribution of mass loss from the Greenland Ice Sheet since AD 1900 |journal=Nature |date=16 December 2015 |volume=528 |issue=7582 |pages=396–400 |doi=10.1038/nature16183 |pmid=26672555 |bibcode=2015Natur.528..396K |hdl=10852/50174 |s2cid=4468824 |url=https://research-information.bris.ac.uk/en/publications/spatial-and-temporal-distribution-of-mass-loss-from-the-greenland-ice-sheet-since-ad-1900(29ed76ed-b8f7-4b99-bf59-a275b0a22ce7).html|hdl-access=free }} Its contribution to sea level rise correspondingly increased from 0.07 mm per year between 1992 and 1997 to 0.68 mm per year between 2012 and 2017. Total ice loss from the Greenland ice sheet between 1992 and 2018 amounted to 3,902 gigatons (Gt) of ice. This is equivalent to a SLR contribution of 10.8 mm.{{Cite journal|last1=Shepherd|first1=Andrew|last2=Ivins|first2=Erik|last3=Rignot|first3=Eric|last4=Smith|first4=Ben|last5=van den Broeke|first5=Michiel|last6=Velicogna|first6=Isabella|author-link6=Isabella Velicogna|last7=Whitehouse|first7=Pippa|last8=Briggs|first8=Kate|last9=Joughin|first9=Ian|last10=Krinner|first10=Gerhard|last11=Nowicki|first11=Sophie|date=2020-03-12|title=Mass balance of the Greenland Ice Sheet from 1992 to 2018|journal=Nature|language=en|volume=579|issue=7798|pages=233–239|doi=10.1038/s41586-019-1855-2|pmid=31822019|hdl=2268/242139|s2cid=219146922|issn=1476-4687|url=https://orbi.uliege.be/handle/2268/242139|access-date=2020-05-11|archive-date=2022-10-23|archive-url=https://web.archive.org/web/20221023151210/https://orbi.uliege.be/handle/2268/242139|url-status=live|hdl-access=free}} The contribution for the 2012–2016 period was equivalent to 37% of sea level rise from land ice sources (excluding thermal expansion).{{cite journal |last1=Bamber |first1=Jonathan L |last2=Westaway |first2=Richard M |last3=Marzeion |first3=Ben |last4=Wouters |first4=Bert |title=The land ice contribution to sea level during the satellite era |journal=Environmental Research Letters |date=1 June 2018 |volume=13 |issue=6 |page=063008 |doi=10.1088/1748-9326/aac2f0 |bibcode=2018ERL....13f3008B |doi-access=free|hdl=1983/58218615-dedd-43a8-a8ea-79fb83130613 |hdl-access=free }} This observed rate of ice sheet melting is at the higher end of predictions from past IPCC assessment reports.{{Cite web|url=https://news.uci.edu/2019/12/19/greenland-ice-loss-is-at-worse-case-scenario-levels-study-finds/|title=Greenland ice loss is at 'worse-case scenario' levels, study finds|date=2019-12-19|website=UCI News|language=en-US|access-date=2019-12-28|archive-date=2020-04-03|archive-url=https://web.archive.org/web/20200403190232/https://news.uci.edu/2019/12/19/greenland-ice-loss-is-at-worse-case-scenario-levels-study-finds/|url-status=live}}

File:Beckmann 2023 Greenland 2300 RCP85 extent.png

In 2021, AR6 estimated that by 2100, the melting of Greenland ice sheet would most likely add around {{cvt|6|cm|in|frac=2}} to sea levels under the low-emission scenario, and {{cvt|13|cm|in|frac=2}} under the high-emission scenario. The first scenario, SSP1-2.6, largely fulfils the Paris Agreement goals, while the other, SSP5-8.5, has the emissions accelerate throughout the century. The uncertainty about ice sheet dynamics can affect both pathways. In the best-case scenario, ice sheet under SSP1-2.6 gains enough mass by 2100 through surface mass balance feedbacks to reduce the sea levels by {{cvt|2|cm|in|frac=2}}. In the worst case, it adds {{cvt|15|cm|in|frac=2}}. For SSP5-8.5, the best-case scenario is adding {{cvt|5|cm|in|frac=2}} to sea levels, and the worst-case is adding {{cvt|23|cm|in|frac=2}}.{{Rp|page=1260}}

Greenland's peripheral glaciers and ice caps crossed an irreversible tipping point around 1997. Sea level rise from their loss is now unstoppable.{{cite journal |last1=Noël |first1=B. |last2=van de Berg |first2=W. J |last3=Lhermitte |first3=S. |last4=Wouters |first4=B. |last5=Machguth |first5=H. |last6=Howat |first6=I. |last7=Citterio |first7=M. |last8=Moholdt |first8=G. |last9=Lenaerts |first9=J. T. M. |last10=van den Broeke |first10=M. R. |title=A tipping point in refreezing accelerates mass loss of Greenland's glaciers and ice caps |journal=Nature Communications |date=31 March 2017 |volume=8 |issue=1 |page=14730 |doi=10.1038/ncomms14730 |pmid=28361871 |pmc=5380968 |bibcode=2017NatCo...814730N}}{{cite news|title=Warming Greenland ice sheet passes point of no return|url=https://news.osu.edu/warming-greenland-ice-sheet-passes-point-of-no-return/|date=13 August 2020|access-date=15 August 2020|work=Ohio State University|archive-date=5 September 2023|archive-url=https://web.archive.org/web/20230905013943/https://news.osu.edu/warming-greenland-ice-sheet-passes-point-of-no-return/|url-status=live}}{{cite journal|last1=King|first1=Michalea D.|last2=Howat|first2=Ian M.|last3=Candela|first3=Salvatore G.|last4=Noh|first4=Myoung J.|last5=Jeong|first5=Seongsu|last6=Noël|first6=Brice P. Y.|last7=van den Broeke|first7=Michiel R.|last8=Wouters|first8=Bert|last9=Negrete|first9=Adelaide|date=13 August 2020|title=Dynamic ice loss from the Greenland Ice Sheet driven by sustained glacier retreat|journal=Communications Earth & Environment|language=en|volume=1|issue=1|pages=1–7|doi=10.1038/s43247-020-0001-2|bibcode=2020ComEE...1....1K |issn=2662-4435|doi-access=free}} 50x50px Text and images are available under a Creative Commons Attribution 4.0 International License. However the temperature changes in future, the warming of 2000–2019 had already damaged the ice sheet enough for it to eventually lose ~3.3% of its volume. This is leading to {{cvt|27|cm|in|frac=2}} of future sea level rise.{{cite journal |last1=Box |first1=Jason E. |last2=Hubbard |first2=Alun |last3=Bahr |first3=David B. |last4=Colgan |first4=William T. |last5=Fettweis |first5=Xavier |last6=Mankoff |first6=Kenneth D. |last7=Wehrlé |first7=Adrien |last8=Noël |first8=Brice |last9=van den Broeke |first9=Michiel R. |last10=Wouters |first10=Bert |last11=Bjørk |first11=Anders A. |last12=Fausto |first12=Robert S. |title=Greenland ice sheet climate disequilibrium and committed sea-level rise |journal=Nature Climate Change |date=29 August 2022 |volume=12 |issue=9 |pages=808–813 |doi=10.1038/s41558-022-01441-2 |bibcode=2022NatCC..12..808B |s2cid=251912711 |doi-access=free |hdl=10037/26654 |hdl-access=free }} At a certain level of global warming, the Greenland ice sheet will almost completely melt. Ice cores show this happened at least once over the last million years, during which the temperatures have at most been {{convert|2.5|C-change|F-change}} warmer than the preindustrial average or {{convert|1|C-change|F-change}} warmer than the 2025 temperature.{{Cite journal|last1=Irvalı|first1=Nil|last2=Galaasen|first2=Eirik V.|last3=Ninnemann|first3=Ulysses S.|last4=Rosenthal|first4=Yair|last5=Born|first5=Andreas|last6=Kleiven|first6=Helga (Kikki) F.|date=18 December 2019 |title=A low climate threshold for south Greenland Ice Sheet demise during the Late Pleistocene|journal=Proceedings of the National Academy of Sciences|volume=117|issue=1|pages=190–195|language=en|doi=10.1073/pnas.1911902116|issn=0027-8424|pmid=31871153|pmc=6955352|doi-access=free}}{{cite journal |last1=Christ |first1=Andrew J. |last2=Bierman |first2=Paul R. |last3=Schaefer |first3=Joerg M.|last4=Dahl-Jensen |first4=Dorthe |last5=Steffensen |first5=Jørgen P. |last6=Corbett |first6=Lee B. |last7=Peteet |first7=Dorothy M. |last8=Thomas |first8=Elizabeth K. |last9=Steig |first9=Eric J. |last10=Rittenour |first10=Tammy M. |last11=Tison |first11=Jean-Louis |last12=Blard |first12=Pierre-Henri |last13=Perdrial |first13=Nicolas |last14=Dethier |first14=David P. |last15=Lini |first15=Andrea |last16=Hidy |first16=Alan J. |last17=Caffee |first17=Marc W. |last18=Southon |first18=John |title=A multimillion-year-old record of Greenland vegetation and glacial history preserved in sediment beneath 1.4 km of ice at Camp Century |journal=Proceedings of the National Academy of Sciences of the United States|date=30 March 2021 |volume=118 |issue=13 |pages=e2021442118 |doi=10.1073/pnas.2021442118 |pmid=33723012 |pmc=8020747 |bibcode=2021PNAS..11821442C |doi-access=free}}

2012 modelling suggested that the tipping point of the ice sheet was between {{convert|0.8|C-change|F-change}} and {{convert|3.2|C-change|F-change}}.{{cite journal |last1=Robinson |first1=Alexander |last2=Calov |first2=Reinhard |last3=Ganopolski |first3=Andrey |title=Multistability and critical thresholds of the Greenland ice sheet |journal=Nature Climate Change |date=11 March 2012 |volume=2 |issue=6 |pages=429–432 |doi=10.1038/nclimate1449 |bibcode=2012NatCC...2..429R}} 2023 modelling has narrowed the tipping threshold to a {{convert|1.7|C-change|F-change}}-{{convert|2.3|C-change|F-change}} range, which is consistent with the empirical {{convert|2.5|C-change|F-change}} upper limit from ice cores. If temperatures reach or exceed that level, reducing the global temperature to {{convert|1.5|C-change|F-change}} above pre-industrial levels or lower would prevent the loss of the entire ice sheet. One way to do this in theory would be large-scale carbon dioxide removal, but there would still be cause of greater ice losses and sea level rise from Greenland than if the threshold was not breached in the first place.{{cite journal |last1=Bochow |first1=Nils |last2=Poltronieri |first2=Anna |last3=Robinson |first3=Alexander |last4=Montoya |first4=Marisa |last5=Rypdal |first5=Martin |last6=Boers |first6=Niklas |date=18 October 2023 |title=Overshooting the critical threshold for the Greenland ice sheet |journal=Nature |volume=622 |issue=7983 |pages=528–536 |bibcode=2023Natur.622..528B |doi=10.1038/s41586-023-06503-9 |pmc=10584691 |pmid=37853149}} If the tipping point instead is durably but mildly crossed, the ice sheet would take between 10,000 and 15,000 years to disintegrate entirely, with a most likely estimate of 10,000 years. If climate change continues along its worst trajectory and temperatures continue to rise quickly over multiple centuries, the ice sheet would only take 1,000 years to melt.{{Cite journal |last1=Aschwanden |first1=Andy |last2=Fahnestock |first2=Mark A. |last3=Truffer |first3=Martin |last4=Brinkerhoff |first4=Douglas J. |last5=Hock |first5=Regine |last6=Khroulev |first6=Constantine |last7=Mottram |first7=Ruth |last8=Khan |first8=S. Abbas |date=19 June 2019 |title=Contribution of the Greenland Ice Sheet to sea level over the next millennium |journal=Science Advances |volume=5 |issue=6 |pages=218–222 |language=EN |doi=10.1126/sciadv.aav9396 |pmid=31223652 |pmc=6584365 |bibcode=2019SciA....5.9396A}}

File:2015-2100 Impacts of global warming on glaciers and sea level rise.svg

There are roughly 200,000 glaciers on Earth, which are spread out across all continents.{{cite journal |last1=Huss |first1=Matthias |last2=Hock |first2=Regine |title=A new model for global glacier change and sea-level rise |journal=Frontiers in Earth Science |date=30 September 2015 |volume=3 |page=54 |doi=10.3389/feart.2015.00054 |bibcode=2015FrEaS...3...54H |s2cid=3256381 |doi-access=free|hdl=20.500.11850/107708 |hdl-access=free }} Less than 1% of glacier ice is in mountain glaciers, compared to 99% in Greenland and Antarctica. However, this small size also makes mountain glaciers more vulnerable to melting than the larger ice sheets. This means they have had a disproportionate contribution to historical sea level rise and are set to contribute a smaller, but still significant fraction of sea level rise in the 21st century.{{cite journal |last1=Radić |first1=Valentina |last2=Hock |first2=Regine |title=Regionally differentiated contribution of mountain glaciers and ice caps to future sea-level rise |journal=Nature Geoscience |date=9 January 2011 |volume=4 |issue=2 |pages=91–94 |doi=10.1038/ngeo1052 |bibcode=2011NatGe...4...91R}} Observational and modelling studies of mass loss from glaciers and ice caps show they contribute 0.2–0.4 mm per year to sea level rise, averaged over the 20th century.{{cite report |doi=10.7265/N52N506F |year=2002 |last1=Dyurgerov |first1=Mark |title=Glacier Mass Balance and Regime Measurements and Analysis, 1945–2003}} The contribution for the 2012–2016 period was nearly as large as that of Greenland. It was 0.63 mm of sea level rise per year, equivalent to 34% of sea level rise from land ice sources. Glaciers contributed around 40% to sea level rise during the 20th century, with estimates for the 21st century of around 30%.

In 2023, a Science paper estimated that at {{convert|1.5|C-change|F-change}}, one quarter of mountain glacier mass would be lost by 2100 and nearly half would be lost at {{convert|4|C-change|F-change}}, contributing ~{{cvt|9|cm|in|frac=2}} and ~{{cvt|15|cm|in|frac=2}} to sea level rise, respectively. Glacier mass is disproportionately concentrated in the most resilient glaciers. So in practice this would remove 49–83% of glacier formations. It further estimated that the current likely trajectory of {{convert|2.7|C-change|F-change}} would result in the SLR contribution of ~{{cvt|11|cm|in|frac=2}} by 2100.{{Cite journal |last1=Rounce |first1=David R. |last2=Hock |first2=Regine |last3=Maussion |first3=Fabien |last4=Hugonnet |first4=Romain |last5=Kochtitzky |first5=William |last6=Huss |first6=Matthias |last7=Berthier |first7=Etienne |last8=Brinkerhoff |first8=Douglas |last9=Compagno |first9=Loris |last10=Copland |first10=Luke |last11=Farinotti |first11=Daniel |last12=Menounos |first12=Brian |last13=McNabb |first13=Robert W. |date=5 January 2023 |title=Global glacier change in the 21st century: Every increase in temperature matters |url=https://www.science.org/doi/10.1126/science.abo1324 |journal=Science |language=en |volume=79 |issue=6627 |pages=78–83 |doi=10.1126/science.abo1324 |pmid=36603094 |bibcode=2023Sci...379...78R |s2cid=255441012 |hdl=10852/108771 |hdl-access=free |access-date=8 January 2023 |archive-date=12 January 2023 |archive-url=https://web.archive.org/web/20230112211316/https://www.science.org/doi/10.1126/science.abo1324 |url-status=live }} Mountain glaciers are even more vulnerable over the longer term. In 2022, another Science paper estimated that almost no mountain glaciers could survive once warming crosses {{convert|2|C-change|F-change}}. Their complete loss is largely inevitable around {{convert|3|C-change|F-change}}. There is even a possibility of complete loss after 2100 at just {{convert|1.5|C-change|F-change}}. This could happen as early as 50 years after the tipping point is crossed, although 200 years is the most likely value, and the maximum is around 1000 years.

Sea ice loss directly contributes only very slightly to global sea level rise. If the melt water from ice floating in the sea was exactly the same as sea water then, according to Archimedes' principle, no rise would occur. However melted sea ice contains less dissolved salt than sea water and is therefore less dense, with a slightly greater volume per unit of mass. If all floating ice shelves and icebergs were to melt sea level would only rise by about {{convert|4|cm|in|frac=2|abbr=on}}.{{cite journal |last1=Noerdlinger |first1=Peter D. |last2=Brower |first2=Kay R. |title=The melting of floating ice raises the ocean level |journal=Geophysical Journal International |date=July 2007 |volume=170 |issue=1 |pages=145–150 |doi=10.1111/j.1365-246X.2007.03472.x |bibcode=2007GeoJI.170..145N |doi-access=free}}

File:Trends-in-land-water-storage-from-GRACE-observations,-April-2002-to-November-2014.jpg observations in gigatons per year, April 2002 to November 2014 (glaciers and ice sheets are excluded).]]

{{See also|Groundwater-related subsidence|}}

Human activity impacts how much water is stored on land. Dams retain large quantities of water, which is stored on land rather than flowing into the sea, though the total quantity stored will vary from time to time. On the other hand, humans extract water from lakes, wetlands and underground reservoirs for drinking and food production. This often causes subsidence. Furthermore, the hydrological cycle is influenced by climate change and deforestation. In the 20th century, these processes had approximately cancelled out each other's impact on sea level rise, but dam building has slowed down and is expected to stay low for the 21st century.{{cite journal |last1=Wada |first1=Yoshihide |last2=Reager |first2=John T. |last3=Chao |first3=Benjamin F. |last4=Wang |first4=Jida |last5=Lo |first5=Min-Hui |last6=Song |first6=Chunqiao |last7=Li |first7=Yuwen |last8=Gardner |first8=Alex S. |title=Recent Changes in Land Water Storage and its Contribution to Sea Level Variations |journal=Surveys in Geophysics |date=15 November 2016 |volume=38 |issue=1 |pages=131–152 |doi=10.1007/s10712-016-9399-6 |pmid=32269399 |pmc=7115037}}{{rp|1155}}

Water redistribution caused by irrigation moving groundwater into the oceans, was estimated at 2,150 GT between 1993 and 2010 - equivalent to a global sea level rise of {{convert|6.24|mm|inches}}, but which could not be directly measured. The net movement of water was also expected to cause caused a drift of Earth's rotational pole by {{convert|78.48|cm|in}}, which was confirmed in 2023.{{cite journal |last1=Seo |first1=Ki-Weon |last2=Ryu |first2=Dongryeol |last3=Eom |first3=Jooyoung |last4=Jeon |first4=Taewhan |last5=Kim |first5=Jae-Seung |last6=Youm |first6=Kookhyoun |last7=Chen |first7=Jianli |last8=Wilson |first8=Clark R. |title=Drift of Earth's Pole Confirms Groundwater Depletion as a Significant Contributor to Global Sea Level Rise 1993–2010 |journal=Geophysical Research Letters |date=15 June 2023 |volume=50 |issue=12 |page=e2023GL103509 |doi=10.1029/2023GL103509 |bibcode=2023GeoRL..5003509S |s2cid=259275991 |doi-access=free |hdl=10397/109234 |hdl-access=free }}

{{Clear}}

{{See also|Coast#Human impacts|l1=Human impacts on coasts|Coastal development hazards|l2=|Coastal erosion|||}}

{{Multiple image|align=left |total_width=450

| image1= 1950- High tide flooding, by year - NOAA tide gauges (U.S.).svg |caption1= High tide flooding, also called tidal flooding, has become much more common in the past seven decades.{{cite web |last1=Sweet |first1=William V. |last2=Dusek |first2=Greg |last3=Obeysekera |first3=Jayantha |last4=Marra |first4=John J. |title=Patterns and Projections of High Tide Flooding Along the U.S. Coastline Using a Common Impact Threshold |url=https://tidesandcurrents.noaa.gov/publications/techrpt86_PaP_of_HTFlooding.pdf |website=tidesandcurrents.NOAA.gov |publisher=National Oceanic and Atmospheric Administration (NOAA) |archive-url=https://web.archive.org/web/20221015221519/https://tidesandcurrents.noaa.gov/publications/techrpt86_PaP_of_HTFlooding.pdf |archive-date=15 October 2022 |page=4 |date=February 2018 |quote=Fig. 2b |url-status=live}}

| image2= 2000- Declared flood disasters - US.svg|caption2= The number of floods declared to be disasters by the Federal Emergency Management Agency (FEMA) has increased, especially since 2010.{{cite news |last1=Flavelle |first1=Christopher |title=America's Flooding Problem |url=https://www.nytimes.com/2024/10/22/briefing/americas-flooding-problem.html |newspaper=The New York Times |date=22 October 2024 |archive-url=https://archive.today/20241022105521/https://www.nytimes.com/2024/10/22/briefing/americas-flooding-problem.html |archive-date=22 October 2024 |url-status=live }}

}}

Sea-level rise has many impacts. They include higher and more frequent high-tide and storm-surge flooding and increased coastal erosion. Other impacts are inhibition of primary production processes, more extensive coastal inundation, and changes in surface water quality and groundwater. These can lead to a greater loss of property and coastal habitats, loss of life during floods and loss of cultural resources. There are also impacts on agriculture and aquaculture. There can also be loss of tourism, recreation, and transport-related functions.{{Cite report|url=https://www.ipcc.ch/site/assets/uploads/2018/03/WGI_TAR_full_report.pdf|title=TAR Climate Change 2001: The Scientific Basis|date=2001|publisher=International Panel on Climate Change, Cambridge University Press|isbn=0521-80767-0|access-date=23 July 2021|archive-date=5 December 2021|archive-url=https://web.archive.org/web/20211205084026/https://www.ipcc.ch/site/assets/uploads/2018/03/WGI_TAR_full_report.pdf|url-status=live}}{{rp|356}} Land use changes such as urbanisation or deforestation of low-lying coastal zones exacerbate coastal flooding impacts. Regions already vulnerable to rising sea level also struggle with coastal flooding. This washes away land and alters the landscape.{{Cite journal|last=Wu|first=Tao|date=October 2021|title=Quantifying coastal flood vulnerability for climate adaptation policy using principal component analysis|journal=Ecological Indicators|language=en|volume=129|page=108006|doi=10.1016/j.ecolind.2021.108006|bibcode=2021EcInd.12908006W|doi-access=free}}

Changes in emissions are likely to have only a small effect on the extent of sea level rise by 2050. So projected sea level rise could put tens of millions of people at risk by then. Scientists estimate that 2050 levels of sea level rise would result in about 150 million people under the water line during high tide. About 300 million would be in places flooded every year. This projection is based on the distribution of population in 2010. It does not take into account the effects of population growth and human migration. These figures are 40 million and 50 million more respectively than the numbers at risk in 2010.{{cite journal |last1=Kulp |first1=Scott A. |last2=Strauss |first2=Benjamin H. |title=New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding |journal=Nature Communications |date=29 October 2019 |volume=10 |issue=1 |page=4844 |doi=10.1038/s41467-019-12808-z |pmid=31664024 |pmc=6820795 |bibcode=2019NatCo..10.4844K}}{{cite news|url=https://www.ecowatch.com/sea-level-rise-predictions-2641159739.html|title=300 Million People Worldwide Could Suffer Yearly Flooding by 2050|last1=Rosane|first1=Olivia|date=October 30, 2019|access-date=31 October 2019|agency=Ecowatch|archive-date=9 December 2019|archive-url=https://web.archive.org/web/20191209224048/https://www.ecowatch.com/sea-level-rise-predictions-2641159739.html|url-status=live}} By 2100, there would be another 40 million people under the water line during high tide if sea level rise remains low. This figure would be 80 million for a high estimate of median sea level rise. Ice sheet processes under the highest emission scenario would result in sea level rise of well over {{convert|1|m|ft|frac=4|spell=in}} by 2100. This could be as much as over {{convert|2|m|ft|frac=2|spell=in}},{{rp|TS-45}} This could result in as many as 520 million additional people ending up under the water line during high tide and 640 million in places flooded every year, compared to the 2010 population distribution.

File:Major cities threatened by sea level rise.png

Over the longer term, coastal areas are particularly vulnerable to rising sea levels. They are also vulnerable to changes in the frequency and intensity of storms, increased precipitation, and rising ocean temperatures. Ten percent of the world's population live in coastal areas that are less than {{Convert|10|m|ft}} above sea level. Two thirds of the world's cities with over five million people are located in these low-lying coastal areas.{{cite journal |last1=McGranahan |first1=Gordon |last2=Balk |first2=Deborah |last3=Anderson |first3=Bridget |title=The rising tide: assessing the risks of climate change and human settlements in low elevation coastal zones |journal=Environment and Urbanization |date=29 June 2016 |volume=19 |issue=1 |pages=17–37 |doi=10.1177/0956247807076960 |s2cid=154588933}} About 600 million people live directly on the coast around the world.{{cite news |last1=Sengupta |first1=Somini |others=Photographer: Chang W. Lee |title=A Crisis Right Now: San Francisco and Manila Face Rising Seas |url=https://www.nytimes.com/interactive/2020/02/13/climate/manila-san-francisco-sea-level-rise.html |access-date=4 March 2020 |work=The New York Times |date=13 February 2020 |archive-date=7 May 2020 |archive-url=https://web.archive.org/web/20200507112647/https://www.nytimes.com/interactive/2020/02/13/climate/manila-san-francisco-sea-level-rise.html |url-status=live }} Cities such as Miami, Rio de Janeiro, Osaka and Shanghai will be especially vulnerable later in the century under warming of 3 °C (5.4 °F). This is close to the current trajectory.{{Cite news|last1=Holder|first1=Josh|last2=Kommenda|first2=Niko|last3=Watts|first3=Jonathan|date=3 November 2017|title=The three-degree world: cities that will be drowned by global warming|work=The Guardian|url=https://www.theguardian.com/cities/ng-interactive/2017/nov/03/three-degree-world-cities-drowned-global-warming|access-date=2018-12-28|archive-date=2020-01-03|archive-url=https://web.archive.org/web/20200103081510/https://www.theguardian.com/cities/ng-interactive/2017/nov/03/three-degree-world-cities-drowned-global-warming|url-status=live}} LiDAR-based research had established in 2021 that 267 million people worldwide lived on land less than {{cvt|2|m|ft|frac=2}} above sea level. With a {{cvt|1|m|ft|frac=2}} sea level rise and zero population growth, that could increase to 410 million people.{{Cite web|last=Storer|first=Rhi|date=2021-06-29|title=Up to 410 million people at risk from sea level rises – study|url=http://www.theguardian.com/environment/2021/jun/29/risk-from-sea-level-rises-unless-emissions-reduced|access-date=2021-07-01|website=The Guardian|language=en|archive-date=2023-05-18|archive-url=https://web.archive.org/web/20230518021028/https://www.theguardian.com/environment/2021/jun/29/risk-from-sea-level-rises-unless-emissions-reduced|url-status=live}}{{Cite journal|last1=Hooijer|first1=A.|last2=Vernimmen|first2=R.|date=2021-06-29|title=Global LiDAR land elevation data reveal greatest sea-level rise vulnerability in the tropics|journal=Nature Communications|language=en|volume=12|issue=1|page=3592|doi=10.1038/s41467-021-23810-9|pmid=34188026|pmc=8242013|bibcode=2021NatCo..12.3592H|issn=2041-1723}}

Potential disruption of sea trade and migrations could impact people living further inland. United Nations Secretary-General António Guterres warned in 2023 that sea level rise risks causing human migrations on a "biblical scale".{{Cite news|last1=Carrington|first1=Damian|date=14 February 2023|title=Rising seas threaten 'mass exodus on a biblical scale', UN chief warns|work=The Guardian|url=https://www.theguardian.com/environment/2023/feb/14/rising-seas-threaten-mass-exodus-on-a-biblical-scale-un-chief-warns|access-date=2023-02-25|archive-date=2023-07-06|archive-url=https://web.archive.org/web/20230706040859/https://www.theguardian.com/environment/2023/feb/14/rising-seas-threaten-mass-exodus-on-a-biblical-scale-un-chief-warns|url-status=live}} Sea level rise will inevitably affect ports, but there is limited research on this. There is insufficient knowledge about the investments necessary to protect ports currently in use. This includes protecting current facilities before it becomes more reasonable to build new ports elsewhere.{{Cite journal|last1=Xia|first1=Wenyi|last2=Lindsey|first2=Robin|date=October 2021|title=Port adaptation to climate change and capacity investments under uncertainty|url=https://linkinghub.elsevier.com/retrieve/pii/S0191261521001600|journal=Transportation Research Part B: Methodological|language=en|volume=152|pages=180–204|doi=10.1016/j.trb.2021.08.009|bibcode=2021TRPB..152..180X|s2cid=239647501|access-date=2021-12-17|archive-date=2023-01-02|archive-url=https://web.archive.org/web/20230102220943/https://linkinghub.elsevier.com/retrieve/pii/S0191261521001600|url-status=live}}{{Cite web|title=Chapter 4: Sea Level Rise and Implications for Low-Lying Islands, Coasts and Communities — Special Report on the Ocean and Cryosphere in a Changing Climate|url=https://www.ipcc.ch/srocc/chapter/chapter-4-sea-level-rise-and-implications-for-low-lying-islands-coasts-and-communities/|access-date=2021-12-17|archive-date=2023-09-02|archive-url=https://web.archive.org/web/20230902021918/https://www.ipcc.ch/srocc/chapter/chapter-4-sea-level-rise-and-implications-for-low-lying-islands-coasts-and-communities/|url-status=live}} Some coastal regions are rich agricultural lands. Their loss to the sea could cause food shortages. This is a particularly acute issue for river deltas such as Nile Delta in Egypt and Red River and Mekong Deltas in Vietnam. Saltwater intrusion into the soil and irrigation water has a disproportionate effect on them.{{Cite web |last=Nagothu |first=Udaya Sekhar |date=2017-01-18 |title=Food security threatened by sea-level rise |url=https://www.nibio.no/nyheter/food-security-threatened-by-sea-level-rise |access-date=2018-10-21 |publisher=Nibio |archive-date=2020-07-31 |archive-url=https://web.archive.org/web/20200731214557/https://www.nibio.no/nyheter/food-security-threatened-by-sea-level-rise |url-status=live }}

In 2025, the World Economic Forum said that rising sea levels caused by climate change were impacting 1 billion people worldwide.{{Cite web |last1=Masterson |first1=Victoria |last2=Hall |first2=Stephen |last3=North |first3=Madeleine |date=25 March 2025 |title=Sea level rise: Everything you need to know |url=https://www.weforum.org/stories/2025/03/rising-sea-levels-global-threat/ |archive-url=https://web.archive.org/web/20250407143406/https://www.weforum.org/stories/2025/03/rising-sea-levels-global-threat/ |archive-date=7 April 2025 |website=World Economic Forum}}

{{See also|Extinction risk from climate change}}

File:Bramble-cay-melomys.jpg, the first known mammal species to go extinct due to sea level rise.]]

Flooding and soil/water salinization threaten the habitats of coastal plants, birds, and freshwater/estuarine fish when seawater reaches inland.{{Cite web|url=https://www.nationalgeographic.com/environment/global-warming/sea-level-rise/|archive-url=https://web.archive.org/web/20170117004107/http://www.nationalgeographic.com/environment/global-warming/sea-level-rise/|archive-date=January 17, 2017|title=Sea Level Rise|date=January 13, 2017|website=National Geographic}} When coastal forest areas become inundated with saltwater to the point no trees can survive the resulting habitats are called ghost forests.{{cite web|url=http://grist.org/article/ghost-forests-are-eerie-evidence-of-rising-seas/|title=Ghost forests are eerie evidence of rising seas|date=18 September 2016|website=Grist.org|access-date=2017-05-17|archive-date=2023-03-29|archive-url=https://web.archive.org/web/20230329190328/https://grist.org/article/ghost-forests-are-eerie-evidence-of-rising-seas/|url-status=live}}{{cite web|url=http://e360.yale.edu/features/ghost_forest_rising_sea_levels_killing_coastal_woodlands|title=How Rising Seas Are Killing Southern U.S. Woodlands - Yale E360|website=e360.yale.edu|access-date=2017-05-17|archive-date=2023-08-19|archive-url=https://web.archive.org/web/20230819015407/https://e360.yale.edu/features/ghost_forest_rising_sea_levels_killing_coastal_woodlands|url-status=live}} Starting around 2050, some nesting sites in Florida, Cuba, Ecuador and the island of Sint Eustatius for leatherback, loggerhead, hawksbill, green and olive ridley turtles are expected to be flooded. The proportion will increase over time.{{Cite journal |last1=Rivas |first1=Marga L. |last2=Rodríguez-Caballero |first2=Emilio |last3=Esteban |first3=Nicole |last4=Carpio |first4=Antonio J. |last5=Barrera-Vilarmau |first5=Barbara |last6=Fuentes |first6=Mariana M. P. B. |last7=Robertson |first7=Katharine |last8=Azanza |first8=Julia |last9=León |first9=Yolanda |last10=Ortega |first10=Zaida |date=2023-04-20 |title=Uncertain future for global sea turtle populations in face of sea level rise |journal=Scientific Reports |language=en |volume=13 |issue=1 |page=5277 |doi=10.1038/s41598-023-31467-1 |pmid=37081050 |pmc=10119306 |bibcode=2023NatSR..13.5277R |issn=2045-2322}} In 2016, Bramble Cay islet in the Great Barrier Reef was inundated. This flooded the habitat of a rodent named Bramble Cay melomys.{{cite web|url=http://www.australiangeographic.com.au/news/2016/06/extinct-bramble-cay-melomys|title=Extinct: Bramble Cay melomys|last=Smith|first=Lauren|date=2016-06-15|website=Australian Geographic|access-date=2016-06-17|archive-date=2020-08-17|archive-url=https://web.archive.org/web/20200817201358/https://www.australiangeographic.com.au/news/2016/06/extinct-bramble-cay-melomys/|url-status=live}} It was officially declared extinct in 2019.{{Cite web|url=https://www.smh.com.au/environment/climate-change/our-little-brown-rat-first-climate-change-caused-mammal-extinction-20190219-p50yry.html|title='Our little brown rat': first climate change-caused mammal extinction|last=Hannam|first=Peter|date=2019-02-19|website=The Sydney Morning Herald|language=en|access-date=2019-06-25|archive-date=2020-06-17|archive-url=https://web.archive.org/web/20200617054703/https://www.smh.com.au/environment/climate-change/our-little-brown-rat-first-climate-change-caused-mammal-extinction-20190219-p50yry.html|url-status=live}}

File:Mangroves.jpg

Some ecosystems can move inland with the high-water mark. But natural or artificial barriers prevent many from migrating. This coastal narrowing is sometimes called 'coastal squeeze' when it involves human-made barriers. It could result in the loss of habitats such as mudflats and tidal marshes.{{Cite web|url=http://datazone.birdlife.org/sea-level-rise-poses-a-major-threat-to-coastal-ecosystems-and-the-biota-they-support|title=Sea level rise poses a major threat to coastal ecosystems and the biota they support|date=2015|website=birdlife.org|publisher=Birdlife International|access-date=2018-09-06|archive-date=2019-05-20|archive-url=https://web.archive.org/web/20190520130929/http://datazone.birdlife.org/sea-level-rise-poses-a-major-threat-to-coastal-ecosystems-and-the-biota-they-support|url-status=live}}{{cite journal |last1=Pontee |first1=Nigel |title=Defining coastal squeeze: A discussion |journal=Ocean & Coastal Management |date=November 2013 |volume=84 |pages=204–207 |doi=10.1016/j.ocecoaman.2013.07.010 |bibcode=2013OCM....84..204P}} Mangrove ecosystems on the mudflats of tropical coasts nurture high biodiversity. They are particularly vulnerable due to mangrove plants' reliance on breathing roots or pneumatophores. These will be submerged if the rate is too rapid for them to migrate upward. This would result in the loss of an ecosystem.{{Cite web|url=https://www.nrc.govt.nz/for-schools/school-information-packs/mangroves/|title=Mangroves – Northland Regional Council|website=www.nrc.govt.nz|access-date=2020-10-28|archive-date=2023-06-02|archive-url=https://web.archive.org/web/20230602174756/https://www.nrc.govt.nz/for-schools/school-information-packs/mangroves|url-status=live}}{{cite journal |last1=Kumara |first1=M. P. |last2=Jayatissa |first2=L. P. |last3=Krauss |first3=K. W. |last4=Phillips |first4=D. H. |last5=Huxham |first5=M. |title=High mangrove density enhances surface accretion, surface elevation change, and tree survival in coastal areas susceptible to sea-level rise |journal=Oecologia |pages=545–553 |date=2010|volume=164 |issue=2 |doi=10.1007/s00442-010-1705-2 |jstor=40864709 |pmid=20593198 |bibcode=2010Oecol.164..545K |s2cid=6929383}}{{cite journal |last1=Krauss |first1=Ken W. |last2=McKee |first2=Karen L. |last3=Lovelock |first3=Catherine E. |last4=Cahoon |first4=Donald R. |last5=Saintilan |first5=Neil |last6=Reef |first6=Ruth |last7=Chen |first7=Luzhen |title=How mangrove forests adjust to rising sea level |journal=New Phytologist |date=April 2014 |volume=202 |issue=1 |pages=19–34 |doi=10.1111/nph.12605 |pmid=24251960 |bibcode=2014NewPh.202...19K |url=https://digitalcommons.unl.edu/usgsstaffpub/986 |access-date=2019-10-31 |archive-date=2020-08-06 |archive-url=https://web.archive.org/web/20200806191108/https://digitalcommons.unl.edu/usgsstaffpub/986/ |url-status=live }}{{cite journal|last1=Soares|first1=M.L.G.|date=2009|title=A Conceptual Model for the Responses of Mangrove Forests to Sea Level Rise|journal=Journal of Coastal Research|pages=267–271|jstor=25737579}} Both mangroves and tidal marshes protect against storm surges, waves and tsunamis, so their loss makes the effects of sea level rise worse.{{cite journal |last1=Crosby |first1=Sarah C. |last2=Sax |first2=Dov F. |last3=Palmer |first3=Megan E. |last4=Booth |first4=Harriet S. |last5=Deegan |first5=Linda A. |last6=Bertness |first6=Mark D. |last7=Leslie |first7=Heather M. |title=Salt marsh persistence is threatened by predicted sea-level rise |journal=Estuarine, Coastal and Shelf Science |date=November 2016 |volume=181 |pages=93–99 |doi=10.1016/j.ecss.2016.08.018 |bibcode=2016ECSS..181...93C |doi-access=free}}{{cite web|url=https://www.nature.org/media/oceansandcoasts/mangroves-for-coastal-defence.pdf|title=Mangroves for coastal defence. Guidelines for coastal managers & policy makers|author1=Spalding, M.|author2=McIvor, A.|date=2014|publisher=Wetlands International and The Nature Conservancy|author3=Tonneijck, F.H.|author4=Tol, S.|author5=van Eijk, P.|access-date=2018-09-07|archive-date=2019-11-12|archive-url=https://web.archive.org/web/20191112063642/http://www.nature.org/media/oceansandcoasts/mangroves-for-coastal-defence.pdf|url-status=live}} Human activities such as dam building may restrict sediment supplies to wetlands. This would prevent natural adaptation processes. The loss of some tidal marshes is unavoidable as a consequence.{{cite journal |last1=Weston |first1=Nathaniel B. |title=Declining Sediments and Rising Seas: an Unfortunate Convergence for Tidal Wetlands |journal=Estuaries and Coasts |date=16 July 2013 |volume=37 |issue=1 |pages=1–23 |doi=10.1007/s12237-013-9654-8 |s2cid=128615335}}

Corals are important for bird and fish life. They need to grow vertically to remain close to the sea surface in order to get enough energy from sunlight. The corals have so far been able to keep up the vertical growth with the rising seas, but might not be able to do so in the future.{{Cite book|title=Climate Change 2014: Impacts, Adaptation, and Vulnerability.|last1=Wong|first1=Poh Poh|last2=Losado|first2=I.J.|last3=Gattuso|first3=J.-P.|last4=Hinkel|first4=Jochen|publisher=Cambridge University Press|year=2014|location=New York|chapter=Coastal Systems and Low-Lying Areas|chapter-url=http://www.ipcc.ch/pdf/assessment-report/ar5/wg2/WGIIAR5-Chap5_FINAL.pdf|access-date=2018-10-07|archive-date=2018-11-23|archive-url=https://web.archive.org/web/20181123125554/http://www.ipcc.ch/pdf/assessment-report/ar5/wg2/WGIIAR5-Chap5_FINAL.pdf}}

{{Further|Relative sea level|Sinking cities}}

File:Ohenhen 2023 EC subsidence.png is one example.{{Cite journal |last1=Ohenhen |first1=Leonard O. |last2=Shirzaei |first2=Manoochehr |last3=Ojha |first3=Chandrakanta |last4=Kirwan |first4=Matthew L. |date=11 April 2023 |title=Hidden vulnerability of US Atlantic coast to sea-level rise due to vertical land motion |journal=Nature Communications |volume=14 |issue=1 |page=2038 |bibcode=2023NatCo..14.2038O |doi=10.1038/s41467-023-37853-7 |pmc=10090057 |pmid=37041168}}]]

When a glacier or ice sheet melts, it loses mass. This reduces its gravitational pull. In some places near current and former glaciers and ice sheets, this has caused water levels to drop. At the same time water levels will increase more than average further away from the ice sheet. Thus ice loss in Greenland affects regional sea level differently than the equivalent loss in Antarctica.{{cite journal |last1=Rovere |first1=Alessio |last2=Stocchi |first2=Paolo |last3=Vacchi |first3=Matteo |date=2 August 2016 |title=Eustatic and Relative Sea Level Changes |journal=Current Climate Change Reports |volume=2 |issue=4 |pages=221–231 |bibcode=2016CCCR....2..221R |doi=10.1007/s40641-016-0045-7 |s2cid=131866367 |doi-access=free}} On the other hand, the Atlantic is warming at a faster pace than the Pacific. This has consequences for Europe and the U.S. East Coast. The East Coast sea level is rising at 3–4 times the global average.{{cite news |year=2016 |title=Why the U.S. East Coast could be a major 'hotspot' for rising seas |url=https://www.washingtonpost.com/news/energy-environment/wp/2016/02/01/why-the-u-s-east-coast-could-be-a-major-hotspot-for-sea-level-rise/ |url-status=live |archive-url=https://web.archive.org/web/20200331080306/https://www.washingtonpost.com/news/energy-environment/wp/2016/02/01/why-the-u-s-east-coast-could-be-a-major-hotspot-for-sea-level-rise/ |archive-date=2020-03-31 |access-date=2016-02-04 |newspaper=The Washington Post}} Scientists have linked extreme regional sea level rise on the US Northeast Coast to the downturn of the Atlantic meridional overturning circulation (AMOC).{{cite news |last1=Yin |first1=Jianjun |last2=Griffies |first2=Stephen |name-list-style=amp |date=March 25, 2015 |title=Extreme sea level rise event linked to AMOC downturn |url=https://usclivar.org/research-highlights/extreme-sea-level-rise-event-linked-amoc-downturn |url-status=live |archive-url=https://web.archive.org/web/20230127023140/https://usclivar.org/research-highlights/extreme-sea-level-rise-event-linked-amoc-downturn |archive-date=January 27, 2023 |access-date=November 23, 2021 |publisher=CLIVAR}}

Many ports, urban conglomerations, and agricultural regions stand on river deltas. Here land subsidence contributes to much higher relative sea level rise. Unsustainable extraction of groundwater and oil and gas is one cause. Levees and other flood management practices are another. They prevent sediments from accumulating. These would otherwise compensate for the natural settling of deltaic soils.{{Cite journal |last1=Tessler |first1=Z. D. |last2=Vörösmarty |first2=C. J. |last3=Grossberg |first3=M. |last4=Gladkova |first4=I. |last5=Aizenman |first5=H. |last6=Syvitski |first6=J. P. M. |last7=Foufoula-Georgiou |first7=E. |date=2015-08-07 |title=Profiling risk and sustainability in coastal deltas of the world |url=https://cloudfront.escholarship.org/dist/prd/content/qt46n8t5mp/qt46n8t5mp.pdf |url-status=live |journal=Science |volume=349 |issue=6248 |pages=638–643 |bibcode=2015Sci...349..638T |doi=10.1126/science.aab3574 |issn=0036-8075 |pmid=26250684 |s2cid=12295500 |archive-url=https://web.archive.org/web/20180724000157/https://cloudfront.escholarship.org/dist/prd/content/qt46n8t5mp/qt46n8t5mp.pdf |archive-date=2018-07-24 |access-date=2019-09-02}}{{rp|638}}{{cite book |last=Bucx |first=Tom |title=Comparative assessment of the vulnerability and resilience of 10 deltas: synthesis report |date=2010 |publisher=Deltares |isbn=978-94-90070-39-7 |publication-place=Delft, Netherlands |oclc=768078077}}{{rp|88}}

Estimates for total human-caused subsidence in the Rhine-Meuse-Scheldt delta (Netherlands) are {{Cvt|3-4|m|ft|0}}, over {{Cvt|3|m|ft|0}} in urban areas of the Mississippi River Delta (New Orleans), and over {{Cvt|9|m|ft|0}} in the Sacramento–San Joaquin River Delta.{{rp|81–90}} On the other hand, relative sea level around the Hudson Bay in Canada and the northern Baltic Sea is falling due to post-glacial isostatic rebound.{{Cite journal |last1=Cazenave |first1=Anny |author-link=Anny Cazenave |last2=Nicholls |first2=Robert J. |date=2010 |title=Sea-Level Rise and Its Impact on Coastal Zones |journal=Science |volume=328 |issue=5985 |pages=1517–1520 |bibcode=2010Sci...328.1517N |doi=10.1126/science.1185782 |issn=0036-8075 |pmid=20558707 |s2cid=199393735}}

{{further|Climate change adaptation|coastal management}}

File:Oosterscheldekering-pohled.jpg, the largest barrier of the Dutch Delta Works.]]

Cutting greenhouse gas emissions can slow and stabilize the rate of sea level rise after 2050. This would greatly reduce its costs and damages, but cannot stop it outright. So climate change adaptation to sea level rise is inevitable.Cooley, S., D. Schoeman, L. Bopp, P. Boyd, S. Donner, D.Y. Ghebrehiwet, S.-I. Ito, W. Kiessling, P. Martinetto, E. Ojea, M.-F. Racault, B. Rost, and M. Skern-Mauritzen, 2022: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_FinalDraft_Chapter03.pdf Ocean and Coastal Ecosystems and their Services (Chapter 3)] {{Webarchive|url=https://web.archive.org/web/20230712212111/https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_FinalDraft_Chapter03.pdf |date=2023-07-12 }}. In: Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [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. In Press. - Cross-Chapter Box SLR: Sea Level Rise{{rp||page=3–127}} The simplest approach is to stop development in vulnerable areas and ultimately move people and infrastructure away from them. Such retreat from sea level rise often results in the loss of livelihoods. The displacement of newly impoverished people could burden their new homes and accelerate social tensions.{{Cite journal |last1=Dasgupta |first1=Susmita |last2=Wheeler |first2=David |last3=Bandyopadhyay |first3=Sunando |last4=Ghosh |first4=Santadas |last5=Roy |first5=Utpal |date=February 2022 |title=Coastal dilemma: Climate change, public assistance and population displacement |url=https://linkinghub.elsevier.com/retrieve/pii/S0305750X21003223 |journal=World Development |language=en |volume=150 |page=105707 |doi=10.1016/j.worlddev.2021.105707 |issn=0305-750X |s2cid=244585347 |access-date=2021-12-17 |archive-date=2022-11-10 |archive-url=https://web.archive.org/web/20221110212423/https://linkinghub.elsevier.com/retrieve/pii/S0305750X21003223 |url-status=live }}

It is possible to avoid or at least delay the retreat from sea level rise with enhanced protections. These include dams, levees or improved natural defenses. Other options include updating building standards to reduce damage from floods, addition of storm water valves to address more frequent and severe flooding at high tide,{{cite web |date=2 May 2016 |title=Climate Adaptation and Sea Level Rise |url=https://www.epa.gov/arc-x/climate-adaptation-and-sea-level-rise |website=US EPA, Climate Change Adaptation Resource Center (ARC-X) |language=en |access-date=13 March 2020 |archive-date=8 May 2020 |archive-url=https://web.archive.org/web/20200508055630/https://www.epa.gov/arc-x/climate-adaptation-and-sea-level-rise |url-status=live }} or cultivating crops more tolerant of saltwater in the soil, even at an increased cost.{{cite journal |last1=Fletcher |first1=Cameron |date=2013 |title=Costs and coasts: an empirical assessment of physical and institutional climate adaptation pathways |url=https://apo.org.au/node/34006 |journal=Apo |access-date=2019-10-31 |archive-date=2020-07-31 |archive-url=https://web.archive.org/web/20200731224002/https://apo.org.au/node/34006 |url-status=live }} These options divide into hard and soft adaptation. Hard adaptation generally involves large-scale changes to human societies and ecological systems. It often includes the construction of capital-intensive infrastructure. Soft adaptation involves strengthening natural defenses and local community adaptation. This usually involves simple, modular and locally owned technology. The two types of adaptation may be complementary or mutually exclusive.{{Cite journal |last=Sovacool |first=Benjamin K. |date=2011 |title=Hard and soft paths for climate change adaptation |url=http://www.adaptation-undp.org/sites/default/files/downloads/sovacool-cp-hardsoft.pdf |url-status=dead |journal=Climate Policy |volume=11 |issue=4 |pages=1177–1183 |bibcode=2011CliPo..11.1177S |doi=10.1080/14693062.2011.579315 |s2cid=153384574 |archive-url=https://web.archive.org/web/20200710010054/https://www.adaptation-undp.org/sites/default/files/downloads/sovacool-cp-hardsoft.pdf |archive-date=2020-07-10 |access-date=2018-09-02}} Adaptation options often require significant investment. But the costs of doing nothing are far greater. One example would involve adaptation against flooding. Effective adaptation measures could reduce future annual costs of flooding in 136 of the world's largest coastal cities from $1 trillion by 2050 without adaptation to a little over $60 billion annually. The cost would be $50 billion per year.{{cite web |date=18 August 2013 |title=Coastal cities face rising risk of flood losses, study says |url=https://phys.org/news/2013-08-coastal-cities-losses.html |access-date=17 April 2023 |publisher=Phys.org |archive-date=22 April 2023 |archive-url=https://web.archive.org/web/20230422005012/https://phys.org/news/2013-08-coastal-cities-losses.html |url-status=live }}{{cite journal |last1=Hallegatte |first1=Stephane |last2=Green |first2=Colin |last3=Nicholls |first3=Robert J. |last4=Corfee-Morlot |first4=Jan |date=18 August 2013 |title=Future flood losses in major coastal cities |url=https://www.nature.com/articles/nclimate1979 |journal=Nature Climate Change |language=en |volume=3 |issue=9 |pages=802–806 |bibcode=2013NatCC...3..802H |doi=10.1038/nclimate1979 |access-date=17 April 2023 |archive-date=26 August 2023 |archive-url=https://web.archive.org/web/20230826224546/https://www.nature.com/articles/nclimate1979 |url-status=live }} Some experts argue that retreat from the coast would have a lower impact on the GDP of India and Southeast Asia then attempting to protect every coastline, in the case of very high sea level rise.{{cite journal |last1=Bachner |first1=Gabriel |last2=Lincke |first2=Daniel |last3=Hinkel |first3=Jochen |date=29 September 2022 |title=The macroeconomic effects of adapting to high-end sea-level rise via protection and migration |journal=Nature Communications |language=en |volume=13 |issue=1 |page=5705 |bibcode=2022NatCo..13.5705B |doi=10.1038/s41467-022-33043-z |pmc=9522673 |pmid=36175422}}

File:Hurk_2022_UK_SLR_adaptation.jpg.]]

To be successful, adaptation must anticipate sea level rise well ahead of time. As of 2023, the global state of adaptation planning is mixed. A survey of 253 planners from 49 countries found that 98% are aware of sea level rise projections, but 26% have not yet formally integrated them into their policy documents. Only around a third of respondents from Asian and South American countries have done so. This compares with 50% in Africa, and over 75% in Europe, Australasia and North America. Some 56% of all surveyed planners have plans which account for 2050 and 2100 sea level rise. But 53% use only a single projection rather than a range of two or three projections. Just 14% use four projections, including the one for "extreme" or "high-end" sea level rise.{{cite journal |last1=Hirschfeld |first1=Daniella |last2=Behar |first2=David |last3=Nicholls |first3=Robert J. |last4=Cahill |first4=Niamh |last5=James |first5=Thomas |last6=Horton |first6=Benjamin P. |last7=Portman |first7=Michelle E. |last8=Bell |first8=Rob |last9=Campo |first9=Matthew |last10=Esteban |first10=Miguel |last11=Goble |first11=Bronwyn |last12=Rahman |first12=Munsur |last13=Appeaning Addo |first13=Kwasi |last14=Chundeli |first14=Faiz Ahmed |last15=Aunger |first15=Monique |date=3 April 2023 |title=Global survey shows planners use widely varying sea-level rise projections for coastal adaptation |journal=Communications Earth & Environment |language=en |volume=4 |issue=1 |page=102 |bibcode=2023ComEE...4..102H |doi=10.1038/s43247-023-00703-x |doi-access=free |last16=Babitsky |first16=Orly |last17=Beal |first17=Anders |last18=Boyle |first18=Ray |last19=Fang |first19=Jiayi |last20=Gohar |first20=Amir |last21=Hanson |first21=Susan |last22=Karamesines |first22=Saul |last23=Kim |first23=M. J. |last24=Lohmann |first24=Hilary |last25=McInnes |first25=Kathy |last26=Mimura |first26=Nobuo |last27=Ramsay |first27=Doug |last28=Wenger |first28=Landis |last29=Yokoki |first29=Hiromune|pmid=38665203 |pmc=11041751}} 50x50px Text and images are available under a Creative Commons Attribution 4.0 International License. Another study found that over 75% of regional sea level rise assessments from the West and Northeastern United States included at least three estimates. These are usually RCP2.6, RCP4.5 and RCP8.5, and sometimes include extreme scenarios. But 88% of projections from the American South had only a single estimate. Similarly, no assessment from the South went beyond 2100. By contrast 14 assessments from the West went up to 2150, and three from the Northeast went to 2200. 56% of all localities were also found to underestimate the upper end of sea level rise relative to IPCC Sixth Assessment Report.{{cite journal |last1=Garner |first1=Andra J. |last2=Sosa |first2=Sarah E. |last3=Tan |first3=Fangyi |last4=Tan |first4=Christabel Wan Jie |last5=Garner |first5=Gregory G. |last6=Horton |first6=Benjamin P. |date=23 January 2023 |title=Evaluating Knowledge Gaps in Sea-Level Rise Assessments From the United States |journal=Earth's Future |volume=11 |issue=2 |pages=e2022EF003187 |bibcode=2023EaFut..1103187G |doi=10.1029/2022EF003187 |s2cid=256227421|doi-access=free }}

{{Further|Climate change in the Middle East and North Africa#Sea level rise}}

File:ANKOMAH 20221122-009.jpg, a suburb of Accra. Sunny day flooding caused by sea level rise, increases coastal erosion that destroys housing, infrastructure and natural ecosystems. A number of communities in Coastal Ghana are already experiencing the changing tides.]]

In Africa, future population growth amplifies risks from sea level rise. Some 54.2 million people lived in the highly exposed low elevation coastal zones (LECZ) around 2000. This number will effectively double to around 110 million people by 2030, and then reach 185 to 230 million people by 2060. By then, the average regional sea level rise will be around 21 cm, with little difference from climate change scenarios. By 2100, Egypt, Mozambique and Tanzania are likely to have the largest number of people affected by annual flooding amongst all African countries. And under RCP8.5, 10 important cultural sites would be at risk of flooding and erosion by the end of the century.

In the near term, some of the largest displacement is projected to occur in the East Africa region. At least 750,000 people there are likely to be displaced from the coasts between 2020 and 2050. By 2050, 12 major African cities would collectively sustain cumulative damages of US$65 billion for the "moderate" climate change scenario RCP4.5 and between US$86.5 billion to US$137.5 billion on average: in the worst case, these damages could effectively triple. In all of these estimates, around half of the damages would occur in the Egyptian city of Alexandria. Hundreds of thousands of people in its low-lying areas may already need relocation in the coming decade.{{cite news|url=https://www.theguardian.com/global-development/2018/aug/29/alexandria-little-venice-egypt-climate-change-frontline|title=Houses claimed by the canal: life on Egypt's climate change frontline|last=Michaelson|first=Ruth|date=25 August 2018|work=The Guardian|access-date=30 August 2018|archive-date=1 August 2020|archive-url=https://web.archive.org/web/20200801005257/https://www.theguardian.com/global-development/2018/aug/29/alexandria-little-venice-egypt-climate-change-frontline|url-status=live}} Across sub-Saharan Africa as a whole, damage from sea level rise could reach 2–4% of GDP by 2050, although this depends on the extent of future economic growth and climate change adaptation.

{{Further|Climate change in Asia#Sea level rise}}

File:20091011松川浦.jpg, located in Fukushima Prefecture of Honshu Island]]

File:Urban-Rural Population and Land Area Estimates, v2, 2010 Bangladesh (13873798283).jpg

Asia has the largest population at risk from sea level due to its dense coastal populations. As of 2022, some 63 million people in East and South Asia were already at risk from a 100-year flood. This is largely due to inadequate coastal protection in many countries. Bangladesh, China, India, Indonesia, Japan, Pakistan, the Philippines, Thailand and Vietnam alone account for 70% of people exposed to sea level rise during the 21st century.{{Cite journal|last=McLeman|first=Robert|date=2018|title=Migration and displacement risks due to mean sea-level rise|journal=Bulletin of the Atomic Scientists|volume=74|issue=3|pages=148–154|doi=10.1080/00963402.2018.1461951|issn=0096-3402|bibcode=2018BuAtS..74c.148M|s2cid=150179939}} Sea level rise in Bangladesh is likely to displace 0.9–2.1 million people by 2050. It may also force the relocation of up to one third of power plants as early as 2030, and many of the remaining plants would have to deal with the increased salinity of their cooling water.{{cite journal |last1=De Lellis |first1=Pietro |last2=Marín |first2=Manuel Ruiz |last3=Porfiri |first3=Maurizio |date=29 March 2021 |title=Modeling Human Migration Under Environmental Change: A Case Study of the Effect of Sea Level Rise in Bangladesh |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020EF001931 |journal=Earth's Future |volume=9 |issue=4 |pages=e2020EF001931 |doi=10.1029/2020EF001931 |bibcode=2021EaFut...901931D |hdl=10317/13078 |s2cid=233626963 |access-date=27 October 2022 |archive-date=27 October 2022 |archive-url=https://web.archive.org/web/20221027180934/https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020EF001931 |url-status=live }} Nations like Bangladesh, Vietnam and China with extensive rice production on the coast are already seeing adverse impacts from saltwater intrusion.{{Cite web|url=http://www.fao.org/nr/climpag/pub/EIre0047_en.asp|title=Potential Impacts of Sea-Level Rise on Populations and Agriculture|website=www.fao.org|access-date=2018-10-21|archive-date=2020-04-18|archive-url=https://web.archive.org/web/20200418035608/http://www.fao.org/nr/climpag/pub/eire0047_en.asp}}

Modelling results predict that Asia will suffer direct economic damages of US$167.6 billion at 0.47 meters of sea level rise. This rises to US$272.3 billion at 1.12 meters and US$338.1 billion at 1.75 meters. There is an additional indirect impact of US$8.5, 24 or 15 billion from population displacement at those levels. China, India, the Republic of Korea, Japan, Indonesia and Russia experience the largest economic losses.Shaw, R., Y. Luo, T. S. Cheong, S. Abdul Halim, S. Chaturvedi, M. Hashizume, G. E. Insarov, Y. Ishikawa, M. Jafari, A. Kitoh, J. Pulhin, C. Singh, K. Vasant, and Z. Zhang, 2022: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter10.pdf Chapter 10: Asia] {{Webarchive|url=https://web.archive.org/web/20230412072953/https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter10.pdf |date=2023-04-12 }}. In [https://www.ipcc.ch/report/ar6/wg2/ Climate Change 2022: Impacts, Adaptation and Vulnerability] {{Webarchive|url=https://web.archive.org/web/20220228114918/https://www.ipcc.ch/report/ar6/wg2/ |date=2022-02-28 }} [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, UK and New York, US, pp. 1457–1579. {{doi|10.1017/9781009325844.012}}. Out of the 20 coastal cities expected to see the highest flood losses by 2050, 13 are in Asia. Nine of these are the so-called sinking cities, where subsidence (typically caused by unsustainable groundwater extraction in the past) would compound sea level rise. These are Bangkok, Guangzhou, Ho Chi Minh City, Jakarta, Kolkata, Nagoya, Tianjin, Xiamen and Zhanjiang.{{Cite journal|last1=Erkens|first1=G.|last2=Bucx|first2=T.|last3=Dam|first3=R.|last4=de Lange|first4=G.|last5=Lambert|first5=J.|date=2015-11-12|title=Sinking coastal cities|url=https://piahs.copernicus.org/articles/372/189/2015/|journal=Proceedings of the International Association of Hydrological Sciences|language=en|volume=372|pages=189–198|doi=10.5194/piahs-372-189-2015|bibcode=2015PIAHS.372..189E|issn=2199-899X|doi-access=free|access-date=2021-02-03|archive-date=2023-03-11|archive-url=https://web.archive.org/web/20230311121820/https://piahs.copernicus.org/articles/372/189/2015/|url-status=live}}

By 2050, Guangzhou would see 0.2 meters of sea level rise and estimated annual economic losses of US$254 million – the highest in the world. In Shanghai, coastal inundation amounts to about 0.03% of local GDP, yet would increase to 0.8% by 2100 even under the "moderate" RCP4.5 scenario in the absence of adaptation. The city of Jakarta is sinking so much (up to {{cvt|28|cm|in|frac=2}} per year between 1982 and 2010 in some areas{{cite journal |last1=Abidin |first1=Hasanuddin Z. |last2=Andreas |first2=Heri |last3=Gumilar |first3=Irwan |last4=Fukuda |first4=Yoichi |last5=Pohan |first5=Yusuf E. |last6=Deguchi |first6=T. |title=Land subsidence of Jakarta (Indonesia) and its relation with urban development |journal=Natural Hazards |date=11 June 2011 |volume=59 |issue=3 |pages=1753–1771 |doi=10.1007/s11069-011-9866-9 |bibcode=2011NatHa..59.1753A |s2cid=129557182}}) that in 2019, the government had committed to relocate the capital of Indonesia to another city.{{Cite news|url=https://www.washingtonpost.com/opinions/2019/05/03/seas-rise-indonesia-is-moving-its-capital-city-other-cities-should-take-note/|title=As seas rise, Indonesia is moving its capital city. Other cities should take note.|last=Englander|first=John|date=3 May 2019|newspaper=The Washington Post|access-date=31 August 2019|archive-date=13 May 2020|archive-url=https://web.archive.org/web/20200513144058/https://www.washingtonpost.com/opinions/2019/05/03/seas-rise-indonesia-is-moving-its-capital-city-other-cities-should-take-note/|url-status=live}}

File:King's Beach since Friday 14th April, 2006 - panoramio.jpg]]

In Australia, erosion and flooding of Queensland's Sunshine Coast beaches is likely to intensify by 60% by 2030. Without adaptation there would be a big impact on tourism. Adaptation costs for sea level rise would be three times higher under the high-emission RCP8.5 scenario than in the low-emission RCP2.6 scenario. Sea level rise of 0.2–0.3 meters is likely by 2050. In these conditions what is currently a 100-year flood would occur every year in the New Zealand cities of Wellington and Christchurch. With 0.5 m sea level rise, a current 100-year flood in Australia would occur several times a year. In New Zealand this would expose buildings with a collective worth of NZ$12.75 billion to new 100-year floods. A meter or so of sea level rise would threaten assets in New Zealand with a worth of NZD$25.5 billion. There would be a disproportionate impact on Maori-owned holdings and cultural heritage objects. Australian assets worth AUS$164–226 billion including many unsealed roads and railway lines would also be at risk. This amounts to a 111% rise in Australia's inundation costs between 2020 and 2100.Lawrence, J., B. Mackey, F. Chiew, M.J. Costello, K. Hennessy, N. Lansbury, U.B. Nidumolu, G. Pecl, L. Rickards, N. Tapper,

A. Woodward, and A. Wreford, 2022: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter11.pdf Chapter 11: Australasia] {{Webarchive|url=https://web.archive.org/web/20230314233029/https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter11.pdf |date=2023-03-14 }}. In [https://www.ipcc.ch/report/ar6/wg2/ Climate Change 2022: Impacts, Adaptation and Vulnerability] {{Webarchive|url=https://web.archive.org/web/20220228114918/https://www.ipcc.ch/report/ar6/wg2/ |date=2022-02-28 }} [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, UK and New York, US, pp. 1581–1688,

|doi=10.1017/9781009325844.013

File:Santos Aérea (cropped).jpg's Port of Santos]]

By 2100, coastal flooding and erosion will affect at least 3–4 million people in South America. Many people live in low-lying areas exposed to sea level rise. This includes 6% of the population of Venezuela, 56% of the population of Guyana and 68% of the population of Suriname. In Guyana much of the capital Georgetown is already below sea level. In Brazil, the coastal ecoregion of Caatinga is responsible for 99% of its shrimp production. A combination of sea level rise, ocean warming and ocean acidification threaten its unique ecosystem. Extreme wave or wind behavior disrupted the port complex of Santa Catarina 76 times in one 6-year period in the 2010s. There was a US$25,000–50,000 loss for each idle day. In Port of Santos, storm surges were three times more frequent between 2000 and 2016 than between 1928 and 1999.Castellanos, E., M.F. Lemos, L. Astigarraga, N. Chacón, N. Cuvi, C. Huggel, L. Miranda, M. Moncassim Vale, J.P. Ometto,

P.L. Peri, J.C. Postigo, L. Ramajo, L. Roco, and M. Rusticucci, 2022: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter12.pdf Chapter 12: Central and South America] {{Webarchive|url=https://web.archive.org/web/20230320192415/https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter12.pdf |date=2023-03-20 }}. In [https://www.ipcc.ch/report/ar6/wg2/ Climate Change 2022: Impacts, Adaptation and Vulnerability] {{Webarchive|url=https://web.archive.org/web/20220228114918/https://www.ipcc.ch/report/ar6/wg2/ |date=2022-02-28 }} [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, UK and New York, US, pp. 1689–1816 {{doi|10.1017/9781009325844.014}}

File:Beach restoration device.jpg in progress in Barcelona.]]

Many sandy coastlines in Europe are vulnerable to erosion due to sea level rise. In Spain, Costa del Maresme is likely to retreat by 16 meters by 2050 relative to 2010. This could amount to 52 meters by 2100 under RCP8.5{{cite journal |last1=Ballesteros |first1=Caridad |last2=Jiménez |first2=José A. |last3=Valdemoro |first3=Herminia I. |last4=Bosom |first4=Eva |date=7 September 2017 |title=Erosion consequences on beach functions along the Maresme coast (NW Mediterranean, Spain) |journal=Natural Hazards |language=en |volume=90 |pages=173–195 |doi=10.1007/s11069-017-3038-5 |s2cid=135328414 |doi-access=free |hdl=2117/114541 |hdl-access=free }} Other vulnerable coastlines include the Tyrrhenian Sea coast of Italy's Calabria region,{{cite journal |last1=Ietto |first1=Fabio |last2=Cantasano |first2=Nicola |last3=Pellicone |first3=Gaetano |date=11 April 2018 |title=A New Coastal Erosion Risk Assessment Indicator: Application to the Calabria Tyrrhenian Littoral (Southern Italy) |url=https://link.springer.com/article/10.1007/s40710-018-0295-6 |journal=Environmental Processes |language=en |volume=5 |issue=2 |pages=201–223 |doi=10.1007/s40710-018-0295-6 |bibcode=2018EProc...5..201I |s2cid=134889581 |access-date=17 April 2023 |archive-date=22 April 2023 |archive-url=https://web.archive.org/web/20230422111655/https://link.springer.com/article/10.1007/s40710-018-0295-6 |url-status=live }} the Barra-Vagueira coast in Portugal{{cite journal |last1=Ferreira |first1=A. M. |last2=Coelho |first2=C. |last3=Narra |first3=P. |date=13 October 2020 |title=Coastal erosion risk assessment to discuss mitigation strategies: Barra-Vagueira, Portugal |url=https://link.springer.com/article/10.1007/s11069-020-04349-2 |journal=Natural Hazards |language=en |volume=105 |pages=1069–1107 |doi=10.1007/s11069-020-04349-2 |s2cid=222318289 |access-date=17 April 2023 |archive-date=21 April 2023 |archive-url=https://web.archive.org/web/20230421025813/https://link.springer.com/article/10.1007/s11069-020-04349-2 |url-status=live }} and Nørlev Strand in Denmark.{{cite journal |last1=Rivero |first1=Ofelia Yocasta |last2=Margheritini |first2=Lucia |last3=Frigaard |first3=Peter |date=4 February 2021 |title=Accumulated effects of chronic, acute and man-induced erosion in Nørlev strand on the Danish west coast |journal=Journal of Coastal Conservation |language=en |volume=25 |issue=1 |page=24 |doi=10.1007/s11852-021-00812-9 |bibcode=2021JCC....25...24R |s2cid=231794192 |doi-access=free }}

In France, it was estimated that 8,000–10,000 people would be forced to migrate away from the coasts by 2080.{{Cite journal|last1=Tierolf|first1=Lars|last2=Haer|first2=Toon Haer|last3=Wouter Botzen|first3=W. J.|last4=de Bruijn|first4=Jens A. |last5=Ton |first5=Marijn J. |last6=Reimann|first6=Lena|last7=Aerts |first7=Jeroen C. J. H. |date=13 March 2023|title=A coupled agent-based model for France for simulating adaptation and migration decisions under future coastal flood risk|journal=Scientific Reports|volume=13 |issue=1 |page=4176 |doi=10.1038/s41598-023-31351-y |pmid=36914726 |pmc=10011601 |bibcode=2023NatSR..13.4176T}} The Italian city of Venice is located on islands. It is highly vulnerable to flooding and has already spent $6 billion on a barrier system.{{cite news |last1=Calma |first1=Justine |title=Venice's historic flooding blamed on human failure and climate change |url=https://www.theverge.com/2019/11/14/20963878/venice-high-tide-climate-change-flood-barrier-sea-levels |access-date=17 November 2019 |agency=The Verge |date=November 14, 2019 |archive-date=1 August 2020 |archive-url=https://web.archive.org/web/20200801002415/https://www.theverge.com/2019/11/14/20963878/venice-high-tide-climate-change-flood-barrier-sea-levels |url-status=live }}{{cite news |last1=Shepherd |first1=Marshall |title=Venice Flooding Reveals A Real Hoax About Climate Change – Framing It As "Either/Or" |url=https://www.forbes.com/sites/marshallshepherd/2019/11/16/venice-flooding-reveals-a-real-hoax-about-climate-changeframing-it-as-eitheror/ |access-date=17 November 2019 |agency=Forbes |date=16 November 2019 |archive-date=2 May 2020 |archive-url=https://web.archive.org/web/20200502135528/https://www.forbes.com/sites/marshallshepherd/2019/11/16/venice-flooding-reveals-a-real-hoax-about-climate-changeframing-it-as-eitheror/ |url-status=live }} A quarter of the German state of Schleswig-Holstein, inhabited by over 350,000 people, is at low elevation and has been vulnerable to flooding since preindustrial times. Many levees already exist. Because of its complex geography, the authorities chose a flexible mix of hard and soft measures to cope with sea level rise of over 1 meter per century.{{Cite journal|last1=van der Hurk|first1=Bart|last2=Bisaro|first2=Alexander|last3=Haasnoot|first3=Marjolijn|last4=Nicholls|first4=Robert J. |last5=Rehdanz |first5=Katrin |last6=Stuparu|first6=Dana|date=28 January 2022|title=Living with sea-level rise in North-West Europe: Science-policy challenges across scales|journal=Climate Risk Management|volume=35|page=100403 |doi=10.1016/j.crm.2022.100403 |bibcode=2022CliRM..3500403V |s2cid=246354121}} In the United Kingdom, sea level at the end of the century would increase by 53 to 115 centimeters at the mouth of the River Thames and 30 to 90 centimeters at Edinburgh.{{cite journal |last1=Howard |first1=Tom |last2=Palmer |first2=Matthew D |last3=Bricheno |first3=Lucy M |date=18 September 2019 |title=Contributions to 21st century projections of extreme sea-level change around the UK |url=https://iopscience.iop.org/article/10.1088/2515-7620/ab42d7 |journal=Environmental Research Communications |language=en |volume=1 |issue=9 |page=095002 |doi=10.1088/2515-7620/ab42d7 |bibcode=2019ERCom...1i5002H |s2cid=203120550 |access-date=17 April 2023 |archive-date=21 April 2023 |archive-url=https://web.archive.org/web/20230421170159/https://iopscience.iop.org/article/10.1088/2515-7620/ab42d7 |url-status=live |doi-access=free }} The UK has divided its coast into 22 areas, each covered by a Shoreline Management Plan. Those are sub-divided into 2000 management units, working across three periods of 0–20, 20–50 and 50–100 years.

The Netherlands is a country that sits partially below sea level and is subsiding. It has responded by extending its Delta Works program.{{Cite news|url=https://www.nytimes.com/interactive/2017/06/15/world/europe/climate-change-rotterdam.html,%20https://www.nytimes.com/interactive/2017/06/15/world/europe/climate-change-rotterdam.html|title=The Dutch Have Solutions to Rising Seas. The World Is Watching.|last1=Kimmelman|first1=Michael|date=2017-06-15|work=The New York Times|access-date=2019-02-02|last2=Haner|first2=Josh|issn=0362-4331}} Drafted in 2008, the Delta Commission report said that the country must plan for a rise in the North Sea up to {{convert|1.3|m|ftin|abbr=on}} by 2100 and plan for a {{convert|2 - 4|m|ft|0|sigfig=1|abbr=on}} rise by 2200.{{Cite news|url=https://www.nytimes.com/2008/09/03/news/03iht-03dutch.15877468.html|title=Dutch draw up drastic measures to defend coast against rising seas|date=3 September 2008|work=The New York Times|access-date=25 February 2017|archive-date=21 August 2017|archive-url=https://web.archive.org/web/20170821050301/http://www.nytimes.com/2008/09/03/news/03iht-03dutch.15877468.html|url-status=live}} It advised annual spending between €1.0 and €1.5 billion. This would support measures such as broadening coastal dunes and strengthening sea and river dikes. Worst-case evacuation plans were also drawn up.{{cite news |title=Rising Sea Levels Threaten Netherlands |url=https://www.newspapers.com/image/514725270/ |access-date=28 October 2022 |work=National Post |agency=Agence France-Presse |date=September 4, 2008 |location=Toronto |page=AL12 |archive-date=28 October 2022 |archive-url=https://web.archive.org/web/20221028180908/https://www.newspapers.com/image/514725270/ |url-status=live }}

File:October 17 2016 sunny day tidal flooding at Brickell Bay Drive and 12 Street downtown Miami, 4.34 MLLW high tide am.jpg in Miami during a king tide (October 17, 2016). The risk of tidal flooding increases with sea level rise.]]

As of 2017, around 95 million Americans lived on the coast. The figures for Canada and Mexico were 6.5 million and 19 million. Increased chronic nuisance flooding and king tide flooding is already a problem in the highly vulnerable state of Florida.{{Cite web|date=2020-02-10|title=Florida Coastal Flooding Maps: Residents Deny Predicted Risks to Their Property|url=https://www.ecowatch.com/florida-coastal-flooding-maps-2645087745.html|access-date=2021-01-31|website=EcoWatch|language=en|archive-date=2023-06-04|archive-url=https://web.archive.org/web/20230604152002/https://www.ecowatch.com/florida-coastal-flooding-maps-2645087745.html|url-status=live}} The US East Coast is also vulnerable.{{cite journal|last1=Sweet & Park |title=Increased nuisance flooding along the coasts of the United States due to sea level rise: Past and future |journal=Geophysical Research Letters |year=2015 |volume=42 |issue=22 |pages=9846–9852 |doi=10.1002/2015GL066072 |bibcode=2015GeoRL..42.9846M |s2cid=19624347}} On average, the number of days with tidal flooding in the US increased 2 times in the years 2000–2020, reaching 3–7 days per year. In some areas the increase was much stronger: 4 times in the Southeast Atlantic and 11 times in the Western Gulf. By the year 2030 the average number is expected to be 7–15 days, reaching 25–75 days by 2050.{{cite web |title=High Tide Flooding |url=https://coast.noaa.gov/states/fast-facts/recurrent-tidal-flooding.html |website=NOAA |access-date=10 July 2023 |archive-date=19 August 2023 |archive-url=https://web.archive.org/web/20230819201149/https://coast.noaa.gov/states/fast-facts/recurrent-tidal-flooding.html |url-status=live }} U.S. coastal cities have responded with beach nourishment or beach replenishment. This trucks in mined sand in addition to other adaptation measures such as zoning, restrictions on state funding, and building code standards.{{cite web|url=http://www.climatecentral.org/news/its-beach-season-enjoy-it-while-you-can|title=Climate Change, Sea Level Rise Spurring Beach Erosion|year=2012|website=Climate Central|access-date=2018-08-20|archive-date=2020-08-06|archive-url=https://web.archive.org/web/20200806010206/https://www.climatecentral.org/news/its-beach-season-enjoy-it-while-you-can|url-status=live}}{{Cite journal|last=Carpenter|first=Adam T.|date=2020-05-04|title=Public priorities on locally-driven sea level rise planning on the East Coast of the United States|journal=PeerJ|language=en|volume=8|pages=e9044|doi=10.7717/peerj.9044|pmid=32411525|pmc=7204830|issn=2167-8359 |doi-access=free}}

Along an estimated ~15% of the US coastline, the majority of local groundwater levels are already below sea level. This places those groundwater reservoirs at risk of sea water intrusion. That would render fresh water unusable once its concentration exceeds 2-3%.{{cite journal |last1=Jasechko |first1=Scott J.|last2=Perrone |first2=Debra |last3=Seybold |first3=Hansjörg |last4=Fan |first4=Ying |last5=Kirchner |first5=James W. |title=Groundwater level observations in 250,000 coastal US wells reveal scope of potential seawater intrusion |date=26 June 2020 |journal=Nature Communications |volume=11 |issue=1 |page=3229 |doi=10.1038/s41467-020-17038-2 |pmid=32591535 |pmc=7319989 |bibcode=2020NatCo..11.3229J}} Damage is also widespread in Canada. It will affect major cities like Halifax and more remote locations like Lennox Island. The Mi'kmaq community there is already considering relocation due to widespread coastal erosion. In Mexico, damage from SLR to tourism hotspots like Cancun, Isla Mujeres, Playa del Carmen, Puerto Morelos and Cozumel could amount to US$1.4–2.3 billion. The increase in storm surge due to sea level rise is also a problem. Due to this effect Hurricane Sandy caused an additional US$8 billion in damage, impacted 36,000 more houses and 71,000 more people.{{cite journal |title=Economic damages from Hurricane Sandy attributable to sea level rise caused by anthropogenic climate change |journal=Nature Communications |date=18 May 2021 |volume=12 |bibcode=2021NatCo..12.2720S |last1=Strauss |first1=Benjamin H. |last2=Orton |first2=Philip M. |last3=Bittermann |first3=Klaus |last4=Buchanan |first4=Maya K. |last5=Gilford |first5=Daniel M. |last6=Kopp |first6=Robert E. |last7=Kulp |first7=Scott |last8=Massey |first8=Chris |last9=Moel |first9=Hans de |last10=Vinogradov |first10=Sergey |issue=1 |page=2720 |doi=10.1038/s41467-021-22838-1 |pmid=34006886 |pmc=8131618 |s2cid=234783225}}{{cite news |last1=Seabrook |first1=Victoria |title=Climate change to blame for $8 billion of Hurricane Sandy losses, study finds |url=https://news.sky.com/story/climate-change-to-blame-for-8-billion-of-hurricane-sandy-losses-study-finds-12309974#:~:text=The%20raised%20water%20levels%20allowed,36%2C000%20homes%20and%2071%2C000%20people. |access-date=9 July 2023 |agency=Sky News |publisher=Nature Communications |date=19 May 2021 |archive-date=9 July 2023 |archive-url=https://web.archive.org/web/20230709130045/https://news.sky.com/story/climate-change-to-blame-for-8-billion-of-hurricane-sandy-losses-study-finds-12309974#:~:text=The%20raised%20water%20levels%20allowed,36%2C000%20homes%20and%2071%2C000%20people. |url-status=live }} In the future, the northern Gulf of Mexico, Atlantic Canada and the Pacific coast of Mexico would experience the greatest sea level rise. By 2030, flooding along the US Gulf Coast could cause economic losses of up to US$176 billion. Using nature-based solutions like wetland restoration and oyster reef restoration could avoid around US$50 billion of this.

File:2050 Projected sea level rise - United States coasts - NOAA.svg predicts different levels of sea level rise through 2050 for several US coastlines.|alt=A comparison of SLR in six parts of the US. The Gulf Coast and East Coast see the most SLR, whereas the West Coast the least]]

By 2050, coastal flooding in the US is likely to rise tenfold to four "moderate" flooding events per year. That forecast is even without storms or heavy rainfall.{{cite web |title=U.S Coastline to See Up to a Foot of Sea Level by 2050 |url=https://www.noaa.gov/news-release/us-coastline-to-see-up-to-foot-of-sea-level-rise-by-2050 |access-date=February 16, 2022 |website=National Oceanic and Atmospheric Administration |date=15 February 2022 |archive-date=5 July 2023 |archive-url=https://web.archive.org/web/20230705195211/https://www.noaa.gov/news-release/us-coastline-to-see-up-to-foot-of-sea-level-rise-by-2050 |url-status=live }}{{cite web |date=2022 |title=More Damaging Flooding, 2022 Sea Level Rise Technical Report |url=https://oceanservice.noaa.gov/hazards/sealevelrise/sealevelrise-tech-report.html#step2 |access-date=2022-03-18 |website=National Ocean Service, NOAA |archive-date=2022-11-29 |archive-url=https://web.archive.org/web/20221129070303/https://oceanservice.noaa.gov/hazards/sealevelrise/sealevelrise-tech-report.html#step2 |url-status=live }} In New York City, current 100-year flood would occur once in 19–68 years by 2050 and 4–60 years by 2080.{{cite web|last=Gornitz|first=Vivien|date=2002|title=Impact of Sea Level Rise in the New York City Metropolitan Area|url=https://eportfolios.macaulay.cuny.edu/bird2012/files/2012/07/Impacts-of-SLR-in-the-NYC-Metropolitan-Area.-pdf.pdf|access-date=2020-08-09|website=Global and Planetary Change|archive-date=2019-09-26|archive-url=https://web.archive.org/web/20190926115312/https://eportfolios.macaulay.cuny.edu/bird2012/files/2012/07/Impacts-of-SLR-in-the-NYC-Metropolitan-Area.-pdf.pdf|url-status=dead}} By 2050, 20 million people in the greater New York City area would be at risk. This is because 40% of existing water treatment facilities would be compromised and 60% of power plants will need relocation.

By 2100, sea level rise of {{cvt|0.9|m|ft|frac=2}} and {{cvt|1.8|m|ft|frac=2}} would threaten 4.2 and 13.1 million people in the US, respectively. In California alone, {{cvt|2|m|ft|frac=2}} of SLR could affect 600,000 people and threaten over US$150 billion in property with inundation. This potentially represents over 6% of the state's GDP. In North Carolina, a meter of SLR inundates 42% of the Albemarle-Pamlico Peninsula, costing up to US$14 billion. In nine southeast US states, the same level of sea level rise would claim up to 13,000 historical and archaeological sites, including over 1000 sites eligible for inclusion in the National Register for Historic Places.Hicke, J.A., S. Lucatello, L.D., Mortsch, J. Dawson, M. Domínguez Aguilar, C.A.F. Enquist, E.A. Gilmore, D.S. Gutzler, S. Harper, K. Holsman, E.B. Jewett, T.A. Kohler, and KA. Miller, 2022: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter14.pdf Chapter 14: North America] {{Webarchive|url=https://web.archive.org/web/20230320192436/https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter14.pdf |date=2023-03-20 }}. In [https://www.ipcc.ch/report/ar6/wg2/ Climate Change 2022: Impacts, Adaptation and Vulnerability] {{Webarchive|url=https://web.archive.org/web/20220228114918/https://www.ipcc.ch/report/ar6/wg2/ |date=2022-02-28 }} [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, UK and New York, US, pp. 1929–2042

File:Malé.jpg, the capital island of Maldives.]]

{{Further|Effects of climate change on island nations|Small Island Developing States|Alliance of Small Island States}}

Small island states are nations with populations on atolls and other low islands. Atolls on average reach {{convert|3-6|ft|m|1|order=flip|abbr=on}} above sea level.{{Cite web|title=Many Low-Lying Atoll Islands Will Be Uninhabitable by Mid-21st Century {{!}} U.S. Geological Survey|url=https://www.usgs.gov/news/national-news-release/many-low-lying-atoll-islands-will-be-uninhabitable-mid-21st-century|access-date=2021-12-17|website=www.usgs.gov|archive-date=2023-06-06|archive-url=https://web.archive.org/web/20230606155303/https://www.usgs.gov/news/national-news-release/many-low-lying-atoll-islands-will-be-uninhabitable-mid-21st-century|url-status=live}} These are the most vulnerable places to coastal erosion, flooding and salt intrusion into soils and freshwater caused by sea level rise. Sea level rise may make an island uninhabitable before it is completely flooded.{{Cite journal|last1=Zhu|first1=Bozhong|last2=Bai|first2=Yan|last3=He|first3=Xianqiang|last4=Chen|first4=Xiaoyan|last5=Li|first5=Teng|last6=Gong|first6=Fang|date=2021-09-18|title=Long-Term Changes in the Land–Ocean Ecological Environment in Small Island Countries in the South Pacific: A Fiji Vision|journal=Remote Sensing|language=en|volume=13|issue=18|page=3740|doi=10.3390/rs13183740|bibcode=2021RemS...13.3740Z|issn=2072-4292|doi-access=free}} Already, children in small island states encounter hampered access to food and water. They suffer an increased rate of mental and social disorders due to these stresses.{{Cite journal|last1=Sly|first1=Peter D|last2=Vilcins|first2=Dwan|date=November 2021|title=Climate impacts on air quality and child health and wellbeing: Implications for Oceania|url=https://onlinelibrary.wiley.com/doi/10.1111/jpc.15650|journal=Journal of Paediatrics and Child Health|language=en|volume=57|issue=11|pages=1805–1810|doi=10.1111/jpc.15650|pmid=34792251|s2cid=244271480|issn=1034-4810|access-date=2021-12-17|archive-date=2023-01-23|archive-url=https://web.archive.org/web/20230123144925/https://onlinelibrary.wiley.com/doi/10.1111/jpc.15650|url-status=live}} At current rates, sea level rise would be high enough to make the Maldives uninhabitable by 2100.{{cite web |author=Megan Angelo |date=1 May 2009 |title=Honey, I Sunk the Maldives: Environmental changes could wipe out some of the world's most well-known travel destinations |url=http://travel.yahoo.com/p-interests-27384279;_ylc=X3oDMTFxcWIyczFpBF9TAzI3MTYxNDkEX3MDMjcxOTQ4MQRzZWMDZnAtdG9kYXltb2QEc2xrA21hbGRpdmVzLTQtMjgtMDk- |archive-url=https://web.archive.org/web/20120717041919/http://travel.yahoo.com/p-interests-27384279 |archive-date=17 July 2012 |access-date=29 September 2009}}{{cite web |author=Kristina Stefanova |date=19 April 2009 |title=Climate refugees in Pacific flee rising sea |url=http://www.washingtontimes.com/news/2009/apr/19/rising-sea-levels-in-pacific-create-wave-of-migran/ |website=The Washington Times |access-date=29 September 2009 |archive-date=18 October 2017 |archive-url=https://web.archive.org/web/20171018075225/http://www.washingtontimes.com/news/2009/apr/19/rising-sea-levels-in-pacific-create-wave-of-migran/ |url-status=live }} Five of the Solomon Islands have already disappeared due to the effects of sea level rise and stronger trade winds pushing water into the Western Pacific.{{Cite web |last=Klein |first=Alice |title=Five Pacific islands vanish from sight as sea levels rise |url=https://www.newscientist.com/article/2087356-five-pacific-islands-vanish-from-sight-as-sea-levels-rise/ |access-date=2016-05-09 |website=New Scientist |archive-date=2020-03-31 |archive-url=https://web.archive.org/web/20200331123810/https://www.newscientist.com/article/2087356-five-pacific-islands-vanish-from-sight-as-sea-levels-rise/ |url-status=live }}

File:Island area change in the Central Pacific and Solomon Islands - erlaa21eff7 hr.jpg and Solomon Islands{{Cite Q|Q29028186}}]]

Adaptation to sea level rise is costly for small island nations as a large portion of their population lives in areas that are at risk.{{Cite book|chapter-url=http://www.ipcc.ch/pdf/assessment-report/ar5/wg2/WGIIAR5-Chap29_FINAL.pdf|title=AR5 WGII|last1=Nurse|first1=Leonard A.|last2=McLean|first2=Roger|publisher=Cambridge University Press|year=2014|editor-last=Barros|editor-first=VR|chapter=29: Small Islands|editor-last2=Field|access-date=2018-09-02|archive-date=2018-04-30|archive-url=https://web.archive.org/web/20180430194832/http://www.ipcc.ch/pdf/assessment-report/ar5/wg2/WGIIAR5-Chap29_FINAL.pdf}} Nations like Maldives, Kiribati and Tuvalu already have to consider controlled international migration of their population in response to rising seas. The alternative of uncontrolled migration threatens to worsen the humanitarian crisis of climate refugees.{{Cite web|last=Nations|first=United|title=Small Islands, Rising Seas|url=https://www.un.org/en/chronicle/article/small-islands-rising-seas|access-date=2021-12-17|website=United Nations|language=en|archive-date=2023-05-06|archive-url=https://web.archive.org/web/20230506043040/https://www.un.org/en/chronicle/article/small-islands-rising-seas|url-status=live}} In 2014, Kiribati purchased 20 square kilometers of land (about 2.5% of Kiribati's current area) on the Fijian island of Vanua Levu to relocate its population once their own islands are lost to the sea.{{cite news|url=https://www.theguardian.com/environment/2014/jul/01/kiribati-climate-change-fiji-vanua-levu|title=Besieged by the rising tides of climate change, Kiribati buys land in Fiji|last1=Caramel|first1=Laurence|date=July 1, 2014|access-date=9 January 2023|agency=The Guardian|archive-date=13 November 2022|archive-url=https://web.archive.org/web/20221113085156/https://www.theguardian.com/environment/2014/jul/01/kiribati-climate-change-fiji-vanua-levu|url-status=live}}

Fiji also suffers from sea level rise.{{Cite journal |last=Long |first=Maebh |author-link=Maebh Long |year=2018 |title=Vanua in the Anthropocene: Relationality and Sea Level Rise in Fiji |url=https://muse.jhu.edu/article/710005 |journal=Symplokē |volume=26 |issue=1–2 |pages=51–70 |doi=10.5250/symploke.26.1-2.0051 |s2cid=150286287 |access-date=2019-10-04 |archive-date=2019-07-28 |archive-url=https://web.archive.org/web/20190728152330/https://muse.jhu.edu/article/710005 |url-status=live }} It is in a comparatively safer position. Its residents continue to rely on local adaptation like moving further inland and increasing sediment supply to combat erosion instead of relocating entirely.{{Cite web|url=http://theconversation.com/many-small-island-nations-can-adapt-to-climate-change-with-global-support-86820|title=Many small island nations can adapt to climate change with global support|last1=Grecequet|first1=Martina|last2=Noble|first2=Ian|date=2017-11-16|website=The Conversation|access-date=2019-02-02|last3=Hellmann|first3=Jessica|archive-date=2020-05-27|archive-url=https://web.archive.org/web/20200527091318/https://theconversation.com/many-small-island-nations-can-adapt-to-climate-change-with-global-support-86820|url-status=live}} Fiji has also issued a green bond of $50 million to invest in green initiatives and fund adaptation efforts. It is restoring coral reefs and mangroves to protect against flooding and erosion. It sees this as a more cost-efficient alternative to building sea walls. The nations of Palau and Tonga are taking similar steps.{{Cite web|url=http://www.unenvironment.org/news-and-stories/video/adaptation-sea-level-rise|title=Adaptation to Sea Level Rise|date=2018-01-11|website=UN Environment|access-date=2019-02-02|archive-date=2020-08-07|archive-url=https://web.archive.org/web/20200807072424/https://www.unenvironment.org/news-and-stories/video/adaptation-sea-level-rise|url-status=live}} Even when an island is not threatened with complete disappearance from flooding, tourism and local economies may end up devastated. For instance, sea level rise of {{cvt|1.0|m|ftin|0}} would cause partial or complete inundation of 29% of coastal resorts in the Caribbean. A further 49–60% of coastal resorts would be at risk from resulting coastal erosion.{{Cite journal|last1=Thomas|first1=Adelle|last2=Baptiste|first2=April|last3=Martyr-Koller|first3=Rosanne|last4=Pringle|first4=Patrick|last5=Rhiney|first5=Kevon|date=2020-10-17|title=Climate Change and Small Island Developing States|journal=Annual Review of Environment and Resources|language=en|volume=45|issue=1|pages=1–27|doi=10.1146/annurev-environ-012320-083355|issn=1543-5938|doi-access=free}}

• {{annotated link|Climate emergency declaration}}
• {{annotated link|Coastal development hazards}}
• {{annotated link|Effects of climate change on oceans}}
• {{annotated link|List of countries by average elevation}}
• {{annotated link|Paleoclimate}}

{{Reflist|24em}}

{{Commons category}}

{{Wikibooks|Historical Geology|Sea level variations}}

{{Portal|Oceans|Climate change|Energy|Renewable energy|Environment}}

• [https://climate.nasa.gov/vital-signs/sea-level/ Vital signs / Sea level (NASA) ]
• [https://sealevel.nasa.gov/ Sea level change / Observations from space] (NASA; links to multiple measurements)
• [https://science2017.globalchange.gov/chapter/12/ Fourth National Climate Assessment (2017) Sea Level Rise Key Message (US government agencies)]
• [https://nca2023.globalchange.gov/chapter/9/ Fifth National Climate Assessment (2023) Coastal Effects Chapter]
• [https://gloss-sealevel.org/ The Global Sea Level Observing System (GLOSS)]
• [https://coast.noaa.gov/slr/ USA Sea Level Rise Viewer (NOAA)]
• [https://coast.noaa.gov/sealevelcalculator USA Sea Level Calculator (NOAA)]
• {{cite web |title=Surging Seas in a Warming World: The latest science on present-day impacts and future projections of sea-level rise |url=https://www.un.org/sites/un2.un.org/files/slr_technical_brief_26_aug_2024.pdf |publisher=United Nations |archive-url=https://archive.today/20241020183035/https://www.un.org/sites/un2.un.org/files/slr_technical_brief_26_aug_2024.pdf |archive-date=20 October 2024 |date=26 August 2024 |url-status=live}}

{{World topic|Sea level rise in|title=Sea level rise by country|noredlinks=yes|state=collapsed}}

{{Physical oceanography|expanded=other}}

{{Climate change}}

{{Doomsday}}

{{DEFAULTSORT:Sea Level Rise}}

Category:Articles containing video clips

Category:Climate change adaptation

Category:Coastal geography

Category:Effects of climate change

Category:Oceanography

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