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Globally,
sea levels Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised ...
are rising due to human-caused
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
. Between 1901 and 2018, the globally averaged
sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardis ...
rose by , or 1–2 mm per year on average.IPCC, 2019
Summary for Policymakers
In
IPCC Special Report on the Ocean and Cryosphere in a Changing Climate
.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M.  Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.) Cambridge University Press, Cambridge, UK and New York, NY, USA. https://doi.org/10.1017/9781009157964.001.
This rate is accelerating, with sea levels now rising by 3.7 mm per year. Climate scientists expect further acceleration during the 21st century. Climate change heats (and therefore expands) the ocean and melts land-based
ice sheet In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are in Antarctica and Greenland; during the Last Glacial Period at La ...
s and
glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such a ...
s. Between 1993 and 2018, the
thermal expansion Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kin ...
of water contributed 42% to sea level rise; melting of
temperate glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as ...
s, 21%;
Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland ...
, 15%; and
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
, 8%. Over the next 2000 years, the sea level is predicted to rise by if global warming is limited to 1.5°C, by if it peaks at 2°C and by if it peaks at 5 °C.IPCC, 2021
Summary for Policymakers
In
Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change
[Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 3−32, doi:10.1017/9781009157896.001.
Sea level rise has a substantial lag in its response to Earth temperature changes. This means that it is virtually certain to continue for a long time, and that its extent in the short term (i.e. around 2050) is insensitive to temperature changes between now and then. Thus, there's confidence that 2050 levels of sea level rise combined with the 2010 population distribution (i.e. absent the effects of
population growth Population growth is the increase in the number of people in a population or dispersed group. Actual global human population growth amounts to around 83 million annually, or 1.1% per year. The global population has grown from 1 billion in 1800 to ...
and
human migration Human migration is the movement of people from one place to another with intentions of settling, permanently or temporarily, at a new location (geographic region). The movement often occurs over long distances and from one country to another (ex ...
) would result in ~150 million people under the water line during high tide and ~300 million in places which are flooded every year – an increase of 40 and 50 million people relative to 2010 values for the same. At the same time, the impact on temperature from changes in
greenhouse gas emissions Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China and ...
over the longer term would greatly influence longer-term sea level rise: by 2100, the spread between the lowest and the highest plausible emission trajectories would result in the sea level rise of when using the best-understood median estimates. When compared to 2050 levels, the difference between the low and high end of that range is equivalent to the difference between ~40 million more people under the water line during high tide and ~50 million more in places which are flooded every year (190 and 350 million people) and ~80 and ~90 million more for the same metrics (230 and 390 million people), respectively. Under the highest emission scenario, less-understood processes may also lead to sea level rise of well over by 2100, and the levels of cannot be excluded. Applying this extent of sea level rise to the 2010 population distribution could mean as many as 520 million more people under the water line during high tide and 640 million in places which are flooded every year. While the rise in sea levels ultimately impacts every coastal and island population on Earth and leads to higher
storm surge A storm surge, storm flood, tidal surge, or storm tide is a coastal flood or tsunami-like phenomenon of rising water commonly associated with low-pressure weather systems, such as cyclones. It is measured as the rise in water level above the ...
s, more dangerous
tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater exp ...
s, damage in cities, loss and degradation of
agricultural Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled peopl ...
land and ultimately permanent loss of land and the displacement of populations, it does not occur uniformly due to local factors like tides, currents, storms,
tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...
effects and land
subsidence Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope mov ...
. For instance, sea level rise along US coasts (and along the US East Coast in particular) is already higher than the global average, and it is expected to be 2 to 3 times greater than the global average by the end of the century. At the same time,
Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...
will be the region where sea level rise would impact the most people: eight Asian countries –
Bangladesh Bangladesh (}, ), officially the People's Republic of Bangladesh, is a country in South Asia. It is the eighth-most populous country in the world, with a population exceeding 165 million people in an area of . Bangladesh is among the mo ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
,
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
,
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Gui ...
,
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
, the
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
,
Thailand Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is b ...
and
Vietnam Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Republic of Vietnam,., group="n" is a country in Southeast Asia, at the eastern edge of mainland Southeast Asia, with an area of and population of 96 million, making ...
– account for 70% of the global population exposed to sea level rise and land subsidence. Altogether, out of the 20 countries with the greatest exposure to sea level rise, 12 are in Asia. Finally, the greatest near-term impact on human populations will occur in the low-lying
Caribbean The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean ...
and
Pacific islands Collectively called the Pacific Islands, the islands in the Pacific Ocean are further categorized into three major island groups: Melanesia, Micronesia, and Polynesia. Depending on the context, the term ''Pacific Islands'' may refer to one of se ...
– many of those would be rendered uninhabitable by sea level rise later this century.Mycoo, M., M. Wairiu, D. Campbell, V. Duvat, Y. Golbuu, S. Maharaj, J. Nalau, P. Nunn, J. Pinnegar, and O. Warrick, 2022
Chapter 15: Small islands
I
Climate Change 2022: Impacts, Adaptation and Vulnerability
.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke,V. Möller, A. Okem, B. Rama (eds.) Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 2043–2121 , doi=10.1017/9781009325844.017
Societies can adapt to sea level rise in three different ways: implement managed retreat, accommodate coastal change, or protect against sea level rise through hard-construction practices like
seawall A seawall (or sea wall) is a form of coastal defense constructed where the sea, and associated coastal processes, impact directly upon the landforms of the coast. The purpose of a seawall is to protect areas of human habitation, conservation ...
s or soft approaches such as dune rehabilitation and
beach nourishment Beach nourishment (also referred to as beach renourishment, beach replenishment, or sand replenishment) describes a process by which sediment, usually sand, lost through longshore drift or erosion is replaced from other sources. A wider beach ...
. Sometimes these adaptation strategies go hand in hand, but at other times choices have to be made among different strategies. For instance, a managed retreat strategy is difficult if the population in the area is quickly increasing: this is a particularly acute problem for
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
, where the population of low-lying coastal areas is projected to increase by around 100 million people within the next 40 years.Trisos, C.H., I.O. Adelekan, E. Totin, A. Ayanlade, J. Efitre, A. Gemeda, K. Kalaba, C. Lennard, C. Masao, Y. Mgaya, G. Ngaruiya, D. Olago, N.P. Simpson, and S. Zakieldeen 2022
Chapter 9: Africa
I
Climate Change 2022: Impacts, Adaptation and Vulnerability
.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke,V. Möller, A. Okem, B. Rama (eds.) Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 2043–2121 , doi=10.1017/9781009325844.011
Poorer nations may also struggle to implement the same approaches to adapt to sea level rise as richer states, and sea level rise at some locations may be compounded by other environmental issues, such as
subsidence Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope mov ...
in so-called
sinking cities Sinking cities are urban environments that are in danger of disappearing due to their rapidly changing landscapes. The largest contributors to these cities becoming unlivable are the combined effects of climate change (manifested through sea level ...
.
Coastal ecosystems A marine coastal ecosystem is a marine ecosystem which occurs where the land meets the ocean. Marine coastal ecosystems include many different types of marine habitats, such as estuaries and lagoons, salt marshes and mangrove forests, seagrass me ...
typically adapt to rising sea levels by moving inland; however, they might not always be able to do so, due to natural or artificial barriers.


Observations

Between 1901 and 2018, the globally averaged
sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardis ...
rose by . More precise data gathered from satellite
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...
measurements reveal an accelerating rise of from 1993 to 2017, accelerating gradually to a rate of per year as of 2021.


Regional variations

Sea level rise is not 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 due to the loss of the weight of ice after melting), so that local relative sea level rise may be higher or lower than the global average. There are even regions near current and former glaciers and ice sheets where sea level falls. Furthermore, gravitational effects of changing ice masses and spatially varying patterns of warming lead to differences in the distribution of sea water around the globe. The gravitational effects comes into play when a large ice sheet melts. With the loss of mass, the gravitational pull becomes less and local water levels might drop. Further away from the ice sheet water levels will increase more than average. In this light, melt in Greenland has a different fingerprint on regional sea level than melt in Antarctica. Many ports, urban conglomerations, and agricultural regions are built on
river delta A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more rare ...
s, where subsidence of land contributes to a substantially increased ''relative'' sea level rise. This is caused by both unsustainable extraction of groundwater (in some places also by extraction of oil and gas), and by
levee A levee (), dike (American English), dyke (Commonwealth English), embankment, floodbank, or stop bank is a structure that is usually earthen and that often runs parallel to the course of a river in its floodplain or along low-lying coastli ...
s and other flood management practices that prevent accumulation of sediments from compensating for the natural settling of deltaic soils. Total human-caused subsidence in the Rhine-Meuse-Scheldt delta (Netherlands) is estimated at , over in urban areas of the
Mississippi River Delta The Mississippi River Delta is the confluence of the Mississippi River with the Gulf of Mexico in Louisiana, southeastern United States. The river delta is a area of land that stretches from Vermilion Bay on the west, to the Chandeleur Isl ...
(
New Orleans New Orleans ( , ,New Orleans
), and over in the
Sacramento–San Joaquin River Delta The Sacramento–San Joaquin River Delta, or California Delta, is an expansive inland river delta and estuary in Northern California. The Delta is formed at the western edge of the Central Valley by the confluence of the Sacramento and Sa ...
. On the other hand, post-glacial isostatic rebound causes relative sea level fall around the
Hudson Bay Hudson Bay ( crj, text=ᐐᓂᐯᒄ, translit=Wînipekw; crl, text=ᐐᓂᐹᒄ, translit=Wînipâkw; iu, text=ᑲᖏᖅᓱᐊᓗᒃ ᐃᓗᐊ, translit=Kangiqsualuk ilua or iu, text=ᑕᓯᐅᔭᕐᔪᐊᖅ, translit=Tasiujarjuaq; french: b ...
in
Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...
and the northern
Baltic Baltic may refer to: Peoples and languages *Baltic languages, a subfamily of Indo-European languages, including Lithuanian, Latvian and extinct Old Prussian *Balts (or Baltic peoples), ethnic groups speaking the Baltic languages and/or originatin ...
. The Atlantic is set to warm at a faster pace than the Pacific. This has consequences for Europe and the
U.S. East Coast The East Coast of the United States, also known as the Eastern Seaboard, the Atlantic Coast, and the Atlantic Seaboard, is the coastline along which the Eastern United States meets the North Atlantic Ocean. The eastern seaboard contains the coa ...
, which received a sea level rise 3–4 times the global average. The downturn of the Atlantic meridional overturning circulation (AMOC) has been also tied to extreme regional sea level rise on the US Northeast Coast.


Projections

There are broadly two ways of modelling sea level rise and making future projections. In one approach, scientists use process-based modelling, where all relevant and well-understood physical processes are included in a global physical model. An
ice-sheet model In climate modelling, Ice-sheet models use numerical methods to simulate the evolution, dynamics and thermodynamics of ice sheets, such as the Greenland ice sheet, the Antarctic ice sheet or the large ice sheets on the northern hemisphere during th ...
is used to calculate the contributions of ice sheets and a
general circulation model A general circulation model (GCM) is a type of climate model. It employs a mathematical model of the general circulation of a planetary atmosphere or ocean. It uses the Navier–Stokes equations on a rotating sphere with thermodynamic ter ...
is used to compute the rising sea temperature and its expansion. A disadvantage of this method is that not all relevant processes might be understood to a sufficient level, but it can predict non-linearities and long delays in the response which studies of the recent past will miss. In the other approach, scientists use semi-empirical techniques that use geological data from the past to determine likely sea level responses to a warming world in addition to some basic physical modelling. These semi-empirical sea level models rely on statistical techniques, using relationships between observed past (contributions to) global mean sea level and global mean temperature. This type of modelling was partially motivated by most physical models in previous literature assessments by the
Intergovernmental Panel on Climate Change The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations. Its job is to advance scientific knowledge about climate change caused by human activities. The World Meteorological Organization (WMO) ...
(IPCC) having underestimated the amount of sea level rise compared to observations of the 20th century.


Projections for the 21st century

In its fifth assessment report (2013) the
Intergovernmental Panel on Climate Change The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations. Its job is to advance scientific knowledge about climate change caused by human activities. The World Meteorological Organization (WMO) ...
(IPCC) estimated how much sea level is likely to rise in the 21st century based on different levels of greenhouse gas emissions. These were conservative projections based on well-known factors which contribute to sea level rise, but exclude other processes which are less well understood. If emissions remain very high, the IPCC projected sea level would rise by . In August 2020 scientists reported that observed ice-sheet losses in Greenland and
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
were tracking worst-case scenarios of those IPCC projections. In 2021, the IPCC Sixth Assessment Report had barely changed its worst-case scenario (updating it to 0.6–1 m), whereas most other reports since 2020 have increased their upper estimates to at least 2 m in the very high emissions scenario. Other attempts have been made to include more physical processes and to develop models that can project sea level rise using paleoclimate data. This typically led to higher estimates of sea level rise. A 2016 study led by Jim Hansen concluded that based on past climate change data, sea level rise could accelerate exponentially in the coming decades, with a doubling time of 10, 20 or 40 years, respectively, raising the ocean by several metres in 50, 100 or 200 years. However, Greg Holland from the National Center for Atmospheric Research, who reviewed the study, noted: "There is no doubt that the sea level rise, within the IPCC, is a very conservative number, so the truth lies somewhere between IPCC and Jim''.''" In addition, one 2017 study's scenario, assuming high
fossil fuel A fossil fuel is a hydrocarbon-containing material formed naturally in the Earth's crust from the remains of dead plants and animals that is extracted and burned as a fuel. The main fossil fuels are coal, oil, and natural gas. Fossil fuels ma ...
use for combustion and strong economic growth during this century, projects sea level rise of up to on average—and an extreme scenario with as much as , by 2100. This could mean rapid sea level rise of up to per year by the end of the century. The study also concluded that the Paris climate agreement emissions scenario, if met, would result in a median of sea level rise by 2100. The Fourth (2017) National Climate Assessment (NCA) of the United States found that it is very likely sea level will rise between 30 and 130 cm (1.0–4.3 feet) in 2100 compared to the year 2000. A rise of 2.4 m (8 feet) is physically possible under a high emission scenario but the authors were unable to say how likely. This worst-case scenario can only come about with a large contribution from Antarctica; a region that is difficult to model. The possibility of a collapse of the West Antarctic ice sheet and subsequent rapid sea level rise was suggested back in the 1970s. For instance, Mercer published a study in 1978 predicting that anthropogenic carbon dioxide warming and its potential effects on climate in the 21st century could cause a sea level rise of around from melting of the West Antarctic ice-sheet alone. In 2019, a study projected that in low emission scenario, sea level will rise 30 cm by 2050 and 70 cm by 2100, relative to the level in 2000. In high emission scenario, it will be roughly 35 cm by 2050 and 110 cm by 2100. There is the probability that the rise will be beyond 2 metres by 2100 in the high emission scenario, which would cause displacement of 187 million people. Long before then, current projections of sea level rise for 2050 will generate an intense rise in the frequency of coastal flooding (a baseline of four "moderate" flooding events per year in the US), even without storms and/or heavy rainfall. In September 2019 the
Intergovernmental Panel on Climate Change The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations. Its job is to advance scientific knowledge about climate change caused by human activities. The World Meteorological Organization (WMO) ...
published SROCC, a report about the impact of climate change on the oceans including sea level rise. In February 2021, a paper suggested that the projections for global sea level rise by 2100 reported in the
IPCC Fifth Assessment Report The Fifth Assessment Report (AR5) of the United Nations Intergovernmental Panel on Climate Change (IPCC) is the fifth in a series of such reports and was completed in 2014.IPCC (2014The IPCC’s Fifth Assessment Report (AR5) leaflet/ref> As ha ...
were well below what one can expect from an extrapolation of past sea level trends, as well as below the combined projections of an expert elicitation, and thus are likely to have been too conservative. The authors noted that the projections in SROCC were substantially closer to the extrapolated trends, but still appeared too conservative and less plausible than the combined expert elicitation. The projections in the August 2021 IPCC Sixth Assessment Report were ultimately slightly larger than those in SROCC for the low-level warming, but much larger at the upper-end for the high-level warming, due to the addition of a "low-confidence" narrative involving marine ice cliff instability.


High-end 21st-century sea level rise

Sea level rise by 2100 that is much higher than the likely range of projection by the IPCC Sixth Assessment Report (AR6) is possible. In particular, AR6 models do not take into consideration many positive feedback loops that would lead to accelerated melting over time. AR6 does offer a speculative narrative about how more extreme melting could occur. It would probably involve a high warming scenario, in which urgent climate action is not taken and strong warming continues.Fox-Kemper, B., H.T. Hewitt, C. Xiao, G. Aðalgeirsdóttir, S.S. Drijfhout, T.L. Edwards, N.R. Golledge, M. Hemer, R.E. Kopp, G.  Krinner, A. Mix, D. Notz, S. Nowicki, I.S. Nurhati, L. Ruiz, J.-B. Sallée, A.B.A. Slangen, and Y. Yu, 2021
Chapter 9: Ocean, Cryosphere and Sea Level Change
I
Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change
[Masson-Delmotte, V., P. Zhai, A. Pirani, S.L.  Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1211–1362, doi:10.1017/9781009157896.011.
This could lead to a faster-than-projected collapse of marine ice shelves and the abrupt, widespread onset of
marine ice cliff instability Marine ice sheet instability (MISI) describes the potential for ice sheets grounded below sea level to destabilize in a runaway fashion. The mechanism was first proposed in the 1970s by Johannes Weertman and was quickly identified as a means by wh ...
(a process in which ice cliffs collapse under their own weight) and ice sheet instability (a positive feedback loop that leads to runaway melting) in Antarctica, and a faster than projected ice loss in Greenland including reduced albedo as its ice melts. Other processes in Antarctica such as hydrofracturing (in which meltwater collects in ice sheet fractures, forcing them open), increased contact of warm ocean water with ice shelves due to climate change induced ocean circulations changes or changes in the weather over Antarctica leading to lower precipitation and ice deposition, could all be contributing factors. The combination of such processes could lead to sea level rise as high as 2.3 metres by 2100.


Long-term sea level rise

There is a widespread consensus among climate scientists that sea level rise lags well behind the temperature increase that triggers it, and that substantial long-term sea level rise will continue for centuries to come even if the temperature stabilizes. Models are able to reproduce paleo records of sea level rise, which provides confidence in their application to long-term future change. Both the Greenland ice sheet and Antarctica have tipping points for warming levels that could be reached before the end of the 21st century. Crossing such tipping points would mean that ice-sheet changes are potentially irreversible: a decrease to pre-industrial temperatures may not stabilize the ice sheet once the tipping point has been crossed. Quantifying the exact temperature change for which this tipping point is crossed remains controversial. For Greenland, estimates roughly range between 1 and 4 °C (2 to 7 °F) above pre-industrial. , the lower of these values has already been passed. A 2021 analysis of sub-glacial sediment at the bottom of a 1.4 km Greenland ice core finds that the Greenland ice sheet melted away at least once during the last million years. Since the maximum positive temperature excursion over that period is 2.5 °C, this strongly suggests that its tipping point is below that value and therefore within the lower half of its range of estimates. Melting of the
Greenland ice sheet The Greenland ice sheet ( da, Grønlands indlandsis, kl, Sermersuaq) is a vast body of ice covering , roughly near 80% of the surface of Greenland. It is sometimes referred to as an ice cap, or under the term ''inland ice'', or its Danish equi ...
would contribute of sea level rise. A 2013 study estimated that each degree of temperature rise translates to a commitment to sea level rise within the next 2,000 years. More recent research, especially into Antarctica, indicates that this is probably a conservative estimate and that the true long-term sea level rise might be higher. Warming beyond the 2 °C (3.6 °F) target potentially leads to rates of sea level rise dominated by ice loss from
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
. Continued carbon dioxide emissions from fossil fuel sources could cause additional tens of metres of sea level rise, over the next millennia, and the available fossil fuel on Earth is even enough to ultimately melt the entire Antarctic ice sheet, causing about of sea level rise. After 500 years, sea level rise from thermal expansion alone may have reached only half of its eventual level, which models suggest may lie within ranges of . In the next 2,000 years the sea level is predicted to rise by 2–3 metres if the temperature rise peaks at 1.5 °C, by 2–6 metres if it peaks at 2 °C and by 19–22 metres if it peaks at 5 °C. If temperature rise stops at 2 °C or at 5 °C, the sea level would still continue to rise for about 10,000 years. In the first case it will reach 8–13 metres above pre-industrial level, and in the second 28–37 metres.


Causes

The three main reasons warming causes global sea level to rise are: oceans expand, ice sheets lose ice faster than it forms from snowfall, and
glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such a ...
s at higher altitudes also melt. Sea level rise since the start of the 20th century has been dominated by retreat of glaciers and expansion of the ocean, but the contributions of the two large ice sheets (Greenland and Antarctica) are expected to increase in the 21st century. The ice sheets store most of the land ice (∼99.5%), with a sea-level equivalent (SLE) of for Greenland and for Antarctica. Each year about of precipitation (liquid equivalent) falls on the ice sheets in Antarctica and
Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland ...
, mostly as snow, which accumulates and over time forms glacial ice. Much of this precipitation began as water vapor evaporated from the ocean surface. Some of the snow is blown away by wind or disappears from the ice sheet by melt or by sublimation (directly changing into water vapor). The rest of the snow slowly changes into ice. This ice can flow to the edges of the ice sheet and return to the ocean by melting at the edge or in the form of
iceberg An iceberg is a piece of freshwater ice more than 15 m long that has broken off a glacier or an ice shelf and is floating freely in open (salt) water. Smaller chunks of floating glacially-derived ice are called "growlers" or "bergy bits". The ...
s. If precipitation, surface processes and ice loss at the edge balance each other, sea level remains the same. However scientists have found that ice is being lost, and at an accelerating rate.


Ocean heating

Most of the additional heat trapped in the Earth's climate system by climate change is stored in oceans. They store more than 90% of the extra heat and act as a buffer against the
effects of climate change The effects of climate change impact the physical environment, ecosystems and human societies. The environmental effects of climate change are broad and far-reaching. They affect the water cycle, oceans, sea and land ice ( glaciers), sea le ...
. The heat needed to raise an average temperature increase of the entire world ocean by 0.01 °C would increase the atmospheric temperature by approximately 10 °C: a small change in the mean temperature of the ocean represents a very large change in the total heat content of the climate system. When the ocean gains heat, the water expands and sea level rises. The amount of expansion varies with both water temperature and pressure. For each degree, warmer water and water under great pressure (due to depth) expand more than cooler water and water under less pressure. Consequently cold
Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five major oceans. It spans an area of approximately and is known as the coldest of all the oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, a ...
water will expand less than warm tropical water. Because different climate models present slightly different patterns of ocean heating, their predictions do not agree fully on the contribution of ocean heating to sea level rise. Heat gets transported into deeper parts of the ocean by winds and currents, and some of it reaches depths of more than . Considering an increase in average global temperature of 2 °C above preindustrial levels, and not considering the potential contributions from ice-sheet processes with limited agreement (low confidence) among modeling approaches, the probability of exceeding 0.5 m rise of sea level globally (0.7 m along the CONUS coastline) by 2100 is about 50%. With 3–5 °C of warming under high emissions pathways, this probability rises to >80% to >99%.


Antarctica

The large volume of ice on the Antarctic continent stores around 70% of the world's fresh water. The Antarctic ice sheet mass balance is affected by snowfall accumulations, and ice discharge along the periphery. Under the influence of global warming, melt at the base of the ice sheet increases. Simultaneously, the capacity of the atmosphere to carry precipitation increases with temperature so that precipitation, in the form of snowfall, increases in global and regional models. The additional snowfall causes increased ice flow of the ice sheet into the ocean, so that the mass gain due to snowfall is partially compensated. Snowfall increased over the last two centuries, but no increase was found in the interior of Antarctica over the last four decades. Based on changes of Antarctica's ice mass balance over millions of years, due to natural climate fluctuations, researchers concluded that the sea-ice acts as a barrier for warmer waters surrounding the continent. Consequently, the loss of sea ice is a major driver of the instability of the entire ice sheet. Different satellite methods for measuring ice mass and change are in good agreement, and combining methods leads to more certainty about how the East Antarctic Ice Sheet, the West Antarctic Ice Sheet, and the
Antarctic Peninsula The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martín in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctic ...
evolve. A 2018
systematic review A systematic review is a scholarly synthesis of the evidence on a clearly presented topic using critical methods to identify, define and assess research on the topic. A systematic review extracts and interprets data from published studies on t ...
study estimated that ice loss across the entire continent was 43 gigatons (Gt) per year on average during the period from 1992 to 2002, but has accelerated to an average of 220 Gt per year during the five years from 2012 to 2017. * Most of the melt comes from the West Antarctic Ice Sheet, but the Antarctic Peninsula and East Antarctic Ice Sheet also contribute. The sea level rise due to Antarctica has been estimated to be 0.25 mm per year from 1993 to 2005, and 0.42 mm per year from 2005 to 2015. All datasets generally show an acceleration of mass loss from the Antarctic ice-sheet, but with year-to-year variations. A May 2021 study projected that limiting global warming to 1.5 °C would reduce the land ice contribution to sea level rise by 2100 from 25 cm to 13 cm (from 10 to 6 in.) compared to current mitigation pledges, with glaciers responsible for half the sea level rise contribution. The physical uncertainty of the Antarctic contribution was more significant than the uncertainty due to the choice of mitigation pathway. Alt URL https://eprints.whiterose.ac.uk/173870/ By 2019, several studies have attempted to estimate 2300 sea level rise caused by ice loss in Antarctica alone: they suggest 16 cm median and 37 cm maximum values under the low-emission scenario but a median of 1.46 metres (with a minimum of 60 cm and a maximum of 2.89 metres) under the highest-emission scenario.


East Antarctica

The world's largest potential source of sea level rise is the East Antarctic Ice Sheet, which holds enough ice to raise global sea levels by . The ice sheet has historically been considered to be relatively stable and has therefore attracted less scientific attention and observations compared to West Antarctica. A combination of satellite observations of its changing volume, flow and gravitational attraction with modelling of its surface mass balance suggests the overall mass balance of the East Antarctic Ice Sheet was relatively steady or slightly positive for much of the period 1992–2017. A 2019 study, however, using different methodology, concluded that
East Antarctica East Antarctica, also called Greater Antarctica, constitutes the majority (two-thirds) of the Antarctic continent, lying on the Indian Ocean side of the continent, separated from West Antarctica by the Transantarctic Mountains. It lies almos ...
is losing significant amounts of ice mass. The lead scientist
Eric Rignot Eric J. Rignot is a chancellor professor of Earth system science at the University of California, Irvine, and senior research scientist for the Radar Science and Engineering Section at NASA's Jet Propulsion Laboratory. Education In 1985, Ri ...
told CNN: "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." Methods agree that the Totten Glacier has lost ice in recent decades in response to ocean warming and possibly a reduction in local sea ice cover. Totten Glacier is the primary outlet of the
Aurora Subglacial Basin Aurora Subglacial Basin is a large subglacial basin of Wilkes Land to the west of Dome Charlie and trending northwest toward the coast in the vicinity of Shackleton Ice Shelf. The basin was delineated by the SPRI- NSF- TUD airborne radio echo so ...
, a major ice reservoir in East Antarctica that could rapidly retreat due to hydrological processes. The global sea level potential of flowing through Totten Glacier alone is of similar magnitude to the entire probable contribution of the West Antarctic Ice Sheet. The other major ice reservoir on East Antarctica that might rapidly retreat is the Wilkes Basin which is subject to marine ice sheet instability. Ice loss from these outlet glaciers is possibly compensated by accumulation gains in other parts of Antarctica. In 2022, it was estimated that the Wilkes Basin, Aurora Basin and other nearby subglacial basins are likely to have a collective tipping point around 3 °C of global warming, although it may be as high as 6 °C, or as low as 2 °C. Once this tipping point is crossed, the collapse of these subglacial basins could take place as little as 500 or as much as 10,000 years: the median timeline is 2000 years. On the other hand, the entirety of the EAIS would not be committed to collapse until global warming reaches 7.5 °C (range between 5 and 10 °C), and would take at least 10,000 years to disappear. It is also suggested that the loss of two-thirds of its volume may require at least 6 °C of warming.


West Antarctica

Even though East Antarctica contains the largest potential source of sea level rise, it is
West Antarctica West Antarctica, or Lesser Antarctica, one of the two major regions of Antarctica, is the part of that continent that lies within the Western Hemisphere, and includes the Antarctic Peninsula. It is separated from East Antarctica by the Transan ...
that currently experiences a net outflow of ice, causing sea levels to rise. Using different satellites from 1992 to 2017 shows melt is increasing significantly over this period. Antarctica as a whole has caused a total of of sea level rise. Considering the mass balance of the East Antarctic Ice Sheet which was relatively steady, the major contributor was West Antarctica. Significant acceleration of outflow glaciers in the Amundsen Sea Embayment may have contributed to this increase. In contrast to East Antarctica and the
Antarctic Peninsula The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martín in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctic ...
, temperatures on West Antarctica have increased significantly with a trend between per decade and per decade between 1976 and 2012. In 2021, it was estimated that while the *median* increase in sea level rise from the West Antarctic ice sheet melt by 2100 is ~11 cm under all emission scenarios (since the increased warming would intensify the water cycle and increase
snowfall Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout ...
accumulation over the ice sheet at about the same rate as it would increase ice loss), the multiple types of instability affecting West Antarctica ice sheet mean that it can conceivably contribute as much as 41 cm by 2100 under the low-emission scenario and 57 cm under the highest-emission one. One is marine ice sheet instability, where the bedrock on which parts of the ice sheet rest is deeper inland. This means that when a part of the ice sheet melts, a thicker part of the ice sheet is exposed to the ocean, which may lead to additional ice loss. Secondly, melting of the ice shelves, the floating extensions of the ice sheet, leads to a process named the Marine Ice Cliff Instability''.'' Because they function as a
buttress A buttress is an architectural structure built against or projecting from a wall which serves to support or reinforce the wall. Buttresses are fairly common on more ancient buildings, as a means of providing support to act against the lateral (s ...
to the ice sheet, their melt leads to additional ice flow (see animation one minute into video). Melt of ice shelves is accelerated when surface melt creates
crevasse A crevasse is a deep crack, that forms in a glacier or ice sheet that can be a few inches across to over 40 feet. Crevasses form as a result of the movement and resulting stress associated with the shear stress generated when two semi-rigid p ...
s and these crevasses cause fracturing. The Thwaites and Pine Island glaciers have been identified to be potentially prone to these processes, since both glaciers bedrock
topography Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sc ...
gets deeper farther inland, exposing them to more warm water intrusion into the grounding zone. With continued melt and retreat they contribute to raising global sea levels. The Thwaites glacier itself will cause a rise of sea level by 65 centimetres if it will completely collapse, but this can also destabilize other glaciers in west Antarctica. The Thwaites Ice Shelf can collapse in three to five years, which would then make the destabilization of the entire Thwaites glacier inevitable. The melting of these two glaciers had accelerated at the beginning of the 21st century. It can destabilize the entire West Antarctic Ice Sheet. However, the process will probably not be finished in this century. Most of the
bedrock In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of be ...
underlying the West Antarctic Ice Sheet lies well below sea level. A rapid collapse of the West Antarctic Ice Sheet could raise sea level by . In 2022, the collapse of the entire West Antarctica was estimated to unfold over a period of about 2000 years, with the absolute minimum of 500 years (and a potential maximum of 13,000 years.) At the same time, this collapse was considered likely to be triggered at around 1.5°C of global warming and would become absolutely unavoidable at 3°C: at worst, it may have even been triggered by now, after the warming passed 1°C in the recent years. Even though the process takes a long time to finish, it has been suggested that the only way to stop it once triggered is by lowering the global temperature to 1°C ''below'' the preindustrial levels (about 2°C below the current levels).


Greenland

Most ice on Greenland is part of the
Greenland ice sheet The Greenland ice sheet ( da, Grønlands indlandsis, kl, Sermersuaq) is a vast body of ice covering , roughly near 80% of the surface of Greenland. It is sometimes referred to as an ice cap, or under the term ''inland ice'', or its Danish equi ...
which is at its thickest. The rest of the ice on Greenland is part of isolated glaciers and ice caps. The sources contributing to sea level rise from Greenland are from ice sheet melting (70%) and from glacier calving (30%). Dust,
soot Soot ( ) is a mass of impure carbon particles resulting from the incomplete combustion of hydrocarbons. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolysed ...
, and
microbe A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s and
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...
living on parts of the ice sheet further enhance melting by darkening its surface and thus absorbing more
thermal radiation Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) i ...
; these regions grew by 12% between 2000 and 2012, and are likely to expand further. Average annual ice loss in Greenland more than doubled in the early 21st century compared to the 20th century. Some of Greenland's largest outlet glaciers, such as
Jakobshavn Isbræ Jakobshavn Glacier ( da, Jakobshavn Isbræ), also known as Ilulissat Glacier ( kl, Sermeq Kujalleq), is a large outlet glacier in West Greenland. It is located near the Greenlandic town of Ilulissat (colonial name in da, Jakobshavn) and ends ...
and
Kangerlussuaq Glacier Kangerlussuaq Glacier ( kl, Kangerlussuaq, meaning 'large fjord'; old spelling ''Kangerdlugssuaq'') is the largest glacier on the east coast of the Greenland ice sheet. It flows into the head of the Kangerlussuaq Fjord, the second largest fjord ...
, are flowing faster into the ocean. A study published in 2017 concluded that Greenland's peripheral glaciers and ice caps crossed an irreversible tipping point around 1997, and will continue to melt. A study published in 2020 estimated that the Greenland Ice Sheet had lost a total of 3,902 gigatons (Gt) of ice between 1992 and 2018, corresponding to a contribution to sea level rise of 10.8 mm. The sea level rise due to the Greenland Ice Sheet has generally increased over time, rising from 0.07 mm per year between 1992 and 1997 to 0.68 mm per year between 2012 and 2017. The contribution for the 2012–2016 period was equivalent to 37% of sea level rise from ''land ice'' sources (excluding thermal expansion). This rate of ice sheet melting is also associated with the higher end of the predictions from the past
IPCC The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations. Its job is to advance scientific knowledge about climate change caused by human activities. The World Meteorological Organization (WMO) ...
assessment reports. As of 2021, it is estimated that under the SSP1-2.6 emission scenario which largely fulfils the
Paris Agreement The Paris Agreement (french: Accord de Paris), often referred to as the Paris Accords or the Paris Climate Accords, is an international treaty on climate change. Adopted in 2015, the agreement covers climate change mitigation, adaptation, and ...
goals, Greenland ice sheet melt adds around 6 cm to global sea level rise by the end of the century, with a plausible maximum of 15 cm (and even a very small chance of the ice sheet gaining mass through the increased surface mass balance feedback and thus reducing the sea levels by around 2 cm). On the other hand, the scenario associated with the highest global warming, SSP5-8.5, would see Greenland add a minimum of 5 cm to sea level rise, a likely median of 13 cm and a plausible maximum of 23 cm. There is also a threshold in surface warming beyond which a partial or near-complete melting of the Greenland ice sheet occurs. Different research has put this threshold value as low as 1 °C (2 °F), and definitely 4 °C (7 °F), above pre-industrial temperatures. A 2021 analysis of sub-glacial sediment at the bottom of a 1.4 km Greenland ice core finds that the Greenland ice sheet melted away at least once during the last million years, and therefore strongly suggests that its tipping point is below the 2.5 °C maximum positive temperature excursion over that period. In 2022, it was estimated that the tipping point of the Greenland Ice Sheet may have been as low as 0.8 °C, and is certainly no higher than 3 °C: there's a high chance that it will be crossed around 1.5 °C. Once crossed, it would take between 1000 and 15,000 years for the ice sheet to disintegrate entirely, with the most likely estimate of 10,000 years.


Glaciers

Less than 1% of glacier ice is in mountain glaciers, compared to 99% in Greenland and
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
. However, this small size also makes them more vulnerable to melting than the larger ice sheets, and it means that mountain glaciers 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. The roughly 200,000 glaciers on earth are spread out across all continents. Different glaciers respond differently to increasing temperatures. For instance, valley glaciers that have a shallow slope retreat under even mild warming. Every glacier has a height above which there is net gain in mass and under which the glacier loses mass. If that height changes a bit, this has large consequences for glaciers with a shallow slope. Many glaciers drain into the ocean and ice loss can therefore increase when ocean temperatures increase. Observational and modelling studies of mass loss from glaciers and ice caps indicate a contribution to sea level rise of 0.2-0.4 mm per year, averaged over the 20th century. The contribution for the 2012–2016 period was nearly as large as that of Greenland: 0.63 mm of sea level rise per year, equivalent to 34% of sea level rise from ''land ice'' sources. Over the 21st century, this is expected to rise, with glaciers contributing to global sea levels. Glaciers contributed around 40% to sea level rise during the 20th century, with estimates for the 21st century of around 30%. In 2022, it was estimated that in general, mountain glaciers are likely to disappear around the world once the warming crosses 2 °C, and this would become largely inevitable around 3 °C: there's even a chance most glaciers would be lost around 1.5 °C. Because mountain glaciers contain much less ice than the other ice masses, their disappearance may require as little 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

Sea ice melt contributes 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 Archimedes' principle (also spelled Archimedes's principle) states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially, is equal to the weight of the fluid that the body displaces. Archimedes' ...
, no rise would occur. However melted sea ice contains less dissolved salt than sea water and is therefore less dense: in other words, although the melted sea ice weighs the same as the sea water it was displacing when it was ice, its volume is still slightly greater. If all floating ice shelves and
icebergs An iceberg is a piece of freshwater ice more than 15 m long that has broken off a glacier or an ice shelf and is floating freely in open (salt) water. Smaller chunks of floating glacially-derived ice are called "growlers" or "bergy bits". Th ...
were to melt sea level would only rise by about .


Land water storage

Humans impact how much water is stored on land. Building dams prevents large masses of water from flowing into the sea and therefore increases the storage of water on land. On the other hand, humans extract water from
lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...
s,
wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (Anoxic waters, anoxic) processes prevailing, especially in t ...
s and underground reservoirs for
food production The food industry is a complex, global network of diverse businesses that supplies most of the food consumed by the world's population. The food industry today has become highly diversified, with manufacturing ranging from small, traditional, ...
leading to rising seas. Furthermore, the
hydrological cycle The water cycle, also known as the hydrologic cycle or the hydrological cycle, is a biogeochemical cycle that describes the continuous movement of water on, above and below the surface of the Earth. The mass of water on Earth remains fairly const ...
is influenced by climate change and
deforestation Deforestation or forest clearance is the removal of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. The most concentrated ...
, which can lead to further positive and negative contributions to sea level rise. In the 20th century, these processes roughly balanced, but dam building has slowed down and is expected to stay low for the 21st century.


Measurement

Sea level changes can be driven either by variations in the amount of water in the oceans, the volume of the ocean or by changes of the land compared to the sea surface. Over a consistent time period, conducting assessments can source contributions to sea level rise and provide early indications of change in trajectory. This type of surveillance can inform plans of prevention. 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, whilst
satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioiso ...
s can also measure absolute sea level changes. To get precise measurements for sea level, researchers studying the ice and the oceans on our planet factor in ongoing deformations of the solid Earth, in particular due to landmasses still rising from past ice masses retreating, and also the
Earth's gravity The gravity of Earth, denoted by , is the net acceleration that is imparted to objects due to the combined effect of gravitation (from mass distribution within Earth) and the centrifugal force (from the Earth's rotation). It is a vector qua ...
and
rotation Rotation, or spin, is the circular movement of an object around a '' central axis''. A two-dimensional rotating object has only one possible central axis and can rotate in either a clockwise or counterclockwise direction. A three-dimensional ...
.


Satellites

Since the launch of
TOPEX/Poseidon TOPEX/Poseidon was a joint satellite altimeter mission between NASA, the U.S. space agency; and CNES, the French space agency, to map ocean surface topography. Launched on August 10, 1992, it was the first major oceanographic research satellite. ...
in 1992, an overlapping series of altimetric satellites has been continuously recording the sea level and its changes. Those 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 which reflects on the ocean's surface and record the time it takes to return. Microwave radiometers correct the additional delay caused by
water vapor (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 J/( kg·K) , - , Heat of vaporization , 2.27 MJ/kg , - , Heat capacity , 1.864 kJ/(kg·K) Water vapor, water vapour or aqueous vapor is the gaseous p ...
in the
atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...
. Combining these data with the precisely known location of the spacecraft determines the sea-surface height to within a few centimetres (about one inch). Current rates of sea level rise from satellite altimetry have been estimated to be per year for the period 1993–2017. Earlier satellite measurements were previously slightly at odds with
tide gauge A tide gauge is a device for measuring the change in sea level relative to a vertical datum. It its also known as mareograph, marigraph, sea-level recorder and limnimeter. When applied to freshwater continental water bodies, the instrument ma ...
measurements. A small calibration error for the Topex/Poseidon satellite was eventually identified as having caused a slight overestimation of the 1992–2005 sea levels, which masked in the satellite measurements the ongoing sea level rise acceleration that was visible in the tide gauge timeseries. Satellites are useful for measuring regional variations in sea level, such as the substantial rise between 1993 and 2012 in the western tropical Pacific. This sharp rise has been linked to increasing
trade winds The trade winds or easterlies are the permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisp ...
, which occur when the Pacific Decadal Oscillation (PDO) and the
El Niño–Southern Oscillation El Niño–Southern Oscillation (ENSO) is an irregular periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean, affecting the climate of much of the tropics and subtropics. The warming phase of the sea te ...
(ENSO) change from one state to the other. The PDO is a basin-wide climate pattern consisting of two phases, each commonly lasting 10 to 30 years, while the ENSO has a shorter period of 2 to 7 years.


Tide gauges

The global network of
tide gauge A tide gauge is a device for measuring the change in sea level relative to a vertical datum. It its also known as mareograph, marigraph, sea-level recorder and limnimeter. When applied to freshwater continental water bodies, the instrument ma ...
s is another important source of sea-level observations. Compared to the satellite record, this record has major spatial gaps but covers a much longer period of time. Coverage of tide gauges started primarily in the Northern Hemisphere, with data for the Southern Hemisphere remaining scarce up to the 1970s. The longest running sea-level measurements, NAP or Amsterdam Ordnance Datum established in 1675, are recorded in
Amsterdam Amsterdam ( , , , lit. ''The Dam on the River Amstel'') is the capital and most populous city of the Netherlands, with The Hague being the seat of government. It has a population of 907,976 within the city proper, 1,558,755 in the urban ar ...
, the Netherlands. In Australia record collection is also quite extensive, including measurements by an amateur meteorologist beginning in 1837 and measurements taken from a sea-level benchmark struck on a small cliff on the Isle of the Dead near the Port Arthur convict settlement in 1841. This network was used, in combination with satellite altimeter data, to establish that global mean sea-level rose between 1870 and 2004 at an average rate of about 1.44 mm/yr (1.7 mm/yr during the 20th century). Data collected by the
Commonwealth Scientific and Industrial Research Organisation The Commonwealth Scientific and Industrial Research Organisation (CSIRO) is an Australian Government agency responsible for scientific research. CSIRO works with leading organisations around the world. From its headquarters in Canberra, CSIRO ...
(CSIRO) in
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
show that the global mean sea level currently rises by per year, at double the average 20th century rate. This is an important confirmation of climate change simulations which predicted that sea level rise would accelerate in response to climate change. Some regional differences are also visible in the tide gauge data. Some of the recorded regional differences are due to differences in the actual sea level, while other are due to vertical land movements. In Europe for instance, considerable variation is found because some land areas are rising while others are sinking. Since 1970, most tidal stations have measured higher seas, but sea levels along the northern
Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and from ...
have dropped due to
post-glacial rebound Post-glacial rebound (also called isostatic rebound or crustal rebound) is the rise of land masses after the removal of the huge weight of ice sheets during the last glacial period, which had caused isostatic depression. Post-glacial rebound ...
.


Impacts

Current and future sea level rise is set to have a number of impacts, particularly on
coast The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...
al systems. Such impacts include higher and more frequent high-tide and storm-surge flooding, increased
coastal erosion Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. The landwar ...
, inhibition of
primary production In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through ...
processes, more extensive coastal inundation, changes in surface
water quality Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through tr ...
and groundwater characteristics. This is projected in turn to increase loss of property and coastal habitats, increased flood risk and potential loss of life, loss of non-monetary cultural resources and values, impacts on agriculture and
aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...
through decline in soil and water quality, and loss of tourism, recreation, and transportation functions. Many of these impacts are detrimental. Owing to the great diversity of coastal environments; regional and local differences in projected relative sea level and climate changes; and differences in the resilience and adaptive capacity of
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
s, sectors, and countries, the impacts will be highly variable in time and space.
River delta A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more rare ...
s in Africa and Asia and small island states are particularly vulnerable to sea level rise. Globally tens of millions of people will be exposed in the latter decades of the century if greenhouse gases are not reduced drastically. Many coastal areas have large population growth, which results in more people at risk from sea level rise. While modest increases in sea level are likely to be offset when cities adapt by constructing sea walls or through relocating, millions of people will be affected in cities such as
Miami Miami ( ), officially the City of Miami, known as "the 305", "The Magic City", and "Gateway to the Americas", is a coastal metropolis and the county seat of Miami-Dade County in South Florida, United States. With a population of 442,241 at ...
,
Rio de Janeiro Rio de Janeiro ( , , ; literally 'River of January'), or simply Rio, is the capital of the state of the same name, Brazil's third-most populous state, and the second-most populous city in Brazil, after São Paulo. Listed by the GaWC as a b ...
,
Osaka is a designated city in the Kansai region of Honshu in Japan. It is the capital of and most populous city in Osaka Prefecture, and the third most populous city in Japan, following Special wards of Tokyo and Yokohama. With a population of ...
and
Shanghai Shanghai (; , , Standard Chinese, Standard Mandarin pronunciation: ) is one of the four Direct-administered municipalities of China, direct-administered municipalities of the China, People's Republic of China (PRC). The city is located on the ...
if following the current trajectory of 3 °C (5.4 °F). The rising seas pose both a direct risk of flooding unprotected areas and indirect threats of higher storm surges, tsunamis and king tides. They are also associated with the highly detrimental second-order effects such as the loss of coastal ecosystems like
mangroves A mangrove is a shrub or tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evolution in sever ...
or the increased risk from
tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater exp ...
s in the
Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...
and
Atlantic Oceans The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Africa, Europe a ...
. Coastal flooding impacts are exacerbated by land use changes such as urbanisation or deforestation of low-lying coastal zones. Regions that are already vulnerable to the rising sea level also struggle with coastal flooding washing away land and altering the landscape. People in these areas struggle increasingly because of these different effects of climate change. Climate change influenced storms also create greater frequency of coastal flooding. Addressing the flooding issues that a region, city, or country is experiencing will be based on the efforts of the affected country. Without much effort these coastal regions could continuously degrade and thus greatly affect the size and influence of a country. Food production in coastal areas is affected by rising sea levels as well. Due to flooding and salt water intrusion into the soil, the salinity of agricultural lands near the sea increases, posing problems for crops that are not salt-resistant. Furthermore, salt intrusion in fresh irrigation water poses a second problem for crops that are irrigated. Newly developed salt-resistant crop variants are currently more expensive than the crops they are set to replace. The farmland in the
Nile Delta The Nile Delta ( ar, دلتا النيل, or simply , is the delta formed in Lower Egypt where the Nile River spreads out and drains into the Mediterranean Sea. It is one of the world's largest river deltas—from Alexandria in the west to ...
is affected by salt water flooding, and there is now more salt in the soil and irrigation water in the
Red River Delta The Red River Delta or Hong River Delta ( vi, Châu thổ sông Hồng) is the flat low-lying plain formed by the Red River and its distributaries merging with the Thái Bình River in northern Vietnam. ''Hồng'' (紅) is a Sino-Vietnamese word ...
and the
Mekong Delta The Mekong Delta ( vi, Đồng bằng Sông Cửu Long, lit=Nine Dragon River Delta or simply vi, Đồng Bằng Sông Mê Kông, lit=Mekong River Delta, label=none), also known as the Western Region ( vi, Miền Tây, links=no) or South-weste ...
in Vietnam. Bangladesh and China are affected in a similar way, particularly their rice production. Sea trade is the dominant form of resource and good trade throughout the world. When talking about the rising sea level there is the possibility for major issues to arise for sea-based trade and the ports that are utilized. What is also of importance for these ports is that we do not yet know how the rising sea level will continue to impact them over time. A variety of factors play into the investment of seaports for this means. Factors that are important for seaports in reference to the rising sea level are where will the important trade ports be in the future, can we alter and protect the ports that are currently being used, how much is needed to protect trade without wasting time or money. The rising sea level for seaports is a concern, but is hard to decipher what changes need to be made since sea levels do not rise at the same rate all over the world. The long-term cumulative effects of rising sea levels pose a serious threat in coastal areas. Coastal areas are sensitive to rising sea levels, 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 above sea level. Furthermore, two thirds of the world's cities with over five million people are located in these low-lying coastal areas. In total, approximately 600 million people live directly on the coast around the world. Using remote laser scanning called
LiDAR Lidar (, also LIDAR, or LiDAR; sometimes LADAR) is a method for determining ranges (variable distance) by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It can also be ...
to measure elevation on the Earth's surface, researchers found that in the year 2021, 267 million people worldwide lived on land less than 2 metres above sea level and that with a 1-metre sea level rise and zero population growth, that number could increase to 410 million people. Populations that move from the coasts because of the effects of rising sea levels could be impacted by loss of livelihoods and could become a heavy strain on the regions or cities that they come to inhabit. Further, both their original government or the receiving countries may lack or withhold resources to help these climate migrants, which compounds their level of poverty.


Ecosystems

Coastal ecosystems are facing drastic changes as a consequence of rising sea levels. Many systems might ultimately be lost when sea levels rise too much or too fast. Some ecosystems can move land inward with the high-water mark, but many are prevented from migrating due to natural or artificial barriers. This coastal narrowing, sometimes called 'coastal squeeze' when considering human-made barriers, could result in the loss of habitats such as
mudflat Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal f ...
s and
marsh A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found ...
es. The mangrove ecosystem is one of the ecosystems affected by rising sea levels. It is an ecological whole composed of mangrove plants growing in and around the mudflats of the tropical coast. Its ecological value is high because it is an ideal home for many species. In recent years, mangroves have been moving inland, but their success depends on various environmental information such as topography and geology. The warmer the climate, the bigger they grow. The mangrove's breathing roots or pneumatophores might grow to be half a metre tall.
Mangroves A mangrove is a shrub or tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evolution in sever ...
and
tidal marsh A tidal marsh (also known as a type of "tidal wetland") is a marsh found along rivers, coasts and estuaries which floods and drains by the tidal movement of the adjacent estuary, sea or ocean. Tidal marshes are commonly zoned into lower marshes ( ...
es adjust to rising sea levels by building vertically using accumulated
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...
and
organic matter Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
. If sea level rise is too rapid, they will not be able to keep up and will instead be submerged. More specifically, if the rate of mangrove deposition does not keep up with sea level rise, the key to the extinction of the mangrove ecosystem is the relationship between the rate of inland migration and the rate of sea level rise. If sea levels rise faster than the mangroves can move to land, this can lead to the loss of ecosystems. The ability of mangroves to survive sea level rise events depend on their ability to migrate inland. As both ecosystems protect against storm surges, waves and tsunamis, losing them makes the effects of sea level rise worse. Human activities, such as dam building, may restrict sediment supplies to wetlands, and thereby prevent natural adaptation processes. The loss of some
tidal marsh A tidal marsh (also known as a type of "tidal wetland") is a marsh found along rivers, coasts and estuaries which floods and drains by the tidal movement of the adjacent estuary, sea or ocean. Tidal marshes are commonly zoned into lower marshes ( ...
es is unavoidable as a consequence. When seawater reaches inland, problems related to contaminated soils may occur. Also, fish, birds, and coastal plants could lose parts of their habitat. Coral, important for bird and fish life, needs to grow vertically to remain close to the sea surface in order to get enough energy from sunlight. It has 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. In 2016, it was reported that the
Bramble Cay melomys The Bramble Cay melomys, or Bramble Cay mosaic-tailed rat (''Melomys rubicola''), is a recently extinct species of rodent in the family Muridae and subfamily Murinae. It was an endemic species of the isolated Bramble Cay, a low-lying vegetat ...
, which lived on a
Great Barrier Reef The Great Barrier Reef is the world's largest coral reef system composed of over 2,900 individual reefs and 900 islands stretching for over over an area of approximately . The reef is located in the Coral Sea, off the coast of Queensland, A ...
island, had probably become extinct because of inundation due to sea level rises. This report was confirmed by the federal government of
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
when it declared the
Bramble Cay melomys The Bramble Cay melomys, or Bramble Cay mosaic-tailed rat (''Melomys rubicola''), is a recently extinct species of rodent in the family Muridae and subfamily Murinae. It was an endemic species of the isolated Bramble Cay, a low-lying vegetat ...
extinct as of February 2019, making this species the first known mammal to go extinct as a result of sea level rise.


Adaptation

Adaptation In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...
options to sea level rise can be broadly classified into ''retreat, accommodate'' and ''protect''. Retreating is moving people and
infrastructure Infrastructure is the set of facilities and systems that serve a country, city, or other area, and encompasses the services and facilities necessary for its economy, households and firms to function. Infrastructure is composed of public and priv ...
to less exposed areas and preventing further development in areas that are at risk. This type of adaptation is potentially disruptive, as displacement of people might lead to tensions. Accommodation options are measurements that make societies more flexible to sea level rise. Examples are the cultivation of food crops that tolerate a high salt content in the soil and making new building standards which require building to be built higher and have less damage in the case a flood does occur. Finally, areas can be protected by the construction of dams, dikes and by improving natural defenses. In more detail, the existing problems are divided into two parts: one is water pollution, and the other is storm surges and floods. Besides, storm surges and flooding can be instantaneous and devastating to cities, and some coastal areas have begun investing in storm water valves to cope with more frequent and severe flooding during high tides. These adaptation options can be further divided into ''hard'' and ''soft''. Hard adaptation relies mostly on capital-intensive human-built infrastructure and involves large-scale changes to human societies and ecological systems. Because of its large scale, it is often not flexible. Soft adaptation involves strengthening natural defenses and adaptation strategies in local communities and the use of simple and modular technology, which can be locally owned. The two types of adaptation might be complementary or mutually exclusive. Cutting greenhouse gas emissions (or climate change mitigation) can stabilize sea level rise rates beyond 2050, but can not prevent sea levels from rising. Thus, mitigation gives more time for adaptation and it leaves more options open, such as nature-based solutions.


Regional examples


Africa

In
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
, risk from sea level rise is amplified by the future
population growth Population growth is the increase in the number of people in a population or dispersed group. Actual global human population growth amounts to around 83 million annually, or 1.1% per year. The global population has grown from 1 billion in 1800 to ...
. It is believed that 54.2 million people lived in the highly exposed low elevation coastal zones (LECZ) around 2000, but this number will effectively double to around 110 million people by 2030, and by 2060 it'll be in the range between 185 and 230 million people, depending on the extent of population growth. While the average regional sea level rise by 2060 will be around 21 cm (with climate change scenarios making little difference at that point), local geography and population trends interact to increase the exposure to hazards like
100-year flood A 100-year flood is a flood event that has a 1 in 100 chance (1% probability) of being equaled or exceeded in any given year. The 100-year flood is also referred to as the 1% flood, since its annual exceedance probability is 1%.Holmes, R.R., Jr. ...
s in a complex manner. In the near term, some of the largest displacement is projected to occur in the
East Africa East Africa, Eastern Africa, or East of Africa, is the eastern subregion of the African continent. In the United Nations Statistics Division scheme of geographic regions, 10-11-(16*) territories make up Eastern Africa: Due to the historica ...
region, where at least 750,000 people are likely to be displaced from the coasts between 2020 and 2050. It was also estimated that by 2050, 12 major African cities (
Abidjan Abidjan ( , ; N’ko: ߊߓߌߖߊ߲߬) is the economic capital of the Ivory Coast. As of the 2021 census, Abidjan's population was 6.3 million, which is 21.5 percent of overall population of the country, making it the sixth most populous city p ...
,
Alexandria Alexandria ( or ; ar, ٱلْإِسْكَنْدَرِيَّةُ ; grc-gre, Αλεξάνδρεια, Alexándria) is the second largest city in Egypt, and the largest city on the Mediterranean coast. Founded in by Alexander the Great, Alexandri ...
,
Algiers Algiers ( ; ar, الجزائر, al-Jazāʾir; ber, Dzayer, script=Latn; french: Alger, ) is the capital and largest city of Algeria. The city's population at the 2008 Census was 2,988,145Census 14 April 2008: Office National des Statistiques d ...
,
Cape Town Cape Town ( af, Kaapstad; , xh, iKapa) is one of South Africa's three capital cities, serving as the seat of the Parliament of South Africa. It is the legislative capital of the country, the oldest city in the country, and the second largest ...
,
Casablanca Casablanca, also known in Arabic as Dar al-Bayda ( ar, الدَّار الْبَيْضَاء, al-Dār al-Bayḍāʾ, ; ber, ⴹⴹⴰⵕⵍⴱⵉⴹⴰ, ḍḍaṛlbiḍa, : "White House") is the largest city in Morocco and the country's econom ...
,
Dakar Dakar ( ; ; wo, Ndakaaru) (from daqaar ''tamarind''), is the capital and largest city of Senegal. The city of Dakar proper has a population of 1,030,594, whereas the population of the Dakar metropolitan area is estimated at 3.94 million in 2 ...
,
Dar es Salaam Dar es Salaam (; from ar, دَار السَّلَام, Dâr es-Selâm, lit=Abode of Peace) or commonly known as Dar, is the largest city and financial hub of Tanzania. It is also the capital of Dar es Salaam Region. With a population of over s ...
,
Durban Durban ( ) ( zu, eThekwini, from meaning 'the port' also called zu, eZibubulungwini for the mountain range that terminates in the area), nicknamed ''Durbs'',Ishani ChettyCity nicknames in SA and across the worldArticle on ''news24.com'' from ...
,
Lagos Lagos (Nigerian English: ; ) is the largest city in Nigeria and the second most populous city in Africa, with a population of 15.4 million as of 2015 within the city proper. Lagos was the national capital of Nigeria until December 1991 fo ...
,
Lomé Lomé is the capital and largest city of Togo. It has an urban population of 837,437
,
Luanda Luanda () is the capital and largest city in Angola. It is Angola's primary port, and its major industrial, cultural and urban centre. Located on Angola's northern Atlantic coast, Luanda is Angola's administrative centre, its chief seapo ...
and
Maputo Maputo (), formerly named Lourenço Marques until 1976, is the capital, and largest city of Mozambique. Located near the southern end of the country, it is within of the borders with Eswatini and South Africa. The city has a population of 1,0 ...
) would collectively sustain cumulative damages of USD 65 billion for the "moderate" climate change scenario RCP 4.5 and USD 86.5 billion for the high-emission scenario RCP 8.5: the version of the high-emission scenario with additional impacts from high ice sheet instability would involve up to 137.5 billion USD in damages. Additional accounting for the "low-probability, high-damage events" may increase aggregate risks to USD 187 billion for the "moderate" RCP4.5, USD 206 billion for RCP8.5 and USD 397 billion under the high-end instability scenario. In all of these estimates, the Egyptian city of Alexandria alone amounts for around half of this figure: hundreds of thousands of people in its low-lying areas may already have to be relocated in the coming decade. Across
sub-Saharan Africa Sub-Saharan Africa is, geographically, the area and regions of the continent of Africa that lies south of the Sahara. These include West Africa, East Africa, Central Africa, and Southern Africa. Geopolitically, in addition to the List of sov ...
as a whole, damages from sea level rise could reach 2–4% of GDP by 2050, although this is strongly affected by the extent of future
economic growth Economic growth can be defined as the increase or improvement in the inflation-adjusted market value of the goods and services produced by an economy in a financial year. Statisticians conventionally measure such growth as the percent rate o ...
and
adaptation In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...
. In the longer term,
Egypt Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a List of transcontinental countries, transcontinental country spanning the North Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via a land bridg ...
,
Mozambique Mozambique (), officially the Republic of Mozambique ( pt, Moçambique or , ; ny, Mozambiki; sw, Msumbiji; ts, Muzambhiki), is a country located in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi ...
and
Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands ...
are also projected to have the largest number of people affected by annual flooding amongst all African countries if global warming reaches 4 °C by the end of the century (a level associated with the RCP 8.5 scenario). Under RCP 8.5, 10 important cultural sites (
Casbah of Algiers The Casbah ( ar, قصبة, ''qaṣba'', meaning citadel) is the citadel of Algiers in Algeria and the traditional quarter clustered around it. In 1992, the United Nations Educational, Scientific and Cultural Organization (UNESCO) proclaimed ' ...
, Carthage Archaeological site, Kerkouane, Leptis Magna Archaeological site,
Medina of Sousse The Medina of Sousse is a Medina quarter in Sousse, Governorate of Sousse, Tunisia. Designated by the UNESCO a World Heritage Site in 1988, it is a typical example of the architecture of the early centuries of Islam in Maghreb. It encompass ...
, Medina of Tunis, Sabratha Archaeological site, Robben Island, Island of Saint-Louis and Tipasa) would be at risk of flooding and erosion by the end of the century, along with a total of 15
Ramsar site A Ramsar site is a wetland site designated to be of international importance under the Ramsar Convention,8 ha (O) *** Permanent 8 ha (P) *** Seasonal Intermittent < 8 ha(Ts) **
Bao Bolong Wetland Reserve, Delta du Saloum National Park,
Diawling National Park The Diawling National Park lies in south west Mauritania around the Senegal River delta. During the rainy season, much of the park consists of large lakes. It is known for having over 220 species of identified birds, including pelicans, black sto ...
,
Golfe de Boughrara Golfe is a Prefecture located in the Maritime Region of Togo. The prefecture's seat is Lomé which is also the administrative capital of the Togolese Republic. Cantons A canton is a type of administrative division of a country. In general, cant ...
,
Kalissaye Kalissaye Avifaunal Reserve (KAR) is a small nature reserve in Senegal, located at the mouth of Kalissaye Pond in the middle of the Casamance River. Like Basse Casamance National Park 35 km away, KAR is currently closed due to the Casamance ...
, Lagune de Ghar el Melh et Delta de la Mejerda,
Marromeu Game Reserve The Marromeu Game Reserve is a protected swath of of floodplain in the Zambezi, the only such area along the river. It was dedicated on 1 January 1969. It is located near Beira. The area is an open grassland with many rivers and streams in the ...
,
Parc Naturel des Mangroves du Fleuve Cacheu The Cacheu River Mangroves Natural Park ( pt, Parque Natural dos Tarrafes do Rio Cacheu) is a national park situated on the Cacheu River in Guinea-Bissau. It was established on 1 December 2000. This site is 886 km. The park has been design ...
,
Seal Ledges Provincial Nature Reserve Seal may refer to any of the following: Common uses * Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly: ** Earless seal, or "true seal" ** Fur seal * Seal (emblem), a device to impr ...
, Sebkhet Halk Elmanzel et Oued Essed, Sebkhet Soliman, Réserve Naturelle d'Intérêt Communautaire de la Somone, Songor Biosphere Reserve,
Tanbi Wetland Complex Tanbi Wetland Complex is a wetland reserve in the Gambia outside of Banjul which was established in 2001. Location The wilderness site of the Tanbi Wetland Complex, in Gambia, is on the southern channel at the mouth of the River Gambia. It encom ...
and Watamu Marine National Park).


Asia

As of 2022, it is estimated that 63 million people in the
East East or Orient is one of the four cardinal directions or points of the compass. It is the opposite direction from west and is the direction from which the Sun rises on the Earth. Etymology As in other languages, the word is formed from the fac ...
and
South Asia South Asia is the southern subregion of Asia, which is defined in both geographical and ethno-cultural terms. The region consists of the countries of Afghanistan, Bangladesh, Bhutan, India, Maldives, Nepal, Pakistan, and Sri Lanka.;;;;; ...
are already at risk from a
100-year flood A 100-year flood is a flood event that has a 1 in 100 chance (1% probability) of being equaled or exceeded in any given year. The 100-year flood is also referred to as the 1% flood, since its annual exceedance probability is 1%.Holmes, R.R., Jr. ...
, in large part due to inadequate coastal protection in many countries. This will be greatly exacerbated in the future: Asia has the largest population at risk from sea level and
Bangladesh Bangladesh (}, ), officially the People's Republic of Bangladesh, is a country in South Asia. It is the eighth-most populous country in the world, with a population exceeding 165 million people in an area of . Bangladesh is among the mo ...
, China,
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
,
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Gui ...
,
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
,
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
,
Thailand Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is b ...
and
Vietnam Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Republic of Vietnam,., group="n" is a country in Southeast Asia, at the eastern edge of mainland Southeast Asia, with an area of and population of 96 million, making ...
alone account for 70% number of people exposed to sea level rise during the 21st century. This is entirely due to the region's densely populated coasts, as the rate of sea level rise in Asia is generally similar to the global average. Exceptions include the
Indo-Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...
region, where it had been around 10% faster since the 1990s, and the coast of
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
, where globally "extreme" sea level rise had been detected since the 1980s, and it is believed that the difference between and of global warming would have a disproportionate impact on flood frequency. It is also estimated that future sea level rise along the Japanese Honshu Island would be up to 25 cm faster than the global average under RCP 8.5, the intense climate change scenario. RCP 8.5 is additionally associated with the loss of at least a third of the Japanese
beach A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc s ...
es and 57–72% of Thai beaches.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
Chapter 10: Asia
I
Climate Change 2022: Impacts, Adaptation and Vulnerability
.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke,V. Möller, A. Okem, B. Rama (eds.) Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1457–1579 , doi=10.1017/9781009325844.012
One estimate finds that Asia will suffer direct economic damages of 167.6 billion USD at 0.47 meters of sea level rise, 272.3 billion USD at 1.12 meters and 338.1 billion USD at 1.75 meters (along with the indirect impact of 8.5, 24 or 15 billion USD from population displacement at those levels), with
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
,
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
, the
Republic of Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korean Peninsula and sharing a land border with North Korea. Its western border is formed by the Yellow Sea, while its ea ...
,
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
,
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Gui ...
and
Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-ei ...
experiencing the largest economic losses. Out of the 20 coastal cities expected to see the highest flood losses by 2050, 13 are in Asia. For nine of those (
Bangkok Bangkok, officially known in Thai as Krung Thep Maha Nakhon and colloquially as Krung Thep, is the capital and most populous city of Thailand. The city occupies in the Chao Phraya River delta in central Thailand and has an estimated populati ...
,
Guangzhou Guangzhou (, ; ; or ; ), also known as Canton () and Chinese postal romanization, alternatively romanized as Kwongchow or Kwangchow, is the Capital city, capital and largest city of Guangdong Provinces of China, province in South China, sou ...
,
Ho Chi Minh City , population_density_km2 = 4,292 , population_density_metro_km2 = 697.2 , population_demonym = Saigonese , blank_name = GRP (Nominal) , blank_info = 2019 , blank1_name = – Total , blank1_ ...
,
Jakarta Jakarta (; , bew, Jakarte), officially the Special Capital Region of Jakarta ( id, Daerah Khusus Ibukota Jakarta) is the capital city, capital and list of Indonesian cities by population, largest city of Indonesia. Lying on the northwest coa ...
,
Kolkata Kolkata (, or , ; also known as Calcutta , the official name until 2001) is the capital of the Indian state of West Bengal, on the eastern bank of the Hooghly River west of the border with Bangladesh. It is the primary business, comme ...
,
Nagoya is the largest city in the Chūbu region, the fourth-most populous city and third most populous urban area in Japan, with a population of 2.3million in 2020. Located on the Pacific coast in central Honshu, it is the capital and the most po ...
,
Tianjin Tianjin (; ; Mandarin: ), alternately romanized as Tientsin (), is a municipality and a coastal metropolis in Northern China on the shore of the Bohai Sea. It is one of the nine national central cities in Mainland China, with a total popu ...
,
Xiamen Xiamen ( , ; ), also known as Amoy (, from Hokkien pronunciation ), is a sub-provincial city in southeastern Fujian, People's Republic of China, beside the Taiwan Strait. It is divided into six districts: Huli, Siming, Jimei, Tong' ...
and
Zhanjiang Zhanjiang (), historically spelled Tsamkong, is a prefecture-level city at the southwestern end of Guangdong province, People's Republic of China, facing Haikou city to the south. As of the 2020 census, its population was 6,981,236 (6,994,832 ...
) sea level rise would be compounded by subsidence. By 2050, Guangzhou would see 0.2 meters of sea level rise and the estimated ''annual'' economic losses of 254 million USD - the highest in the world. One estimate calculates that in the absence of adaptation, cumulative economic losses caused by sea level rise in Guangzhou under RCP8.5 would reach ~331 billion USD by 2050, ~660 billion USD by 2070 and 1.4 trillion USD by 2100, while the impact of high-end ice sheet instability would increase these figures to ~420 billion USD, ~840 billion USD and ~1.8 trillion USD, respectively. In
Shanghai Shanghai (; , , Standard Chinese, Standard Mandarin pronunciation: ) is one of the four Direct-administered municipalities of China, direct-administered municipalities of the China, People's Republic of China (PRC). The city is located on the ...
, coastal inundation amounts to ~0.03% of local GDP; but would increase to 0.8% (
confidence interval In frequentist statistics, a confidence interval (CI) is a range of estimates for an unknown parameter. A confidence interval is computed at a designated ''confidence level''; the 95% confidence level is most common, but other levels, such as 9 ...
of 0.4–1.4%) by 2100 even under the "moderate" RCP 4.5 scenario in the absence of adaptation. Likewise, failing to adapt to sea level rise in
Mumbai Mumbai (, ; also known as Bombay — the official name until 1995) is the capital city of the Indian state of Maharashtra and the ''de facto'' financial centre of India. According to the United Nations, as of 2018, Mumbai is the secon ...
would result in the damages of 112–162 billion USD by 2050, which would nearly triple by 2070. As the result, efforts like the Mumbai Coastal Road are being implemented, although they are likely to affect coastal ecosystems and fishing livelihoods. It is estimated that sea level rise in Bangladesh may force the relocation of up to one-third of
power plant A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid. Many ...
s as early as 2030, while a similar proportion would have to deal with the increased salinity of their cooling water by then. Research from 2010s indicates that by 2050, between 0.9 and 2.1 million people would be displaced by sea level rise alone: this would likely necessitate the creation of ~594,000 additional jobs and ~197,000
housing Housing, or more generally, living spaces, refers to the construction and assigned usage of houses or buildings individually or collectively, for the purpose of shelter. Housing ensures that members of society have a place to live, whether ...
units in the areas receiving the displaced persons, as well as to secure the supply of additional ~783 billion
calorie The calorie is a unit of energy. For historical reasons, two main definitions of "calorie" are in wide use. The large calorie, food calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the temperature of o ...
s worth of food. in 2021, another paper estimated that 816,000 would be directly displaced by sea level rise by 2050, but this would be increased to 1,3 million when the indirect effects are taken into account. Both studies assume that the majority of the displaced people would travel to the other areas of Bangladesh, and attempt to estimate population changes in different localities. In an attempt to address these challenges, the Bangladesh Delta Plan 2100 has been launched in 2018. As of 2020, it was seen falling short of most of its initial targets. The progress is being monitored. Sea level rise also disrupts freshwater fisheries in Bangladesh by making the waters too saline for many fish species. In 2019, the
president of Indonesia The President of the Republic of Indonesia ( id, Presiden Republik Indonesia) is both the head of state and the head of government of the Republic of Indonesia. The president leads the executive branch of the Indonesian government an ...
,
Joko Widodo Joko Widodo (; born 21 June 1961), popularly known as Jokowi, is an Indonesian politician and businessman who is the 7th and current president of Indonesia. Elected in July 2014, he was the first Indonesian president not to come from an elit ...
, declared that the city of
Jakarta Jakarta (; , bew, Jakarte), officially the Special Capital Region of Jakarta ( id, Daerah Khusus Ibukota Jakarta) is the capital city, capital and list of Indonesian cities by population, largest city of Indonesia. Lying on the northwest coa ...
is sinking to a degree that requires him to move
the capital ''The Capital'' (also known as ''Capital Gazette'' as its online nameplate and informally), the Sunday edition is called ''The Sunday Capital'', is a daily newspaper published by Capital Gazette Communications in Annapolis, Maryland, to serve ...
to another city. A study conducted between 1982 and 2010 found that some areas of Jakarta have been sinking by as much as 28 cm (11 inches) per year due to ground water drilling and the weight of its buildings, and the problem is now exacerbated by sea level rise. However, there are concerns that building in a new location will increase tropical deforestation. Other so called
sinking cities Sinking cities are urban environments that are in danger of disappearing due to their rapidly changing landscapes. The largest contributors to these cities becoming unlivable are the combined effects of climate change (manifested through sea level ...
, such as
Bangkok Bangkok, officially known in Thai as Krung Thep Maha Nakhon and colloquially as Krung Thep, is the capital and most populous city of Thailand. The city occupies in the Chao Phraya River delta in central Thailand and has an estimated populati ...
or
Tokyo Tokyo (; ja, 東京, , ), officially the Tokyo Metropolis ( ja, 東京都, label=none, ), is the capital and largest city of Japan. Formerly known as Edo, its metropolitan area () is the most populous in the world, with an estimated 37.46 ...
, are vulnerable to these compounding subsidence with sea level rise.


Australasia

In
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
, erosion and flooding of
Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , establishe ...
's
Sunshine Coast Sunshine Coast may refer to: * Sunshine Coast, Queensland, Australia **Sunshine Coast Region, a local government area of Queensland named after the region **Sunshine Coast Stadium * Sunshine Coast (British Columbia), geographic subregion of the Br ...
beaches is projected to intensify by 60% by 2030, with severe impacts on tourism in the absence of adaptation. Adaptation costs to sea level rise under the high-emission RCP 8.5 scenario are projected to be three times greater than the adaptation costs to low-emission RCP 2.6 scenario. For 0.2- to 0.3-m sea level rise (set to occur by 2050), what is currently a
100-year flood A 100-year flood is a flood event that has a 1 in 100 chance (1% probability) of being equaled or exceeded in any given year. The 100-year flood is also referred to as the 1% flood, since its annual exceedance probability is 1%.Holmes, R.R., Jr. ...
would occur every year in
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...
cities of
Wellington Wellington ( mi, Te Whanganui-a-Tara or ) is the capital city of New Zealand. It is located at the south-western tip of the North Island, between Cook Strait and the Remutaka Range. Wellington is the second-largest city in New Zealand by ...
and
Christchurch Christchurch ( ; mi, Ōtautahi) is the largest city in the South Island of New Zealand and the seat of the Canterbury Region. Christchurch lies on the South Island's east coast, just north of Banks Peninsula on Pegasus Bay. The Avon Rive ...
. Under 0.5 m sea level rise, the current 100-year flood in Australia would be likely to occur several times a year, while in New Zealand, buildings with a collective worth of NZ$12.75 billion would become exposed 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 (with a disproportionate impact on Maori-owned holdings and cultural heritage objects), and Australian assets with a worth of AUD$164–226 billion (including many unsealed roads and
railway line Rail terminology is a form of technical terminology. The difference between the American term ''railroad'' and the international term ''railway'' (used by the International Union of Railways and English-speaking countries outside the United Sta ...
s). The latter represents 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
Chapter 11: Australasia
I
Climate Change 2022: Impacts, Adaptation and Vulnerability
.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke,V. Möller, A. Okem, B. Rama (eds.) Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1581–1688, , doi=10.1017/9781009325844.013


Central and South America

By 2100, a minimum of 3-4 million people in
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...
would be directly affected by coastal flooding and erosion. 6% of the population of
Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in th ...
, 56% of the population of
Guyana Guyana ( or ), officially the Cooperative Republic of Guyana, is a country on the northern mainland of South America. Guyana is an indigenous word which means "Land of Many Waters". The capital city is Georgetown. Guyana is bordered by the ...
(including in the capital, Georgetown, much of which is already below the sea level) and 68% of the population of
Suriname Suriname (; srn, Sranankondre or ), officially the Republic of Suriname ( nl, Republiek Suriname , srn, Ripolik fu Sranan), is a country on the northeastern Atlantic coast of South America. It is bordered by the Atlantic Ocean to the nor ...
are already living in low-lying areas exposed to sea level rise. In
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
, the coastal ecoregion of
Caatinga Caatinga (, ) is a type of semi-arid tropical vegetation, and an ecoregion characterized by this vegetation in interior northeastern Brazil. The name "Caatinga" is a Tupi word meaning "white forest" or "white vegetation" (''caa'' = forest, v ...
is responsible for 99% of its
shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are ref ...
production, yet its unique conditions are threatened by a combination of sea level rise, ocean warming and
ocean acidification Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxid ...
. The port complex of Santa Catarina had been interrupted by extreme wave or wind behavior 76 times in one 6-year period in 2010s, with a 25,000-50,000 USD loss for each idle day. In Port of Santos,
storm surge A storm surge, storm flood, tidal surge, or storm tide is a coastal flood or tsunami-like phenomenon of rising water commonly associated with low-pressure weather systems, such as cyclones. It is measured as the rise in water level above the ...
s 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
Chapter 12: Central and South America
I
Climate Change 2022: Impacts, Adaptation and Vulnerability
.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke,V. Möller, A. Okem, B. Rama (eds.) Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1689–1816 , doi=10.1017/9781009325844.014


Europe

Venice Venice ( ; it, Venezia ; vec, Venesia or ) is a city in northeastern Italy and the capital of the Veneto Regions of Italy, region. It is built on a group of 118 small islands that are separated by canals and linked by over 400  ...
is one of the cities which had been the most threatened by flooding. The city is located on islands in the delta of the Po and Piave rivers. Sea level rise causes an increase in frequency and magnitude of floodings in the city which had already spent more than $6 billion on the flood barrier system.
Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...
is a country that sits partially below sea level and is subsiding. It has responded to that reality by extending its Delta Works program. In 2008, the Dutch ''Delta Commission'', advised in a report that the Netherlands would need a massive new building program to strengthen the country's water defenses against the rising sea for the following 190 years. This included drawing up worst-case plans for evacuations. The plan also included between €1.0 and €1.5 billion in annual spending through to the year 2100 for precautionary measures, such as broadening coastal
dunes A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, fl ...
and strengthening sea and river
dikes Dyke (UK) or dike (US) may refer to: General uses * Dyke (slang), a slang word meaning "lesbian" * Dike (geology), a subvertical sheet-like intrusion of magma or sediment * Dike (mythology), ''Dikē'', the Greek goddess of moral justice * Dikes ...
. The commission said the country must plan for a rise in the
North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian ...
up to by 2100 and plan for a rise by 2200. Analysis of the impacts of Hurricane Sandy determined that communities located behind wetlands experienced 20% less damage (Narayan et al., 2016). Coral reefs are providing 544 million USD yr−1 (Beck et al., 2018a) and mangroves 22 billion USD yr−1 in property protection for coastal communities in the USA and Mexico


North America

As of 2017, around 95 million Americans lived on the coast: for Canada and Mexico, this figure amounts to 6.5 million and 19 million people. Northern
Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United ...
,
Atlantic Canada Atlantic Canada, also called the Atlantic provinces (french: provinces de l'Atlantique), is the region of Eastern Canada comprising the provinces located on the Atlantic coast, excluding Quebec. The four provinces are New Brunswick, Newfoundla ...
and the
Pacific coast of Mexico The Pacific Coast of Mexico or West Coast of Mexico stretches along the coasts of western Mexico at the Pacific Ocean and its Gulf of California (Sea of Cortez). Geography Baja California Peninsula On the western Baja California Peninsula coas ...
would experience the greatest sea level rise. By 2030, flooding along the US
Gulf Coast The Gulf Coast of the United States, also known as the Gulf South, is the coast, coastline along the Southern United States where they meet the Gulf of Mexico. The list of U.S. states and territories by coastline, coastal states that have a shor ...
may result in economic losses of up to 176 billion USD: around 50 billion USD could be potentially avoided through nature-based solutions such as
wetland restoration A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The p ...
and
oyster reef The term ''oyster reef'' refers to dense aggregations of oysters that form large colonial communities. Because oyster larvae need to settle on hard substrates, new oyster reefs may form on stone or other hard marine debris. Eventually the oyster ...
restoration. By 2050, 20 million people in the greater
New York City New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...
area would be threatened, as 40% of the existing
water treatment Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, inc ...
facilities would be compromised and 60% of
power plant A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid. Many ...
s will need to be relocated. By 2100, sea level rise of 0.9 metres and 1.8 metres would threaten 4.2 and 13.1 million people in the US, respectively. In
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
alone, 2 metres of SLR could affect 600,000 people and threaten over 150 billion USD in property with inundation, potentially representing more than 6% of the state's GDP. In
North Carolina North Carolina () is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. The state is the List of U.S. states and territories by area, 28th largest and List of states and territories of the United ...
, a meter of SLR inundates 42% of the
Albemarle-Pamlico Peninsula Albemarle-Pamlico Peninsula is a large peninsula (about 3,200 square miles) on the North Carolina coast, lying between the Albemarle Sound to the north and the Pamlico Sound to the south. The 5 counties of Dare, Hyde, Beaufort, Tyrrell, and ...
, incurring losses of up to 14 billion USD (at 2016 value of the currency). In nine southeast US states, the same level of sea level rise would amount to the loss over 1000 sites eligible for inclusion in the
National Register for Historic Places The National Register of Historic Places (NRHP) is the United States federal government's official list of districts, sites, buildings, structures and objects deemed worthy of preservation for their historical significance or "great artistic ...
and up to 13,000 historical and archaeological sites overall.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
Chapter 14: North America
I
Climate Change 2022: Impacts, Adaptation and Vulnerability
.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke,V. Möller, A. Okem, B. Rama (eds.) Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1929–2042 , doi=10.1017/9781009325844.016
Sea level rise causes the mixing of sea water into the coastal
groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit ...
, rendering it unusable once it amounts to more than 2-3% of the reservoir. Along an estimated 15% of the US coastline, the majority of local groundwater levels are already below the sea level. It also favors chronic flooding at high tide, as evidenced e.g. in the US East Coast. Similarly, Florida, which is extremely vulnerable to climate change, is already experiencing substantial
nuisance flooding Tidal flooding, also known as sunny day flooding or nuisance flooding, is the temporary inundation of low-lying areas, especially streets, during exceptionally high tide events, such as at full and new moons. The highest tides of the year may b ...
and king tide flooding. Nonpartisan think tank ''
Resources for the Future Resources for the Future (RFF) is an American nonprofit organization, founded in 1952 that conducts independent research into environmental, energy, and natural resource issues, primarily via economics and other social sciences. Headquartered in ...
'' describes Miami as "the most vulnerable major coastal city in the world" to damages associated with storm-related coastal flooding and sea level rise.
Storm surge A storm surge, storm flood, tidal surge, or storm tide is a coastal flood or tsunami-like phenomenon of rising water commonly associated with low-pressure weather systems, such as cyclones. It is measured as the rise in water level above the ...
s can cause the largest loss of life and property in the world's coastal areas, and their frequency and intensity has increased in the recent years. New York City is one of the worst affected areas, and simulations show that the current
100-year flood A 100-year flood is a flood event that has a 1 in 100 chance (1% probability) of being equaled or exceeded in any given year. The 100-year flood is also referred to as the 1% flood, since its annual exceedance probability is 1%.Holmes, R.R., Jr. ...
would occur once in 19–68 years by 2050 and 40–60 years by 2080. U.S. coastal cities conduct
beach nourishment Beach nourishment (also referred to as beach renourishment, beach replenishment, or sand replenishment) describes a process by which sediment, usually sand, lost through longshore drift or erosion is replaced from other sources. A wider beach ...
, also known as ''beach replenishment'', where mined sand is trucked in and added, in addition to other adaptation measures such as zoning, restrictions on state funding, and building code standards. In Mexico, the damages from SLR to
tourism Tourism is travel for pleasure or business; also the theory and practice of touring (disambiguation), touring, the business of attracting, accommodating, and entertaining tourists, and the business of operating tour (disambiguation), tours. Th ...
hotspots like Cancun,
Isla Mujeres Isla Mujeres (, Spanish for "Women Island" (formally “Isla de Mujeres”) is an island where the Gulf of Mexico and the Caribbean Sea meet, about off the Yucatán Peninsula coast in the State of Quintana Roo, Mexico. It is approximately long ...
,
Playa del Carmen Playa del Carmen, known colloquially as 'Playa', is a resort city located along the Caribbean Sea in the state of Quintana Roo, Mexico. It is part of the municipality of Solidaridad. As of 2020, the city's population was just over 300,000 peopl ...
, Puerto Morelos and
Cozumel Cozumel (; yua, Kùutsmil) is an island and municipality in the Caribbean Sea off the eastern coast of Mexico's Yucatán Peninsula, opposite Playa del Carmen. It is separated from the mainland by the Cozumel Channel and is close to the Yucat� ...
could amount to 1.4–2.3 billion USD. The damages are also widespread in Canada and will affect both major cities like Halifax and the more remote locations like Lennox Island, whose
Mi'kmaq The Mi'kmaq (also ''Mi'gmaq'', ''Lnu'', ''Miꞌkmaw'' or ''Miꞌgmaw''; ; ) are a First Nations people of the Northeastern Woodlands, indigenous to the areas of Canada's Atlantic Provinces and the Gaspé Peninsula of Quebec as well as the no ...
community A community is a social unit (a group of living things) with commonality such as place, norms, religion, values, customs, or identity. Communities may share a sense of place situated in a given geographical area (e.g. a country, village, t ...
is already considering relocation due to widespread coastal erosion.


Island nations

Atoll An atoll () is a ring-shaped island, including a coral rim that encircles a lagoon partially or completely. There may be coral islands or cays on the rim. Atolls are located in warm tropical or subtropical oceans and seas where corals can gro ...
s,
low islands The Low Islands are one of the many uninhabited Canadian arctic island groups in Qikiqtaaluk Region, Nunavut. They are located in Ungava Bay, stretching between Young Island to the south and Lookout Island to the north. References Extern ...
and low-lying coastal areas on islands are particularly vulnerable to sea level rise. Possible impacts include
coastal erosion Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. The landwar ...
, flooding and salt intrusion into soils and freshwater. None are more vulnerable than small island nations, particularly those with population concentrations on atolls. Atolls on average reach above sea level. This type of island is a final stage in the geologic history of an island of volcanic origin (all volcanic islands usually become an atoll, eventually). With climate change causing sea levels rise, the process of atoll formation has sped up. Since atolls are low-lying islands, they are vulnerable to rising waters or storms covering them in water. Atolls are vital because they are the home to many distinct cultures and sovereign nations. As ocean water prematurely covers atolls, saltwater can intrude into drinking water supplies and undermine the ecosystems that the population utilizes to survive. Sea level rise has the potential to devastate tourism and local economies; a sea level rise of would cause partial or complete inundation of 29% of coastal resorts in the
Caribbean The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean ...
. A further 49–60% of coastal resorts would be at risk from resulting coastal erosion. It is difficult to assess how much of past erosion and floods have been caused by sea level change, compared to other environmental events such as hurricanes. 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.
Maldives Maldives (, ; dv, ދިވެހިރާއްޖެ, translit=Dhivehi Raajje, ), officially the Republic of Maldives ( dv, ދިވެހިރާއްޖޭގެ ޖުމްހޫރިއްޔާ, translit=Dhivehi Raajjeyge Jumhooriyyaa, label=none, ), is an archipelag ...
,
Tuvalu Tuvalu ( or ; formerly known as the Ellice Islands) is an island country and microstate in the Polynesian subregion of Oceania in the Pacific Ocean. Its islands are situated about midway between Hawaii and Australia. They lie east-northea ...
, and other low-lying countries are among the areas that are at the highest level of risk. At current rates, sea level would be high enough to make the Maldives uninhabitable by 2100. The Island nation of Fiji is being impacted by sea level rise. Five of the
Solomon Islands Solomon Islands is an island country consisting of six major islands and over 900 smaller islands in Oceania, to the east of Papua New Guinea and north-west of Vanuatu. It has a land area of , and a population of approx. 700,000. Its capit ...
have disappeared due to the combined effects of sea level rise and stronger trade winds that were pushing water into the Western Pacific. Countries becoming uninhabitable could exacerbate the humanitarian crisis of climate refugees. Some island nations, such as the
Republic of Maldives Maldives (, ; dv, ދިވެހިރާއްޖެ, translit=Dhivehi Raajje, ), officially the Republic of Maldives ( dv, ދިވެހިރާއްޖޭގެ ޖުމްހޫރިއްޔާ, translit=Dhivehi Raajjeyge Jumhooriyyaa, label=none, ), is an archipelag ...
,
Kiribati Kiribati (), officially the Republic of Kiribati ( gil, ibaberikiKiribati),Kiribati
''The Wor ...
and
Tuvalu Tuvalu ( or ; formerly known as the Ellice Islands) is an island country and microstate in the Polynesian subregion of Oceania in the Pacific Ocean. Its islands are situated about midway between Hawaii and Australia. They lie east-northea ...
are considering international migration of their population in response to rising seas. Moving to different countries is not an easy solution, as those who move need to have a steady income and social network in their new country. It might be easier to adapt locally by moving further inland and increasing sediment supply needed for natural erosion protection. In the island nation of
Fiji Fiji ( , ,; fj, Viti, ; Fiji Hindi: फ़िजी, ''Fijī''), officially the Republic of Fiji, is an island country in Melanesia, part of Oceania in the South Pacific Ocean. It lies about north-northeast of New Zealand. Fiji consis ...
, residents are restoring coral reefs and mangroves to protect themselves against flooding and erosion, which is estimated to be more cost-efficient than building sea-walls. Of interest is how the rising sea level will affect children in these communities. Children without stability at home and their communities can experience a variety of issues in their development. Already, children in small island states are encountering hampered access to food and water, displacement, and resulting mental and social disorders from these stressors. In the case all islands of an island nation become uninhabitable or completely submerged by the sea, the states themselves would theoretically also become dissolved. Once this happens, all rights on the surrounding area (sea) are removed. This area can be significant as rights extend to a radius of around the entire island state. Any resources, such as fossil oil, minerals and metals, within this area can be freely dug up by anyone and sold without needing to pay any commission to the (now dissolved) island state.


Changes in other geologic periods

Understanding past sea level is an important guide to current and future changes. 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 warmer than pre-industrial temperatures was 120 thousand years ago, when warming because of changes in the amount of sunlight due to slow changes in the Earth's orbit caused the
Eemian The Eemian (also called the last interglacial, Sangamonian Stage, Ipswichian, Mikulin, Kaydaky, penultimate,NOAA - Penultimate Interglacial Period http://www.ncdc.noaa.gov/global-warming/penultimate-interglacial-period Valdivia or Riss-Würm) wa ...
interglacial An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene i ...
; sea levels during that warmer interglacial were at least higher than now. The Eemian warming was sustained over a period of thousands of years, and the magnitude of the rise in sea level implies a large contribution from the Antarctic and Greenland ice sheets. Further into the past, a report by the Royal Netherlands Institute for Sea Research states that, around three million years ago, levels of carbon dioxide in the Earth's atmosphere similar to today's levels increased temperature by two to three degrees Celsius and melted one third of Antarctica's ice sheets. This in turn caused sea-levels to rise 20 metres over their present values. Since the
last glacial maximum The Last Glacial Maximum (LGM), also referred to as the Late Glacial Maximum, was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent. Ice sheets covered much of Northern North America, Northern Eu ...
about 20,000 years ago, the sea level has risen by more than , with rates varying from less than a mm/year during the pre-industrial era to 40+ mm/year when major ice sheets over Canada and Eurasia melted. Rapid disintegration of these ice sheets led to so called ' meltwater pulses', periods during which sea level rose rapidly. The rate of rise started to slow down about 8,200 years before present; the sea level was then almost constant in the last 2,500 years, before the recent rising trend that started at the end of the 19th century or in the beginning of the 20th.


See also

*
Climate emergency declaration A climate emergency declaration or ''declaring a climate emergency'' is an action taken by governments and scientists to acknowledge humanity is in a climate emergency. The first such declaration was made by a local government in December 2016. ...
* Climate engineering * Coastal development hazards * Coastal sediment supply *
Effects of climate change on oceans Among the effects of climate change on oceans are: an increase in sea surface temperature as well as ocean temperatures at greater depths, more frequent marine heatwaves, a reduction in pH value, a rise in sea level from ocean warming and ic ...
*
Effects of climate change on small island countries The effect of climate change on small island countries can be extreme because of low-lying coasts, relatively small land masses, and exposure to extreme weather. The effects of climate change, particularly sea level rise and increasingly intense ...
*
Hydrosphere The hydrosphere () is the combined mass of water found on, under, and above the surface of a planet, minor planet, or natural satellite. Although Earth's hydrosphere has been around for about 4 billion years, it continues to change in shape. This ...
*
Islands First Islands First is a non-governmental organization working on behalf of the Small Island Developing States to confront the challenges of climate change, the depletion of ocean resources (including ocean acidification and biodiversity loss), and o ...
* List of countries by average elevation


References


External links


NASA Satellite Data 1993-presentFourth National Climate Assessment Sea Level Rise Key MessageIncorporating Sea Level Change Scenarios at the Local Level
Outlines eight steps a community can take to develop site-appropriate scenarios
The Global Sea Level Observing System (GLOSS)USA Sea Level Rise Viewer (NOAA)
{{DEFAULTSORT:Sea Level Rise Oceanography
Rise Rise or RISE may refer to: Arts, entertainment, and media Fictional entities * '' Rise: The Vieneo Province'', an internet-based virtual world * Rise FM, a fictional radio station in the video game ''Grand Theft Auto 3'' * Rise Kujikawa, a vide ...
Effects of climate change Coastal geography Climate change adaptation Articles containing video clips