Contenido

Entre 1901 y 2018, el promedio mundial del nivel del mar aumentó entre 15 y 15–25 cm.[1]​ Los datos más precisos recopilados de las mediciones de radar satelital revelan un aumento acelerado de 7.5 centímetros de 1993 a 2017,[2]​para una tasa promedio de 31 mm por década.

Regional variations

Sea level rise is not uniform around the world. Some land masses move up or down as a result of subsidence (land sinks or settles) or post-glacial rebound (land rises due to loss of ice weight after melting), so 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 levels are falling. Additionally, the gravitational effects of changing ice masses and spatially varying warming patterns lead to differences in the distribution of seawater around the world.[18]​[19]​ Gravitational effects come into play when a large ice sheet melts. With mass loss, the gravitational pull becomes less and local water levels may fall. Farther from the ice sheet, water levels will rise more than average. In this sense, melting in Greenland has a different effect on regional sea level than melting in Antarctica.[20]​.

Many ports, urban conglomerates, and agricultural regions are built in river deltas, where land subsidence contributes to substantial relative rise in sea level. This is caused both by unsustainable groundwater extraction (in some places also by oil and gas extraction), and by levees and other flood management practices that prevent sediment buildup from compensating for the natural settlement of deltaic soils.[21] Complete subsidence caused by man in the Rhine-Meuse-Scheldt delta (Netherlands) is estimated at 3–4 m, more than 3 meters in urban areas of the Mississippi River Delta (New Orleans), and more than 9 meters in the Sacramento-San Joaquin River Delta (California).[22] On the other hand, postglacial isostatic rebound causes a relative fall in sea level around Hudson Bay in Canada and the north. of the Baltic Sea.[23]​.

The Atlantic is warming at a faster rate than the Pacific. This has implications for Europe and the US East Coast, which has seen sea level rise 3 to 4 times the global average.[24] The decline of the Atlantic Meridional Overturning Circulation (AMOC) has also been linked to extreme regional sea level rise on the US northeast coast.[25]​.

En términos generales, existen dos formas de modelar el aumento del nivel del mar y así hacer proyecciones futuras. Una manera es cuando los científicos utilizan el modelado basado en procesos, donde todos los procesos físicos relevantes y bien entendidos se incluyen en un modelo físico global. Se utiliza un modelo de capa de hielo") para calcular las contribuciones de las capas de hielo en el aumento del nivel del mar, y un modelo de circulación general para calcular el aumento de la temperatura del mar y la dilatación de esta. Una desventaja de este método es que no todos los procesos relevantes pueden comprenderse a un nivel suficiente, pero puede predecir no linealidades y largos retrasos en la respuesta que los estudios del pasado reciente no detectarán.

La otra metodología aplicada es la que donde los científicos utilizan técnicas semiempíricas que utilizan datos geológicos del pasado para determinar las respuestas probables del nivel del mar a un mundo en calentamiento, además de algunos modelos físicos básicos.[3]​ Estos modelos semiempíricos del nivel del mar se basan en técnicas estadísticas, utilizando relaciones (los efectos y contribuciones) entre el nivel medio global del mar y la temperatura media global observados en el pasado.[27]​ Este tipo de modelado fue parcialmente motivado por la mayoría de los modelos físicos en evaluaciones de literatura anteriores realizadas por el Panel Intergubernamental sobre Cambio Climático (IPCC) que subestimaron la cantidad de aumento del nivel del mar en comparación con las observaciones del siglo .[19]​.

Projections for the 21st century

In its fifth assessment report (2013), the Intergovernmental Panel on Climate Change estimated how much sea level is likely to rise over the century based on different levels of greenhouse gas emissions. These projections are based on well-known factors contributing to sea level rise, but exclude other processes that are less understood. If countries make rapid cuts in emissions (RCP2.6 scenario), the IPCC considers it likely that sea level will rise by an average of 26-55 cm with a 67% confidence interval. If emissions remain very high, the IPCC projects that sea level will rise by 52 to 98 cm.[19]​ In August 2020, scientists reported that the ice sheet losses observed in Greenland and Antarctica have followed the worst-case scenarios of the IPCC Fifth Assessment Report's sea level rise projections.[28][29][30][31]​.

Since the publication of the 2013 IPCC assessment, attempts have been made to include more physical processes and develop models that can project sea level rise using paleoclimatic data. This generally led to higher estimates of sea level rise.[32][33][34] For example, a 2016 study led by Jim Hansen concluded that, based on data from a previous event that led to another period of planetary climate change, sea level rise could accelerate exponentially in the coming decades, with a doubling time of 10, 20, or 40 years, respectively, raising the ocean several meters by 50. 100 or 200 years.[34]​ However, Greg Holland of the National Center for Atmospheric Research, who reviewed the study, noted: "There is no doubt that sea level rise, within the IPCC, is a very conservative number, so the truth lies somewhere between the IPCC and Jim.".[35]​.

Furthermore, a 2017 study's scenario, assuming high use of fossil fuels for combustion and strong economic growth during this century, projects sea level rise of up to 132 centimeters on average, and an extreme scenario with as much as 189 cm by 2100. This could mean rapid sea level rise of up to 19 mm 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 sea level rise of 52 cm by 2100.[36][37]​.

The United States' Fourth (2017) National Climate Assessment (NCA) found that sea level is very likely to rise between 30 and 130 cm in 2100 compared to the year 2000. A rise of 2.4 m is physically possible in a high greenhouse gas emission scenario, but the authors were unable to indicate how likely it is that this figure will become a reality. This case (the worst-case scenario) can only occur if a great contribution from Antarctica, which is a difficult region to model.[8]​.

The possibility of a collapse of the West Antarctic Ice Sheet and subsequent rapid rise in sea level was suggested in the 1970s.[32] For example, Mercer published a study in 1978 predicting that the global greenhouse effect from carbon dioxide emissions and its potential effects on climate within the century could cause sea level rise of around 5 meters due to the melting of the Antarctic Ice Sheet alone. Western.[38][32]​.

In 2019, a study projected that in a low emissions scenario, sea level will rise by 30 centimeters by 2050 and 69 centimeters by 2100, relative to the existing sea level in 2000. In a high emissions scenario, it will be 34 cm by 2050 and 111 cm by 2100. There is a likelihood that the rise will exceed 2 meters by 2100 in the high emissions scenario. emissions, which will cause the displacement of 187 million people. Sea level rise projected by 2050 will generate a sharp increase in the frequency of coastal flooding (four “moderate” flooding events per year in the US), despite the absence of storms and/or heavy rainfall.[39][40][41]​.

In September 2019, the Intergovernmental Panel on Climate Change released a report on the impact of climate change on the oceans, including sea level rise. It found that if humanity sharply reduces greenhouse gas emissions in the coming decades, the problem will be difficult but manageable. On the contrary, if the increase in emissions continues, the problem will become unmanageable.[42]​.

In February 2021, researchers suggested that previous projections of global sea level rise by 2100 reported by the IPCC were likely conservative and that sea levels will rise more than expected.[9]​.

According to the IPCC's Sixth Assessment Report published in 2021, it indicates that in the very low emissions scenario, by 2100 sea level will rise between 28 and 55 centimeters, in the intermediate scenario between 44 and 76 centimeters and in the very high emissions scenario between 63 and 101 centimeters. An elevation of approximately two meters cannot be ruled out in the very high emissions scenario.[43]​.

Sea level rise by 2100 is likely to be greater than the likely projection range presented in the IPCC's Sixth Assessment Report. Ice sheet processes and feedback mechanisms affecting ocean and ice sheet melt, which are not well understood by scientists and are not accounted for in model projections, could lead to this low-probability, high-impact event.

The IPCC's Sixth Assessment Report (AR6) presents a speculative narrative about how such warming could occur. It would likely involve a high ocean warming scenario, in which no urgent climate action is taken and strong warming continues.[44] This could lead to a faster-than-anticipated collapse of sea ice shelves and the abrupt and widespread onset of sea ice cliff instability (a process in which ice cliffs collapse under their own weight) and sea ice sheet instability (a positive feedback loop leading to runaway melting). in Antarctica, and a faster-than-projected ice loss in Greenland, leading to extreme sea level rise.[44]​ While some studies provide evidence for these processes, substantial uncertainty and low agreement between studies and a lack of understanding of these processes lead to them not being accounted for in many models, including those in AR6.[44]​ Other processes in Antarctica combined with high warming could also contribute to higher-than-projected sea level rise. expected. For example, hydrofracturing (in which meltwater builds up in ice sheet fractures, forcing them to open), increased contact of warm ocean water with ice shelves due to climate change-induced changes in ocean circulations[45]​[46][47]​ or climate change-induced changes in the climate over Antarctica, leading to lower precipitation and therefore less ice deposition.[47]​ The combination of such processes could lead to a rise in sea level of up to 2.3 meters by the year 2100.[44]​.

Long-term sea level rise

There is widespread consensus among climate scientists that sea level rise lags far behind the temperature rise that triggers it, and that substantial long-term sea level rise will continue for centuries to come, even if temperatures stabilize.[48]​ Models can reproduce paleoclimate records of sea level rise, providing confidence in their application to future long-term changes.[19]​.

Both the Greenland and Antarctic ice sheets have tipping points (Tipping Point (Climatology)) for levels of warming that could be reached before the end of the century. Crossing such tipping points would mean that changes in the ice sheet are potentially irreversible: a drop to pre-industrial temperatures may not stabilize the ice sheet once the tipping point is crossed. Quantifying the exact temperature change by which this tipping point is crossed remains controversial. For Greenland, estimates range between approximately 1 and 4 °C above the pre-industrial average temperature.[49]​[19]​ By 2020, the lower of these values ​​has already been exceeded. A 2021 analysis of subglacial sediments at the bottom of a 1.4 km-deep Greenland ice core reveals that the Greenland ice sheet melted at least once over the last million years. This strongly suggests that its inflection point is below the maximum positive temperature excursion of 2.5 °C during that period, and is therefore within the lower half of its range of estimates.[50]​[51]​ The melting of the Greenland ice sheet would contribute to sea level rise of between 4 to 7.5 m over thousands of years.[12]​.

A 2013 study estimated that each centigrade of temperature rise implies 2.3 m of sea level rise over the next 2,000 years.[52] More recent research, especially in Antarctica, indicates that this is probably a conservative estimate and that the true long-term sea level rise could be greater.[8] Warming beyond 2 °C potentially leads to rates of sea level rise dominated by ice loss from the sea. Antarctica. Continued emissions of carbon dioxide from fossil fuel sources could cause tens of additional meters of sea level rise over the next few millennia, and the fossil fuel available on Earth is even enough to eventually melt the entire Antarctic ice sheet, causing about 58 meters of sea level rise.[53] After 500 years, sea level rise from thermal expansion alone may have reached only half its final level, leaving Models suggest that it may be within the ranges of 0.5-2 m.[54]​.

Over the next 2,000 years, sea level is forecast to rise by 2 to 3 meters if the temperature peaks at 1.5 °C, by 2 to 6 meters if it peaks at 2 °C, and by 19 to 22 meters if the temperature peaks at 5 °C.[43] If temperature rise stops at 2 or 5 °C, sea level will continue to rise for about ten thousand years. In the first case it will reach 8 to 13 meters above the pre-industrial level and in the second 28 to 37 meters.[55]​.

Las tres razones principales por las que el calentamiento hace que aumente el nivel del mar en el mundo son: los océanos se expanden (por efecto de la dilatación térmica), las capas de hielo pierden hielo más rápido de lo que se forma a partir de las nevadas y los glaciares en altitudes más altas también se derriten. El aumento del nivel del mar desde principios del siglo ha estado dominado por el retroceso de los glaciares y la expansión del océano, pero se espera que las contribuciones de las dos grandes capas de hielo (Groenlandia y la Antártida) aumenten en el siglo .[3]​ Las capas de hielo almacenan la mayor parte del hielo terrestre (∼99.5%), con un equivalente al nivel del mar (SLE) de 7.4 m para Groenlandia y 58.3 m para la Antártida.[2]​.

Cada año cerca de 8 mm de precipitaciones "Precipitación (meteorología)") (equivalente líquido) cae sobre las capas de hielo en la Antártida y Groenlandia, principalmente en forma de nieve, que se acumula y con el tiempo forma hielo glacial. Gran parte de esta precipitación comienza cuando el vapor de agua se evapora de la superficie del océano. Parte de la nieve es arrastrada por el viento o desaparece de la capa de hielo por derretimiento o por sublimación (convirtiéndose directamente en vapor de agua). El resto de la nieve se transforma lentamente en hielo. Este hielo puede fluir hacia los bordes de la capa de hielo y regresar al océano derritiéndose en el borde o en forma de icebergs. Si la precipitación, los procesos superficiales y la pérdida de hielo en el borde se equilibran entre sí, el nivel del mar permanece igual. Sin embargo, los científicos han descubierto que el hielo se está perdiendo a un ritmo acelerado.[57]​[58]​.

Ocean warming

Most of the additional heat trapped in Earth's climate system generated by climate change is stored in the oceans. The oceans store more than 90% of additional heat and act as a buffer against the effects of climate change. The heat required to increase the mean temperature of the entire global ocean by 0.01 °C would cause the atmospheric temperature to increase by approximately 10 °C.[60]​ Therefore, a small change in the mean ocean temperature 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 the temperature and pressure of the water. For each degree, warmer water and water with a lot of pressure (due to depth) expands more than colder water and water with less pressure.[19] This means that cold Arctic Ocean water will expand less compared to warm tropical water. Because different climate models have slightly different patterns of ocean warming, there is not complete agreement in predictions about the contribution of ocean warming to sea level rise.[61]​ Due to the phenomenon of subsidence&action=edit&redlink=1 "Sinking (oceanography) (not yet drafted)"), heat stored in water is transported to the deeper parts of the ocean by winds and currents, and some of it reaches depths of more than 2000 m.[62]​.

Considering an increase in average global temperature of 2°C above pre-industrial levels, and without considering potential contributions from ice sheet processes with limited agreement (low confidence) between modeling approaches, the probability of exceeding 0.5 m of global sea level rise (0.7 m along the US coastline) by 2100 is about 50%. With 3°–5°C of warming under high-emission pathways, this probability increases from more than 80% to more than 99%.[63]​.

Antarctica

The large volume of ice on the Antarctic continent stores about 70% of the world's fresh water.[64] The mass balance of the Antarctic ice sheet is affected by snow accumulations and ice discharge along the periphery. Under the influence of global warming, melting at the base of the ice sheet increases. Simultaneously, the capacity of the atmosphere to transport precipitation increases with temperature, so that precipitation, in the form of snowfall, increases in global and regional models. The additional snowfall causes a greater flow of ice from the ice sheet into the ocean, so that the mass gain due to snowfall is partially offset.[65]​ Snowfall has increased over the past two centuries, but no increase was found in the interior of Antarctica over the past four decades.[66]​ Based on changes in Antarctica's ice mass balance over the past few million years due to natural climate fluctuations, the researchers concluded that ice marine acts as a barrier to the warmer waters surrounding the continent. Consequently, the loss of sea ice is one of the main causes of the instability of the entire ice sheet.[66]​.

Different satellite methods for measuring ice mass and change manage to agree in their measurements, and combining methods leads to greater certainty about how the East Antarctic Ice Sheet, the West Antarctic Ice Sheet, and the Antarctic Peninsula are evolving.[67] A systematic review study published in 2018 estimated that continent-wide ice loss was 43 gigatonnes (Gt) per year on average over the period. from 1992 to 2002, but accelerated to an average of 220 Gt per year during the five years from 2012 to 2017.[68] Most of the melt comes from the West Antarctic Ice Sheet, but the Antarctic Peninsula and the East Antarctic Ice Sheet also contribute. Sea level rise due to Antarctica has been estimated at 0.25 mm per year from 1993 to 2005, and 0.42 mm per year from 2005 to 2015. All data sets generally show an acceleration of mass loss from the Antarctic ice sheet, but with variations from year to year.[2]​.

A May 2021 study projected that limiting global warming to 1.5 °C would reduce the contribution of continental ice to sea level rise by 2100 from 25 cm to 13 cm compared to current mitigation goals, with glaciers responsible for half of the contribution to sea level rise.[69]​ In this study, the physical uncertainty of the Antarctic contribution was more significant than the uncertainty due to the choice of pathway. mitigation.[69]​.

The largest potential source of sea level rise in the world is the East Antarctic Ice Sheet, which contains enough ice to raise global sea level by 53.3 m.[70] Historically, the ice sheet has been considered relatively stable and has therefore attracted less attention and scientific observations compared to West Antarctica.[66] A combination of satellite observations of its changing volume, flow and gravitational pull with modeling of its balance surface mass suggests that the overall mass balance of the East Antarctic Ice Sheet has been relatively constant or slightly positive for much of the period between 1992 and 2017.[68] However, a 2019 study using a different methodology concluded that East Antarctica is losing significant amounts of ice mass. Scientist Eric Rignot") told CNN: "The melting is occurring in the most vulnerable parts of Antarctica [...] parts that have the potential for several meters of sea level rise over the next century or two."[66]

Greenland

Most of the ice in Greenland is part of the Greenland Ice Sheet, which is 3 km at its thickest. The rest of Greenland's ice is part of glaciers and isolated polar caps. The main reasons contributing to sea level rise in Greenland are melting ice sheet (70%) and calving glaciers (30%). Dust, soot, microbes and algae living on parts of the ice sheet further increase melting by darkening its surface and thus causing greater absorption of thermal radiation; These surface darkening regions increased in area by 12% between 2000 and 2012, and are likely to expand further.[88] The average annual ice loss in Greenland more than doubled at the beginning of the century compared to the century.[89] Some of Greenland's largest outlet glaciers, such as Jakobshavn Isbræ") and the Kangerlussuaq"), are those that contribute a greater flow of water to the ocean.[90][91]​.

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.[92][93]​ The Greenland Ice Sheet and its glaciers and ice caps are the largest contributors to sea level rise from land-based ice sources (excluding thermal expansion), and together account for the 71%, or 1.32 mm per year during the period 2012-2016.[94]​[95]​.

A study published in 2020 estimated that the Greenland ice sheet had lost a total of 3,902 gigatonnes (Gt) of ice between 1992 and 2018, corresponding to a contribution to sea level rise of 10.8 millimeters. Sea level rise due to melting of 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.[96]​.

Estimates of Greenland's future contribution to sea level rise range from 0.3 to 3 m by the year 2100.[88] By the end of the century, Greenland will contribute 2 to 10 centimeters annually.[97] The contribution of the Greenland ice sheet to sea level over the next two centuries may be very high due to a self-reinforcing cycle (the so-called positive feedback). After an initial period of melting, the height of the ice sheet will have decreased. As the air temperature increases closer to the sea surface, more melting will begin to occur. This melting can be accelerated further because the color of the ice is darker while it is melting. There is a threshold in surface warming beyond which partial or almost complete melting of the Greenland ice sheet occurs.[98] Different investigations have put this threshold value as low as 1 °C, and definitely 4 °C, above pre-industrial temperatures.[99]​[19]​ A 2021 analysis of subglacial sediments from the bottom of a Greenland ice core from 1.4 km depth reveals that the Greenland ice sheet melted at least once during the last million years and therefore strongly suggests that its tipping point is below the maximum positive temperature excursion of 2.5 °C during that period.[50][51]​.

Other glaciers

Less than 1% of glacial ice is found in mountain glaciers, compared to 99% in Greenland and Antarctica. Still, mountain glaciers have contributed appreciably to historical sea level rise and will contribute a smaller, but still significant, fraction of sea level rise over the century.[100] Earth's approximately two hundred thousand glaciers can be found on every continent.[101] Different glaciers respond differently to rising temperatures. For example, valley glaciers that have a shallow slope recede even with mild warming. Each glacier has a height above which there is a net gain in mass and below which the glacier loses mass. If that height changes a little, this has big consequences for glaciers with low slope.[102]​ Many glaciers flow into the ocean, and therefore ice loss can increase as ocean temperatures rise.[101]​.

Observational and modeling 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 century. Over the century, it is expected to rise, with glaciers contributing 7-24 cm to global sea levels.[19]​ Glaciers contributed around 40% to sea level rise over the century, with estimates for the century of around 30%.[2]​.

sea ​​ice

Melting sea ice contributes very little to global sea level rise. If the density of melted ice water floating in the sea were exactly the same as seawater, according to Archimedes' principle, no rise would occur. However, melted sea ice contains less dissolved salt than seawater and is therefore less dense: in other words, although melted sea ice weighs the same as the seawater it was displacing when it was ice, its volume is still slightly larger. If all floating ice shelves and icebergs were to melt, sea level would only rise by about 4 cm.[103]​.

Terrestrial water storage

Humans affect the amount of water stored on earth. Building dams prevents large bodies of water from flowing into the sea and therefore increases water storage on land. On the other hand, humans extract water from lakes, wetlands and underground reservoirs for food production leading to rising sea levels. Additionally, the hydrological cycle has been influenced by climate change and deforestation, which may lead to further positive and negative contributions to sea level rise. In the century, these processes more or less balanced, but dam construction has slowed and is expected to remain low throughout the century.[104][19]​.

Los cambios en el nivel del mar pueden ser provocados por variaciones en la cantidad de agua en los océanos, el volumen del océano o por cambios en la tierra en comparación con la superficie del mar. A lo largo de un período de tiempo uniforme, la realización de evaluaciones puede determinar las contribuciones a la subida del nivel del mar y proporcionar indicaciones tempranas de cambios en la trayectoria. Este tipo de vigilancia puede motivar planes de prevención.[106]​ Las diferentes técnicas utilizadas para medir los cambios en el nivel del mar no miden exactamente el mismo nivel. Los mareógrafos solo pueden medir el nivel relativo del mar, mientras que los satélites artificiales también pueden medir cambios absolutos en el nivel del mar.[20]​ Para obtener mediciones precisas del nivel del mar, los investigadores que estudian el hielo y los océanos en nuestro planeta tienen en cuenta las continuas deformaciones de la Tierra sólida, en particular debido a las masas de tierra que aún se elevan debido a la retirada de las masas de hielo del pasado, y también a la gravedad y la rotación de la Tierra.[2]​.

Satellites

Since the launch of TOPEX/Poseidon in 1992, an overlapping series of altimetry satellites has been continuously recording sea level and its changes. These satellites can measure hills and valleys in the sea caused by currents and detect trends in their height. To measure the distance to the sea surface, satellites send a microwave pulse that reflects off the ocean surface and records the time it takes to return. Microwave radiometers correct for the additional delay caused by water vapor in the atmosphere. Combining this data with the precisely known location of the spacecraft determines the height of the sea surface to within a few centimeters (about one inch). Current rates of sea level rise from satellite altimetry have been estimated to be 3.0 ± 0.4 mm per year for the period 1993–2017.[109] Early satellite measurements were slightly at odds with tide gauge measurements. Eventually, it was identified that a small calibration error for the Topex/Poseidon satellite had caused a slight overestimation of sea levels from 1992-2005, which masked in the satellite measurements the acceleration of ongoing sea level rise that was visible in the time series of the tide gauge.[110]​.

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 increase has been linked to increased trade winds, which occur when the Pacific Decadal Oscillation (PDO) and El Niño-Southern Oscillation (ENSO) shift from one state to another.[111] The PDO is a basin-wide climate pattern consisting of two phases, each typically lasting 10 to 30 years, while ENSO has a shorter period of 2 to 7 years.[112]​.

Tide gauges

The global network of tide gauges is another important source of sea level observations. Compared to the satellite record, this record has large spatial gaps but covers a much longer period of time.[114] Tide gauge coverage began primarily in the Northern Hemisphere, and data for the Southern Hemisphere remained scarce until the 1970s.[114] The oldest sea level measurements, NAP or Amsterdam Ordnance Datum established in 1675, are recorded in Amsterdam, Countries Lows.[115]​ In Australia, the collection of records is also quite extensive, including measurements made by an amateur meteorologist from 1837 and measurements taken from a sea level reference point on a small cliff on the Isle of the Dead&action=edit&redlink=1 "Isle of the Dead (Tasmania) (not yet redacted)"), in Tasmania, near the Port Arthur convict settlement "Port Arthur (Tasmania)") in 1841.[116]​.

This network was used, in combination with satellite altimeter data, to establish that global mean sea level rose by 19.5 cm between 1870 and 2004 at an average rate of around 1.44 mm/year (1.7 mm/year over the century).[117] Data collected by the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia show that global mean sea level is currently rising by 3.2 mm per year, double the century average rate.[118]​[119]​ This is an important confirmation of climate change simulations that predicted sea level rise would accelerate in response to climate change.

Some regional differences are also visible in the tide gauge data. Some of the regional differences recorded are due to differences in actual sea level, while others are due to vertical land movements. In Europe, for example, considerable variation is found because some areas of land rise while others sink. Since 1970, most tide stations have measured higher seas, but sea levels along the northern Baltic Sea have decreased due to postglacial rebound.[120]​.

Se espera que el aumento actual y futuro del nivel del mar tenga una serie de impactos, particularmente en los sistemas costeros. Tales impactos incluyen mayores y más frecuentes inundaciones por mareas altas y marejadas, aumento de la erosión costera, inhibición de los procesos de producción primaria, inundaciones costeras más extensas, cambios en la calidad del agua superficial y características de las aguas subterráneas. A su vez, se prevé que esto aumente la pérdida de propiedades y hábitats costeros, mayor riesgo de inundación y posible pérdida de vidas, pérdida de recursos y valores culturales no monetarios, impactos en la agricultura y la acuicultura a través de la disminución de la calidad del suelo y el agua, y pérdida del turismo, recreación y funciones de transporte.[122]​Muchos de estos impactos son perjudiciales. Debido a la gran diversidad de ambientes costeros, las diferencias regionales y locales en el nivel relativo del mar proyectado y los cambios climáticos, y las diferencias en la resiliencia y capacidad de adaptación de los ecosistemas, sectores y países, los impactos serán muy variables en el tiempo y el espacio. Los deltas de los ríos en África y Asia y los pequeños estados insulares son particularmente vulnerables al aumento del nivel del mar.[123]​.

Además de la subida del nivel del mar, hay otros efectos del cambio climático que pueden influir mucho en las poblaciones. Esto incluye, por ejemplo, la pérdida de ecosistemas costeros como los corales debido al calentamiento de los océanos o al aumento de las precipitaciones extremas causadas por el cambio climático. Los impactos de las inundaciones costeras se ven exacerbados por los cambios en el uso de la tierra, como la urbanización o la deforestación de las zonas costeras bajas. Las regiones que ya son vulnerables al aumento del nivel del mar también luchan contra las inundaciones costeras que arrastran la tierra y alteran el paisaje.[124]​ Las personas en estas áreas luchan cada vez más debido a estos diferentes efectos del cambio climático. Las tormentas influenciadas por el cambio climático también crean una mayor frecuencia de inundaciones costeras. Abordar los problemas de inundaciones que experimenta una región, ciudad o país se basará en los esfuerzos del país afectado. Sin mucho esfuerzo, estas regiones costeras podrían degradarse continuamente y, por lo tanto, afectar en gran medida el tamaño y la influencia de un país.

A nivel mundial, decenas de millones de personas estarán expuestas en las últimas décadas del siglo si los gases de efecto invernadero no se reducen drásticamente. Muchas áreas costeras tienen un gran crecimiento demográfico, lo que resulta en más personas en riesgo por el aumento del nivel del mar. El aumento del nivel del mar plantea un riesgo directo: las casas desprotegidas pueden inundarse, y amenazas indirectas de mayores marejadas ciclónicas, tsunamis y mareas reales"). Asia tiene la población más grande en riesgo por el nivel del mar con países como Bangladés, China, India, Indonesia y Vietnam que tienen áreas costeras muy densamente pobladas.[125]​ Los efectos de los desplazamientos dependen en gran medida del éxito de los gobiernos a la hora de poner en práctica las defensas contra la subida del nivel del mar, lo que preocupa a los países más pobres, como los subsaharianos y las naciones insulares.[126]​.

Un estudio de 2019 encontró que la cantidad de personas expuestas al aumento del nivel del mar durante el siglo es tres veces mayor de lo que se pensaba anteriormente. Para 2050, 150 millones estarán bajo la línea de agua durante la marea alta y 300 millones vivirán en zonas con inundaciones cada año. Para el año 2100, esos números difieren considerablemente según el escenario de emisión. En un escenario de bajas emisiones, 140 millones quedarán bajo el agua durante la marea alta y 280 millones sufrirán inundaciones cada año. En el escenario de altas emisiones, las cifras llegan a 540 millones y 640 millones respectivamente. El setenta por ciento de ellos son de ocho países de Asia: China, Bangladés, India, Indonesia, Tailandia, Vietnam, Japón y Filipinas.[127]​[128]​.

Una revisión en 2020 de 33 publicaciones encontró que «la mayoría de las estimaciones globales son del orden de decenas o cientos de millones de personas expuestas a inundaciones costeras permanentes e inundaciones costeras esporádicas en diferentes períodos y escenarios» debido al aumento del nivel del mar.[129]​.

Coastal areas

Due to numerous factors, sea level is rising at a rapid rate, posing a major threat to the human environment, both now and in the future. Although this is a slow and continuous process, its long-term cumulative effects on the world, especially in coastal areas, represent a serious threat. In recent years, some coastal areas have already had to deal with the cumulative effects of a long period of change. These areas are sensitive to sea level rise, changes in storm frequency and intensity, increased precipitation, and rising ocean temperatures. 10% of the world's population lives in coastal areas less than 10 meters above sea level. Additionally, two-thirds of the world's cities with more than five million inhabitants are located in these low-lying coastal areas.[130]​ In total, approximately 600 million people live directly in coastal areas around the world.[131]​ Using remote laser scanning called LiDAR to measure the elevation of the Earth's surface, researchers found that in 2021, 267 million people worldwide lived on land less than 2 meters above sea level and that with a sea level rise of 1 meter and zero population growth, that number could increase to 410 million people.[132]​[133]​.

The advantage that coastal region populations have is that they would technically have other parts of the country or region to which they could move or migrate. Also, the idea with these countries is that they can possibly receive assistance from their government or their compatriots. The challenges for people in low-lying nations is that they must uproot their entire life and culture to move to safer areas. Populations moving away from the coasts would also be affected by loss of livelihoods and could become a major strain on the regions or cities they inhabit.[134] Additionally, both their original government and the receiving countries may lack or withhold resources to assist these climate migrants, exacerbating their level of poverty.

Rising sea levels favor chronic flooding at high tide, as evidenced, for example, on the US East Coast.[135]​ Similarly, Florida, which is extremely vulnerable to climate change, is already experiencing significant floods and giant tides.[136] Another area at risk is Venice, which has experienced significant flooding; This city is located on islands in the delta of the Po and Piave rivers. Rising sea levels cause an increase in the frequency and magnitude of flooding in the city that has already spent more than $6 billion on the flood barrier system.[137]​[138]​.

Food production in coastal areas is also affected by rising sea levels. Due to flooding and the intrusion of salt water into the soil, the salinity of agricultural lands near the sea increases, posing problems for crops that are not resistant to salt. Additionally, salt intrusion into fresh irrigation water poses a second problem for irrigated crops. Recently developed salt-resistant crop variants are currently more expensive than the crops they are intended to replace.[139] Cropland in the Nile Delta is affected by saltwater flooding,[140] and there is now more salt in the soil and irrigation water in the Red River Delta and the Mekong Delta in Vietnam.[139] Bangladesh and China are similarly affected, particularly in their production of salt. rice.[141]​.

Island nations

Atolls, low-lying islands and low-lying coastal areas of islands are particularly vulnerable to sea level rise. Potential impacts include coastal erosion, flooding, and salt intrusion into soils and freshwater. No country is more vulnerable than small island nations, particularly those with population concentrations on atolls. Atolls on average reach 1 to 2 meters above sea level.[147] This type of island is a final stage in the geological history of an island of volcanic origin (all volcanic islands usually become atolls, eventually). With climate change causing sea levels to rise, the process of atoll formation has accelerated. Because atolls are low-lying islands, they are vulnerable to rising waters or storms that cover them with water. Atolls are vital because many different cultures and sovereign nations are based there. As ocean water prematurely covers atolls, salt water can intrude into drinking water supplies and undermine the ecosystems that people use to survive.[148] Sea level rise has the potential to devastate tourism and local economies; A sea level rise of 1.0 meter would result in the partial or complete flooding of 29% of coastal resorts in the Caribbean "Caribbean (region)"), while the other 49-60% of coastal resorts would be at risk from resulting coastal erosion.[149] It is difficult to assess how much of past erosion and flooding has 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.[150]​.

Millions of people in these island nations or nations with many islands are incredibly vulnerable to sea level rise. Some countries and regions will be submerged, pushing people living there to struggle, adapt or relocate. Developed countries could see a giant wave of refugees arrive due to the loss of refugee homes and therefore have security problems.[151] While islanders around the world have been very adaptable people, they have also relied heavily on the resources they acquire from their islands. While it may seem like the oceans are abundant and can provide everything, they also tend to be very difficult environments in which to thrive. Of interest is how sea level rise will affect children in these communities. Being a child who does not have stability at home and in their community can create a variety of problems in their development. Children in small island states already face obstacles in accessing food and water, displacement, and mental and social disorders resulting from these stressors.[152]​.

The Maldives, Tuvalu and other low-lying countries are among the areas most at risk. At the current rate, sea level would be high enough to make the Maldives uninhabitable by 2100.[153]​[154]​ Geomorphological events such as storms tend to have greater impacts on island reefs than sea level rise on, for example, one of the Marshall Islands. These effects include immediate erosion and subsequent regeneration process that can vary in duration from decades to centuries, even resulting in land areas larger than pre-storm values. With an expected increase in the frequency and intensity of storms, they may become more important in determining the shape and size of islands than sea level rise.[155] The island nation of Fiji is being affected by rising sea levels.[156] Five of the Solomon Islands have disappeared due to the combined effects of rising sea levels and stronger trade winds pushing water into the Pacific. western.[157]​.

Ecosystems

Coastal ecosystems are facing drastic changes as a result of rising sea levels. Many systems could end up being lost when sea levels rise too much or too fast. Some ecosystems can move inland due to the influence of altered high tides, but many are prevented from migrating due to natural or artificial barriers. This coastal narrowing, sometimes called "shoreline compression" when artificial barriers are considered, could lead to the loss of habitats such as salt marshes and marshes.[17]​[159]​.

The mangrove ecosystem is one of the ecosystems affected by sea level rise. This is an ecological complex composed of mangrove plants that grow in and around the marshes of the tropical coast. Its ecological value is high because it is an ideal habitat for many species. In recent years, mangroves have moved inland, but their success depends on various environmental information, such as topography and geology. The warmer the climate, the larger they grow. Mangrove respiratory roots or pneumatophores can reach half a meter in height.[160]​[161]​ Mangroves and salt marshes adapt to rising sea levels by building vertically using accumulated sediments and organic matter. If sea level rise is too rapid, they will not be able to keep up with the pace of adaptation and will instead become submerged.[162]​ More specifically, if the rate of mangrove deposition does not keep pace 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 level rises faster than mangroves can move landward, this can lead to ecosystem loss.[163]​ The ability of mangroves to survive sea level rise events depends on their ability to migrate inland.[161]​ As both ecosystems protect against storm surges, waves, and tsunamis, losing them worsens the effects of sea level rise. sea.[164]​[165]​ Human activities, such as dam construction, can restrict the supply of sediment to wetlands and therefore impede natural adaptation processes. As a consequence, the loss of some marshes is, theoretically, inevitable.[166]​.

When seawater reaches inland, problems related to contaminated soil can occur. In addition, fish, birds and coastal plants could lose parts of their habitat.[15]​ Coral, important for bird and fish life, needs to grow vertically to stay close to the sea surface to obtain enough energy from sunlight. It has so far been able to maintain vertical growth with rising sea levels, but may not be able to do so in the future.[167]​ In 2016, it was reported that the Bramble Cay melomys, which lived on an island in the Great Barrier Reef, had likely become extinct due to flooding caused by rising sea levels.[168]​ This report was confirmed by Australia's federal government when it declared the Bramble Cay melomys extinct in February 2019, making this species the first known mammal to become extinct as a result of sea level rise.[169]​.

Adaptation options to sea level rise can be broadly classified into retreat, accommodate and protect. Retreat is moving people and infrastructure to less exposed areas and preventing further development in areas that are at risk. This type of adaptation is potentially disruptive, since the displacement of people can generate social and/or political tensions. Accommodate options are measures that make societies more flexible in the face of sea level rise. Examples are growing food crops that tolerate high salt content in the soil and creating new building standards that require construction to be built higher and have less damage if a flood occurs. Finally, areas can be protected by building dams, levees and improving natural defenses.[16]​[170]​ In more detail, the existing problems are divided into two parts: one is water pollution and the other is storm surges and flooding.[171]​ Furthermore, storm surges and floods can be instantaneous and devastating to cities, and some coastal areas have begun to invest in water valves. stormwater to deal with more frequent and severe flooding during high tides.[171]​.

These adaptation options can be divided into hard and soft. Hard adaptation relies primarily on capital-intensive man-made infrastructures that involve large-scale changes to human societies and ecological systems. Due to its large scale, it is not usually flexible. Soft adaptation involves strengthening the natural defenses and adaptation strategies of local communities, as well as the use of simple, modular technology, which can be locally owned. The two types of adaptation can be complementary or mutually exclusive.[170]​[172]​.

Maritime trade is the dominant form of trade in resources and goods around the world. When talking about sea level rise, there is the possibility of major problems for maritime trade and the ports that are used. What is also important for these ports is that it is not yet known how the rise in sea level will continue to affect them over time.[173] Various factors intervene in the investment of seaports. Factors that are important for seaports in relation to sea level rise are where major commercial ports will be in the future, whether ports currently in use can be altered and protected, and how much is needed to protect trade without wasting time or money. Sea level rise is a concern for seaports, but it is difficult to figure out what changes need to be made since sea level does not rise at the same rate around the world.[174]​.

Many countries are developing concrete plans for adaptation. An example is the extension of the Delta Works in the Netherlands, a country that lies partially below sea level and is sinking.[175] In 2008, the Dutch Delta Commission warned in a report that the Netherlands would need a massive new construction program to strengthen the country's aquatic defenses against rising sea levels over the next 190 years. This included developing worst-case evacuation plans. The plan also included more than €100 billion in new spending until the year 2100 for precautionary measures, such as widening coastal dunes and strengthening sea and river dikes. The commission said the country should plan for a rise in the North Sea of ​​up to 1.3 m by 2100 and plan for rise between 2 to 4 meters by 2200.[176]​.

To address the threat of sea level rise in Bangladesh, the Bangladesh Delta Plan 2100 was launched in 2018.[177]​[178]​ As of 2020, it was seen to have missed most of its initial targets.[179]​ Progress is being monitored.[180]​.

U.S. coastal cities conduct beach nourishment, also known as beach replenishment, where sand is transported and added, in addition to other adaptation measures, such as zoning, restrictions on state funding of infrastructure projects, and building code standards.[181][182] Some island nations, such as the Republic of Maldives, Kiribati, and Tuvalu, are considering international migration of their populations in response. to sea level rise. Moving to different countries is not an easy solution, as those who move must have a stable income and social network in their new country. It may be easier to adapt locally by moving inland and increasing the supply of sediment needed for protection against natural erosion.[183]​ In the island nation of Fiji, residents are restoring coral reefs and mangroves to protect against flooding and erosion, which is estimated to be more cost-effective than building. dams.[184]​.

Adaptation to sea level rise often has to take into account other environmental problems, such as land subsidence or habitat destruction. In 2019, Indonesian President Joko Widodo declared that the city of Jakarta is sinking to such an extent that it is forcing him to move the capital to another city.[185] A study conducted between 1982 and 2010 found that some areas of Jakarta have been sinking by up to 28 cm per year[186] due to groundwater drilling and the weight of its buildings, and the problem is now exacerbated by rising sea levels. sea However, there are concerns that building in a new location will increase tropical deforestation.[187][188] Other so-called sinking cities, such as Bangkok or Tokyo, are vulnerable to sinking combined with rising sea levels.[189]

Methods that can be used to prevent or slow further sea level rise are called climate change mitigation. Climate change mitigation can stabilize rates of sea level rise, but it cannot prevent it from rising. Mitigation therefore allows more time for adaptation and leaves more options open, such as nature-based solutions.[190]​.

Climate change mitigation consists of actions to limit global warming and its related effects. These are mainly reductions in human emissions of greenhouse gases (GHG), as well as activities that reduce their concentration in the atmosphere.[191]​ It is one of the ways to respond to climate change, along with adaptation.[192]​ Fossil fuels emit the majority of carbon dioxide (CO) and greenhouse gases as a whole.[193]​ The most important challenge is to stop burning coal, oil and gas and use only clean energy. Due to massive price declines, wind power and solar photovoltaics (PV) are increasingly outperforming oil, gas and coal[194]​ although these require energy storage and improved electrical grids. As low-emission energy is deployed on a large scale, transportation and heating can shift to these primarily electric sources.[195] Climate change mitigation can also be achieved through changes in agriculture (to reduce greenhouse gas emissions from agriculture), transportation, forest management (reforestation and conservation), waste management, buildings and industrial systems.[196] Methane emissions, which have a high short-term impact, can be addressed through reductions in product consumption. dairy "Tambo (dairy)") and meat.[197]​.

Political and economic responses to date include ways to price carbon through carbon taxes and carbon trading, reductions in fossil fuel subsidies, making national pledges and laws, subsidies, simplified regulations for low-carbon energy integration, and divestment from fossil fuel finance.

Understanding past sea level is an important guide to current and future changes. In the recent geological past, thermal expansion due to rising temperatures and changes in land ice are the dominant reasons for sea level rise. The last time the Earth was 2°C warmer than pre-industrial temperatures was 120 thousand years ago, when warming due to changes in the amount of sunlight due to slow changes in the Earth's orbit caused the Eemian interglacial period; Sea levels during that warmer interglacial period were at least 5 m higher than now.[198] Eemian warming continued steadily over a period of thousands of years, and the magnitude of sea level rise meant that a large contribution of water came from the ice sheets of Antarctica and Greenland.[19] Further back in the past, a report from the Royal Institute of Marine Research in the Netherlands states that, about three million years ago, years, levels of carbon dioxide in the Earth's atmosphere similar to current levels increased the temperature by two to three degrees Celsius and melted a third of the Antarctic ice sheet. This, in turn, caused sea levels to rise 20 meters above their current values.[199]​.

Since the last glacial maximum about 20,000 years ago, sea level has risen more than 125 metres, with rates varying from less than one mm/year during the pre-industrial era to more than 40 mm/year when the major ice sheets over Canada and Eurasia melted. The rapid disintegration of these ice sheets led to so-called "meltwater pulses", periods during which sea level rose rapidly. The rate of rise began to slow around 8,200 years before the present; sea level was then almost constant for the last 2,500 years, before the recent upward trend that began at the end of the century or the beginning of the century.[200]

• - Declaration of climate emergency.

• - climate engineering.

• - Dangers of coastal development").

• - Coastal sediment supply").

• - Effects of climate change on the oceans").

• - Effects of climate change on island nations").

• - Hydrosphere.

• - Islands First").

• - List of countries by average elevation").

Sources

• - This work contains a translation derived from "Sea level rise" from Wikipedia in English, specifically this version, published by its editors under the GNU Free Documentation License and the Creative Commons Attribution-ShareAlike 4.0 International License.

• - Wikimedia Commons hosts a multimedia category on Sea level rise.

• - NASA satellite data 1993-present.

• - Key message on sea level rise from the Fourth National Climate Assessment.

• - Incorporating local sea level change scenarios Describes eight steps a community can take to develop site-appropriate scenarios.

• - The Global Sea Level Observing System (GLOSS).

• - US (NOAA) Sea Level Rise Viewer.

Contenido

Entre 1901 y 2018, el promedio mundial del nivel del mar aumentó entre 15 y 15–25 cm.[1]​ Los datos más precisos recopilados de las mediciones de radar satelital revelan un aumento acelerado de 7.5 centímetros de 1993 a 2017,[2]​para una tasa promedio de 31 mm por década.

Regional variations

Sea level rise is not uniform around the world. Some land masses move up or down as a result of subsidence (land sinks or settles) or post-glacial rebound (land rises due to loss of ice weight after melting), so 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 levels are falling. Additionally, the gravitational effects of changing ice masses and spatially varying warming patterns lead to differences in the distribution of seawater around the world.[18]​[19]​ Gravitational effects come into play when a large ice sheet melts. With mass loss, the gravitational pull becomes less and local water levels may fall. Farther from the ice sheet, water levels will rise more than average. In this sense, melting in Greenland has a different effect on regional sea level than melting in Antarctica.[20]​.

Many ports, urban conglomerates, and agricultural regions are built in river deltas, where land subsidence contributes to substantial relative rise in sea level. This is caused both by unsustainable groundwater extraction (in some places also by oil and gas extraction), and by levees and other flood management practices that prevent sediment buildup from compensating for the natural settlement of deltaic soils.[21] Complete subsidence caused by man in the Rhine-Meuse-Scheldt delta (Netherlands) is estimated at 3–4 m, more than 3 meters in urban areas of the Mississippi River Delta (New Orleans), and more than 9 meters in the Sacramento-San Joaquin River Delta (California).[22] On the other hand, postglacial isostatic rebound causes a relative fall in sea level around Hudson Bay in Canada and the north. of the Baltic Sea.[23]​.

The Atlantic is warming at a faster rate than the Pacific. This has implications for Europe and the US East Coast, which has seen sea level rise 3 to 4 times the global average.[24] The decline of the Atlantic Meridional Overturning Circulation (AMOC) has also been linked to extreme regional sea level rise on the US northeast coast.[25]​.

En términos generales, existen dos formas de modelar el aumento del nivel del mar y así hacer proyecciones futuras. Una manera es cuando los científicos utilizan el modelado basado en procesos, donde todos los procesos físicos relevantes y bien entendidos se incluyen en un modelo físico global. Se utiliza un modelo de capa de hielo") para calcular las contribuciones de las capas de hielo en el aumento del nivel del mar, y un modelo de circulación general para calcular el aumento de la temperatura del mar y la dilatación de esta. Una desventaja de este método es que no todos los procesos relevantes pueden comprenderse a un nivel suficiente, pero puede predecir no linealidades y largos retrasos en la respuesta que los estudios del pasado reciente no detectarán.

La otra metodología aplicada es la que donde los científicos utilizan técnicas semiempíricas que utilizan datos geológicos del pasado para determinar las respuestas probables del nivel del mar a un mundo en calentamiento, además de algunos modelos físicos básicos.[3]​ Estos modelos semiempíricos del nivel del mar se basan en técnicas estadísticas, utilizando relaciones (los efectos y contribuciones) entre el nivel medio global del mar y la temperatura media global observados en el pasado.[27]​ Este tipo de modelado fue parcialmente motivado por la mayoría de los modelos físicos en evaluaciones de literatura anteriores realizadas por el Panel Intergubernamental sobre Cambio Climático (IPCC) que subestimaron la cantidad de aumento del nivel del mar en comparación con las observaciones del siglo .[19]​.

Projections for the 21st century

In its fifth assessment report (2013), the Intergovernmental Panel on Climate Change estimated how much sea level is likely to rise over the century based on different levels of greenhouse gas emissions. These projections are based on well-known factors contributing to sea level rise, but exclude other processes that are less understood. If countries make rapid cuts in emissions (RCP2.6 scenario), the IPCC considers it likely that sea level will rise by an average of 26-55 cm with a 67% confidence interval. If emissions remain very high, the IPCC projects that sea level will rise by 52 to 98 cm.[19]​ In August 2020, scientists reported that the ice sheet losses observed in Greenland and Antarctica have followed the worst-case scenarios of the IPCC Fifth Assessment Report's sea level rise projections.[28][29][30][31]​.

Since the publication of the 2013 IPCC assessment, attempts have been made to include more physical processes and develop models that can project sea level rise using paleoclimatic data. This generally led to higher estimates of sea level rise.[32][33][34] For example, a 2016 study led by Jim Hansen concluded that, based on data from a previous event that led to another period of planetary climate change, sea level rise could accelerate exponentially in the coming decades, with a doubling time of 10, 20, or 40 years, respectively, raising the ocean several meters by 50. 100 or 200 years.[34]​ However, Greg Holland of the National Center for Atmospheric Research, who reviewed the study, noted: "There is no doubt that sea level rise, within the IPCC, is a very conservative number, so the truth lies somewhere between the IPCC and Jim.".[35]​.

Furthermore, a 2017 study's scenario, assuming high use of fossil fuels for combustion and strong economic growth during this century, projects sea level rise of up to 132 centimeters on average, and an extreme scenario with as much as 189 cm by 2100. This could mean rapid sea level rise of up to 19 mm 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 sea level rise of 52 cm by 2100.[36][37]​.

The United States' Fourth (2017) National Climate Assessment (NCA) found that sea level is very likely to rise between 30 and 130 cm in 2100 compared to the year 2000. A rise of 2.4 m is physically possible in a high greenhouse gas emission scenario, but the authors were unable to indicate how likely it is that this figure will become a reality. This case (the worst-case scenario) can only occur if a great contribution from Antarctica, which is a difficult region to model.[8]​.

The possibility of a collapse of the West Antarctic Ice Sheet and subsequent rapid rise in sea level was suggested in the 1970s.[32] For example, Mercer published a study in 1978 predicting that the global greenhouse effect from carbon dioxide emissions and its potential effects on climate within the century could cause sea level rise of around 5 meters due to the melting of the Antarctic Ice Sheet alone. Western.[38][32]​.

In 2019, a study projected that in a low emissions scenario, sea level will rise by 30 centimeters by 2050 and 69 centimeters by 2100, relative to the existing sea level in 2000. In a high emissions scenario, it will be 34 cm by 2050 and 111 cm by 2100. There is a likelihood that the rise will exceed 2 meters by 2100 in the high emissions scenario. emissions, which will cause the displacement of 187 million people. Sea level rise projected by 2050 will generate a sharp increase in the frequency of coastal flooding (four “moderate” flooding events per year in the US), despite the absence of storms and/or heavy rainfall.[39][40][41]​.

In September 2019, the Intergovernmental Panel on Climate Change released a report on the impact of climate change on the oceans, including sea level rise. It found that if humanity sharply reduces greenhouse gas emissions in the coming decades, the problem will be difficult but manageable. On the contrary, if the increase in emissions continues, the problem will become unmanageable.[42]​.

In February 2021, researchers suggested that previous projections of global sea level rise by 2100 reported by the IPCC were likely conservative and that sea levels will rise more than expected.[9]​.

According to the IPCC's Sixth Assessment Report published in 2021, it indicates that in the very low emissions scenario, by 2100 sea level will rise between 28 and 55 centimeters, in the intermediate scenario between 44 and 76 centimeters and in the very high emissions scenario between 63 and 101 centimeters. An elevation of approximately two meters cannot be ruled out in the very high emissions scenario.[43]​.

Sea level rise by 2100 is likely to be greater than the likely projection range presented in the IPCC's Sixth Assessment Report. Ice sheet processes and feedback mechanisms affecting ocean and ice sheet melt, which are not well understood by scientists and are not accounted for in model projections, could lead to this low-probability, high-impact event.

The IPCC's Sixth Assessment Report (AR6) presents a speculative narrative about how such warming could occur. It would likely involve a high ocean warming scenario, in which no urgent climate action is taken and strong warming continues.[44] This could lead to a faster-than-anticipated collapse of sea ice shelves and the abrupt and widespread onset of sea ice cliff instability (a process in which ice cliffs collapse under their own weight) and sea ice sheet instability (a positive feedback loop leading to runaway melting). in Antarctica, and a faster-than-projected ice loss in Greenland, leading to extreme sea level rise.[44]​ While some studies provide evidence for these processes, substantial uncertainty and low agreement between studies and a lack of understanding of these processes lead to them not being accounted for in many models, including those in AR6.[44]​ Other processes in Antarctica combined with high warming could also contribute to higher-than-projected sea level rise. expected. For example, hydrofracturing (in which meltwater builds up in ice sheet fractures, forcing them to open), increased contact of warm ocean water with ice shelves due to climate change-induced changes in ocean circulations[45]​[46][47]​ or climate change-induced changes in the climate over Antarctica, leading to lower precipitation and therefore less ice deposition.[47]​ The combination of such processes could lead to a rise in sea level of up to 2.3 meters by the year 2100.[44]​.

Long-term sea level rise

There is widespread consensus among climate scientists that sea level rise lags far behind the temperature rise that triggers it, and that substantial long-term sea level rise will continue for centuries to come, even if temperatures stabilize.[48]​ Models can reproduce paleoclimate records of sea level rise, providing confidence in their application to future long-term changes.[19]​.

Both the Greenland and Antarctic ice sheets have tipping points (Tipping Point (Climatology)) for levels of warming that could be reached before the end of the century. Crossing such tipping points would mean that changes in the ice sheet are potentially irreversible: a drop to pre-industrial temperatures may not stabilize the ice sheet once the tipping point is crossed. Quantifying the exact temperature change by which this tipping point is crossed remains controversial. For Greenland, estimates range between approximately 1 and 4 °C above the pre-industrial average temperature.[49]​[19]​ By 2020, the lower of these values ​​has already been exceeded. A 2021 analysis of subglacial sediments at the bottom of a 1.4 km-deep Greenland ice core reveals that the Greenland ice sheet melted at least once over the last million years. This strongly suggests that its inflection point is below the maximum positive temperature excursion of 2.5 °C during that period, and is therefore within the lower half of its range of estimates.[50]​[51]​ The melting of the Greenland ice sheet would contribute to sea level rise of between 4 to 7.5 m over thousands of years.[12]​.

A 2013 study estimated that each centigrade of temperature rise implies 2.3 m of sea level rise over the next 2,000 years.[52] More recent research, especially in Antarctica, indicates that this is probably a conservative estimate and that the true long-term sea level rise could be greater.[8] Warming beyond 2 °C potentially leads to rates of sea level rise dominated by ice loss from the sea. Antarctica. Continued emissions of carbon dioxide from fossil fuel sources could cause tens of additional meters of sea level rise over the next few millennia, and the fossil fuel available on Earth is even enough to eventually melt the entire Antarctic ice sheet, causing about 58 meters of sea level rise.[53] After 500 years, sea level rise from thermal expansion alone may have reached only half its final level, leaving Models suggest that it may be within the ranges of 0.5-2 m.[54]​.

Over the next 2,000 years, sea level is forecast to rise by 2 to 3 meters if the temperature peaks at 1.5 °C, by 2 to 6 meters if it peaks at 2 °C, and by 19 to 22 meters if the temperature peaks at 5 °C.[43] If temperature rise stops at 2 or 5 °C, sea level will continue to rise for about ten thousand years. In the first case it will reach 8 to 13 meters above the pre-industrial level and in the second 28 to 37 meters.[55]​.

Las tres razones principales por las que el calentamiento hace que aumente el nivel del mar en el mundo son: los océanos se expanden (por efecto de la dilatación térmica), las capas de hielo pierden hielo más rápido de lo que se forma a partir de las nevadas y los glaciares en altitudes más altas también se derriten. El aumento del nivel del mar desde principios del siglo ha estado dominado por el retroceso de los glaciares y la expansión del océano, pero se espera que las contribuciones de las dos grandes capas de hielo (Groenlandia y la Antártida) aumenten en el siglo .[3]​ Las capas de hielo almacenan la mayor parte del hielo terrestre (∼99.5%), con un equivalente al nivel del mar (SLE) de 7.4 m para Groenlandia y 58.3 m para la Antártida.[2]​.

Cada año cerca de 8 mm de precipitaciones "Precipitación (meteorología)") (equivalente líquido) cae sobre las capas de hielo en la Antártida y Groenlandia, principalmente en forma de nieve, que se acumula y con el tiempo forma hielo glacial. Gran parte de esta precipitación comienza cuando el vapor de agua se evapora de la superficie del océano. Parte de la nieve es arrastrada por el viento o desaparece de la capa de hielo por derretimiento o por sublimación (convirtiéndose directamente en vapor de agua). El resto de la nieve se transforma lentamente en hielo. Este hielo puede fluir hacia los bordes de la capa de hielo y regresar al océano derritiéndose en el borde o en forma de icebergs. Si la precipitación, los procesos superficiales y la pérdida de hielo en el borde se equilibran entre sí, el nivel del mar permanece igual. Sin embargo, los científicos han descubierto que el hielo se está perdiendo a un ritmo acelerado.[57]​[58]​.

Ocean warming

Most of the additional heat trapped in Earth's climate system generated by climate change is stored in the oceans. The oceans store more than 90% of additional heat and act as a buffer against the effects of climate change. The heat required to increase the mean temperature of the entire global ocean by 0.01 °C would cause the atmospheric temperature to increase by approximately 10 °C.[60]​ Therefore, a small change in the mean ocean temperature 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 the temperature and pressure of the water. For each degree, warmer water and water with a lot of pressure (due to depth) expands more than colder water and water with less pressure.[19] This means that cold Arctic Ocean water will expand less compared to warm tropical water. Because different climate models have slightly different patterns of ocean warming, there is not complete agreement in predictions about the contribution of ocean warming to sea level rise.[61]​ Due to the phenomenon of subsidence&action=edit&redlink=1 "Sinking (oceanography) (not yet drafted)"), heat stored in water is transported to the deeper parts of the ocean by winds and currents, and some of it reaches depths of more than 2000 m.[62]​.

Considering an increase in average global temperature of 2°C above pre-industrial levels, and without considering potential contributions from ice sheet processes with limited agreement (low confidence) between modeling approaches, the probability of exceeding 0.5 m of global sea level rise (0.7 m along the US coastline) by 2100 is about 50%. With 3°–5°C of warming under high-emission pathways, this probability increases from more than 80% to more than 99%.[63]​.

Antarctica

The large volume of ice on the Antarctic continent stores about 70% of the world's fresh water.[64] The mass balance of the Antarctic ice sheet is affected by snow accumulations and ice discharge along the periphery. Under the influence of global warming, melting at the base of the ice sheet increases. Simultaneously, the capacity of the atmosphere to transport precipitation increases with temperature, so that precipitation, in the form of snowfall, increases in global and regional models. The additional snowfall causes a greater flow of ice from the ice sheet into the ocean, so that the mass gain due to snowfall is partially offset.[65]​ Snowfall has increased over the past two centuries, but no increase was found in the interior of Antarctica over the past four decades.[66]​ Based on changes in Antarctica's ice mass balance over the past few million years due to natural climate fluctuations, the researchers concluded that ice marine acts as a barrier to the warmer waters surrounding the continent. Consequently, the loss of sea ice is one of the main causes of the instability of the entire ice sheet.[66]​.

Different satellite methods for measuring ice mass and change manage to agree in their measurements, and combining methods leads to greater certainty about how the East Antarctic Ice Sheet, the West Antarctic Ice Sheet, and the Antarctic Peninsula are evolving.[67] A systematic review study published in 2018 estimated that continent-wide ice loss was 43 gigatonnes (Gt) per year on average over the period. from 1992 to 2002, but accelerated to an average of 220 Gt per year during the five years from 2012 to 2017.[68] Most of the melt comes from the West Antarctic Ice Sheet, but the Antarctic Peninsula and the East Antarctic Ice Sheet also contribute. Sea level rise due to Antarctica has been estimated at 0.25 mm per year from 1993 to 2005, and 0.42 mm per year from 2005 to 2015. All data sets generally show an acceleration of mass loss from the Antarctic ice sheet, but with variations from year to year.[2]​.

A May 2021 study projected that limiting global warming to 1.5 °C would reduce the contribution of continental ice to sea level rise by 2100 from 25 cm to 13 cm compared to current mitigation goals, with glaciers responsible for half of the contribution to sea level rise.[69]​ In this study, the physical uncertainty of the Antarctic contribution was more significant than the uncertainty due to the choice of pathway. mitigation.[69]​.

The largest potential source of sea level rise in the world is the East Antarctic Ice Sheet, which contains enough ice to raise global sea level by 53.3 m.[70] Historically, the ice sheet has been considered relatively stable and has therefore attracted less attention and scientific observations compared to West Antarctica.[66] A combination of satellite observations of its changing volume, flow and gravitational pull with modeling of its balance surface mass suggests that the overall mass balance of the East Antarctic Ice Sheet has been relatively constant or slightly positive for much of the period between 1992 and 2017.[68] However, a 2019 study using a different methodology concluded that East Antarctica is losing significant amounts of ice mass. Scientist Eric Rignot") told CNN: "The melting is occurring in the most vulnerable parts of Antarctica [...] parts that have the potential for several meters of sea level rise over the next century or two."[66]

Greenland

Most of the ice in Greenland is part of the Greenland Ice Sheet, which is 3 km at its thickest. The rest of Greenland's ice is part of glaciers and isolated polar caps. The main reasons contributing to sea level rise in Greenland are melting ice sheet (70%) and calving glaciers (30%). Dust, soot, microbes and algae living on parts of the ice sheet further increase melting by darkening its surface and thus causing greater absorption of thermal radiation; These surface darkening regions increased in area by 12% between 2000 and 2012, and are likely to expand further.[88] The average annual ice loss in Greenland more than doubled at the beginning of the century compared to the century.[89] Some of Greenland's largest outlet glaciers, such as Jakobshavn Isbræ") and the Kangerlussuaq"), are those that contribute a greater flow of water to the ocean.[90][91]​.

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.[92][93]​ The Greenland Ice Sheet and its glaciers and ice caps are the largest contributors to sea level rise from land-based ice sources (excluding thermal expansion), and together account for the 71%, or 1.32 mm per year during the period 2012-2016.[94]​[95]​.

A study published in 2020 estimated that the Greenland ice sheet had lost a total of 3,902 gigatonnes (Gt) of ice between 1992 and 2018, corresponding to a contribution to sea level rise of 10.8 millimeters. Sea level rise due to melting of 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.[96]​.

Estimates of Greenland's future contribution to sea level rise range from 0.3 to 3 m by the year 2100.[88] By the end of the century, Greenland will contribute 2 to 10 centimeters annually.[97] The contribution of the Greenland ice sheet to sea level over the next two centuries may be very high due to a self-reinforcing cycle (the so-called positive feedback). After an initial period of melting, the height of the ice sheet will have decreased. As the air temperature increases closer to the sea surface, more melting will begin to occur. This melting can be accelerated further because the color of the ice is darker while it is melting. There is a threshold in surface warming beyond which partial or almost complete melting of the Greenland ice sheet occurs.[98] Different investigations have put this threshold value as low as 1 °C, and definitely 4 °C, above pre-industrial temperatures.[99]​[19]​ A 2021 analysis of subglacial sediments from the bottom of a Greenland ice core from 1.4 km depth reveals that the Greenland ice sheet melted at least once during the last million years and therefore strongly suggests that its tipping point is below the maximum positive temperature excursion of 2.5 °C during that period.[50][51]​.

Other glaciers

Less than 1% of glacial ice is found in mountain glaciers, compared to 99% in Greenland and Antarctica. Still, mountain glaciers have contributed appreciably to historical sea level rise and will contribute a smaller, but still significant, fraction of sea level rise over the century.[100] Earth's approximately two hundred thousand glaciers can be found on every continent.[101] Different glaciers respond differently to rising temperatures. For example, valley glaciers that have a shallow slope recede even with mild warming. Each glacier has a height above which there is a net gain in mass and below which the glacier loses mass. If that height changes a little, this has big consequences for glaciers with low slope.[102]​ Many glaciers flow into the ocean, and therefore ice loss can increase as ocean temperatures rise.[101]​.

Observational and modeling 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 century. Over the century, it is expected to rise, with glaciers contributing 7-24 cm to global sea levels.[19]​ Glaciers contributed around 40% to sea level rise over the century, with estimates for the century of around 30%.[2]​.

sea ​​ice

Melting sea ice contributes very little to global sea level rise. If the density of melted ice water floating in the sea were exactly the same as seawater, according to Archimedes' principle, no rise would occur. However, melted sea ice contains less dissolved salt than seawater and is therefore less dense: in other words, although melted sea ice weighs the same as the seawater it was displacing when it was ice, its volume is still slightly larger. If all floating ice shelves and icebergs were to melt, sea level would only rise by about 4 cm.[103]​.

Terrestrial water storage

Humans affect the amount of water stored on earth. Building dams prevents large bodies of water from flowing into the sea and therefore increases water storage on land. On the other hand, humans extract water from lakes, wetlands and underground reservoirs for food production leading to rising sea levels. Additionally, the hydrological cycle has been influenced by climate change and deforestation, which may lead to further positive and negative contributions to sea level rise. In the century, these processes more or less balanced, but dam construction has slowed and is expected to remain low throughout the century.[104][19]​.

Los cambios en el nivel del mar pueden ser provocados por variaciones en la cantidad de agua en los océanos, el volumen del océano o por cambios en la tierra en comparación con la superficie del mar. A lo largo de un período de tiempo uniforme, la realización de evaluaciones puede determinar las contribuciones a la subida del nivel del mar y proporcionar indicaciones tempranas de cambios en la trayectoria. Este tipo de vigilancia puede motivar planes de prevención.[106]​ Las diferentes técnicas utilizadas para medir los cambios en el nivel del mar no miden exactamente el mismo nivel. Los mareógrafos solo pueden medir el nivel relativo del mar, mientras que los satélites artificiales también pueden medir cambios absolutos en el nivel del mar.[20]​ Para obtener mediciones precisas del nivel del mar, los investigadores que estudian el hielo y los océanos en nuestro planeta tienen en cuenta las continuas deformaciones de la Tierra sólida, en particular debido a las masas de tierra que aún se elevan debido a la retirada de las masas de hielo del pasado, y también a la gravedad y la rotación de la Tierra.[2]​.

Satellites

Since the launch of TOPEX/Poseidon in 1992, an overlapping series of altimetry satellites has been continuously recording sea level and its changes. These satellites can measure hills and valleys in the sea caused by currents and detect trends in their height. To measure the distance to the sea surface, satellites send a microwave pulse that reflects off the ocean surface and records the time it takes to return. Microwave radiometers correct for the additional delay caused by water vapor in the atmosphere. Combining this data with the precisely known location of the spacecraft determines the height of the sea surface to within a few centimeters (about one inch). Current rates of sea level rise from satellite altimetry have been estimated to be 3.0 ± 0.4 mm per year for the period 1993–2017.[109] Early satellite measurements were slightly at odds with tide gauge measurements. Eventually, it was identified that a small calibration error for the Topex/Poseidon satellite had caused a slight overestimation of sea levels from 1992-2005, which masked in the satellite measurements the acceleration of ongoing sea level rise that was visible in the time series of the tide gauge.[110]​.

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 increase has been linked to increased trade winds, which occur when the Pacific Decadal Oscillation (PDO) and El Niño-Southern Oscillation (ENSO) shift from one state to another.[111] The PDO is a basin-wide climate pattern consisting of two phases, each typically lasting 10 to 30 years, while ENSO has a shorter period of 2 to 7 years.[112]​.

Tide gauges

The global network of tide gauges is another important source of sea level observations. Compared to the satellite record, this record has large spatial gaps but covers a much longer period of time.[114] Tide gauge coverage began primarily in the Northern Hemisphere, and data for the Southern Hemisphere remained scarce until the 1970s.[114] The oldest sea level measurements, NAP or Amsterdam Ordnance Datum established in 1675, are recorded in Amsterdam, Countries Lows.[115]​ In Australia, the collection of records is also quite extensive, including measurements made by an amateur meteorologist from 1837 and measurements taken from a sea level reference point on a small cliff on the Isle of the Dead&action=edit&redlink=1 "Isle of the Dead (Tasmania) (not yet redacted)"), in Tasmania, near the Port Arthur convict settlement "Port Arthur (Tasmania)") in 1841.[116]​.

This network was used, in combination with satellite altimeter data, to establish that global mean sea level rose by 19.5 cm between 1870 and 2004 at an average rate of around 1.44 mm/year (1.7 mm/year over the century).[117] Data collected by the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia show that global mean sea level is currently rising by 3.2 mm per year, double the century average rate.[118]​[119]​ This is an important confirmation of climate change simulations that predicted sea level rise would accelerate in response to climate change.

Some regional differences are also visible in the tide gauge data. Some of the regional differences recorded are due to differences in actual sea level, while others are due to vertical land movements. In Europe, for example, considerable variation is found because some areas of land rise while others sink. Since 1970, most tide stations have measured higher seas, but sea levels along the northern Baltic Sea have decreased due to postglacial rebound.[120]​.

Se espera que el aumento actual y futuro del nivel del mar tenga una serie de impactos, particularmente en los sistemas costeros. Tales impactos incluyen mayores y más frecuentes inundaciones por mareas altas y marejadas, aumento de la erosión costera, inhibición de los procesos de producción primaria, inundaciones costeras más extensas, cambios en la calidad del agua superficial y características de las aguas subterráneas. A su vez, se prevé que esto aumente la pérdida de propiedades y hábitats costeros, mayor riesgo de inundación y posible pérdida de vidas, pérdida de recursos y valores culturales no monetarios, impactos en la agricultura y la acuicultura a través de la disminución de la calidad del suelo y el agua, y pérdida del turismo, recreación y funciones de transporte.[122]​Muchos de estos impactos son perjudiciales. Debido a la gran diversidad de ambientes costeros, las diferencias regionales y locales en el nivel relativo del mar proyectado y los cambios climáticos, y las diferencias en la resiliencia y capacidad de adaptación de los ecosistemas, sectores y países, los impactos serán muy variables en el tiempo y el espacio. Los deltas de los ríos en África y Asia y los pequeños estados insulares son particularmente vulnerables al aumento del nivel del mar.[123]​.

Además de la subida del nivel del mar, hay otros efectos del cambio climático que pueden influir mucho en las poblaciones. Esto incluye, por ejemplo, la pérdida de ecosistemas costeros como los corales debido al calentamiento de los océanos o al aumento de las precipitaciones extremas causadas por el cambio climático. Los impactos de las inundaciones costeras se ven exacerbados por los cambios en el uso de la tierra, como la urbanización o la deforestación de las zonas costeras bajas. Las regiones que ya son vulnerables al aumento del nivel del mar también luchan contra las inundaciones costeras que arrastran la tierra y alteran el paisaje.[124]​ Las personas en estas áreas luchan cada vez más debido a estos diferentes efectos del cambio climático. Las tormentas influenciadas por el cambio climático también crean una mayor frecuencia de inundaciones costeras. Abordar los problemas de inundaciones que experimenta una región, ciudad o país se basará en los esfuerzos del país afectado. Sin mucho esfuerzo, estas regiones costeras podrían degradarse continuamente y, por lo tanto, afectar en gran medida el tamaño y la influencia de un país.

A nivel mundial, decenas de millones de personas estarán expuestas en las últimas décadas del siglo si los gases de efecto invernadero no se reducen drásticamente. Muchas áreas costeras tienen un gran crecimiento demográfico, lo que resulta en más personas en riesgo por el aumento del nivel del mar. El aumento del nivel del mar plantea un riesgo directo: las casas desprotegidas pueden inundarse, y amenazas indirectas de mayores marejadas ciclónicas, tsunamis y mareas reales"). Asia tiene la población más grande en riesgo por el nivel del mar con países como Bangladés, China, India, Indonesia y Vietnam que tienen áreas costeras muy densamente pobladas.[125]​ Los efectos de los desplazamientos dependen en gran medida del éxito de los gobiernos a la hora de poner en práctica las defensas contra la subida del nivel del mar, lo que preocupa a los países más pobres, como los subsaharianos y las naciones insulares.[126]​.

Un estudio de 2019 encontró que la cantidad de personas expuestas al aumento del nivel del mar durante el siglo es tres veces mayor de lo que se pensaba anteriormente. Para 2050, 150 millones estarán bajo la línea de agua durante la marea alta y 300 millones vivirán en zonas con inundaciones cada año. Para el año 2100, esos números difieren considerablemente según el escenario de emisión. En un escenario de bajas emisiones, 140 millones quedarán bajo el agua durante la marea alta y 280 millones sufrirán inundaciones cada año. En el escenario de altas emisiones, las cifras llegan a 540 millones y 640 millones respectivamente. El setenta por ciento de ellos son de ocho países de Asia: China, Bangladés, India, Indonesia, Tailandia, Vietnam, Japón y Filipinas.[127]​[128]​.

Una revisión en 2020 de 33 publicaciones encontró que «la mayoría de las estimaciones globales son del orden de decenas o cientos de millones de personas expuestas a inundaciones costeras permanentes e inundaciones costeras esporádicas en diferentes períodos y escenarios» debido al aumento del nivel del mar.[129]​.

Coastal areas

Due to numerous factors, sea level is rising at a rapid rate, posing a major threat to the human environment, both now and in the future. Although this is a slow and continuous process, its long-term cumulative effects on the world, especially in coastal areas, represent a serious threat. In recent years, some coastal areas have already had to deal with the cumulative effects of a long period of change. These areas are sensitive to sea level rise, changes in storm frequency and intensity, increased precipitation, and rising ocean temperatures. 10% of the world's population lives in coastal areas less than 10 meters above sea level. Additionally, two-thirds of the world's cities with more than five million inhabitants are located in these low-lying coastal areas.[130]​ In total, approximately 600 million people live directly in coastal areas around the world.[131]​ Using remote laser scanning called LiDAR to measure the elevation of the Earth's surface, researchers found that in 2021, 267 million people worldwide lived on land less than 2 meters above sea level and that with a sea level rise of 1 meter and zero population growth, that number could increase to 410 million people.[132]​[133]​.

The advantage that coastal region populations have is that they would technically have other parts of the country or region to which they could move or migrate. Also, the idea with these countries is that they can possibly receive assistance from their government or their compatriots. The challenges for people in low-lying nations is that they must uproot their entire life and culture to move to safer areas. Populations moving away from the coasts would also be affected by loss of livelihoods and could become a major strain on the regions or cities they inhabit.[134] Additionally, both their original government and the receiving countries may lack or withhold resources to assist these climate migrants, exacerbating their level of poverty.

Rising sea levels favor chronic flooding at high tide, as evidenced, for example, on the US East Coast.[135]​ Similarly, Florida, which is extremely vulnerable to climate change, is already experiencing significant floods and giant tides.[136] Another area at risk is Venice, which has experienced significant flooding; This city is located on islands in the delta of the Po and Piave rivers. Rising sea levels cause an increase in the frequency and magnitude of flooding in the city that has already spent more than $6 billion on the flood barrier system.[137]​[138]​.

Food production in coastal areas is also affected by rising sea levels. Due to flooding and the intrusion of salt water into the soil, the salinity of agricultural lands near the sea increases, posing problems for crops that are not resistant to salt. Additionally, salt intrusion into fresh irrigation water poses a second problem for irrigated crops. Recently developed salt-resistant crop variants are currently more expensive than the crops they are intended to replace.[139] Cropland in the Nile Delta is affected by saltwater flooding,[140] and there is now more salt in the soil and irrigation water in the Red River Delta and the Mekong Delta in Vietnam.[139] Bangladesh and China are similarly affected, particularly in their production of salt. rice.[141]​.

Island nations

Atolls, low-lying islands and low-lying coastal areas of islands are particularly vulnerable to sea level rise. Potential impacts include coastal erosion, flooding, and salt intrusion into soils and freshwater. No country is more vulnerable than small island nations, particularly those with population concentrations on atolls. Atolls on average reach 1 to 2 meters above sea level.[147] This type of island is a final stage in the geological history of an island of volcanic origin (all volcanic islands usually become atolls, eventually). With climate change causing sea levels to rise, the process of atoll formation has accelerated. Because atolls are low-lying islands, they are vulnerable to rising waters or storms that cover them with water. Atolls are vital because many different cultures and sovereign nations are based there. As ocean water prematurely covers atolls, salt water can intrude into drinking water supplies and undermine the ecosystems that people use to survive.[148] Sea level rise has the potential to devastate tourism and local economies; A sea level rise of 1.0 meter would result in the partial or complete flooding of 29% of coastal resorts in the Caribbean "Caribbean (region)"), while the other 49-60% of coastal resorts would be at risk from resulting coastal erosion.[149] It is difficult to assess how much of past erosion and flooding has 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.[150]​.

Millions of people in these island nations or nations with many islands are incredibly vulnerable to sea level rise. Some countries and regions will be submerged, pushing people living there to struggle, adapt or relocate. Developed countries could see a giant wave of refugees arrive due to the loss of refugee homes and therefore have security problems.[151] While islanders around the world have been very adaptable people, they have also relied heavily on the resources they acquire from their islands. While it may seem like the oceans are abundant and can provide everything, they also tend to be very difficult environments in which to thrive. Of interest is how sea level rise will affect children in these communities. Being a child who does not have stability at home and in their community can create a variety of problems in their development. Children in small island states already face obstacles in accessing food and water, displacement, and mental and social disorders resulting from these stressors.[152]​.

The Maldives, Tuvalu and other low-lying countries are among the areas most at risk. At the current rate, sea level would be high enough to make the Maldives uninhabitable by 2100.[153]​[154]​ Geomorphological events such as storms tend to have greater impacts on island reefs than sea level rise on, for example, one of the Marshall Islands. These effects include immediate erosion and subsequent regeneration process that can vary in duration from decades to centuries, even resulting in land areas larger than pre-storm values. With an expected increase in the frequency and intensity of storms, they may become more important in determining the shape and size of islands than sea level rise.[155] The island nation of Fiji is being affected by rising sea levels.[156] Five of the Solomon Islands have disappeared due to the combined effects of rising sea levels and stronger trade winds pushing water into the Pacific. western.[157]​.

Ecosystems

Coastal ecosystems are facing drastic changes as a result of rising sea levels. Many systems could end up being lost when sea levels rise too much or too fast. Some ecosystems can move inland due to the influence of altered high tides, but many are prevented from migrating due to natural or artificial barriers. This coastal narrowing, sometimes called "shoreline compression" when artificial barriers are considered, could lead to the loss of habitats such as salt marshes and marshes.[17]​[159]​.

The mangrove ecosystem is one of the ecosystems affected by sea level rise. This is an ecological complex composed of mangrove plants that grow in and around the marshes of the tropical coast. Its ecological value is high because it is an ideal habitat for many species. In recent years, mangroves have moved inland, but their success depends on various environmental information, such as topography and geology. The warmer the climate, the larger they grow. Mangrove respiratory roots or pneumatophores can reach half a meter in height.[160]​[161]​ Mangroves and salt marshes adapt to rising sea levels by building vertically using accumulated sediments and organic matter. If sea level rise is too rapid, they will not be able to keep up with the pace of adaptation and will instead become submerged.[162]​ More specifically, if the rate of mangrove deposition does not keep pace 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 level rises faster than mangroves can move landward, this can lead to ecosystem loss.[163]​ The ability of mangroves to survive sea level rise events depends on their ability to migrate inland.[161]​ As both ecosystems protect against storm surges, waves, and tsunamis, losing them worsens the effects of sea level rise. sea.[164]​[165]​ Human activities, such as dam construction, can restrict the supply of sediment to wetlands and therefore impede natural adaptation processes. As a consequence, the loss of some marshes is, theoretically, inevitable.[166]​.

When seawater reaches inland, problems related to contaminated soil can occur. In addition, fish, birds and coastal plants could lose parts of their habitat.[15]​ Coral, important for bird and fish life, needs to grow vertically to stay close to the sea surface to obtain enough energy from sunlight. It has so far been able to maintain vertical growth with rising sea levels, but may not be able to do so in the future.[167]​ In 2016, it was reported that the Bramble Cay melomys, which lived on an island in the Great Barrier Reef, had likely become extinct due to flooding caused by rising sea levels.[168]​ This report was confirmed by Australia's federal government when it declared the Bramble Cay melomys extinct in February 2019, making this species the first known mammal to become extinct as a result of sea level rise.[169]​.

Adaptation options to sea level rise can be broadly classified into retreat, accommodate and protect. Retreat is moving people and infrastructure to less exposed areas and preventing further development in areas that are at risk. This type of adaptation is potentially disruptive, since the displacement of people can generate social and/or political tensions. Accommodate options are measures that make societies more flexible in the face of sea level rise. Examples are growing food crops that tolerate high salt content in the soil and creating new building standards that require construction to be built higher and have less damage if a flood occurs. Finally, areas can be protected by building dams, levees and improving natural defenses.[16]​[170]​ In more detail, the existing problems are divided into two parts: one is water pollution and the other is storm surges and flooding.[171]​ Furthermore, storm surges and floods can be instantaneous and devastating to cities, and some coastal areas have begun to invest in water valves. stormwater to deal with more frequent and severe flooding during high tides.[171]​.

These adaptation options can be divided into hard and soft. Hard adaptation relies primarily on capital-intensive man-made infrastructures that involve large-scale changes to human societies and ecological systems. Due to its large scale, it is not usually flexible. Soft adaptation involves strengthening the natural defenses and adaptation strategies of local communities, as well as the use of simple, modular technology, which can be locally owned. The two types of adaptation can be complementary or mutually exclusive.[170]​[172]​.

Maritime trade is the dominant form of trade in resources and goods around the world. When talking about sea level rise, there is the possibility of major problems for maritime trade and the ports that are used. What is also important for these ports is that it is not yet known how the rise in sea level will continue to affect them over time.[173] Various factors intervene in the investment of seaports. Factors that are important for seaports in relation to sea level rise are where major commercial ports will be in the future, whether ports currently in use can be altered and protected, and how much is needed to protect trade without wasting time or money. Sea level rise is a concern for seaports, but it is difficult to figure out what changes need to be made since sea level does not rise at the same rate around the world.[174]​.

Many countries are developing concrete plans for adaptation. An example is the extension of the Delta Works in the Netherlands, a country that lies partially below sea level and is sinking.[175] In 2008, the Dutch Delta Commission warned in a report that the Netherlands would need a massive new construction program to strengthen the country's aquatic defenses against rising sea levels over the next 190 years. This included developing worst-case evacuation plans. The plan also included more than €100 billion in new spending until the year 2100 for precautionary measures, such as widening coastal dunes and strengthening sea and river dikes. The commission said the country should plan for a rise in the North Sea of ​​up to 1.3 m by 2100 and plan for rise between 2 to 4 meters by 2200.[176]​.

To address the threat of sea level rise in Bangladesh, the Bangladesh Delta Plan 2100 was launched in 2018.[177]​[178]​ As of 2020, it was seen to have missed most of its initial targets.[179]​ Progress is being monitored.[180]​.

U.S. coastal cities conduct beach nourishment, also known as beach replenishment, where sand is transported and added, in addition to other adaptation measures, such as zoning, restrictions on state funding of infrastructure projects, and building code standards.[181][182] Some island nations, such as the Republic of Maldives, Kiribati, and Tuvalu, are considering international migration of their populations in response. to sea level rise. Moving to different countries is not an easy solution, as those who move must have a stable income and social network in their new country. It may be easier to adapt locally by moving inland and increasing the supply of sediment needed for protection against natural erosion.[183]​ In the island nation of Fiji, residents are restoring coral reefs and mangroves to protect against flooding and erosion, which is estimated to be more cost-effective than building. dams.[184]​.

Adaptation to sea level rise often has to take into account other environmental problems, such as land subsidence or habitat destruction. In 2019, Indonesian President Joko Widodo declared that the city of Jakarta is sinking to such an extent that it is forcing him to move the capital to another city.[185] A study conducted between 1982 and 2010 found that some areas of Jakarta have been sinking by up to 28 cm per year[186] due to groundwater drilling and the weight of its buildings, and the problem is now exacerbated by rising sea levels. sea However, there are concerns that building in a new location will increase tropical deforestation.[187][188] Other so-called sinking cities, such as Bangkok or Tokyo, are vulnerable to sinking combined with rising sea levels.[189]

Methods that can be used to prevent or slow further sea level rise are called climate change mitigation. Climate change mitigation can stabilize rates of sea level rise, but it cannot prevent it from rising. Mitigation therefore allows more time for adaptation and leaves more options open, such as nature-based solutions.[190]​.

Climate change mitigation consists of actions to limit global warming and its related effects. These are mainly reductions in human emissions of greenhouse gases (GHG), as well as activities that reduce their concentration in the atmosphere.[191]​ It is one of the ways to respond to climate change, along with adaptation.[192]​ Fossil fuels emit the majority of carbon dioxide (CO) and greenhouse gases as a whole.[193]​ The most important challenge is to stop burning coal, oil and gas and use only clean energy. Due to massive price declines, wind power and solar photovoltaics (PV) are increasingly outperforming oil, gas and coal[194]​ although these require energy storage and improved electrical grids. As low-emission energy is deployed on a large scale, transportation and heating can shift to these primarily electric sources.[195] Climate change mitigation can also be achieved through changes in agriculture (to reduce greenhouse gas emissions from agriculture), transportation, forest management (reforestation and conservation), waste management, buildings and industrial systems.[196] Methane emissions, which have a high short-term impact, can be addressed through reductions in product consumption. dairy "Tambo (dairy)") and meat.[197]​.

Political and economic responses to date include ways to price carbon through carbon taxes and carbon trading, reductions in fossil fuel subsidies, making national pledges and laws, subsidies, simplified regulations for low-carbon energy integration, and divestment from fossil fuel finance.

Understanding past sea level is an important guide to current and future changes. In the recent geological past, thermal expansion due to rising temperatures and changes in land ice are the dominant reasons for sea level rise. The last time the Earth was 2°C warmer than pre-industrial temperatures was 120 thousand years ago, when warming due to changes in the amount of sunlight due to slow changes in the Earth's orbit caused the Eemian interglacial period; Sea levels during that warmer interglacial period were at least 5 m higher than now.[198] Eemian warming continued steadily over a period of thousands of years, and the magnitude of sea level rise meant that a large contribution of water came from the ice sheets of Antarctica and Greenland.[19] Further back in the past, a report from the Royal Institute of Marine Research in the Netherlands states that, about three million years ago, years, levels of carbon dioxide in the Earth's atmosphere similar to current levels increased the temperature by two to three degrees Celsius and melted a third of the Antarctic ice sheet. This, in turn, caused sea levels to rise 20 meters above their current values.[199]​.

Since the last glacial maximum about 20,000 years ago, sea level has risen more than 125 metres, with rates varying from less than one mm/year during the pre-industrial era to more than 40 mm/year when the major ice sheets over Canada and Eurasia melted. The rapid disintegration of these ice sheets led to so-called "meltwater pulses", periods during which sea level rose rapidly. The rate of rise began to slow around 8,200 years before the present; sea level was then almost constant for the last 2,500 years, before the recent upward trend that began at the end of the century or the beginning of the century.[200]

• - Declaration of climate emergency.

• - climate engineering.

• - Dangers of coastal development").

• - Coastal sediment supply").

• - Effects of climate change on the oceans").

• - Effects of climate change on island nations").

• - Hydrosphere.

• - Islands First").

• - List of countries by average elevation").

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• - This work contains a translation derived from "Sea level rise" from Wikipedia in English, specifically this version, published by its editors under the GNU Free Documentation License and the Creative Commons Attribution-ShareAlike 4.0 International License.

• - Wikimedia Commons hosts a multimedia category on Sea level rise.

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• - Key message on sea level rise from the Fourth National Climate Assessment.

• - Incorporating local sea level change scenarios Describes eight steps a community can take to develop site-appropriate scenarios.

• - The Global Sea Level Observing System (GLOSS).

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