Maxsea Time Zero 198 14: Tips and Tricks for Smart Marine Navigators

Societies can adapt to sea level rise in three different ways: implement managed retreat, accommodate coastal change, or protect against sea level rise through hard-construction practices like seawalls or soft approaches such as dune rehabilitation and beach nourishment. Sometimes these adaptation strategies go hand in hand, but at other times choices have to be made among different strategies.[19] For instance, a managed retreat strategy is difficult if the population in the area is quickly increasing: this is a particularly acute problem for Africa, where the population of low-lying coastal areas is projected to increase by around 100 million people within the next 40 years.[20] Poorer nations may also struggle to implement the same approaches to adapt to sea level rise as richer states, and sea level rise at some locations may be compounded by other environmental issues, such as subsidence in so-called sinking cities.[21] Coastal ecosystems typically adapt to rising sea levels by moving inland; however, they might not always be able to do so, due to natural or artificial barriers.[22]

Maxsea Time Zero 198 14

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By 2020, the observed ice-sheet losses in Greenland and Antarctica were found to track the upper-end range of the AR5 projections.[44][45] Consequently, the updated SLR projections in the 2019 IPCC Special Report on the Ocean and Cryosphere in a Changing Climate were somewhat larger than in AR5. A February 2021 paper found that while AR5 projections appeared unrealistically low next to the extrapolation of observed sea level trends, the projections in SROCC were a much better fit. At the same time, they cautioned that the mismatch between SROCC numbers and expert elicitations was likely to indicate excessive conservatism in the IPCC reports.[46]

The world's largest potential source of sea level rise is the East Antarctic Ice Sheet (sometimes abbreviated as EAIS), which holds enough ice to raise global sea levels by 53.3 m (174 ft 10 in).[68] Historically, it was less studied than the West Antarctica as it had been considered relatively stable,[64] and this impression was often backed up by satellite observations and modelling of its surface mass balance.[66] However, a 2019 study employed different methodology and concluded that East Antarctica is already losing ice mass overall.[64] All methods agree that the Totten Glacier has lost ice in recent decades in response to ocean warming[69][70] and possibly a reduction in local sea ice cover.[71] Totten Glacier is the primary outlet of the Aurora Subglacial Basin, a major ice reservoir in East Antarctica that could rapidly retreat due to hydrological processes.[36] The global sea level potential of 3.5 m (11 ft 6 in) flowing through Totten Glacier alone is of similar magnitude to the entire probable contribution of the West Antarctic Ice Sheet.[72]

The other major ice reservoir on East Antarctica that might rapidly retreat is the Wilkes Basin which is subject to marine ice sheet instability.[36] Ice loss from these outlet glaciers is possibly compensated by accumulation gains in other parts of Antarctica.[66] In 2022, it was estimated that the Wilkes Basin, Aurora Basin and other nearby subglacial basins are likely to have a collective tipping point around 3 C (5.4 F) of global warming, although it may be as high as 6 C (11 F), or as low as 2 C (3.6 F). Once this tipping point is crossed, the collapse of these subglacial basins could take place as little as 500 or as much as 10,000 years: the median timeline is 2000 years. On the other hand, the entirety of the EAIS would not be committed to collapse until global warming reaches 7.5 C (13.5 F) (range between 5 C (9.0 F) and 10 C (18 F)), and would take at least 10,000 years to disappear.[73][74] It is also suggested that the loss of two-thirds of its volume may require at least 6 C (11 F) of warming.[75]

Moreover, the crucial buttressing position of the Thwaites Glacier means that its loss can destabilize the entire West Antarctic Ice Sheet.[89] Most of the bedrock underlying the West Antarctic Ice Sheet lies well below sea level.[36] This possibility of complete destabilization was first proposed back in the 1970s.[35] A 1978 study by J.H. Mercer predicted that anthropogenic CO2 emissions doubling by 2050 would cause 5 m (15 ft) of SLR due to the rapid loss of the West Antarctic ice sheet alone.[90][35] Since then, improved modelling concluded that the ice within WAIS would raise the sea level by 3.3 m (10 ft 10 in).[91][92] In 2022, the collapse of the entire West Antarctica was estimated to unfold over a period of about 2000 years, with the absolute minimum of 500 years (and a potential maximum of 13,000 years.) At the same time, this collapse was considered likely to be triggered at around 1.5 C (2.7 F) of global warming and would become absolutely unavoidable at 3 C (5.4 F) : at worst, it may have even been triggered by now, after the warming passed 1 C (1.8 F) in the recent years.[73][74] Even though the process takes a long time to finish, it has been suggested that the only way to stop it once triggered is by lowering the global temperature to 1 C (1.8 F) below the preindustrial levels (about 2 C (3.6 F) below the current levels).[75]

Sea level changes can be driven either by variations in the amount of water in the oceans, the volume of the ocean or by changes of the land compared to the sea surface. Over a consistent time period, conducting assessments can source contributions to sea level rise and provide early indications of change in trajectory. This type of surveillance can inform plans of prevention.[116] The different techniques used to measure changes in sea level do not measure exactly the same level. Tide gauges can only measure relative sea level, whilst satellites can also measure absolute sea level changes.[26] To get precise measurements for sea level, researchers studying the ice and the oceans on our planet factor in ongoing deformations of the solid Earth, in particular due to landmasses still rising from past ice masses retreating, and also the Earth's gravity and rotation.[4]

The global network of tide gauges is another important source of sea-level observations. Compared to the satellite record, this record has major spatial gaps but covers a much longer period of time.[124] Coverage of tide gauges started primarily in the Northern Hemisphere, with data for the Southern Hemisphere remaining scarce up to the 1970s.[124] The longest running sea-level measurements, NAP or Amsterdam Ordnance Datum established in 1675, are recorded in Amsterdam, the Netherlands.[125] In Australia record collection is also quite extensive, including measurements by an amateur meteorologist beginning in 1837 and measurements taken from a sea-level benchmark struck on a small cliff on the Isle of the Dead near the Port Arthur convict settlement in 1841.[126]

At the same time, even the populations who live further inland may be impacted by a potential disruption of sea trade, as it is the dominant form of resource and good trade throughout the world. Sea level rise will inevitably affect ports, but the current research into this subject is limited. Not enough is known about the investments required to protect the ports currently in use, and for how they may be protected before it becomes more reasonable to build new port facilities elsewhere.[140][141] Moreover, some coastal regions are rich agricultural lands, whose loss to the sea can result in food shortages elsewhere. This is a particularly acute issue for river deltas such as Nile Delta in Egypt and Red River and Mekong Deltas in Vietnam, which are disproportionately affected by saltwater intrusion into the soil and irrigation water.[142][143]

While some ecosystems can move land inward with the high-water mark, many are prevented from migrating due to natural or artificial barriers. This coastal narrowing, sometimes called 'coastal squeeze' when considering human-made barriers, could result in the loss of habitats such as mudflats and tidal marshes.[22][149] Mangrove ecosystems on the mudflats of tropical coasts nurture high biodiversity, yet they are particularly vulnerable due to mangrove plants' relliance on breathing roots or pneumatophores, which might grow to be half a metre tall.[150][151] While mangroves can adjust to rising sea levels by migrating inland and building vertically using accumulated sediment and organic matter, they will be submerged if the rate is too rapid, resulting in the loss of an ecosystem.[152][153][151] Both mangroves and tidal marshes protect against storm surges, waves and tsunamis, so their loss makes the effects of sea level rise worse.[154][155] Human activities, such as dam building, may restrict sediment supplies to wetlands, and thereby prevent natural adaptation processes. The loss of some tidal marshes is unavoidable as a consequence.[156]

By 2100, a minimum of 3-4 million people in South America would be directly affected by coastal flooding and erosion. 6% of the population of Venezuela, 56% of the population of Guyana (including in the capital, Georgetown, much of which is already below the sea level) and 68% of the population of Suriname are already living in low-lying areas exposed to sea level rise. In Brazil, the coastal ecoregion of Caatinga is responsible for 99% of its shrimp production, yet its unique conditions are threatened by a combination of sea level rise, ocean warming and ocean acidification. The port complex of Santa Catarina had been interrupted by extreme wave or wind behavior 76 times in one 6-year period in 2010s, with a 25,000-50,000 USD loss for each idle day. In Port of Santos, storm surges were three times more frequent between 2000 and 2016 than between 1928 and 1999.[176]

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.[199] Nations like Maldives, Kiribati and Tuvalu are already forced to consider controlled international migration of their population in response to rising seas, [200] since the alternative of uncontrolled migration threatens to exacerbate the humanitarian crisis of climate refugees.[201] In 2014, Kiribati had purchased 20 square kilometers of land (an area 6 times greater than the current area of Kiribati) on the Fijian island of Vanua Levu to relocate its population there once their own islands are lost to the sea.[202] 2ff7e9595c