sea level rise
Sea level is very likely to rise 1 to 4 feet (0.3 to 1.3 meters) by the end of the century. [171]
New estimates of sea level rise triple older estimates. Even with sharp, immediate cuts to carbon emissions, sea level could rise another 0.5 meters within this century. [162] [163]
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Under RCP 4.5, the most likely emissions pathway representing moderate efforts to mitigate emissions, global sea level is expected to rise between 0.5 and 0.7 meters by the end of the century. [162] [164]
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Under a business-as-usual (RCP 8.5) scenario, sea levels increase by 1.5 meters globally. [165]
Global mean sea level rise10 from 2006 to 2100 as determined by multi-model simulations. All changes are relative to 1986–2005. Time series of projections and a measure of uncertainty (shading) are shown for scenarios RCP2.6 (blue) and RCP8.5 (red). The mean and associated uncertainties averaged over 2081–2100 are given for all RCP scenarios as coloured vertical bars at the right hand side of each panel. [167]
Steric expansion of the ocean (thermal expansion of water due to temperature increase) is adding an estimated 1.1 (±0.3) mm per year to global sea level.
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Satellite measurements of ocean bottom pressure estimate the net contribution of ocean mass increase on sea level rise to be about 1.8 (±0.5) mm per year, which is largely in agreement with estimates of land water storage changes (retreating glaciers, polar ice sheets loss, and anthropogenic freshwater storage) of 1.66 (±0.73) mm per year. [168]
Source: [166]
One billion people now occupy land less than 10 m above current high tide lines, and 230 million below 1 m. Under low emission scenarios, 80 million more people will live below high tide lines projected for 2100 (190 million, versus 110 million today). Under high emission scenarios, up to 630 million people will be living in areas below annual flood levels by 2100, and up to 340 million at mid-century (up from 250 million at present). [162]
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New estimates put the number of people whose homes will be submerged by 2100 at 153 million. [165]
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70% of the total number of people worldwide currently living on land expected to be inundated are in eight Asian countries: China, Bangladesh, India, Vietnam, Indonesia, Thailand, the Philippines, and Japan. [162]
Sea level rise will not stop at 2100, and current sea level rise predictions do not take into account catastrophic collapse of the Antarctic ice sheet. [165] [170]
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Some reconstructions of mid-Pliocene global sea level (3 million years ago, when carbon dioxide concentrations were comparable to today) place it at 10 to 30 meters higher, which requires a significant reduction in the size of the Antarctic ice sheet. [170]
Projected sea level rise (SLR) until 2300. The inset shows an assessment of the likely range of the projections for RCP2.6 and RCP8.5 up to 2100 (medium confidence). Projections for longer time scales are highly uncertain but a range is provided (4.2.3.6; low confidence). For context, results are shown from other estimation approaches in 2100 and 2300. The two sets of two bars labelled B19 are from an expert elicitation for the Antarctic component (Bamber et al., 2019), and reflect the likely range for a 2ºC and 5ºC temperature warming (low confidence; details section 4.2.3.3.1). The bar labelled “prob.” indicates the likely range of a set of probabilistic projections (4.2.3.2). The arrow indicated by S18 shows the result of an extensive sensitivity experiment with a numerical model for the Antarctic Ice Sheet (AIS) combined, like the results from B19 and “prob.”, with results from Church et al. (2013) for the other components of SLR. S18 also shows the likely range. [169]
The relationship between peak global mean temperature, maximum global mean sea level (GMSL), and source(s) of meltwater for two periods in the past with global mean temperature comparable to or warmer than present. Light blue shading indicates uncertainty of GMSL maximum. Red pie charts over Greenland and Antarctica denote fraction, not location, of ice retreat. Atmospheric CO2 levels in 2100 are shown under RCP8.5. [170]
"The paleo sea level record suggests that even 2°C of global average warming above the preindustrial temperature may represent a commitment to several meters of rise. One modeling study suggesting a 2,000-year commitment of 2.3 m/°C (4.2 feet/°F) indicates that emissions through 2100 would lock in a likely 2,000-year global mean sea level rise commitment of about 0.7–4.2 meters (2.3–14 feet) under an even lower scenario (RCP2.6), about 1.7–5.6 meters (5.6–19 feet) under a low scenario (RCP4.5), and about 4.3–9.9 meters (14–33 feet) under the higher scenario (RCP8.5). However, as with the 21st century projections, emerging science regarding the sensitivity of the Antarctic Ice Sheet may increase the estimated sea level rise over the next millennium, especially for a higher scenario." [170]
Representative communities were assembled to replicate the natural communities of the Heron Island reef slope (5 m), southern Great Barrier Reef. Black arrows highlight bleaching, recovery and bleaching in Fungia. [172]
Coral reef die-offs mean that coastal communities around the world are losing their benefits as protection from storm surges and ocean erosion. [172]
Seawater infiltration of shallow groundwater aquifers threatens areas that are not currently considered prone to future flooding by rising seas. [173] [174]
The groundwater saltwater–freshwater interface moves inland unevenly with water-table responses to sea-level rise in San Francisco and northern San Mateo counties. [174]