Sea level rise has been 4.5 mm/yr during the period 2013-22, with human influence likely to be the main driver of these increases since at least 1971, finds the report
India, along with Bangladesh, China and Netherlands face a major threat from rising sea levels. According to a new report by the World Meteorological Organisation (WMO), sea-level rise is a huge risk to cities around the world such as Shanghai, Dhaka, Bangkok, Jakarta, Mumbai, Maputo, Lagos, Cairo, London, Copenhagen, New York, Los Angeles, Buenos Aires and Santiago.
Sea-level rise threatens coastal farmlands and water reserves and resilience of infrastructures as well as human lives and livelihoods. The report mentioned that the global mean sea-level increased by 0.20m between 1901 and 2018. The average rate of sea level rise was 1.3 mm/yr–1 between 1901 and 1971, increasing to 1.9 mm/yr–1 between 1971 and 2006, and further increasing to 3.7 mm/yr between 2006 and 2018.
WMO reported that during the period 2013-22, sea level rise has been 4.5 mm/yr. Human influence was very likely the main driver of these increases since at least 1971. Global mean sea-level has risen faster since 1900 than over any preceding century in at least the past 3,000 years. The report also revealed that the global ocean has warmed faster over the past century than since the end of the last deglacial transition (around 11,000 years ago).
Quickening pace, sinking ground
Global mean sea level has risen due to heating of the climate system, ice loss on land, glacier and ice sheet melting, and thermal expansion from warming oceans. Thermal expansion accounted for 50% of the rise in sea level between 1971 and 2018, whereas glacier ice loss, ice sheet melting, and changes in land-water storage made up 22%, 20%, and 8% of the total. Between 1992-1999 and 2010-2019, the pace of ice-sheet loss accelerated by a factor of four. Between 2006 and 2018, mass loss from ice sheets and glaciers together made up the majority of the global mean sea level rise.
Scenarios: Relative to 1995–2014, the likely global mean sea level rise by 2100 is 0.28–0.55 m under the very low GHG emissions scenario (SSP1-1.9, equals about 1.5 C target); 0.32–0.62 m under the low GHG emissions scenario (SSP1-2.6, equals about 2 C target); 0.44–0.76 m under the intermediate GHG emissions scenario (SSP2-4.5); and 0.63–1.01 m under the very high GHG emissions scenario (SSP5-8.5); and by 2150 is 0.37–0.86 m under the very low scenario (SSP1-1.9); 0.46–0.99 m under the low scenario (SSP1-2.6); 0.66–1.33 m under the intermediate scenario (SSP2-4.5); and 0.98– 1.88 m under the very high scenario (SSP5-8.5)
The report warned that over the next 2000 years, global mean sea-level will rise by about 2-3 m if warming is limited to 1.5°C, 2-6m if limited to 2°C and 19 to 22 m with 5°C of warming, and it will continue to rise over subsequent millennia.
The Greenland and West Antarctic ice sheets will be lost almost entirely and irrevocably over a period of millennia, perhaps leading to a sea level increase of several metres. This will happen at sustained warming levels between 2-3°C. Higher warming rates are accompanied by greater mass loss. Sea levels might rise by 2m by 2100 and perhaps 15 m by 2300 in the event of extremely high greenhouse gas emissions (complete failure of mitigation). However, the report noted that sea-level rise is not globally uniform and varies regionally.
Cascading impacts
Sea-level rise imposes significant risks for small islands, coastal ecosystems, people and infrastructure and will continue to increase beyond 2100. The report warned that ongoing and accelerating sea level rise will bring cascading and compounding impacts resulting in losses of coastal ecosystems and ecosystem services, groundwater salinisation, flooding and damage to coastal infrastructure that cascade into risks to livelihoods, settlements, health, well-being, food, displacement and water security, and cultural values in the near to long-term.
The report further mentioned that continued sea level rise will increase risks to food security in vulnerable regions between 1.5°Cand 2°C global warming levels.
According to the WMO, the population potentially exposed to a 100-year coastal flood is projected to increase by about 20% if global mean sea level rises by 0.15m relative to 2020 levels; this exposed population doubles at a 0.75m rise in mean sea level and triples at 1.4m without population change and additional adaptation.
Almost 11% of the global population—896 million people—lived within the Low Elevation Coastal Zone in 2020, potentially increasing to beyond 1 billion people by 2050. These coastal cities and settlements make key contributions to climate resilient development through their vital role in national economies and inland communities, global trade supply chains, cultural exchange, and centres of innovation.
Responses to ongoing sea-level rise and land subsidence in low-lying coastal cities and settlements and small islands include protection, accommodation, advance and planned relocation and ecosystem based approaches. The report recommended that these responses are more effective if combined and/or sequenced, planned well ahead, aligned with sociocultural values and development priorities, and underpinned by inclusive community engagement processes. Urban systems, noted WMO, are critical and interconnected sites to enable climate resilient development, especially at the coast.
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