Sea level rose by 4.5 mm per year during 2013-22 period: WMO

New Delhi: Global mean sea level rose by 4.5 mm per year during the period 2013-22 and human influence was very likely the main driver of these increases since at least 1971, the World Meteorological Department (WMO) said on Tuesday.

Sea level rise threatens several low-lying small islands. It is a major threat for countries such as India, China, Netherlands and Bangladesh, some of which comprise large coastal populations.

Several big cities on all continents are threatened such as Mumbai, Shanghai, Dhaka, Bangkok, Jakarta, Maputo, Lagos, Cairo, London, Copenhagen, New York, Los Angeles, Buenos Aires and Santiago. It is a major economic, social and humanitarian challenge, the WMO said in a report.

Global mean sea level increased by 0.20 m between 1901 and 2018. The average rate of sea level rise was 1.3 mm per year between 1901 and 1971, 1.9 mm per year between 1971 and 2006, and 3.7 mm per year between 2006 and 2018, it said.

Sea-level has risen faster since 1900 than over any preceding century in at least the last 3,000 years. The global ocean has warmed faster over the past century than since the end of the last deglacial transition (around 11,000 years ago), the department said.

Over the next 2,000 years, global mean sea-level will rise by about two to three m if warming is limited to 1.5 degrees Celsius, two to six m if limited to two degrees Celsius and 19 to 22 m with five degrees of warming, and it will continue to rise over subsequent millennia.

In case of very high greenhouse gas emissions (total failure of mitigation) there is a risk of sea-level rise of two m by 2100 and even 15 m by 2300, the WMO said.

The 2015 Paris Agreement aims to limit global warming to well below two degrees Celsius above pre-industrial levels and pursue efforts to limit the temperature increase to 1.5 degrees Celsius. Global temperature has increased by around 1.1 degree Celsius compared with the average in 1850–1900.

The population, potentially exposed to a 100-year coastal flood is projected to increase by about 20 per cent if global mean sea level rises by 0.15 m relative to 2020 levels; this exposed population doubles at a 0.75 m rise in mean sea level and triples at 1.4 m without population change and additional adaptation.