WMO Report: Global Sea-Level Rise and Implications

In February 2023, the World Meteorological Organization (WMO) released a report “Global Sea-Level Rise & Implications: Key facts and figures”.

The Key Messages of the Report were:

• Sea-level rise threatens several low-lying small islands and high-population coastal cities. It is a major threat for countries like Netherlands, Bangladesh, India and China, some of which comprise large coastal populations.
• Several big cities on all continents are threatened, such as Shanghai, Dhaka, Bangkok, Jakarta, Mumbai, Maputo, Lagos, London, Copenhagen, New York, Los Angeles, and Buenos Aires. It is a major economic, social and humanitarian challenge.
• Sea-level rise threatens coastal farmlands and water reserves and resilience of infrastructures as well as human lives and livelihoods. The impacts of average sea-level rise are boosted by storm surges and tidal variations, as was the situation during the landfall of hurricane Sandy in New York and Cyclone Idai in Mozambique.
• According to future estimates based on climate models and ocean-atmosphere physics, the speed of the melting of the largest global ice mass Antarctica is uncertain. There is a risk of a much higher sea-level rise due to potential intrusion of sea water under the Antarctic glaciers.
• Global mean sea-level has risen faster since 1900 than over any preceding century in at least the last 3000 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). 
• Global mean sea-level increased by 0.20m between 1901 and 2018. Human influence was very likely the main driver of this increase since at least 1971. 
• Heating of the climate system has caused global mean sea-level rise through ice loss on land, melting of glaciers and ice sheets and thermal expansion from ocean warming. Thermal expansion explained 50% of sea level rise during 1971–2018, while ice loss from glaciers contributed 22%, ice sheets 20% and changes in land-water storage 8%. The rate of ice-sheet loss increased by a factor of four between 1992–1999 and 2010–2019. Together, ice-sheet and glacier mass loss were the dominant contributors to global mean sea level rise during 2006–2018. 
• It is virtually certain that global mean sea-level will continue to rise over the 21st century. Over the next 2000 years, global mean sea-level will rise by about 2 to 3 m if warming is limited to 1.5°C, 2 to 6 m 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 likelihood and impacts of abrupt and/or irreversible changes increase with further global warming. At sustained warming levels between 2-3 C, the Greenland and West Antarctic ice sheets will be almost completely and irreversibly lost over multiple millennia causing potentially multi-meter sea-level rise. The mass loss is higher with higher warming rates. In case of very high greenhouse gas emissions (total failure of mitigation) there is a risk of sea-level rise by of 2 m by 2100 and even 15 m by 2300. 
• Continued sea-level rise will increase risks to food security in vulnerable regions between 1.5 C and 2 C Global warming level. 
• Sea-level rise poses a distinctive and severe adaptation challenge as it implies dealing with slow onset changes and increased frequency and magnitude of extreme sea-level events which will escalate in the coming decades. 
• There are significant specific impacts and challenges to those populations faced with sea-level rise living in coastal urban areas in least developed and low-middle income countries.