Sea level rise is a major threat for India and China among other countries that have large coastal population, the World Meteorological Organization warned in a report on Tuesday.

The report, titled “Global Sea-Level Rise and Implications”, said that Mumbai, Shanghai, Dhaka, Bangkok, Jakarta, Maputo, Lagos, Cairo, London, Copenhagen, New York, Los Angeles, Buenos Aires, and Santiago are among the cities most threatened by rise in sea levels.

Rising sea levels can cause erosion of coastal areas which could worsen the intensity of storm surges and flooding. It can also cause an increase in salt levels in soil and groundwater, affecting food security.

The World Meteorological Organization report said the global mean sea-level has increased by 0.2 metres between 1901 and 2018. It said there has been an average increase in the global mean sea-level of 1.3 millimeter every year between 1901 and 1971, 1.9 millimeter a year between 1971 and 2006 and 3.7 millimeter per year between 2006 and 2018.

Between 2013 and 2022, there has been 4.5 millimeter average increase every year in the the global mean sea-level, the report said, adding that “human influence was very likely the main driver of these increases since at least 1971”.

“WMO tells us that even if global heating is miraculously limited to 1.5 degrees Celsius [over pre-industrial levels], there will still be a sizeable sea level rise,” said United Nations Secretary General Antonio Guterres. “But every fraction of a degree counts.”

He added: “If temperatures rise by 2 degrees Celsius, that level rise could double, with further temperature increases bringing exponential sea level increases. Under any scenario, countries like Bangladesh, China, India and the Netherlands are all at risk.”

According to the report, thermal expansion contributed to 50% of rise in sea level between 1971 and 2018. In the same period, ice loss from glaciers contributed to 22% rise in sea level, ice-sheet loss 20% and changes in land-water storage 8%, the report said.

It said that sea levels will rise by 2-3 metres over the next 2,000 years if the increase in global temperatures is limited to 1.5 degrees Celsius (above pre-industrial levels) till the end of the century. However, the report said, higher temperatures would mean bigger rise in sea levels, estimating that 2 degrees Celsius increase would mean a rise of 2-6 metres, while 5 degrees Celsius warming would lead to 19-22 metre rise in sea levels.

According to UN estimates, the world could see a 2.4-2.6 degrees Celsius rise in temperatures by the end of this century.

The report said that “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”.

“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,” it added.