Sea level rise is a major threat for India and China along with Bangladesh, the Netherlands and other countries which have large coastal populations, the World Meteorological Organisation warned in a report, “Global Sea-Level Rise and Implications Key facts and figures” on Tuesday, flagging large-scale impacts on Mumbai, Chennai, Kolkata and other coastal cities in the country.
Global mean sea-level increased by 0.20m between 1901 and 2018, with an average rate increase of 1.3 mm/ year between 1901 and 1971,1.9 mm/year between 1971 and 2006, and 3.7 mm/year between 2006 and 2018, WMO said in its report.
Between 2013 and 2022, this has been 4.5 mm/yr and “human influence was very likely the main driver of these increases since at least 1971,” the report said.
“ 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. But every fraction of a degree counts. If temperatures rise by 2 degrees, 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,” said Antonio Guterres, UN Secretary General on Tuesday.
Thermal expansion contributed to 50% of sea level rise during 1971-2018, while ice loss from glaciers contributed to 22%, ice-sheet loss to 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, the report said.
WMO said sea levels will continue to rise in all emission 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 (green house gas) emissions scenario; 0.44-0.76 m under the intermediate GHG emissions scenario and 0.63-1.01 m under the very high emissions scenario. At the upper end, that’s around half a metre. For context, Chennai has an average elevation of just around 6.7 metres above sea level; Mumbai is around 10 m.
“The likelihood and impacts of abrupt and/or irreversible changes increase with further global warming. At sustained warming levels between 2-3 degree C, the Greenland and West Antarctic ice sheets will be almost completely and irreversibly lost over multiple millennia causing potentially multimeter sea-level rise. The mass loss is higher with higher warming rates,” the report said, flagging concerns of massive economic losses and coastal flooding in regions with high coastal populations.
The population potentially exposed to a 100-year coastal flood is projected to increase by about 20% if global mean sea level rises by 0.15 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. Sea-level rise poses an existential threat for some small Islands and some low-lying coasts. By 2100 the value of global assets within the future 1-in-100-year coastal floodplains is projected to be between US$7.9 and US$12.7 trillion rising to between US$8.8 and US$14.2 trillion.
“Sea-level rise will bring cascading and compounding impacts resulting in losses of coastal ecosystems and ecosystem services, groundwater salinization, 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,” WMO said.
Experts said India is most vulnerable to compounding impacts of sea level rise. “In the Indian ocean half of sea level rise is due to the volume of water expanding since the ocean is warming up rapidly. The contribution from glacier melt is not as high. Indian Ocean is the fastest warming ocean in terms of surface warming. The impacts India is facing are due to compound extreme events which are not in the future but already happening along our coastline. Cyclones are intensifying rapidly due to more moisture and heat from ocean warming. The amount of flooding also increases because storm surges are compounding sea level rise decade by decade. Another compounding impact in this region is that cyclones are bringing more rain than earlier. Super Cyclone Amphan (2020) caused largescale flooding and inundated tens of kms inland with saline water intruding. This can damage agriculture in the region for years and decades,” explained Roxy Mathew Koll, a climate scientist at the Indian Institute of Tropical Meteorology, Pune and author of Intergovernmental Panel on Climate Change.
According to a response by the ministry of earth sciences in Lok Sabha in 2021, on average, the sea level along the Indian coast was observed to be rising at a rate of about 1.7 mm/year during the last century (1900-2000).
Koll said even small changes in sea level can have a huge impact on the coastline. “How much is the land intrusion proportional to a sea level rise of 3 cm/decade?
A 3 cm sea level rise could cause the sea to intrude inland by about 17 meters. At future rates of 5 cm/decade, this could be 300 metres of land taken by the sea in a century,” he added.
“Mega-cities on every continent will face serious impacts including Cairo, Lagos, Maputo, Bangkok, Dhaka, Jakarta, Mumbai, Shanghai, Copenhagen, London, Los Angeles, New York, Buenos Aires and Santiago. The danger is especially acute for nearly 900 million people who live in coastal zones at low elevations — that’s one out of ten people on earth. Some coastlines have already seen triple the average rate of sea-level rise,” Guterres said in his statement.
“And consider the hundreds of millions of people living in the river basins of the Himalayas. We’ve already seen how Himalayan melts have worsened flooding in Pakistan. But as these glaciers recede over the coming decades, over time, the Indus, Ganges and Brahmaputra rivers will shrink. And rising sea levels combined with a deep intrusion of saltwater will make large parts of their huge deltas simply uninhabitable,” Guterres said referring to impacts on India.
Source- Hindustan Times.