India among nations facing highest threat from sea-level rise: WMO

By Suja Mary James

Rising seas pose “unthinkable” risks to billions around the world, United Nations Secretary-General António Guterres said while addressing what was the Security Council’s first-ever debate about the global implications of sea level rise.

The latest report of the World Meteorological Organisation(WMO) published on 15th February 2023 emphasizes the looming threat being posed by sea-level rise. According to the report, “countries from Bangladesh to China, India and the Netherlands and the mega-cities on every continent are under extreme stress”.

WMO Secretary-General HE Prof. Petteri Taalas stated that the Global Mean Sea-level (GMSL) changes will exert a significant impact on communities worldwide especially small island developing states, in densely populated low-lying urban areas, coastal farmlands, and water reserves.

What is GMSL?

GMSL or Global Mean Sea Level is defined by the NASA website as the average height of the entire ocean surface. An essential climate indicator, the global mean sea level shows how the ocean is warming and how much land ice is melting.

Causes for GMSL

Since 1880, the GMSL has increased by 8–9 inches (21–24 centimeters) and is caused primarily by three factors related to global warming: the addition of water from glaciers, loss of Greenland and Antarctica’s ice sheet, and the thermal expansion of seawater as it warms.

The GMSL in 2021 was 97 millimeters (3.8 inches) and in 2022 it was 103 (± 4.0) mm. 

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. From 1992-1999 and 2010-2019, the pace of ice-sheet loss accelerated by a factor of four. According to the report, between 2006 and 2018, mass loss from ice sheets and glaciers together accounted for the majority of the rise in the global mean sea level.

Relying on nearly a 30-year record of satellite measurements, Sea level rise is estimated to be occurring at a rate of 0.13 inches (3.4 mm) per year. Between 2006 and 2015, the average global water level in the ocean increased by 0.14 inches (3.6 millimeters) each year, which is 2.5 times faster than the average growth rate of 0.06 inches (1.4 millimeters) per year during the majority of the twentieth century. According to the WMO, the sea level has risen at a rate of 4.5 mm per year between 2013 and 22. “The human influence was very likely the main driver of these increases since at least 1971”.

Sea level rise is not globally uniform and varies regionally. In several ocean basins, the sea level has increased by as much as 6-8 inches (15-20 cm). The strength of winds and ocean currents naturally varies by region, affecting how much and where the deeper ocean layers store heat.

Even if greenhouse gas emissions continue to rise at a relatively slow rate in the next decades, the average global sea level is still anticipated to rise by at least one foot (0.3 meters) by the end of the century.

Global Concern on Sea-Level Rise

Coastal mareographs (Tide Gauges) have been used to measure sea level rise since the beginning of the industrial era, and in more recent years, satellite altimeters have also been used.

Sea-level rise poses a serious threat to countries like the Netherlands, Bangladesh, India, and China, some of which have substantial coastline populations and several low-lying small islands. Numerous major cities, including Shanghai, Dhaka, Bangkok, Jakarta, Bombay, Maputo, Lagos, London, Copenhagen, New York, Los Angeles, and Buenos Aires, are under threat. 

The effects of sea level rise will be felt in coastal regions that are constantly changing and already experience a variety of natural and man-made stresses, including erosion, storms, land subsidence, wetland loss, and environmental degradation from recreation and development pressures.

In the WMO report, Taalas has stated that groundwater salinization, floods, and damage to coastal infrastructure are just a few of the negative effects of sea-level rise that will have cascading and compounding effects. In the short to long term, it poses hazards to cultures, economies, livelihoods, communities, health, and well-being as well as to the security of food and water. The impacts of average sea-level rise are boosted by storm surges and tidal variation.

Global mean sea level will almost certainly continue to rise throughout the twenty-first century. In comparison to 1995–2014, the likely global mean sea level rise by 2100 ranges from 0.28–0.55 m under the very low GHG emissions scenario (SSP1–1.9, equals about 1.5 C target), to 0.3–0.22 m under the low GHG emissions scenario (SSP1-2.6), to 0.4–0.76 m under the intermediate GHG emissions scenario (SSP2-4.5), and to 0.63–1.01 m under the very high GHG emissions scenario (SSP5-8 (SSP5-8.5). the long-term over a highly populated region like India is needed to address. Already major coastlines of India are under extreme stress due to elevated sea level rise.

How Indian coastlines are at risk?

Apart from other global oceans, the sea-surface temperature over the Indian Ocean region has increased one degree Celsius between 1951 and 2015, compared to the global average of 0.7°C. “Regional patterns of sea-level change are dominated by local changes in ocean heat content and salinity”. Sea level rise in the southwestern Indian Ocean region is occurring at a rate of 2.5 mm/year faster than the global average and in other parts of the Indian Ocean region, the rate is between 0 to 2.5mm/year.

Indian coastlines covering more than 7,500 square kilometers are very vulnerable to climate change-related sea level rise. Scientists anticipate that by 2100, 36 million Indians will likely live in locations that regularly flood because of the 8.5 cm rise in sea levels along the Indian coast over the past 50 years. 

The millions of people living along the Indian coastline could suffer major impacts from such a sea level rise. While progressive coastal erosion, land subsidence, and delta inundation are long-term worries for those who live near the sea, the combined effect of tropical storms and sea level rise is of more immediate concern.

According to the WMO report “ 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 rise in sea level poses a larger risk to some Indian states that have had rapid coastal erosion, including Gujarat, Tamil Nadu, and West Bengal. 

“Coastal erosion is the displacement or loss of land caused due to rise in sea level, resulting in strong waves and coastal flooding” and is accelerated by both anthropogenic or natural causes. According to a National Centre for Coastal Research (NCCR) research from 2018, the West Bengal coast alone lost almost 99 sq. km of land between 1990 and 2016. More than 40% of erosion is noticed in four states: West Bengal (63%); Pondicherry (57%); Kerala (45%) and Tamil Nadu (41%). In the last century, sea levels rose by 40 cm and it is anticipated to rise by an additional 60 cm in the coming decade. According to the IPCC assessment, an increase of 1 mm per year can inundate around 0.5 m per year.

SLR is linked with cyclones and storm surges. Recently, the intensity and wind speed of cyclones in the Indian Ocean region has increased, leading to bigger storm surges. Storm surges will intensify with rising sea levels, carrying more water ashore and flooding areas. For instance: Super cyclone Amphan in 2020 brought sea water 25 kilometers inland, flooding major portions of the Sunderbans delta, which is already the area of India that is most susceptible to both cyclones and sea level rise. Frequent cyclonic incidence along Sunderbans delta has increased the sea level by 30mm per year.

Land subsidence prominently impacted the coastlines of Mumbai. A study published in the Geophysical Research Letters journal says that the coastal city is sinking into the sea at the rate of 2 mm per year. According to the study, global warming along with groundwater extraction, mining, reclamation of natural wetlands, infrastructure projects, and ecological disturbance leads to land subsidence. Along with gradual sea-level rise would sink the city in the near future as the average elevation of the city is around 10m. 

The megacities like Mumbai, Kolkata, and Chennai are located in India’s Low Elevation Coastal Zone, which has an average elevation of 2 to 10 meters (LECZ). LECZs are areas with a coastline elevation of lower than 10 meters. Roughly 81,000 square kilometers of land in India are covered with LECZ.  Therefore, a one-meter sea level rise will severely affect these regions as it will inundate 6000 square kilometers in India. Around 1.4 billion people living on Indian Coastlines are experiencing a sea-level rise, erosion, and natural disasters such as tropical storms and cyclones. According to the Internal Displacement Monitoring Centre, about 3.6 million Indians were displaced annually between 2008 and 2018 due to these events. 

In the most recent Special Report on “Global Warming of 1.5°C” from the Intergovernmental Panel on Climate Change, sea level rise is one of the key issues mentioned. In the next 80 years, according to certain predictions, the sea level will rise by at least one meter, making it almost certain that we will witness this. Infrastructure destruction, land loss, and community dislocation will all result in major consequences.

Sea levels will keep rising for millennia due to emissions we have already committed to, even if we are successful in keeping the temperature rise to 1.5 degrees. Climate change will affect our beaches, and we must be ready for this even if living near the ocean has always carried some level of risk of flooding and erosion.