Rising Sea-level and its Sinking Consequences
Sea level rise refers to the gradual increase in the water level of the earth’s oceans, primarily caused by the melting of glaciers and ice sheets, as well as the expansion of seawater as it warms due to climate change. This phenomenon has become a major concern in recent years due to its potential impacts on coastal communities, infrastructure, and ecosystems. Rising sea levels can result in increased coastal erosion, flooding, and storm surges, leading to displacement of people and loss of property. It also threatens critical infrastructure such as ports, airports, and power plants, and can impact marine ecosystems by altering the habitat of marine species. Sea level rise is a complex issue that requires urgent action to mitigate its effects and protect vulnerable communities and ecosystems.
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Sea level rise may be defiend as relative sea level change, considered as the change in the height of oceans rising or falling relative to the land at any specific location, or absolute sea level change, which is measured as the change in height of the ocean surface above the centre of the earth without any consideration to the nearby land (United States Environmental Protection Agency, 2022).
As per the World Meteorological Organisation (WMO) State of the Global Climate Report, 2021, the rate of sea level rise at a global level is 4.5mm per year (2013-2021), almost double the rate from 1993-2002 (Sangomla, 2022).
However, the rise is not uniform in all the parts of the global oceans. The rise of sea levels in the southwestern Indian Ocean Region has been the fastest with a rate of 2.5 mm per year, compared to the global average. The rate of rise for other regions of the oceans ranges between 0 and 2.5 mm per year, faster than the global average (Panickal, 2020).
FACTORS AND TRENDS
Global Mean Sea Level Rise
Thermal expansion of sea, land ice loss, and freshwater mass exchange between oceans and land water reservoirs with groundwater storage change have been termed as the causative factors for global mean sea level rise. Anthropogenic greenhouse gas emissions are seen as the derivative of recent trends (Panickal, 2020).
Ocean Warming, Glaciers Melt, Ice-sheets
Since the last 50 years, there has been a significant sea level rise due to the thermal expansion of seawater. As per various reports, 93 per cent of the excess heat due to greenhouse gases have been absorbed by the ocean and the rest contributed to warming the atmosphere, continents, melting sea and land ice (Wallace, 2016). Ocean warming has been the reason behind 30-40 per cent of the observed sea-level rise in the last few decades. The melting of continental ice storage has been contributing to the sea level rise to a great extent. For instance, as per World Climate Research Programme (2018), melting glaciers have accounted for almost 21 per cent of the global-sea level rise (Panickal, 2020).
Several institutions such as the Geological Survey of India (GSI), Wadia Institute of Himalayan Geology (WIHG), and National Institute of Polar and Ocean Research (NCPOR), amongst others have been observing and monitoring the Himalayan glaciers and their mass loss. As per the scientific reports, the mean retreat rate of the Hindu Kush Himalayan glacier is 14.9 ± 15.1 m per year; which varies from 12.7 ± 13.2 m per year in Indus, 15.5 ± 14.4 m per year in Ganga and 20.2 ± 19.7 m per year in Brahmaputra River basins (Press Information Bureau, 2022). As per the study on the mass balance of glaciers by GSI, majority of Himalayan glaciers out of 76 studied for recession/advancement are observed melting/retreating at different rates.
The melting of ice-sheets has been contributing to the rise in sea level significantly. As per IPCC, the loss of ice from the ice sheets of the Arctic and Antarctic has been termed as one of the significant causes of this accelerated rise. The ice-sheet mass loss explains almost 25 per cent of the rate of global sea-level rise during 2003–2010. As per IPCC AR5, a near-complete loss of the Greenland ice sheet over a million years due to sustained global warming can cause a global mean sea level rise of almost 7 m having severe implications (Panickal, 2020).
Regional Variability in Sea-Level Rise
Localised factors such as changes in ocean heat and salinity content, and seawater density contribute to the variability in regional patterns of sea-level change, known as the ‘steric’ sea-level changes, predominantly for tropical reasons. For instance, the Indian Ocean is known to be the body with the fastest warming rate. Surface winds and ocean circulation are some of the geographical phenomena that drive the ocean-atmosphere dynamics, impacting steric sea-level changes. The temperature has increased by 1°C from 1951-2015 whereas the global average has been 0.7°C for the same period (Panickal, 2020). Moreover, as the land ice melts, land water storage changes occur which has been causing mass redistribution leading to Earth’s deformation and geoid changes.
Different modes of measurement have shown different trends of sea level rise along the Indian Ocean coasts. For instance, in Indian Ocean as per the gauge measurement, the rate of sea-level rise of about 1.06-1.75 mm per year has been observed between the periods from 1874-2004. Whereas as per satellite altimeter and reanalysis, within the Indian Ocean a diverse spatial pattern has been seen with a significant increase in the north and the south Indian Ocean. Mean sea-level rise in the Indian Ocean from satellite altimetry shows a rise of 3.28 mm per year during 1993 to 2017 (Panickal, 2020).
SEA-LEVEL RISE: IMPLICATIONS FOR INDIA
The phenomenon has the potential to impact millions of people along the Indian coastline of 7,516.6 km. Along with the geomorphic changes such as erosion, accretion, subsidence, and inundation of deltas, there could be various, socio-economic and structural implications. For instance, there has been a rise in the rate of sea level by 30 mm per year in the Sunderban delta since the last two decades. As per NASA, this has led to 12 per cent loss in the shoreline of the region, leading to the displacement of 1.5 million people (Akshit Sangomla, 2022).
Implications of Sea-level rise,
Image Source: https://www.ipcc.ch/srocc/
As per as projections by NASA, the rise of sea level could have disastrous impact on the coastal cities and ports such as Kochi, Mormugao, Chennai, Vizag, Paradip, amongst others; as reported by the latest IPCC Report.
Sea-rise predictions for ports
Sea-rise predictions for coastal cities
Sea level rise also impacts water security of a region due to the sea water ingression and rising salinity of groundwater aquifers. In case of Super Cyclone Amphan in 2020, the ingression of saline water into the agricultural fields, drinking water storages impacted the lives of millions of people. Furthermore, the implications in terms of disasters such as an increase in intensity and variability of tropical cyclones with externalities such as storm surges, heavier rainfall, high tides herald huge destruction.
WAY FORWARD
Dynamism in the sea level rise and emerging trends demand the immediate and thought-through responses for resilience and management of the implications. Structural responses in terms of protective measures such as dykes, seawalls, breakwaters, barriers, barrages, and usages of geotextiles should be considered at a faster pace to build resilience against flooding, coastal erosion and saltwater intrusion. Sea-level rise also needs to be measured in the context of beach and shore nourishment, dunes, marsh green-belt, sea wall, and other ecosystem-based adaptations (Intergovernmental Panel on Climate Change, 2023).
Non-structural measures such as building codes delineating standards like raising house elevation, floating houses, gardens, and changes in land use with institutional responses such early warning systems, emergency plans, rescue plans, mock drills, insurance schemes, etc must be taken to have a comprehensive mitigation and adaptation plan. Cooperation among the coastal nations in the Indian Ocean Region is imperative to address the issue comprehensively.
Different types of responses to coastal risk and sea level rise
Image Source:https://www.ipcc.ch/srocc/
References
Akshit Sangomla (2022). Sea levels along Indian coast rising at faster rate than global average: WMO report. Retrieved from downtoearth.org.in: https://www.downtoearth.org.
Interngovernmental Panel on Climate Change (2023). Sea Level Rise and Implications for Low-Lying Islands, Coasts and Communities: https://www.ipcc.ch/: https://www.ipcc.ch/srocc/
Panickal, S (2020). Sea-Level Rise. In S. Panickal, Assessment of Climate Change over the Indian Region (pp. 175-189). Springer.
Press Information Bureau (2022). Melting of Himalayan Glaciers: https://pib.gov.in/
Sangomla, A. (2022) Sea levels along Indian coast rising at faster rate than global average: WMO report: https://www.downtoearth.org.
United States Environmental Protection Agency (2022). Climate Change Indicators: Sea Level: https://www.epa.gov/climate-
Wallace, T. (2016). Oceans Are Absorbing Almost All of the Globe's Excess Heat: https://www.nytimes.com/
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