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Editorials/Opinions Analyses for UPSC – 23 September 2021


  1. Sea level rise is certain

Sea level rise is certain


The recently published Intergovernmental Panel on Climate Change (IPCC) Assessment Report from Working Group I — ‘Climate Change 2021: The Physical Science Basis’ — is a clarion call for climate action. It provides one of the most expansive scientific reviews on the science and impacts of climate change.


GS-III: Environment and Ecology (Climate Change and its issues, Environmental Pollution and Degradation)

Dimensions of the Article:

  1. What is Sea Level Rise?
  2. Factors leading to Sea Level Rise
  3. Impact of Rising Sea Levels
  4. Issues with Estimation models
  5. Vulnerability in India
  6. Way Forward

What is Sea Level Rise?

  • Sea Level Rise is an increase in the level of the world’s oceans due to the effects of climate change, especially global warming, induced by three primary factors: Thermal Expansion, Melting Glaciers and Loss of Greenland and Antarctica’s ice sheets.
  • Sea level is primarily measured using tide stations and satellite laser altimeters.

Trends in rising Sea Levels

  • Global sea level has been rising over the past century, and the rate has accelerated in recent decades. The average global sea level has risen 8.9 inches between 1880 and 2015. That’s much faster than in the previous 2,700 years.
  • SLR is not uniform across the world. Regional SLR may be higher or lower than Global SLR due to subsidence, upstream flood control, erosion, regional ocean currents, variations in land height, and compressive weight of Ice Age glaciers.
  • Earlier, IPCC released ‘The Special Report on the Ocean and Cryosphere in a Changing Climate’ which underlined the dire changes taking place in oceans, glaciers, and ice-deposits on land and sea. The report expects oceans to rise between 10 and 30 inches by 2100 with temperatures warming 1.5 °C.

Why is Sea Level Rise a Major Concern?

  • Sea level rise will continue after emissions no longer increase, because oceans respond slowly to warming.
  • The centennial-scale irreversibility of sea-level rise has implications for the future even under the low emissions scenarios.
  • Sea level rise occurs mainly due to the expansion of warm ocean waters, the melting of glaciers on land, and the melting of ice sheets in Greenland and Antarctica.
  • Projections based on structured expert judgments indicate that sea-level rise as high as 2.3m by 2100 cannot be ruled out.
  • According to the UN Environment Programme Emissions Gap Report, the world is heading for a temperature rise above 3°C this century (double the Paris Agreement aspiration). And there is deep uncertainty in sea-level projections for warming above 3°C.
  • Understanding the risks involved from climate change and sea-level rise in the 21st and 22nd centuries is crucial.

Factors leading to Sea Level Rise

  • Thermal Expansion: When water heats up, it expands. About half of the sea-level rise over the past 25 years is attributable to warmer oceans simply occupying more space.
  • Melting Glaciers: Higher temperatures caused by global warming have led to greater-than-average summer melting of large ice formations like mountain glaciers as well as diminished snowfall due to later winters and earlier springs. That creates an imbalance between runoff and ocean evaporation, causing sea levels to rise.
  • Loss of Greenland and Antarctic Ice Sheets: As with mountain glaciers, increased heat is causing the massive ice sheets that cover Greenland and Antarctica to melt more quickly, and also move more quickly into the sea.

Impact of Rising Sea Levels

  • Coastal Flooding: Globally, eight of the world’s 10 largest cities are near a coast, which is threatened by coastal flooding. Jakarta (Indonesia) is being known as the world’s fastest-sinking city, by about 25 cm into the ground every year. Other cities that regularly feature in the lists endangered by climate change include Guangzhou, Jakarta, Miami, Mumbai and Manila.
  • Destruction of Coastal Biodiversity: SLR can cause destructive erosion, wetland flooding, aquifer and agricultural soil contamination with salt, and lost habitat for biodiversity.
  • Dangerous Storm Surges: Higher sea levels are coinciding with more dangerous hurricanes and typhoons leading to loss of life and property.
  • Lateral and Inland Migration: Flooding in low-lying coastal areas is forcing people to migrate to the higher ground causing displacement and dispossession and in turn a refugee crisis worldwide.
  • Effect on Communications Infrastructure: The prospect of higher coastal water levels threatens basic services such as internet access.
  • Threat to Inland Life: Rising seas can contaminate soil and groundwater with salt threatening life farther away from coasts.
  • Tourism and Military Preparedness: Tourism to coastal areas and military preparedness will also be negatively affected by an increase in SLR.

Issues with Estimation models

  • Scientists rely on ice sheet models to estimate future glacier melt.
  • While these models have improved over the years, there are shortcomings in the knowledge and representation of the physical processes.
  • Ice sheets can destabilise rapidly as the water gets warm. Such changes are difficult to model and marine ice cliff instability (MICI) events are not included in the sea-level projections.
  • The models do not capture the abrupt and non-linear dynamics of changes that take place.
  • Besides, changes in ice-ocean interactions can cause extensive and rapid sea-level rise.
  • This happens from the mass loss of ice shelves (ice that flows into cold oceans while attached to the land), which may disintegrate suddenly.
  • Therefore, using ice sheet models coupled with ocean models to create probabilistic scenarios for the future is tricky.

Vulnerability in India

  • Communities along the coast in India are vulnerable to sea-level rise and storms.
  • With climate change, storms will become more intense and frequent. They will be accompanied by storm surges, heavy rain and flooding.
  • Even the 0.1m to 0.2m rise expected along India in the next few decades can cause frequent coastal flooding.

Way Forward

  • The uncertainty regarding a metre or more of sea-level rise before 2100 is related to a lack of knowledge and inability to run models with the accuracy needed. Ignoring the unknowns can prove dangerous.
  • Adaptation to sea-level rise must include a range of measures, along with coastal regulation, which should be stricter.
  • Coastal communities should be alerted in advance and protected during severe weather events.
  • Natural and other barriers should be considered in a limited manner to protect certain vulnerable areas.
  • Retreat should be part of the adaptation strategies for some very low-lying areas.

-Source: The Hindu

December 2023