Context: Melting glaciers worldwide have caused nearly 2 cm of sea level rise this century, according to a recent study published in Nature on February 19, 2024. The study, conducted by scientists from the University of Edinburgh and the University of Zurich, found that glaciers have been losing 273 billion tonnes of ice annually for the past 25 years.

• This ice loss equals the amount of water the global population would consume over 30 years. Further, every centimetre of sea level rise exposes an additional 2 million people to annual flooding.

Causes of Sea Level Rise

• Two primary factors drive sea level rise:

• The first is glacier and ice sheet melting due to global warming. Since 2000, glaciers have lost 2% to 39% of their regional ice and around 5% globally—18% more than the ice loss from the Greenland and Antarctic ice sheets combined.

• The second factor is the thermal expansion of seawater, where warming oceans expand in volume. NASA estimates that thermal expansion contributes to one-third to half of the current global sea level rise.

Rising Sea Levels: By the Numbers

• The global sea level has risen by approximately 21 cm since 1880, according to the US National Oceanic and Atmospheric Administration (NOAA). However, the rise has accelerated significantly, doubling from 0.18 cm per year in 1993 to 0.42 cm per year in 2024.

• NASA reports that global sea levels have increased by over 10 cm between 1993 and 2024, a rate unprecedented in the past 2,500 years. The rise is uneven, with regions like the southwestern Indian Ocean experiencing a 2.5 mm per year increase, faster than the global average, as per a 2022 World Meteorological Organization report.

Factors Contributing to the Decline

• Warming Air and Oceans: Higher-than-usual air temperatures and warm seas are primary drivers of the sea ice loss. In the Antarctic, warm air and waters in the Southern Hemisphere’s summer (December-February) melt the ice, while the Arctic’s delayed freezing due to unusually warm oceans around Hudson Bay also contributed to the decline.

• Winds and Storms: Antarctic sea ice is particularly vulnerable to ice-breaking winds because it is surrounded by the ocean. In the Arctic, storms have also contributed to breaking up ice in regions like the Barents Sea and Bering Sea, where thinner ice is more prone to disruption.

Implications of the Dip

• Feedback Loop: The loss of sea ice exposes more water to the Sun, increasing heat absorption and leading to further warming. Sea ice’s reflective white surface helps cool the planet by reflecting solar radiation, but as more ice melts, darker ocean water absorbs more sunlight, accelerating warming.

• Global Climate Impact: The decrease in sea ice slows the flow of water through global oceans, as melting freshwater reduces ocean salinity and disrupts ocean currents. This can lead to severe consequences for the global climate, marine ecosystems, and ice shelf stability.

Impact on Indian Coastal Cities

• India’s coastal cities have also experienced rising sea levels. Mumbai recorded a 4.44 cm rise between 1987 and 2021, the highest among Indian cities, according to a 2024 report by the Centre for Study of Science, Technology, and Policy (CSTEP). This is concerning, as Mumbai’s average elevation is around 10 meters above sea level.

• Other cities, such as Haldia in West Bengal, witnessed a rise of 2.726 cm, Visakhapatnam in Andhra Pradesh 2.381 cm, and Kochi in Kerala 2.213 cm, the report added.

Why It Matters?

• Rising sea levels threaten both human and natural systems. Coastal flooding becomes more frequent and severe, accelerating erosion and displacing communities. Between 1990 and 2016, West Bengal alone lost nearly 99 sq km of land, according to a 2018 National Centre for Coastal Research (NCCR) report.

• A 2024 Scientific Reports study revealed that by 2018, 29% of the global population lived within 50 km of the coast, with 15% residing just 10 km away.

Future Risks and the Need for Action

• Higher sea levels lead to intensified storm surges, which push water further inland during tropical storms. This damages coastal ecosystems like mangroves, coral reefs, and salt marshes, contaminates freshwater supplies, and disrupts daily life. If greenhouse gas emissions remain unchecked, the situation could worsen.

• The director of NASA’s sea level change team, warned in 2024 that current acceleration rates could result in an additional 20 cm rise by 2050, doubling the increase of the past century and significantly amplifying flood risks worldwide.