Sea-Level Rise and India’s Coasts Explained

Sea-level rise is the gradual increase in the average height of the world’s oceans, caused mainly by global warming expanding seawater and melting glaciers and ice sheets, and it threatens India’s roughly 7,500 km coastline. The rise is slow from year to year, but it raises the base level for every high tide, storm surge and cyclone, so floods reach farther inland and coastal land is lost more easily.

For India, the concern is concentrated in low-lying coastal cities such as Mumbai, Kolkata and Chennai, in river deltas such as the Ganga-Brahmaputra delta that holds the Sundarbans, and in island and coastal communities that depend on fishing and farming. This explainer sets out the causes, the observed and projected rise, how India’s coasts differ, the effects of saltwater intrusion, and how uncertain the numbers are. It was last reviewed on 30 October 2026.

Key Takeaways

• Global mean sea level rose by about 20 cm between 1900 and 2018, and the rate of rise has accelerated to several millimetres a year in recent decades.
• Sea-level rise has two main physical causes: the thermal expansion of warming ocean water and the addition of meltwater from glaciers and the Greenland and Antarctic ice sheets.
• Sea level in the north Indian Ocean has risen at a pace broadly similar to the global average, with regional variations driven by ocean currents, winds and land movement.
• Local land subsidence, caused by groundwater pumping and sediment compaction in deltas, can make relative sea-level rise at a city or delta faster than the ocean rise alone.
• Projections for 2100 range from a few tens of centimetres to over a metre depending on emissions, and the upper end is uncertain because of unpredictable ice-sheet behaviour.
• The effects in India include coastal flooding, loss of land in the Sundarbans, saltwater intrusion into rivers and aquifers, and worse storm surges during cyclones.

What Causes Sea-Level Rise?

Sea-level rise is caused by the warming of the planet, which makes the ocean expand and adds meltwater to it from ice on land. Together these two processes account for most of the rise measured since the nineteenth century.

• Thermal expansion: Water expands as it warms. The oceans have absorbed the large majority of the extra heat trapped by greenhouse gases, so the upper layers have grown warmer and taken up more volume.
• Melting mountain glaciers: Glaciers in the Himalaya, the Andes, the Alps, Alaska and elsewhere are losing mass and adding water to rivers and the sea.
• Ice sheets: Greenland and Antarctica hold enough ice to raise global sea level by many metres if they melted, and they are now losing mass at an increasing rate.
• Changes in land water storage: Pumping groundwater and draining wetlands moves water to the ocean, a smaller but real contribution.

Ice that is already floating, such as sea ice, does not raise sea level when it melts. It is the land-based ice of glaciers and ice sheets, and the expansion of warming water, that drives the rise.

How Fast Is Global Sea Level Rising?

Global mean sea level is rising by several millimetres a year at present, and the pace has increased over the twentieth and twenty-first centuries. The IPCC’s Sixth Assessment Report states that the global mean rise between 1901 and 2018 was about 0.2 metres and that the rate in recent years was about double the rate in the middle of the twentieth century.

Scientists measure sea level in two ways. Tide gauges at ports record height relative to the land beside them, some with records going back more than a century. Since 1993, satellite altimeters have measured the height of the ocean surface from space with very high precision and give a near-global picture.

The most important feature of the rise is that it is committed to continue. Oceans respond slowly to warming, and ice sheets take decades or centuries to adjust, so sea level will keep rising for generations even if emissions fall quickly. What the future emissions path changes is how fast and how far the rise goes.

What Is Happening to Sea Level Around India?

Sea level along India’s coast has been rising at a rate broadly similar to the global average, and recent decades show a faster rise than the long-term record. Assessments by the Ministry of Earth Sciences have reported that the north Indian Ocean rose by roughly 1 to 2 mm a year across the long tide-gauge record from the late nineteenth century, and by roughly 3 mm a year over the last couple of decades.

These are averages, and sea-level rise is not uniform across the globe or even along one country’s coast. Regional differences arise from:

• Ocean circulation and winds: Patterns such as the monsoon and the Indian Ocean Dipole shift water around the basin from year to year.
• Heat distribution: The Indian Ocean has been warming quickly, which increases local thermal expansion.
• Land movement: The land itself may be rising slowly, as in some rocky coasts, or sinking, as in many deltas.
• Gravity and Earth’s shape: Melting ice sheets change the pull of gravity on the ocean, so the rise is not evenly spread over the globe.

India has a limited number of long, good-quality tide-gauge records, and some are affected by local land movement. This is one reason scientists use satellite data alongside tide gauges, and why they give ranges rather than exact numbers.

Which Indian Cities and Regions Are Most at Risk?

The Indian coastal areas at greatest risk from sea-level rise are the Sundarbans delta, low-lying parts of Mumbai, Kolkata and Chennai, and the flat deltas and lagoons of Odisha, Andhra Pradesh, Gujarat and Kerala. Risk depends on how low the land is, whether it is sinking, how exposed it is to cyclones, and how many people and assets are located there.

Because India has several large coastal cities and dense coastal populations, the number of people affected is large even if the rise is measured in centimetres. Ports, power plants, refineries, fishing harbours and tourism infrastructure also line the shore.

How Does Sea-Level Rise Threaten the Sundarbans?

Sea-level rise threatens the Sundarbans by gradually flooding and eroding the low islands of the Ganga-Brahmaputra delta, which sit barely above the high-tide line. The Sundarbans, shared by India and Bangladesh, is the largest mangrove forest in the world and a UNESCO World Heritage Site on the Indian side.

Several islands in the Indian Sundarbans have lost land over recent decades. Lohachara island was reported to have gone under water in the early 2000s, and Ghoramara island has been shrinking, forcing people to relocate to nearby islands. Scientists attribute this loss to a combination of rising seas, stronger cyclone surges, erosion, and the natural sinking of the delta, as it compacts and receives less fresh sediment because of upstream dams and diversions.

Several million people live in the Indian Sundarbans, and many depend on farming, fishing and honey collection. Embankments protect much of the inhabited land, but they are breached during major cyclones such as Aila in 2009 and Amphan in 2020, letting saltwater flood fields and ponds. The mangroves themselves act as a natural buffer against waves, but they can only survive if they receive enough sediment to build up with the sea level.

What Is Saltwater Intrusion and Why Does It Matter?

Saltwater intrusion is the movement of seawater into coastal rivers, estuaries and underground aquifers, and it matters because it spoils drinking water and farmland. Higher seas push salt farther up rivers and into the soil, while heavy groundwater pumping near the coast lowers freshwater pressure and lets saline water enter the aquifer.

The effects are most visible in delta regions. Farmers in coastal Odisha, West Bengal, Gujarat and Tamil Nadu have reported rising soil and water salinity, which cuts rice yields and forces a shift to shrimp ponds or salt-tolerant crops. In the Sundarbans, saline water affects drinking supplies, and many households must fetch fresh water from distant ponds or tube wells.

Saltwater intrusion tends to be a gradual, hidden process, and it is difficult to reverse. Once an aquifer is salinised, it can take years or decades to flush out, which makes prevention through controlled pumping and freshwater recharge more practical than cure.

How Do Cyclones and Storm Surges Combine with Sea-Level Rise?

Cyclones and storm surges combine with sea-level rise by adding a higher starting level to every surge, so the same storm reaches farther and floods more land than it would have decades ago. A surge is the abnormal rise of water pushed ashore by a cyclone’s winds and low pressure, and it is the main killer in coastal cyclones.

India’s east coast, facing the Bay of Bengal, has a funnel-shaped geography and shallow waters that amplify surges, and it has seen devastating events in Odisha, West Bengal and Andhra Pradesh. Gujarat on the west coast is exposed to Arabian Sea storms. Even without any change in cyclone strength, a higher mean sea level means more land is below the reach of a given surge.

Extreme sea levels that were once rare, such as a once-in-a-century coastal flood, are expected to become far more frequent in many places as the baseline rises. This is why coastal engineers and planners focus on the combination of mean sea level, tide, surge and wave height rather than on the average alone.

How Much Will Seas Rise by 2100, and How Uncertain Is It?

The IPCC projects that global sea level will rise by roughly a few tens of centimetres to a little over a metre by 2100, depending on greenhouse gas emissions. Under very low emissions the central estimate is under about half a metre, while under very high emissions it is closer to one metre, and the rise continues beyond 2100.

The range is wide for good reasons. The main source of uncertainty is how quickly the Greenland and Antarctic ice sheets will lose mass, which depends on processes such as ocean warming under ice shelves and the collapse of ice cliffs that are not yet well understood. The IPCC therefore also describes a low-likelihood, high-impact scenario in which the rise could exceed these ranges, and it cannot be ruled out that two metres or more is reached by the end of the century.

Scientists give these figures as projections under assumed emissions paths, not as predictions of a single outcome. What is certain is the direction: every credible scenario shows continued rise, and the sooner emissions fall, the smaller the long-term commitment.

What Can India Do About Sea-Level Rise?

India can reduce the harm from sea-level rise by combining measures that protect, adapt and retreat, together with global action to cut emissions. Local conditions decide which mix works, and planners increasingly use shoreline maps and hazard lines to guide where to build.

• Monitoring and forecasting: The Indian National Centre for Ocean Information Services (INCOIS) issues ocean state and storm surge forecasts, and the National Centre for Coastal Research (NCCR) maps shoreline change.
• Regulation of coastal land use: The Coastal Regulation Zone (CRZ) rules limit construction near the high-tide line, and a hazard line drawn by the Survey of India is used to map flood and erosion risk.
• Nature-based protection: Restoring mangroves, dunes, wetlands and coral reefs absorbs wave energy and traps sediment.
• Engineered defences: Embankments, sea walls and drainage upgrades protect cities and ports, though hard structures can be costly and can move erosion elsewhere.
• Early warning and shelters: Cyclone warnings and shelters, built after the 1999 Odisha super cyclone, have greatly reduced deaths from surges.
• Planned relocation: In places that cannot be protected, such as sinking island villages, communities may need to be moved with proper compensation.

Bottom Line

Sea-level rise is a slow but steady threat that magnifies every coastal hazard along India’s long shore. The Sundarbans, Mumbai, Kolkata and Chennai face the greatest exposure, where rising seas combine with sinking land, cyclones and heavy rain. The range of future outcomes is wide and depends on global emissions, so India needs both coastal adaptation and strong support for emission cuts.

Frequently Asked Questions

How much has sea level risen globally?

Global mean sea level rose by about 20 cm between 1900 and 2018, according to the IPCC. The rise has accelerated, and recent rates are several millimetres a year. Satellite and tide-gauge records both show the trend.

Is sea level rising around India?

Sea level around India is rising at a pace broadly similar to the global average, with regional and local differences. Assessments by the Ministry of Earth Sciences put the north Indian Ocean rise at roughly 1 to 2 mm a year over the long record and around 3 mm a year in recent decades. Land sinking in deltas and cities can make the local rise larger.

Which Indian cities are most at risk from rising seas?

Mumbai, Kolkata and Chennai are generally considered the Indian megacities most at risk, along with low-lying coastal towns in Gujarat, Odisha, Andhra Pradesh and Kerala. Their risk comes from low elevation, dense population and exposure to cyclone surges and heavy rain. The Sundarbans delta is the most vulnerable large region.

What is saltwater intrusion?

Saltwater intrusion is the movement of seawater into coastal rivers, soils and groundwater. It happens when higher seas push salt inland or when over-pumping lowers freshwater levels along the coast. It damages crops and drinking water supplies, especially in deltas such as the Sundarbans.

How much will the sea rise by 2100?

The sea is projected to rise by roughly a few tens of centimetres to a little over a metre by 2100, depending on how much greenhouse gas is emitted. Lower emissions give a lower rise. The upper end is uncertain because of the unpredictable behaviour of ice sheets in Greenland and Antarctica.

Can sea-level rise be stopped?

Sea-level rise cannot be stopped in the short term because oceans and ice sheets respond slowly to warming that has already occurred. Cutting greenhouse gas emissions can slow the rate and limit the total rise over the long term. Coastal adaptation, such as protecting mangroves and planning land use, reduces the damage meanwhile.

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