More than 14 million people in low-lying parts of South Asia, including Mumbai, Kolkata and Dhaka, face an immediate risk of losing their homes to permanent inundation, the United Nations has warned.
The finding puts India’s two major coastal cities at the centre of a problem that is no longer confined to long-term climate projections. Rising seas are increasingly becoming an infrastructure, housing, public-health and economic-risk issue for cities built around vulnerable coastlines.
Sea Levels Are Rising Faster
The UN’s latest assessment, published on August 31, 2026, says global sea level rose at an average rate of 4.7 mm a year between 2014 and 2023. In 2024, the annual increase reached a record 5.9 mm.
The UN attributes rising seas primarily to human-driven climate change, including the melting of glaciers and ice sheets and the expansion of seawater as oceans warm.
The exposure is already substantial. Around 770 million people, or roughly 10% of the world’s population, live in coastal areas less than five metres above the high-tide line.
The UN identifies low-lying delta cities such as Mumbai, Kolkata and Dhaka as particularly exposed, with more than 14 million people collectively facing the immediate risk of losing homes, livelihoods and lives through permanent inundation.
The 14-million figure should not be interpreted as 14 million people in Mumbai and Kolkata alone. It refers to the wider group of low-lying South Asian delta cities identified by the UN.
Kolkata’s Sea Level Outlook
Kolkata’s exposure is also reflected in city-specific projections. A 2024 UN technical brief estimates that sea level in Kolkata could rise by 18 cm between 2020 and 2050, with an uncertainty range of 15–23 cm. The table’s projections are based on a scenario corresponding to 3°C of end-of-century warming.
That projection does not mean 18 cm of water will suddenly cover Kolkata in 2050. It represents projected sea-level change relative to the 2020 baseline. The actual consequences will depend on factors including tides, storm surges, coastal flooding, local geography and changes in land elevation.
The distinction matters because sea-level rise can amplify existing coastal hazards. Even modest increases in average sea level can make high-water events more damaging by starting from a higher baseline.
Mumbai’s Economic Exposure
Mumbai’s vulnerability carries a particularly large economic dimension. The IPCC’s Sixth Assessment Report cites estimates that sea-level-rise damages in Mumbai could amount to $112–162 billion by 2050 and could increase by a factor of 2.8–2.9 by 2070. The figures come from research cited by the IPCC, rather than from the UN’s latest 2026 assessment.
For a city with extensive coastal development and infrastructure, the implications extend beyond individual properties. Flooding and other coastal hazards can affect transport networks, buildings, utilities and other infrastructure, creating costs for households, businesses and governments.
The UN’s latest assessment makes the broader economic stakes clear. It says damage to coastal infrastructure globally has already exceeded $1.8 trillion and warns that, without adaptation, potential annual global losses could reach $1.4 trillion. It also notes that ports handling more than 80% of global trade are increasingly exposed to flooding and rising seas.
India Maps Coastal Vulnerability
India is already developing more detailed assessments of coastal exposure. In a July 2025 response to Parliament, the Ministry of Earth Sciences said the Indian National Centre for Ocean Information Services had prepared an interim assessment of future climate-change-induced extreme sea levels and coastal vulnerability along selected parts of India’s coast.
The government said Coastal Vulnerability Index maps had been prepared for locations including Mumbai, Chennai and Kolkata. The assessment considers factors such as sea-level rise, coastal slope, shoreline-change rate, coastal elevation, geomorphology, tidal range and significant wave height.
The government has also demarcated a coastal hazard line through the Survey of India, taking into account flooding from water-level fluctuations, sea-level rise and shoreline changes.
These assessments matter because vulnerability is not determined by sea-level rise alone. A city’s exposure also depends on its elevation, coastline, infrastructure and ability to prepare for and recover from flooding.
Adaptation Becomes Economic Priority
The UN’s warning does not mean Mumbai or Kolkata will simply disappear beneath the sea. It points to a more gradual and complex risk: higher seas can increase the frequency and severity of coastal flooding, damage infrastructure, disrupt livelihoods and force some communities to relocate.
The UN says some additional sea-level rise is already locked in, but the amount of further rise will depend partly on future emissions. It therefore calls for both emissions reductions and adaptation, including early-warning systems, coastal protection, ecosystem restoration, better data and, where necessary, managed retreat.
For India, the economic question is increasingly about the cost of preparing before losses become unavoidable. Mumbai and Kolkata are not facing an overnight climate event. They are confronting a long-term change in the physical conditions under which their homes, infrastructure and economies operate.
The latest UN assessment makes one point difficult to ignore: for vulnerable coastal cities, sea-level rise is no longer only a future climate scenario. It is becoming a present-day planning and economic risk.
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