Rising seas could displace 14 million in South Asia, with Mumbai and Kolkata among the major cities facing growing exposure as ocean levels climb and land subsidence worsens coastal flooding. A new United Nations Secretary-General’s Special Report warns that sea-level rise is accelerating at an unusual rate in human history, turning what was once viewed as a long-term climate concern into an immediate threat to homes, infrastructure, freshwater and livelihoods. In 2024, global mean sea level rose by nearly 6 millimetres in a single year, the highest annual increase recorded.

Presented on August 31 during the 55th Pacific Islands Forum Leaders Meeting in Palau, the UN report says around 770 million people, or roughly one in every 10 people worldwide, already live in coastal areas less than five metres above the high-tide line.

Mumbai and Kolkata Face Growing Coastal Exposure

Mumbai and Kolkata in India, along with Dhaka in Bangladesh, are identified among low-lying South Asian cities and delta regions facing increasing displacement risks. More than 14 million people in these areas are considered at immediate risk of losing their homes to permanent inundation. The danger is not caused by rising oceans alone. Land subsidence can cause coastal areas to sink while sea levels rise, effectively increasing the pace at which flooding becomes a problem.

Saltwater intrusion adds another layer of risk. As seawater moves into freshwater wells, soils and groundwater systems, it can affect drinking water supplies, agriculture and irrigation. Coastal roads, ports, utilities and other essential infrastructure are also increasingly exposed to both regular and extreme sea levels.

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Sea-Level Threat Extends Across Global Coastlines

The warning is not limited to South Asia.

• Even under a very low-emissions scenario, the IPCC projects global mean sea level could rise around 0.23 metres by 2050.
• In Europe, extreme sea levels are already increasing at many coastal locations, while historically rare coastal floods could become substantially more frequent before mid-century.

The economic exposure is equally serious.

• Coastal infrastructure damage is already estimated at more than $1.8 trillion, while annual global losses could reach $1.2 trillion to $4 trillion by the end of the century without adequate adaptation.
• Tourism-dependent regions face additional pressure, with nearly 40% of Caribbean beaches potentially disappearing by 2050.

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Rising Seas Create a Human Rights Challenge

The UN warns that rising seas could displace 14 million in South Asia and threaten access to housing, safe drinking water, sanitation, food, healthcare, and education. Indigenous communities and residents of small island states face additional risks from the loss of cultural heritage and ancestral lands.

Several Pacific Island communities have already begun relocation processes as territories become increasingly difficult to inhabit. The UN also highlights complex legal questions surrounding state sovereignty and maritime boundaries, arguing that changing coastlines should not undermine rights recognised under international law.

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UN Calls for Faster Climate Action

The report proposes 18 recommendations for governments, including faster greenhouse gas reductions, stronger early-warning systems, increased financing for climate adaptation and improved scientific monitoring.

It also calls for stronger international cooperation to protect vulnerable populations and maintain legal stability as sea levels continue to rise. For cities such as Mumbai and Kolkata, the warning highlights why adaptation cannot be treated as a distant planning exercise. Coastal protection, resilient infrastructure, water security and early-warning systems will increasingly determine how communities cope with a changing shoreline.

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