Rising sea threat comes closer home as UN flags millions in Kolkata, Mumbai at risk

Millions of people in Kolkata and Mumbai are at “immediate risk” of losing their homes to permanent inundation as sea levels rise, according to a United Nations report cited by news agency PTI.

The report, titled Challenges related to sea level rise and ways and approaches to address it, said more than 14 million people in low-lying deltas of South Asia, including Kolkata and Mumbai as well as Dhaka, face the risk of displacement due to permanent inundation.

The UN report warned that rising sea levels are already damaging coastal infrastructure, water systems, transport networks, energy grids, buildings and groundwater resources, posing growing risks to human rights, long-term development and financial stability.


The nature of the threat varies across regions.

While cities such as Miami, New York and Guangzhou face an estimated $2 trillion-$3.5 trillion in financial exposure from vulnerable coastal assets, the defining risk in South Asian cities is human displacement, the report said.

Sea-level rise is also worsening public health risks through damage to sanitation and health infrastructure, greater exposure to water-borne diseases, disruption to sanitation systems and increased risks of injury and mortality. It is also contributing to rising mental health stress, the report said.

The combination of rising seas and land subsidence is further intensifying flooding, damaging coastal ecosystems and threatening lives, livelihoods and aquatic habitats.

The report said saltwater is also moving inland into coastal aquifers, increasing the salinisation of freshwater wells and soils. Storm-driven overwash can cause long-lasting contamination of surface and groundwater, threatening drinking water supplies, agriculture and irrigation.

Globally, nearly 770 million people, or around 10% of the world's population, live in coastal areas less than 5 metres above the high tide line, putting them at acute risk from rising seas, according to the report.

Global sea levels rose at an average rate of 4.7 mm per year between 2014 and 2023, while the rise reached 5.9 mm in 2024, a record rate driven primarily by exceptional ocean warming.

The annual rate of sea-level rise was 4.75 mm during 2012-2025, with global mean sea level in 2025 remaining comparable to the record-high level of 2024, the report said.

The UN attributed accelerating sea-level rise primarily to melting glaciers and thermal expansion of warming oceans, driven by human-induced global warming.

The report called for early and long-term adaptation planning, backed by predictable financing, stronger scientific and data capabilities, and robust technical, institutional and legal frameworks, particularly for populations and countries facing the greatest risks.