A new United Nations report warns that millions of people in Kolkata and Mumbai are at immediate risk of losing their homes as rising sea levels lead to permanent inundation.

The report, titled "Challenges related to sea level rise and ways and approaches to address it," was released Monday and states that more than 14 million people in low-lying deltas of South Asia, including Kolkata, Mumbai, and Dhaka, face displacement.

"Rising seas are no longer a distant threat: they are happening now, faster than at any point in recorded history, and the pace is accelerating, making sea level rise one of the most profound threats to populations around the world in developed and developing States alike," the report said.

Regional impacts vary

The report notes that the nature of the threat varies across regions. In wealthier coastal cities such as Miami, New York, and Guangzhou, the primary impact is the financial exposure of coastal infrastructure, with assets at risk estimated between $2 trillion and $3.5 trillion.

In contrast, in South Asia's low-lying deltas, the defining impact is human displacement. "In the low-lying deltas of South Asia, in cities such as Kolkata and Mumbai in India, and Dhaka, the defining impact is human displacement, with more than 14 million people at immediate risk of losing their homes to permanent inundation," the report states.

Broader consequences

Rising sea levels are already damaging urban infrastructure, water systems, transport networks, energy grids, buildings, and groundwater resources. The report warns of consequences that threaten human rights, long-term development, and financial stability.

Public health is also at risk, with damage to sanitation and health infrastructure, increased exposure to water-borne diseases, and heightened risks of injury and mortality. The report notes that sea level rise is contributing to rising mental health stress.

The combination of rising seas and land subsidence is intensifying flooding, while saltwater is moving inland into coastal aquifers, threatening drinking water and agriculture.

Global context

The UN report says nearly 770 million people—about 10% of the global population—live in coastal areas less than five metres above the high-tide line. It describes sea level rise as a "threat multiplier" that exacerbates existing vulnerabilities.

At a news conference, UN Assistant Secretary-General Navid Hanif said rising sea levels "set a challenge" because people in those areas "are losing their coastline." He urged governments to treat sea level rise as a systemic threat requiring comprehensive planning.

The report calls 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.