UN Warns Rising Seas Could Put Millions at Risk in Kolkata and Mumbai
A new United Nations report has placed Kolkata and Mumbai among the major South Asian cities facing growing risks from rising sea levels, warning that millions of people could eventually face displacement as oceans continue to rise.
The UN's latest assessment highlights the increasing threat posed by sea-level rise to coastal communities around the world. For India, the warning is particularly important because Mumbai and Kolkata are two of the country's largest and most economically significant cities.
The report says that more than 14 million people across Kolkata, Mumbai and Dhaka are at immediate risk of losing their homes to permanent inundation. The figure applies to the three cities combined and should not be interpreted as saying that 14 million people in each city are currently facing displacement.
The warning does not mean that Kolkata or Mumbai will suddenly disappear underwater. Instead, it points to a serious long-term risk as rising seas increase the possibility of permanent flooding, coastal erosion, saltwater intrusion and damage to infrastructure.
Sea Levels Are Rising Faster
One of the most concerning points in the UN's latest assessment is the accelerating rate of global sea-level rise.
According to the United Nations, global mean sea level increased by approximately 4.7 millimetres per year between 2014 and 2023. In 2024, the annual increase reached approximately 5.9 millimetres, the highest annual rate recorded in the available satellite-era measurements.
While a few millimetres may appear insignificant, the impact becomes much greater when the increase continues year after year.
The UN says the main drivers include human-caused climate change, particularly the warming of oceans and the melting of glaciers and ice sheets.
As the sea rises, coastal areas can become increasingly vulnerable to flooding during high tides, storms and extreme weather events.
Why Mumbai Is Particularly Vulnerable
Mumbai's location makes the city highly exposed to coastal hazards.
The financial capital of India is surrounded by the Arabian Sea and includes extensive coastal infrastructure, residential areas, commercial districts, roads, railway networks and major economic facilities.
Rising sea levels can increase the baseline water level during storms and extreme weather events. This means that flooding that might previously have been relatively unusual could become more frequent or severe over time.
The concern is therefore not that the entire city will suddenly be submerged.
Instead, the greater risk is that low-lying and vulnerable areas could experience increasingly frequent flooding, damaging homes, roads, businesses and public infrastructure.
Mumbai's importance to India's economy makes this issue even more significant.
A major disruption to transport or commercial activity in the city could affect businesses and supply chains well beyond the areas directly affected by flooding.
Kolkata Faces a Different Coastal Challenge
Kolkata faces its own set of environmental challenges.
The city is located near the Hooghly River and is part of the wider Ganges-Brahmaputra delta region, one of the world's major low-lying delta systems.
Its geography makes the region particularly sensitive to flooding and changes in water levels.
Sea-level rise can also interact with other environmental problems.
These include heavy rainfall, flooding, land subsidence and saltwater intrusion.
When several of these factors occur together, the potential impact can become much more serious.
For Kolkata and surrounding areas, long-term water management and flood protection could therefore become increasingly important.
More Than 14 Million People Could Face Displacement
One of the most widely reported findings from the UN report is the potential scale of human displacement.
More than 14 million people across Kolkata, Mumbai and Dhaka are identified as being at risk of losing homes to permanent inundation.
This does not mean that millions of people are being forced from their homes today.
Rather, it represents a significant long-term risk if sea levels continue to rise and vulnerable areas are not adequately protected.
For governments and city authorities, the warning is important because relocating large populations is extremely difficult.
Displacement can affect employment, education, healthcare, housing and local economies.
The social and economic costs can therefore extend far beyond the areas directly affected by rising water.
The Threat Is Not Limited to Homes
Sea-level rise is often discussed as a housing issue, but its consequences can be much broader.
The UN has warned that rising seas can threaten:
- Homes and residential communities
- Roads and transport networks
- Electricity infrastructure
- Freshwater supplies
- Groundwater resources
- Ports and coastal businesses
- Agriculture
- Tourism
- Healthcare facilities
- Schools and public services
This is why the United Nations describes sea-level rise as a “threat multiplier.” It can make existing environmental, economic and social problems more difficult to manage.
For a densely populated city, even temporary flooding can disrupt everyday life.
Repeated flooding could create additional repair and maintenance costs while placing pressure on local governments and residents.
Freshwater Could Become Another Major Concern
One of the less visible consequences of rising seas is the risk to freshwater.
As seawater moves further inland, it can enter rivers, groundwater systems and other freshwater sources.
This process, known as saltwater intrusion, can make freshwater more difficult to use.
For a city with millions of residents, maintaining a reliable supply of clean water is essential.
The UN has warned that rising sea levels could threaten freshwater systems and groundwater resources in vulnerable coastal regions.
This means that future climate planning will need to consider not only flood barriers and drainage but also the protection of water supplies.
What Could This Mean for Everyday Life?
The impact of rising seas may eventually become visible in everyday activities.
More frequent flooding could disrupt roads and public transportation.
Businesses could face interruptions when commercial areas are flooded.
Residents may experience higher costs for building maintenance and repairs.
Public authorities may need to spend more money on drainage, coastal protection and infrastructure upgrades.
In particularly vulnerable communities, repeated flooding could eventually make some locations increasingly difficult to live in.
The UN says rising sea levels could affect housing, livelihoods, food security, healthcare, sanitation and education.
That is why the issue is not simply about the environment.
It is also an economic and social challenge.
Why Early Preparation Matters
One of the most important messages from the UN is that governments should begin preparing before the impacts become unmanageable.
Sea-level rise happens gradually, giving governments an opportunity to strengthen infrastructure and improve planning.
But major adaptation projects can take many years.
Cities may need stronger drainage systems, improved flood defenses, better early-warning systems and stronger protection for critical infrastructure.
Authorities may also need to identify areas where long-term development should be limited because of future climate risks.
Planning early can potentially reduce the cost of dealing with much larger problems later.
Can Future Sea-Level Rise Still Be Limited?
The UN's warning is serious, but it does not mean that the future is already completely determined.
Some additional sea-level rise is already unavoidable because of warming that has already occurred.
However, the amount of further rise will depend significantly on future greenhouse-gas emissions and global climate action.
This creates two major priorities.
The first is mitigation—reducing greenhouse-gas emissions and limiting additional global warming.
The second is adaptation—preparing cities and communities for changes that can no longer be avoided.
Both are necessary.
Reducing emissions can limit the scale of future sea-level rise, while adaptation can help protect people from the impacts that are already expected.
What Is the UN Calling For?
The United Nations is calling for stronger international cooperation and more investment in climate adaptation.
The recommendations include better monitoring of sea-level changes, stronger scientific data, improved early-warning systems and increased financing for vulnerable communities.
The UN report contains 18 recommendations aimed at strengthening international cooperation and improving the global response to rising sea levels.
Financial support is particularly important for developing countries because large-scale coastal protection and infrastructure projects can require enormous investments.
Why This Matters for India
India has a long coastline and many densely populated coastal regions.
Mumbai and Kolkata are particularly important because of their size and economic significance.
Mumbai is one of India's leading financial and commercial centers, while Kolkata is a major economic and cultural center in eastern India.
Climate-related disruption in either city could therefore have consequences beyond individual neighborhoods.
Damage to transportation, infrastructure and businesses could affect regional economies and supply chains.
The UN warning provides another reason for India and other coastal countries to strengthen long-term urban and climate planning.
What Happens Next?
The issue is expected to receive continued international attention.
The United Nations has scheduled a High-level Plenary Meeting on the Existential Threats Posed by Sea Level Rise for September 24, 2026, bringing the issue of rising seas to the attention of world leaders.
The meeting could provide an opportunity for countries to discuss climate adaptation, financing and international cooperation.
For cities such as Mumbai and Kolkata, the discussions could become increasingly relevant as governments consider how to protect growing urban populations from future climate risks.
Final Takeaway
The latest UN warning about Kolkata and Mumbai is not a prediction that either city will soon disappear beneath the sea.
It is a warning about a growing long-term risk.
Rising sea levels can increase flooding, threaten homes and infrastructure, affect freshwater resources and eventually force vulnerable communities to relocate.
For millions of people living in and around major South Asian cities, the issue is directly connected to homes, jobs, transportation, water, businesses and everyday life.
The good news is that there is still an opportunity to prepare.
Better infrastructure, stronger flood protection, improved planning and international climate action can reduce the risks.
But the UN's message is that preparation needs to begin early.
For Mumbai and Kolkata, the challenge will be to continue developing as major global cities while making sure that their infrastructure and communities are resilient enough to deal with a changing climate.
Disclaimer: This article is based on the latest available United Nations report and related reporting. The figures describe assessed long-term risk and should not be interpreted as a prediction that all residents of Kolkata or Mumbai will lose their homes. Climate impacts can vary significantly between locations