Kolkata Under Threat? UN Flags Rising Sea-Level Risk

Kolkata could face a growing threat from rising seas and sinking land, but claims that the city is about to disappear underwater are misleading. A fresh United Nations warning on rising sea levels has put Kolkata under renewed scrutiny, triggering fears among residents about what the future could hold for the city. However, before alarming headlines fuel unnecessary panic, there is an important distinction to make: the UN has not predicted that Kolkata will be completely submerged by 2050, or by any other specific year.

The latest UN report, Challenges related to sea level rise and ways and approaches to address it, has brought the issue back into focus. The UN has described sea-level rise as “no longer a distant threat but an unfolding global crisis”, warning that it is already affecting coastal communities, infrastructure and economies. In its assessment of South Asia, the UN specifically highlights low-lying cities including Kolkata and Mumbai, where rising seas combined with land subsidence could intensify the risks of flooding and displacement.

One of the figures that has attracted the most attention is the UN’s warning that more than 14 million people in low-lying South Asian areas face the risk of losing their homes to permanent inundation. But this figure needs to be understood correctly. It is not a prediction that 14 million people in Kolkata alone will lose their homes, nor does it mean that the entire city is destined to be underwater. The figure relates to vulnerable low-lying areas across the region, including the cities highlighted by the UN.

The concern surrounding Kolkata is nevertheless scientifically real. The city lies within the wider Ganga-Brahmaputra delta system, a low-lying landscape shaped by rivers and layers of sediment. Its geography makes it naturally more exposed to tidal flooding, heavy rainfall and changes in sea level. But the concern is not simply that the ocean is getting higher. The ground beneath parts of the city is also changing.

A 2025 study published in Nature Sustainability used satellite radar observations to examine vertical land movement across five Indian megacities, including Kolkata. For Kolkata, researchers analysed data from 2017 to 2023 and found an average vertical land-motion rate of approximately −2.2 millimetres per year, meaning that the land was, on average, moving downward. However, the rate was not uniform across the city. The researchers found considerable spatial variation, with some areas experiencing substantially greater subsidence.

The same study found that around 55% of the analysed Kolkata pixels showed subsidence after accounting for measurement uncertainty, while the maximum observed rate in the study area reached about 16.4 millimetres per year. These figures should not be interpreted as meaning that the whole city is sinking at that speed. They demonstrate why looking at local differences is important when assessing Kolkata’s future vulnerability.

This becomes important because sea-level rise and land subsidence can effectively work in the same direction. If the sea rises while land in a particular area gradually sinks, the relative difference between the land and the water increases. That can make flooding more frequent or severe, particularly during high tides, intense rainfall or extreme weather events.

But does that mean Kolkata is going to disappear beneath the water by 2050? No. There is no scientific evidence supporting such a definitive prediction.

The Intergovernmental Panel on Climate Change, or IPCC, has projected continued global sea-level rise throughout this century, with the eventual amount depending heavily on future greenhouse-gas emissions and the behaviour of ice sheets. These are global projections, however, not a prediction that Kolkata itself will be covered by a particular depth of water on a particular date.

That distinction is crucial. Global sea-level rise does not translate into an identical rise in every city. Local land movement, tides, rainfall, river flows, drainage infrastructure, coastal geography and flood-control measures can all alter the actual risk experienced by individual neighbourhoods.

This is why the most realistic climate threat to Kolkata is not an overnight scenario in which the entire city suddenly vanishes beneath the sea. Instead, scientists are concerned about a gradual increase in the frequency and severity of flooding and water-related risks in vulnerable areas. Places that already experience waterlogging could become more difficult to protect as the baseline sea level rises.

The problem can also become more complicated because of human activity. Groundwater extraction is recognised internationally as one contributor to land subsidence in vulnerable geological settings. Excessive withdrawal can contribute to the compaction of underground sediments, lowering the ground surface. Rapid urbanisation, heavy construction, changes to natural drainage and the characteristics of soft deltaic sediments can also influence how land responds over time. The 2025 Nature Sustainability research similarly points to groundwater pumping and human management decisions as important considerations when assessing subsidence in Indian megacities.

That does not mean every part of Kolkata is sinking at the same rate, nor does it mean every building in the city is facing an imminent threat. The scientific research measures land movement and models potential future consequences; it is not a prediction that Kolkata’s buildings will suddenly collapse or that the entire city will become uninhabitable. In fact, the researchers’ purpose is precisely to help authorities identify vulnerable areas and prioritise mitigation and adaptation.

There is, therefore, a considerable amount that can be done to reduce the danger. Protecting Kolkata’s wetlands and natural drainage systems, improving storm-water drainage, monitoring groundwater extraction, strengthening flood forecasting and early-warning systems and making infrastructure more resilient can all help reduce the impact of future flooding. Urban planning can also take projected climate risks into account when deciding where and how new construction should take place.

Nature-based measures can be particularly valuable in a delta environment. Wetlands and other natural ecosystems can help retain excess water and provide an additional buffer against flooding. Protecting such areas is consequently not merely an environmental concern; it can also be an important part of Kolkata’s long-term climate resilience. Better satellite monitoring can similarly help authorities identify areas where land is subsiding more rapidly and focus resources on the places facing the greatest risks.

The recent UN warning should therefore be viewed as a call for preparation rather than a reason for residents to panic. Panic cannot stop sea-level rise, but planning can reduce its consequences. A frightening headline suggesting that Kolkata is about to disappear underwater may attract attention, but it does not reflect the way climate risk actually develops.

Climate change is generally a gradual process. The greater concern is that the combination of rising seas, sinking land, extreme rainfall and inadequate infrastructure could progressively make certain areas more vulnerable. That gives governments, scientists and urban planners something extremely important: time to prepare.

The other half of the solution lies beyond Kolkata. Greenhouse-gas emissions need to be reduced globally because the amount of warming ultimately influences how much additional sea-level rise the world faces. The difference between lower- and higher-emissions futures is significant, which means future impacts are not completely fixed.

At the same time, adaptation cannot wait for global climate policy to solve everything. Kolkata can act locally even while the world works on the larger problem. Better drainage, wetland protection, groundwater management, stronger infrastructure, accurate flood mapping and early-warning systems can all reduce vulnerability.

For residents who have been frightened by recent headlines, the most important message is therefore this: Kolkata is not being given a countdown to disappear.

The risk identified by the UN is serious, but it is a risk that unfolds over time and varies from place to place. The report does not announce a date on which the city will go underwater. It does not say that every neighbourhood will be submerged. And it does not mean that residents need to fear an imminent catastrophe.

What it does say is that rising seas are already changing the risk landscape and that cities such as Kolkata need to prepare before those changes become more difficult and expensive to manage.

So, should Kolkata be concerned? Yes — concerned enough to demand better planning, stronger infrastructure and serious climate action.

Should residents panic because they have been told their city will soon be underwater? No.

The sea may be rising, and parts of the ground may be sinking, but Kolkata is not facing an inevitable date with the sea. The real challenge is to use the warning while there is still time — because the best defence against a future climate threat is not fear, but preparation.