New Delhi: A United Nations report, titled ‘Challenges related to sea level rise and ways and approaches to address it,’ has warned that more than 14 million people in low-lying South Asian cities, including Kolkata, Mumbai and Dhaka, are at “immediate risk” of losing their homes and livelihoods, while putting their lives at stake, due to rising sea levels and permanent inundation.The UN Secretary-General’s Special Report, presented on August 31 by UN Deputy Secretary-General Amina J. Mohammed during the 55th Pacific Islands Forum Leaders’ Meeting in Palau, said global sea levels rose by 4.7mm per year between 2014 and 2023, before reaching a record high of 5.9mm in 2024.In light of persistent human-induced climate change, which is manifesting in the form of melting glaciers and ice sheets and the thermal expansion of warming oceans, ocean levels are predicted to rise exponentially, even under an emissions pathway consistent with the Paris Agreement’s temperature goal.The report cautioned that “rising seas are no longer a distant threat,” especially with the pace of sea-level rise accelerating.The Intergovernmental Panel on Climate Change has projected that even under a very low greenhouse-gas emissions scenario, global mean sea level could rise by 0.23 metres by 2050. By 2100, the increase could reach between 0.28 and 0.55 metres under very low emissions and between 0.63 and 1.01 metres under very high emissions scenarios.The plausible worst case, albeit low-probability, scenario, on the other hand, paints a much bleaker image. Sea levels could approach two metres by the end of the century.Mumbai, Kolkata face risk of permanent inundationFor Mumbai and Kolkata, the threat is not limited to a gradual loss of coastal land. The report identified the low-lying deltas of South Asia, including Kolkata, Mumbai and Dhaka in Bangladesh, as places where “the defining impact” would be large-scale human displacement.As sea-level rise is a slow-onset phenomenon, even relatively modest increases can make existing flooding and coastal hazards more damaging and frequent over time.“As a slow-onset event, it could eventually contribute to a massive displacement of people, with some estimates suggesting up to 1.2 billion people potentially displaced globally by 2050,” the report said.Repeated flooding could also inflict severe damage to transport networks, energy systems, building and water supplies and urban infrastructure in densely-populated metropolitan centres.Flooding, contaminated water reservoirs, damaged infrastructureThe report describes sea level rise as a “threat multiplier,” capable of intensifying, coastal flooding erosion, freshwater installation and ecosystem degradation. These risks combine with existing vulnerabilities in densely populated coastal cities, putting homes, public infrastructure, livelihoods and essential services under increasing pressure.As the freshwater-saltwater boundary moves inland, coastal aquifers could become increasingly saline, contaminating freshwater wells and soils. Storm-driven seawater can also cause prolonged contamination of surface and groundwater, threatening drinking-water security, agricultural productivity, irrigation systems and groundwater-dependent ecosystems.Sea-level rise can also harm coastal health and sanitation infrastructure, increase exposure to water-borne diseases and raise mental-health stress among affected populations, the report said.Nearly 770 million people globally, around one in 10 people, currently live in coastal areas less than five metres above the high-tide line, according to the UN. Meanwhile, nearly 500 million people live in low-lying zones where rivers meet the ocean.Once-in-a-century floods could become annual eventsThe frequency of extreme sea-level events is expected to increase as global temperatures rise. An event that historically occurred once every 100 years could occur at least annually at more than half of the world’s tide-gauge locations by 2100 under all scenarios considered by the report.For Mumbai and Kolkata, that could mean persistent disruption rather than isolated episodes of extreme flooding. The report notes that rising seas are already placing critical infrastructure, agricultural productivity, trade, tourism and cultural heritage at risk.Economic implications, too, would be enormous. Damage to coastal infrastructure is conservatively estimated at more than $1.8 trillion globally, according to the UN report.Most critically, sea-level rise threatens fundamental human rights, including the rights to life, health, adequate housing, safe drinking water, sanitation, food and education.The report stated that climate-induced displacement and the loss of ancestral lands can also impose “profound emotional and psychological burdens” on affected populations. Separation from territories that anchor cultural and spiritual identity can disrupt the intergenerational transmission of practices, values and traditional knowledge.Adaptation cannot keep pace with high-rate of warmingThe irreversible nature of sea-level rise makes early and long-term adaptation planning essential. The UN report called for stronger scientific monitoring, better coastal data, improved early-warning systems and greater investment in measures to protect communities facing escalating risks.These measures include engineered coastal defences, flood-control systems, drainage infrastructure and nature-based solutions such as mangroves, wetlands and reefs. The report also points to managed retreat and relocation as possible long-term measures in areas where continued protection becomes increasingly difficult.However, the reported addd that “adaptation alone cannot keep pace with high warming scenarios.” Rapid emissions reductions are therefore needed alongside large-scale investment in adaptation to limit further losses and damage.It also emphasised the need for sea-level rise to be incorporated into national and local planning, including land-use decisions, infrastructure design, disaster-risk reduction and fiscal planning and urged governments to threat the crisis as a “systemic risk” instead of an isolated one.The warning comes in the wake of a devastating glacial flood in Nepal last week, triggered by the collapse of a glacier near Langtang Lirung. The flood killed more than 1,000 people and left thousands missing, according to a senior UN official.Previously in 2020, researchers had identified 47 potentially dangerous glacial lakes across Nepal, China and India, but the actual number is now believed to be significantly higher.“The risks are particularly acute for Nepal, which depends heavily on glaciers for both water supplies and hydropower, while communities living along river systems face increasing exposure to sudden glacial floods,” the report said.Together the risk of permanent inundation in low-lying cities like Mumbai and Kolkata and the threat of sudden and destructive glacial floods in the Himalayan region, highlight why early warning systems, resilient infrastructure and long-term adaptation can no longer be treated as distant priorities.