Imagine that we are on holiday in a much-loved seaside town. Would we not enjoy looking out towards the horizon? Yet if an oceanographer or geologist were sitting in our place, they would enjoy the view while remaining conscious that it contains not only seawater, but also melted ice.
At least half of the world's population is beginning to experience the direct effects of climate change. Extreme weather events are increasing and already damaged ecosystems are becoming progressively less able to perform their functions. The change we initiated with our own hands is turning into an increasingly destructive risk multiplier.
One consequence, although it receives relatively little attention, is global sea-level rise. Sea level also changed naturally in the past, but it is no exaggeration to describe the current rate of increase as extraordinary. As greenhouse gas emissions from human activity warm the planet, the expansion of warmer ocean water and the melting of glaciers and ice sheets worldwide are the principal causes.
Understanding these two causes and detecting the acceleration tells us a great deal about how the growing amount of heat trapped in the atmosphere affects the global climate system.
From the 1970s until recently, melting ice and thermal expansion contributed approximately equally to sea-level rise. Ice loss has accelerated in recent years. According to NASA data, summer sea ice around Antarctica in 2025 fell to the second-lowest minimum in the 47-year satellite record, approximately 30% below the 1981-2010 average.
NASA data also show that global sea level has risen by 9-10 centimetres since 1993.
The Intergovernmental Panel on Climate Change (IPCC), one of the most reliable authorities on the subject, has published projections for global sea level in 2100. Even with substantial greenhouse gas reductions, the IPCC projects an unavoidable rise of 30-60 centimetres by around 2100, rising to 50-75 centimetres under an intermediate scenario and 75 centimetres to one metre under a fossil-fuel-intensive scenario.
The Social, Economic and Environmental Effects Will Be Profound
Sea-level rise brings many consequences. For centuries, humanity has tended to settle in coastal areas because of transport links, quality of life and access to marine resources. Coastal locations offer many benefits, but they also expose ecosystems and people to a range of hazards.
Sea-level rise caused by climate change will increase these risks, acting as a multiplier for hazards affecting coastlines worldwide. It will raise the risk of flooding and erosion and could completely inundate some areas. As risks increase, so will the economic and human costs of extreme events and slow-onset change. Rising seas will also undoubtedly increase the cost of coastal protection.
In addition to economic effects on sectors including fisheries, agriculture and tourism, the threat to roads, bridges, water resources and energy infrastructure will cause loss of housing, migration and displacement.
İstanbul Ranks 15th Among Cities at Risk
Listing these effects may sound like a disaster scenario, but the danger is real. The newly published 2050 Climate Change City Index identifies many major cities already at risk from sea-level rise. Bangkok, the capital of Thailand, tops the list.
This low-lying city, situated an average of 1.5 metres above sea level, is already paying the price. With extreme weather expected to become more frequent, one-third of Bangkok could be completely submerged by 2050, displacing as many as 11 million people.
Amsterdam, the capital of the Netherlands, ranks second for vulnerability. The city already has some of the world's most advanced flood-control systems. Yet as the climate crisis rapidly worsens, sea-level projections place Amsterdam in a dangerous position. Flooding is expected to become more intense and extreme, and the city's existing infrastructure may prove inadequate in the coming years.
If melting of the Antarctic ice sheet accelerates, sea level is projected to rise by 1.2 to 2 metres over the next 79 years. Under that scenario, more than 700,000 people - 97% of the city's population - could be displaced by the end of the century.
Amsterdam is followed by Ho Chi Minh City in Vietnam, Cardiff in the United Kingdom and New Orleans in the United States. İstanbul ranks 15th and is also at considerable risk. The Global Balance Association's report Sea-Level Rise and Its Potential Impacts for the Provinces of İstanbul and İzmir demonstrates the situation in Türkiye.
According to the report, climate-related sea-level rise of 0.5 metres by mid-century and one metre by the end of the century could inundate a 120-square-kilometre area of İstanbul inhabited by more than six million people. Historic structures such as Dolmabahçe Palace, Beylerbeyi Palace and Ortaköy Mosque could be affected. In İzmir, the Gulf and Kordon, the resort towns of Alaçatı and Sığacık, and the Gediz Delta Bird Sanctuary are also at risk.
Emissions Reduction and Risk Preparedness Must Advance Together
These realities require holistic thinking. Alongside the need to move away from dependence on fossil fuels, it is equally important to increase the resilience of communities already living with the consequences in coastal areas. Only then can we protect people's lives while sustaining the delicate balance of ocean and marine ecosystems.
Approximately 900 million people worldwide currently live in high-risk coastal zones. Sea walls and barriers, floating homes, water-management systems and other nature-based solutions are already being implemented to strengthen coastal resilience. Helping coastal communities recover more quickly after disasters is critical to preventing a single event from becoming a long-term social catastrophe.
Parametric insurance is likely to receive greater attention. Unlike conventional insurance, it pays according to measurable parameters of natural events rather than physical damage and can accelerate post-disaster recovery and support crisis response.
The question is no longer whether sea level will rise. It is how much it will rise, how quickly and with what consequences. Because we have contributed to this change, we should not forget that the scale of what lies ahead is also in our hands.
7 May 2026
