Acceleration of sea level rise (SLR) is one of the most visible and worrying manifestations of climate change, radically altering coastal landscapes and challenging communities around the world. From eroding coastlines to threatened infrastructure, what was once a scientific prediction has become a tangible reality that demands immediate attention and deep understanding.

This rise poses a significant threat to coastal communities, ecosystems and economies worldwide, particularly in densely populated areas where vulnerable infrastructure is at risk of flooding and erosion from rising waters. The urgency of addressing SLR is heightened by its expected impacts on global displacement, resource availability and socio-economic inequalities, which have placed it at the centre of climate change discourse and policy initiatives.

The urgency of addressing sea level rise has never been greater, with approximately 40% of the world's population living within 100 kilometers of coastlines estimated in 2018. This concentration of human settlement in coastal areas makes sea level rise not just an environmental concern, but a critical socio-economic challenge. The World Bank estimated in 2013 that without adaptation, the cost of damage from coastal flooding could reach $1 trillion annually by 2050.

Scientific understanding of sea level rise has improved significantly in recent decades. According to the latest IPCC report (AR6, 2023), the rate of rise has increased from 1.3 mm/year in 1901-1971 to 3.7 mm/year in 2006-2018, with a particularly marked acceleration in the last decade. Copernicus website indicates an average of 3.4mm/yr since 1993, with a trend of 2.1 mm/year over 1993–2003 to a trend of 4.3 mm/year over 2013–2023.

Drivers of sea level rise

Sea-level rise is governed by complex physical processes operating on different time scales.

The thermal expansion of the ocean, caused by the absorption of atmospheric heat, contributes about 38% of the observed rise. Simona Masina, Director of the Institute for Earth System Prediction at the Euro-Mediterranean Centre for Climate Change Foundation, explains: “Ocean models show us that the warming is not uniform: the surface layers of the ocean are warming faster, creating thermal stratification that affects global ocean circulation and heat transport”.

Melting of continental glaciers and ice sheets is the other major contributor, about 41%. Greenland is losing mass at a rate of about 278 ± 11 Gt/year in the period 2006-2015, while Antarctica is losing 155 ± 19 Gt/year. “The contribution of the polar ice caps to sea level rise has quadrupled between 1992-1999 and 2010-2019,” points out Begona Pérez Gómez of the Ports of Spain Organisation. “This trend is particularly worrying because it points to a possible future acceleration of the phenomenon”.

Johannes Pein, a scientist at the Institute for Coastal Systems, Analysis and Modelling, Hereon Research Centre, Geesthacht, Germany, points out: “The greatest uncertainty in the projections relates to the ice sheets. The West Antarctic Ice Sheet and the East Antarctic Margin contain ice equivalent to about 20 metres of global sea-level rise”. Analyses from the Helmholtz Centre's Sea Level Monitor clearly show that the global mean sea level of recent years is the highest since data have been available, and the trend is rising.

Projections

The Special Report on the Ocean and Cryosphere in a Changing Climate (2019) warns that SLR will keep accelerating under all future scenarios. But how much the sea level will rise depends a lot on what we do about emissions. If we follow a low-emission path, with drastic action to cut down emissions, sea levels are projected to rise by about 0.43 meters by 2100 (compared to 1986–2005 levels). But if emissions keep climbing unchecked, the rise could reach up to 0.84 meters by the end of the century. And it won’t stop there. After 2100, they'll keep rising for centuries, if not millenia, as the deep ocean will continue to warm and ice sheets in Greenland and Antarctica will take time to catch up to the warming caused by past and present emissions. The choices we make today will reshape coastlines for generations to come.

Sea level rise will continue for millennia, but how fast and how much depends on future emissions.

A crucial aspect of understanding sea level rise is the quality of measurements. Data on SLR come from two main sources: in-situ observations, such as tide gauges that track sea level changes at specific coastal locations, and satellite altimetry, which provides measurements of sea level variations across the globe since its introduction in the 1990s.

The Global Sea Level Observing System (GLOSS) coordinates over 300 tide gauge stations worldwide, providing essential data for monitoring local variations.

The advent of satellite altimetry in the 1990s revolutionised our understanding of global sea level patterns. Modern tide gauges use radar or acoustic sensors that measure the time it takes for the signal to return from the water surface, ensuring millimetre accuracy. These data, combined with satellite observations, provide a comprehensive picture of global and local sea level changes.

The European Union's Copernicus programme represents a quantum leap in our ability to monitor sea level changes. Through its Sentinel satellites and integration with in-situ measurements, it provides unprecedented coverage and accuracy. The Sentinel-6 Michael Freilich satellite, launched in 2020, can measure sea level changes with millimeter precision, while the program's Marine Service combines satellite data with measurements from over 4,000 Argo floats to create a comprehensive picture of ocean dynamics.

While sea level rise itself is a gradual process, its effects are manifold and interconnected, creating cascading impacts on coastal environments and communities.

Impacts on the coastal environment

Flooding and inundation are primary consequences of SLR. As sea levels increase, low-lying coastal areas face more frequent flooding during high tides, a phenomenon known as “high-tide flooding” or “nuisance flooding.” This is particularly concerning for coastal megacities and Small Island Developing States (SIDS), where even small increases in sea level can lead to significant territorial losses. Major cities around the world are at risk of flooding due to SLR, from Miami and Houston in North America, to Jakarta, Shanghai or Dakha in Asia, Lagos in Africa, or Venice and Alexandria in the Mediterranean. This phenomenon is amplified by land subsidence, a process driven by natural events and/or human activities, such as groundwater and hydrocarbon pumping combined to the weight of urban development, that leads some megacities to sink. Without adequate and effective adaptation measures, flooding risks will only intensify, threatening the environment, the infrastructure, and communities

Storm surges represent another critical impact, as higher sea levels provide an elevated baseline for storm-driven waves and surges. This means that storms of the same intensity now cause more severe flooding than in the past. The combination of SLR with extreme weather events can lead to catastrophic impacts, as demonstrated by events like Hurricane Katrina, where storm surge effects were amplified by the underlying sea level rise.

Coastal erosion is significantly enhanced by SLR, though not directly caused by it. Higher water levels allow waves to reach further inland, accelerating erosion processes. Around 80% of beaches worldwide are experiencing retreat and generalized erosion. This is particularly evident in areas where the “coastal squeeze” phenomenon occurs - where natural coastal habitats are trapped between rising seas and fixed infrastructure or settlements, preventing their natural landward migration.

“Saltwater intrusion is a less visible but equally serious consequence” says Claudia Romagnoli, professor of Marine and Coastal Geology at the University of Bologna. As sea levels rise, saltwater pushes inland through surface waters and underground aquifers, contaminating freshwater resources. This process affects not only drinking water supplies but also agricultural activities in coastal areas, as increased soil salinity can render farmland unsuitable for traditional crops. The intrusion of saltwater into coastal aquifers is particularly problematic in areas where groundwater extraction is intensive, as it can accelerate the process.

The combined effects of SLR are reshaping coastal ecosystems, threatening biodiversity and disrupting entire food webs. As SLR accelerates, intertidal habitats such as salt marshes, mangroves, and wetlands face risks of being fragmented or lost, reducing critical breeding and feeding grounds for many species. Species unable to migrate or adapt, including shorebirds, shellfish, and seagrasses, are exposed to population declines or extinction.

Economic and infrastructure challenges

SLR acceleration poses growing threats to key economic activities, from agriculture and tourism to urban development and port operations.

Coastal tourism is particularly vulnerable to the impacts of SLR, posing major economic challenges. Generating €140 billion of turnover in 2021 (and over than €200 billion annually before the COVID-19 crisis), it is the largest sector of the EU’s blue economy. The main threats? Beach erosion, the submersion of cultural heritage sites – key assets for attracting visitors – and the growing exposure of tourist infrastructure, especially hotels and transportation systems, to erosion and flooding. These risks could lead to a decline in the appeal of coastal destinations, reducing demands. At the same time, the degradation of natural and cultural assets may lower the quality of tourism offerings, resulting in significant economic losses.

Agriculture in coastal areas faces a threefold challenge as SLR accelerates. Coastal squeeze risks shrinking available farmland, land submergence could lead to the degradation or loss of already-planted crops, while saltwater intrusion threatens to contaminate freshwater resources that are in high demand for irrigation. In the Mediterranean basin, agricultural lands in the plains of Nile, Ebro and Po deltas are known to be particularly at risk. Rising salinity in soils could further reduce crop yields, with cascading impacts on the food production chain in affected regions.

Coastal urban areas, home to an ever-growing population, are increasingly exposed to chronic flooding and infrastructure damage, which leads to further costs for governments and businesses. Average global flood losses in 2005 were estimated to be approximately US$6 billion per year, and is projected to increase up to US$52 billion by 2050. In many cities, inadequate drainage systems and obsolete flood defenses further amplify these risks. Coastal cities therefore face particularly difficult economic decisions. Studies led by the OECD indicate that by 2070, assets worth over US$35 trillion could be at risk from coastal flooding in the world's major port cities if no adaptation measures are taken.

Ports, essential hubs for global trade, are also under threat. As such, they require special attention, with specific minimum freeboards to maintain operability. Port vulnerability is classified on a scale of 0 to 5, with level 5 indicating a very high risk condition, corresponding to the inoperability of more than 80% of mooring structures.

Monitoring of the effectiveness of the interventions is based on increasingly sophisticated early warning systems (EWS). “The cost-benefit ratio of EWS systems is greater than 10:1”, emphasises Augustin Sanchez-Arcilla of the Polytechnic University of Catalonia, “and they allow proactive management that significantly increases the durability of coastal protection measures”.

Urban development, the construction of coastal defense structures, and the modification of natural sediment transport systems can interfere with natural coastal processes, making these areas even more susceptible to SLR impacts. In areas where natural dynamics are altered and the coast is “stiffened”, the functional integrity of coastal resources and ecological systems is disrupted.

SLR impacts create a complex web of challenges for coastal communities and ecosystems. The combination of SLR with other climate change factors (such as increased storm intensity) and non-climatic drivers (like population growth and coastal development) requires integrated approaches to coastal management and adaptation strategies. Understanding these interconnected impacts is crucial for developing effective responses to protect both human settlements and natural coastal systems in the face of rising seas.

Addressing these challenges require substantial financial investments in order to prevent damage with severe human, but also economic consequences. Funding sustainable, resilient, and equitable adaptation solutions is key to mitigate the impacts of SLR. Public investment plays a crucial role in protecting vulnerable communities and setting the ambition for much-needed private sector engagement. The financial implications of sea level rise present a stark choice: investing in adaptation now or paying for damage later. The Global Commission on Adaptation estimated that investing $1.8 trillion globally in adaptation measures could generate $7.1 trillion in total net benefits. These adaptation efforts include:

• Infrastructure strengthening ($1 trillion)
• Early warning systems ($100 billion)
• Water security improvements ($200 billion)
• Nature-based solutions ($500 billion)

Social and cultural vulnerabilities

Less direct but no less significant, SLR also presents far-reaching impacts on our societies. Social and cultural consequences include the exacerbation of socio-economic and gender-based inequalities, displacement of communities, and loss of cultural heritage. Low-income and marginalized populations, including women and Indigenous Peoples, often lack the resources to adapt or relocate, making them disproportionately vulnerable to flooding and land loss. Coastal displacement is already forcing difficult choices, from entire neighborhoods retreating inland to Indigenous communities losing ancestral lands. In the Mediterranean basin only, up to 20 million people could be affected by permanent displacement due to SLR by the end of the 21^st century if no effective adaptation policies are implemented.

Kiribati, an archipelago of about 30 islands in the Central Pacific, represents one of the most striking examples of how sea level rise threatens the very existence of Small Island Developing States (SIDS). Rising sea levels are already having severe impacts on Kiribati's communities. Several coastal villages have been forced to relocate inland or to other islands as their traditional lands become uninhabitable due to flooding and erosion.

Beyond the loss of homes and livelihoods, SLR also threatens cultural and natural heritage, submerging historical sites, sacred places, and centuries-old traditions tied to coastal landscapes, including in the Mediterranean where dozens of UNESCO World Heritage sites are deemed to be at risk from coastal hazards due to SLR. The emotional and psychological toll of forced relocation further aggravates the crisis, disrupting social networks and identity. Without proactive adaptation policies that address these social dimensions, sea level rise risks becoming not just an environmental disaster, but a driver of profound social and cultural upheaval.

Combining engineering approaches and nature-based solutions

Dealing with sea-level rise requires an integrated approach that combines traditional engineering solutions (such as dikes and sea walls) with nature-based interventions (such as wetland, river and floodplain maintenance and restoration or managed realignment). As Ivan Federico of CMCC points out, “the conservation, restoration and use of coastal vegetated habitats for coastal protection is a promising strategy that offers significant mitigation and adaptation capacity to climate change”.

An innovative example is the concept of the 'climate dike ' introduced in Schleswig-Holstein, Germany, which includes a 50-centimetre construction reserve to deal with uncertainties in future sea-level rise projections. As emphasised by Hofstede (2019), this approach involves not only raising the dike, but also widening its crest and creating a gentler slope on the outside, providing greater security against wave overtopping.

In the case study on the Emilia-Romagna coast, four species of seagrass (Zostera marina, Zostera noltii, Posidonia oceanica and Cymodocea nodosa) were studied, showing how these meadows can significantly reduce wave height, with the effectiveness varying seasonally. “Wave energy reduction due to the presence of vegetation shows a strong seasonality, with greater attenuation in winter,” explains Ivan Federico of CMCC.

Governance and decision-making

Adaptation to sea-level rise (SLR) implies a rethink of governance and decision-making, with greater emphasis on participatory approaches that actively involve local communities. Coastal communities are on the front line of climate change, and their knowledge, needs and experiences are essential to designing effective adaptation strategies and avoiding maladaptation. Governance mechanisms must also be reevaluated and revised to take into account the growing complexity of adapting to SLR given the long time horizons and uncertainty associated with SLR planning. Further cross-scale and cross-domain coordination, as highlighted in the First Assessment Report of the Knowledge Hub on Sea Level Rise, will help address the scale of the challenge while ensuring equity".

Legal frameworks

Adapting legal frameworks is key to address the impacts of SLR, particularly in compensating and supporting affected communities. Nationally, governments must expand climate risk insurance and develop compensation mechanisms to protect those losing homes and livelihoods. Public-private insurance schemes and state-backed funds, such as the one introduced by Italy in January 2025, can help distribute financial risks more equitably. At the international level, developing nations, especially Small Island Developing States (SIDS), need stronger legal support. The World Bank calls for an increase in climate adaptation and loss and damage funds, and more comprehensive legal protections for climate-displaced populations.

Two possible adaptation scenarios for the year 2100 were developed for the Ravenna area: “rigid-conservative” and “soft-evolutionary”. The rigid-conservative scenario aims to maintain the current coastline by reinforcing existing defences. “This approach,” explains Vittoria Mencarini from Ravenna Municipality, Naturalistic Area Office, “would require the development of a territorial management system very similar to that used in the poldered areas of northern Europe. The main elements are synthesised in a landscape completely protected from the sea by a defensive infrastructure comparable to a breakwater”.

The soft evolutionary scenario proposes a more flexible strategy that accepts the dynamism of the coastal system. In this case, it's proposed to absorb the impact of sea-level rise through a gradual reconfiguration of the territory, fully protecting only the coastal urban centres and programming a controlled retreat of the coastline. “The landscape resulting from this scenario,” explains Mencarini, “is characterised by a brackish lagoon that could develop in the recessed areas between the current beach and the new dune system”.

An intermediate strategy for 2050 has also been developed, which could evolve towards either scenario. It involves two main “active defence” systems: the first in the coastal strip directly affected by sea-level rise, where the main need is to strengthen dune systems and bring freshwater closer to the coast; the second, further inland, relies on the existing topography, articulating along the water network and traces of ancient coastal ridges.

Bridging the knowledge gap

Nadia Pinardi, Director of the UN Decade Collaborative Center for Coastal Resilience and Professor at the University of Bologna, observes that integrating diverse data sources necessitates a “coupling between hydrographic basins, urban areas and marine zones”, a concept she terms “systemic vision” which extends beyond conventional administrative boundaries. As co-chair of the Knowledge Hub on Sea Level Rise, Pinardi points to the importance of actionable knowledge for successful adaptation in the Mediterranean: "What we need and what we are working on is a trustworthy, comprehensive and interconnected marine data and information infrastructure, designed and implemented to link science-based knowledge on climate change to decision-making and coastal management”.

The Knowledge Hub on Sea Level Rise represents an innovative model of science-policy interface. Its structure, organised into four task groups (co-design, policy, science and outreach), allows for the integration of different perspectives and expertise, contributing to address the need for science-based information in European policy-making and coastal planning communities.

Basin-specific workshops organized in 2022 as part of the Knowledge Hub on Sea Level Rise revealed that research priorities vary significantly between European seas. In the Mediterranean and Black Seas, coastal erosion management emerges as an absolute priority, while in the Baltic Sea, concerns are more focused on extreme storm events. As emphasised during the proceedings, “every 18 months the information doubles, while the options for maintaining control are halved”, highlighting the urgent need for effective tools for synthesis and decision support.

The way forward requires what the Knowledge Hub defines as the “last mile”: building a reliable, comprehensive and interconnected ocean data and information infrastructure. This concept goes beyond mere data collection to encompass the entire chain from scientific understanding to practical implementation of adaptation measures.

Adaptation measures can take different forms, depending on the context and its social organisation, and the risk they seek to reduce. There is no single solution. Adaptation measures themselves have an environmental impact and can lead to an increase in greenhouse gas emissions. It is therefore important to adopt solutions that minimise risk and increase resilience.

This need for interdisciplinary and holistic perspectives has guided the development of CMCC’s Strategic Programme on Global Coasts as a New Frontier. This Strategic Programme involves the development of multidisciplinary digital twins of the global coastal ocean, integrating new satellites and in-situ observations, and developing advanced modelling and artificial intelligence methods to provide tools, information, and solutions for decision-makers

The role of education

The FERS course on sea level rise is a crucial step in training the next generation of coastal scientists and managers. Through its comprehensive curriculum and hands-on approach, it provides the tools and knowledge necessary to address one of the most pressing challenges of our time. As coastal regions face increasing threats from rising seas, the need for well-trained professionals who understand both the scientific principles and practical applications of coastal management has never been greater.

The FERS course addresses these challenges through an interdisciplinary lens, bringing together experts from different fields to explore both the scientific understanding of sea level rise and practical approaches to adaptation. The complexity of these phenomena requires the implementation of multi-sectoral adaptation strategies. It's necessary to develop innovative coastal defence systems, rethink surface and groundwater management, and plan the transformation of coastal habitats based on their resilience to expected changes.

Sources

1. IPCC Sixth Assessment Report (AR6), 2021: The physical science basis
2. IPCC Special Report on the Ocean and Cryosphere in a Changing Climate, 2019
3. Sea Level Rise Knowledge Hub, European Assessment Report 2023
4. Global Sea Level Observing System (GLOSS) Implementation Plan 2023
5. Spanish Maritime Works Recommendations (ROM)
6. OECD (2023). The Economic Consequences of Sea Level Rise: Assessment and Recommendations
7. World Bank (2021). The Economics of Coastal Zone Adaptation to Climate Change