Sea level rise now inevitable, say researchers

Levels rose faster than expected in 2024 due to an unusual amount of ocean warming, combined with meltwater from land-based ice such as glaciers.

This threatens not only coastal communities and species but also infrastructure and food security. Not to mention the threat of conflict over land and resources as millions of people are forced to migrate as the problem worsens. 

As the climate crisis accelerates, predicting and preparing for these changes is more urgent than ever.

Enter the PROTECT project, an ambitious EU-funded research initiative dedicated to transforming how we understand and predict sea-level rise. By integrating advanced modelling techniques and enriched information, they're equipping decision-makers and coastal communities with new tools to face an uncertain future.  

To learn more, we caught up with Gael Durand, Senior Scientist at the Institute of Environmental Geosciences (CNRS-IGE) and PROTECT Coordinator, and Anne Chapuis, PROTECT Communication Officer. 

We need to be humble when we talk about advances like these in PROTECT. Science is, in most cases, a long-term and incremental process, and we’re very much part of that continuum. We didn’t start from scratch—we built on decades of earlier work, using the best available data and models, and we aimed to push the boundaries a bit further.

That said, earlier projections—by necessity—left some of these processes out or treated them in highly simplified ways. For example, relying on a single ice sheet per study or model or extrapolations or expert judgements. This limited their ability to fully capture potential instabilities in the ice sheet. 

What PROTECT brought was the ability to integrate improved process representations into multi-model ensemble projections. This helps to quantify uncertainties and understand the range of plausible futures more comprehensively.

Specifically, we focused on improving the representation of key physical processes in Antarctic Ice Sheet models. That means things like melting beneath ice shelves, the coupling between the ocean and the ice sheet and the way ice fractures and accumulates damage over time. These processes are complex, and modelling them is extremely challenging, but we made real progress in capturing their behaviour more realistically.

At the same time, our projections still have limitations. There are uncertainties we haven’t resolved yet, and it will take future research to address them. So PROTECT doesn’t close the book on sea-level rise projections—but it turns the page forward.

The modelling gap (between our models and previous ones) means that past decision-making may have underestimated future risks, particularly in terms of timing and magnitude of sea-level rise. Our more complete modelling provides more realistic high-end scenarios, which better support precautionary planning and risk management. 

Glacier behaviour and water supply vary greatly across regions. While these weren’t the main focus of the project, our results offer useful insights. 

Communities in areas like the Alps or the Himalayas experience different impacts depending on glacier type, melt rate and seasonal water flow patterns. These changes influence freshwater availability, increase the risk of natural hazards, and affect local economies—especially those reliant on tourism.

Sea-level rise varies significantly across regions due to a combination of physical processes. These include changes in ocean density and circulation, the redistribution of mass between land and ocean (from melting glaciers, ice sheets and land water storage) and local vertical land movement. As a result, some coastal areas are experiencing faster or more severe sea-level rise than others. 

For decision-makers, this underscores the importance of using high-resolution, region-specific data (such as found in our sea-level-rise projection tool) to guide adaptation efforts such as coastal protection, infrastructure planning and potential relocation strategies. 

Sea-level rise projections are shaped by many sources of uncertainty—some physical, others societal. 

One of the most critical scientific unknowns is how ice sheets, particularly in West Antarctica, will respond to continued warming. Processes like ice damage, calving, and interactions between ice and ocean currents are not yet fully understood, making it difficult to predict how quickly ice shelves and outlet glaciers might destabilise. Additionally, uncertainties in surface mass balance as the evolution of melt and the impact of liquid water remain difficult to evaluate in a warming climate. 

At a local scale, vertical land motion  can influence local sea-level drastically, they have been so far difficult to monitor and remain difficult to forecast.

In the face of such complexity, decision-makers can’t afford to wait for perfect predictions. Instead, they need to adopt robust and flexible adaptation strategies—plans that remain effective across a wide range of possible futures. 

This means designing infrastructure and policies that can evolve over time, based on ongoing monitoring and updated scientific insights. It also means engaging local communities early and often, so they can co-create adaptation pathways that reflect both the best available science and the values, needs and lived experience of those most affected.

One key outcome of PROTECT was the distinction between broad-scale (e.g., global policy or finance) and local-scale decisions (e.g., municipal zoning or infrastructure siting). 

Each decision type demands different kinds of information. Traditional "static" SLR scenarios—like high-end, low-end, or probabilistic projections—serve some purposes, but they fall short when planning must evolve alongside science. 

In contrast, learning-based scenarios, such as probabilistic learning scenarios and interval learning scenarios, represent a major advance. These account for future updates in knowledge and observed data, enabling stakeholders to refine their strategies as real-world conditions change.

By incorporating learning scenarios, policymakers and planners can avoid the trap of "over- or under-building" for uncertain futures. These products support adaptive decision-making, allowing for regular revision of coastal risk assessments and investment plans. For example, infrastructure projects can be designed for initial conditions but leave room for modular upgrades as sea levels rise or confidence in projections improves.

In parallel, the typology of decision types developed in PROTECT provides a practical guide to matching stakeholder needs with appropriate data products. This helps ensure that risk information is usable by both multilateral actors shaping global frameworks and local authorities tasked with implementation on the ground.

The integration of learning-based products into risk assessments also aids in developing trigger-based adaptation pathways. These are strategies that implement specific actions when predetermined thresholds are crossed (e.g., certain rates of SLR or frequency of flooding). This is crucial in addressing the long-term social dimensions of climate impacts, such as the risk of mass migration. 

While providing region-specific solutions everywhere is beyond the scope of PROTECT, several key principles are emerging from related European projects like CoCliCo, which aims to develop coastal climate services and offer insights that could help guide other regions worldwide in adapting to sea-level rise across diverse contexts.

Strengthening international scientific cooperation and open data sharing is essential. Especially to ensure that vulnerable countries have access to the latest research, models and tools for coastal adaptation. 

Prioritising funding and technical support for those countries most at risk is also crucial, not only as a matter of climate justice, but to reduce the long-term risk of displacement and cross-border migration pressures.

CoCliCo and partner projects have shown that transformational adaptation—going beyond incremental fixes—is urgently needed. Yet many vulnerable nations lack the resources or institutional capacity to implement such far-reaching strategies. 

International collaboration must therefore go beyond research partnerships: it must include investment in dedicated climate services, long-term funding mechanisms, inclusive governance and equitable adaptation pathways.

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