Sea Level Rise in Europe: Summary for Policymakers – SP

Sea Level Rise in Europe: Summary for Policymakers – SP

Sea level rise (SLR) is a chronic hazard that poses significant challenges for the governance of environmental and economic development across all of Europe’s coastal regions. The mean rate of absolute SLR in Europe slightly exceeds the global average trend and is accelerating, although regional variability is large. Relative SLR, which accounts for vertical land motion, exhibits more contrasting trends, with some areas in the northern Baltic Sea even experiencing a relative sea level fall.

Future SLR rates are highly uncertain and depend heavily on greenhouse gas emission scenarios. Under a very high emission pathway, a 1-meter SLR is projected over most European coasts south of 60°N during the first half of the 22nd century. The frequency at which historical centennial water levels are reached is also expected to amplify, especially in southern European seas, necessitating more adaptation.

The European Knowledge Hub on Sea Level Rise (KH-SLR), a joint effort by the Joint Programming Initiatives for “Connecting Climate Knowledge for Europe” (JPI Climate) and “Healthy and Productive Seas and Oceans” (JPI Oceans), has developed the 1st Assessment Report (SLRE1) to address the challenges posed by SLR in Europe. The report’s target audience includes national and subnational bodies focused on research and policy advice for coastal management and climate adaptation, as well as European experts who contribute to shaping policy frameworks and collecting information at a pan-European scale.

Gaps in Regional SLR Information and Impacts

The SLRE1 report was preceded by a series of targeted surveys and workshops with researchers and stakeholders, which revealed significant gaps in regional-local data and information on SLR. Approximately 32% of respondents indicated a lack of essential regional-local SLR data, with disparities across different sea basins and stakeholder groups. Overall, global SLR projections were most accessible and widely used.

Information gaps primarily revolve around regional SLR projections, uncertainties, and ice sheet mass loss contributions, highlighting the need for better long-term SLR projections and a more comprehensive understanding. While government respondents prioritized precise regional projections as the ultimate product, scientists focused on gaining a deeper comprehension of the factors influencing regional projections, considering this as the final goal.

Improving local SLR projections, understanding the impact on extreme water levels, and addressing coastal erosion were all deemed important. Shoreline erosion emerged as a dominant concern in all basins except the Arctic, reflecting the critical role of beaches in regional economies. Other significant impacts include increased flooding, damage to infrastructure, and groundwater salinization, with notable disparities across sea basins.

Adaptation Challenges and Policy Implications

The survey results show that many stakeholders deem existing adaptation plans to be inadequate, with scientists being more critical than government respondents. Flexibility of existing adaptation strategies to address SLR-induced impacts is considered insufficient, highlighting the need for adaptive planning approaches.

SLR impacts that were mostly neglected by stakeholders include those on coastal ecosystems, urban planning frameworks, river discharge characteristics, and freshwater management. Respondents unanimously agree on the usefulness of IPCC reports for informing policy and decision-making, but identified needs for periodic updates to SLR projections, comprehensive impact assessments, and enhanced exploration of adaptation strategies.

The SLRE1 also reports on four online scoping workshops that gathered insights from stakeholders, policymakers, and experts, further informing the understandings from the survey. For all European sea basins, the workshops identified significant data and information gaps, particularly in climate projections that capture local processes and coastline details. There is also a need for a robust data delivery and quality control system, as well as a solid methodology to assess the effectiveness of coastal adaptation measures.

The policy implications of the SLRE1 report include the recognition of the value of incorporating nature-based solutions (NBSs) in coastal adaptation plans, although their implementation requires rigorous evaluation and evidence of long-term sustainability under site-specific circumstances. Both scientists and policymakers emphasized the importance of community engagement and effective communication strategies in addressing the challenges posed by SLR.

Observed and Projected SLR across Europe’s Sea Basins

The SLRE1 delves into observed and projected SLR and extreme sea levels (ESLs) in the various European sea basins. Despite some variability in SLR trends, satellite altimetry shows a consistent upward trend in the basin-averaged sea level for the past 30 years, slightly above the global mean SLR. Relative sea level will rise throughout the 21st century over most European seas, except in the northern Baltic Sea and parts of the European Arctic.

In the north-eastern Atlantic Ocean basin, rates of SLR have accelerated over the past century, with regional patterns mostly explained by ocean current changes and mass loss from the Greenland ice sheet and mountain glaciers. Projections suggest that relative sea level over this region will rise close to the fastest among European seas.

The North Sea experiences complex dynamics, with relative SLR largely driven by temperature, salinity, and current changes, as well as factors like ice mass loss and subsidence. Projections indicate that relative SLR in the North Sea will vary spatially, with higher rates in the southern parts of the basin.

In the European Arctic, ongoing ice mass loss contributes to local land uplift, resulting in a below-global-average SLR projection. However, temperature-, salinity-, and current-driven SLR in the Arctic is expected to be larger than the global average, primarily due to ocean freshening.

The Mediterranean Sea’s SLR is primarily driven by mass contributions at the basin scale, while the Black Sea’s SLR appears to be more related to salinity reduction. Projections suggest that the Mediterranean Sea will experience some of the highest basin-averaged SLR rates among European seas.

The Baltic Sea is characterized by pronounced seasonal variations in sea level and a clear north-south gradient in relative sea level, with a relative sea level fall in the northernmost subbasins due to the effects of ice mass loss. Future changes in extreme sea levels in the Baltic will depend on mean SLR, atmospheric-circulation patterns, and wind changes.

Adapting to the Multifaceted Impacts of SLR

The analysis of the primary impacts of SLR in Europe employs the Source-Pathway-Receptor-Consequence framework, focusing on coastal flooding, coastal erosion, and saltwater intrusion. Coastal flooding, influenced by rising sea levels and various other factors, has profound social, economic, and environmental consequences across Europe, despite high flood-defense standards.

Extreme waves, storm surges, and human activities also influence coastal erosion, which affects over 8,200 km of European sandy beaches, leading to habitat loss, infrastructure damage, and increased flood risk. Saltwater intrusion, the encroachment of saltwater into freshwater resources, poses significant challenges to agriculture, freshwater availability, and coastal communities’ livelihoods.

A wide range of adaptation measures exist, classified into four main strategies: accommodate, protect, advance, and retreat. These include hard (engineering) and soft (nature-based) infrastructure measures, upgrading or restoring existing coastal assets, preventive and recovery measures, and changes in land occupation.

Coastal adaptation decision-making is complex, demanding thoughtful approaches to address uncertainties about future climate and societal developments. Methods such as multi-criteria decision analysis help manage this balance by organizing decisions and highlighting preferences and priorities. Inherent SLR uncertainties require the flexibility and adaptability of strategies, with an iterative revision of decisions and monitoring progress to enable timely adjustments.

Across Europe’s sea basins, countries are implementing a variety of adaptation measures, often integrating traditional engineering solutions with ecosystem-based approaches and incorporating SLR information into coastal planning. However, challenges persist in addressing uncertainty, ensuring the long-term sustainability of adaptation measures, and fostering collaboration among stakeholders.

The governance of coastal adaptation policies includes institutional organization, stakeholder engagement, and the practice of decision-making, which must consider the socioeconomic and political contexts of each region. Strengthening the capacities for climate action of various actors, along with international cooperation, can support the implementation of ambitious actions to address the multifaceted impacts of SLR in Europe.

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