Coastal Adaptation and Retreat

As ecosystems from arctic forests to tropical coral reefs[1] edge toward extinction, and sea level rises, it is time for a radical rethinking of coastal management. Here is a comprehensive strategy for coastal adaptation and retreat, assuming worst-case climate change.

Sea Walls and Flood Barriers

As sea levels rise, many coastal communities will turn to massive sea walls and flood barriers as their first line of defense. These engineering marvels, while impressive, must be recognized for what they are: temporary measures in a long-term battle against the encroaching seas.

The MOSE project in Venice, Italy, serves as a prime example of both the potential and limitations of such approaches. This complex system of 78 mobile gates, designed to protect the Venice lagoon from high tides, came at a staggering cost of €5.5 billion and took nearly two decades to complete[2]. While it has prevented several flooding events since its activation in 2020, it also highlights the enormous financial and energy investments required for such solutions.

Implementing adaptive designs is crucial[3]. For instance, the Maeslant Barrier in the Netherlands was built with future sea-level rise in mind, capable of being modified to withstand an additional 50 cm rise. However, even these adaptive designs have their limits. Sea walls and flood barriers can increase flood risk for adjacent areas by altering natural water flow patterns[4].

Managed Retreat

As the inadequacies of physical barriers become increasingly clear, many coastal communities will confront an unavoidable reality: retreat is their sole sustainable option in the long term. Managed retreat, the planned relocation of communities away from vulnerable coastal zones, will emerge as one of the most extensive and organized migrations in human history[5].

The Isle de Jean Charles in Louisiana serves as a poignant case study of the necessity for managed retreat. In 2016, this community became the first in the United States to receive federal funding for relocation because of the direct impacts of climate change. Once a vibrant community of 400 people, the island has tragically lost 98% of its landmass to erosion and rising sea levels over the past century. The relocation project, estimated at a cost of $48 million, aims to relocate the remaining residents to a more secure location[6].

Implementing managed retreat on a global scale will require comprehensive relocation plans, including the development of new housing and infrastructure[7]. Financial mechanisms must compensate property owners, and policies must be put in place to prevent development in high-risk zones[8]. The social, economic, and psychological effects of this mass migration will be profound and long-lasting, requiring extensive support systems for displaced communities[9].

Floating and Amphibious Architecture

For certain coastal cities that are unwilling or unable to pursue the path of retreat, innovative solutions like floating or amphibious architecture may present a viable alternative for the future. The concept of constructing large-scale floating districts is already being actively explored in cities such as Rotterdam, where the Floating Pavilion serves as a tangible prototype for potential floating urban developments[10].

Amphibious foundation systems, which enable buildings to elevate themselves in response to rising floodwaters and then settle back down as the waters recede, are being progressively implemented in flood-prone areas. A prime example can be found in Maasbommel, Netherlands, where a community of amphibious homes has been withstanding floods since 2005[11].

As we look further into the future, the concept of establishing entirely new floating cities is gaining momentum. A notable example is the Oceanix City project, undertaken in collaboration with the UN-Habitat program. This project envisions a modular maritime metropolis designed to withstand the challenges of rising sea levels, hurricanes, and tsunamis[12].

Coastal Ecosystem Adaptation

In the ongoing battle against rising sea levels, the preservation and enhancement of coastal ecosystems will prove vital for natural flood protection, carbon sequestration, and biodiversity conservation. Mangrove forests, salt marshes, and oyster and coral reefs all serve as natural buffers against storm surges and erosion while simultaneously capturing and storing substantial amounts of carbon[13],[14].

The Mekong Delta in Vietnam offers an insightful illustration of ecosystem-based adaptation in practice. Grappling with the challenges of severe coastal erosion and saltwater intrusion, the region has started a large-scale mangrove restoration project. Between 1998 and 2015, over 9,000 hectares of mangroves were planted, effectively serving as a natural barrier against coastal erosion while also creating livelihood opportunities for the local communities[15].

The concept of “living shorelines,” which integrate natural elements with engineered structures, is gaining increasing recognition as a more resilient and ecologically sound alternative to traditional hardened shorelines. A prime example can be observed in the Chesapeake Bay in the United States, where many living shoreline projects have been implemented. These projects use native plants, sand, and a limited amount of rock to stabilize shorelines while simultaneously providing valuable habitat for marine life[16].

However, it is important to acknowledge that many of these vital ecosystems would be significantly altered or even lost in a world experiencing a 5°C increase in temperature. In such a scenario, assisted migration programs for key coastal species may become necessary to safeguard biodiversity in the face of these drastically changing conditions.

Comprehensive Coastal Zone Management

Adapting to the impending reality of rising sea levels will necessitate a radical transformation of coastal zone management practices. We must implement innovative approaches such as rolling easements that allow wetlands to migrate inland as sea levels rise, develop adaptive zoning regulations that evolve in response to changing conditions, and establish international frameworks for compassionately managing the displacement of climate refugees from vulnerable low-lying nations[17].

The state of California’s adaptation strategy serves as an example of this comprehensive approach to addressing sea level rise. California’s Coastal Plan includes provisions for managed retreat, ecosystem-based adaptation, and integrating sea-level rise considerations into all coastal planning and development decisions[18].

This level of integrated coastal management will necessitate an unprecedented level of cooperation between local, national, and international entities. The challenges are undeniably immense, but the consequences of inaction are too catastrophic to contemplate.

Psychological and Cultural Adaptation

The most formidable aspect of coastal adaptation lies in the profound sense of loss. The concept of ecological grief – the mourning of ecosystems and species lost to climate change – is gaining increasing relevance as we witness the irreversible transformation of our coastlines[19].

It is imperative that we proactively develop programs to preserve the cultural heritage of communities facing an uncertain future. The Scottish island of St Kilda, abandoned in 1930 due to harsh living conditions, serves as a poignant illustration of how we can safeguard the memory of lost communities. The island, now a UNESCO World Heritage Site, meticulously preserves structures and artifacts that tell the story of its former inhabitants[20].

Mental health initiatives designed to help people cope with displacement and loss will be crucial. The concept of solastalgia – the distress experienced because of environmental change impacting people while they remain connected to their home environment – is likely to become increasingly prevalent[21].

Creating new cultural narratives that embrace humanity’s evolving relationship with the coast will be essential for fostering resilience and hope. Artists, writers, and community leaders will play a vital role in guiding societies through this transformative period.

Coastal Conclusion

Coastal regions are at the forefront of the climate crisis. The strategies outlined here, ranging from engineered defenses and managed retreat to floating cities and ecosystem-based adaptation, represent our best efforts to navigate an uncertain and challenging future. Adaptive planning will be indispensable in addressing the complex technical, social, economic, and cultural transformations that lie ahead.