By 2050 an estimated 1bn people globally will be living in coastal areas, which are already threatened by rising tides that put at risk their homes, livelihoods and the cities they call home. As sea levels rise as a result of melting ice caps and warming oceans, storms, intensified by shifting temperatures, also contribute to increased flooding.

Major metropolises are on the frontline, facing some of the highest risks from coastal flooding. According to Théophile Bongarts Lebbe, project manager at the Sea'ties initiative for climate change and coastal adaptation, emerging markets cities with tens of millions of inhabitants such as Kolkata, Mumbai, Dhaka and Jakarta are among the cities with the highest number of people at risk from coastal flooding, while Miami, Guangzhou and New York are the most vulnerable cities in terms of assets exposed. 

“Yet, it is not just megalopolises that are threatened – medium-sized cities worldwide are [also] concerned. In Europe, one third of the population lives less than 50 km from the coast (over 200mn people), nearly 50mn of whom live in low-lying coastal areas,” Lebbe tells bne IntelliNews. 

“Furthermore, it is estimated that around 72,000 people in the EU are exposed to coastal hazards every year. In the Baltic region, coastal cities such as Gdansk and Riga are vulnerable to coastal erosion (which can be worsened by human activities along the shoreline), coastal floods and the severity and frequency of storms.”

Appeal to COP28 nations 

In response to these mounting dangers, the Ocean & Climate Platform (OCP) initiated the Sea’ties project in 2020, dedicated to supporting threatened coastal cities by facilitating the conception and implementation of effective adaptation strategies. In the run-up to COP28, the platform unveiled a set of comprehensive policy recommendations aimed at assisting coastal cities in adapting to the inevitable rise in sea levels. 

Sea level rise is a consequence of the ice sheet and glaciers melting due to human-induced climate change. The acceleration of the sea level rise observed in the 20th century may lead to a potential one-metre increase by 2100 if greenhouse gas (GHG) emissions are not curbed sufficiently. This is an irreversible phenomenon that is set to persist for centuries, posing existential threats to coastal cities. 

The gradual rise in sea levels is just part of the picture; it is combined with sudden extreme levels, often induced by tropical cyclones, resulting in land loss, chronic tidal flooding, coastal erosion, salinisation and ecosystem degradation.

As outlined in a paper from the Sea’ties Ocean & Climate Platform, the exposure of coastal communities to such threats is heightened by urban development and other human activities. Extracting resources like sand, groundwater and hydrocarbons contributes to subsidence. 

This is an unprecedented phenomenon and no one knows how fast sea levels will rise; it depends on how successful humans are in cutting greenhouse gas emissions, the speed at which the Antarctic and Greenland ice sheets melt and other variations. Despite the uncertainties, it is certain that risks associated with sea level rise will increase, as the target of limiting global warming to 1.5°C above pre-industrial levels by 2100, in line with the Paris Agreement, looks increasingly ambitious.

Short-term solutions 

Coastal cities, despite the occasional headline-grabbing climate disaster like Hurricane Katrina or Jakarta's relocation, are for the most part shockingly underprepared. 

Sea level rise adaptation only recently became a political priority, and there is not currently a unified vision for a climate-resilient future for coastal cities at national and international levels.

City authorities often resort to short-term engineering solutions like seawalls that may exacerbate the problem. The lack of financial, human and technical resources, combined with insufficient engagement from regional authorities, hampers effective co-ordination.

In response to erosion and flooding, cities often resort to engineering solutions like seawalls, which may exacerbate the issue. Ambitious adaptation strategies are rare, hindered by a lack of financial, human, and technical resources. Regional authorities are insufficiently engaged, hindering coordination, and knowledge exchange among practitioners is limited. 

Call for international action 

The mission of Sea’ties is to elevate the adaptation of coastal cities on the international agenda. Ahead of COP28, they are advocating for greater support, sharing key messages with elected representatives, scientists, project developers and private companies to secure the transition needed.

“Our role is to advocate for greater support for the adaptation of coastal cities faced with rising sea levels,” says Lebbe. 

“We want this eminently important issue to be high up on the list of priorities on the international agenda. To date, we are still underestimating the scale of the population displacements and economic losses that rising sea levels will cause. The financial and technical tools are also lacking.”

The set of Policy Recommendations to Coastal Cities to Adapt to Sea Level Rise were developed over four years. Currently endorsed by 80 organisations globally, these policy recommendations target local, national, regional and international decision-makers, with four key priorities, namely: planning long-term adaptation responses tailored to the local context; prioritising social imperatives in adaptation policies: developing new ways to generate and share operational knowledge on adaptation; and, building a sustainable finance approach for coastal cities. 

As explained by the Sea-ties Ocean & Climate Platform, adaptation requires a shift towards long-term planning that anticipates diverse scenarios of sea level rise while remaining flexible to potential environmental and societal changes. The recommendations advocate for a mix of solutions ranging from hard and soft protection to ecosystem-based adaptation, hybrid solutions, accommodation, planned relocation, and others.

Immediate and substantial GHG emission reductions are paramount, necessitating a systemic societal transformation for effective adaptation measures, says the document. 

Adapting coastal cities demands long-term planning that integrates diverse sea level rise scenarios and remains flexible. It also calls for urban development and other activities such as sand extraction to be limited along shorelines and vulnerable inland areas to avoid disrupting natural processes and weakening buffering ecosystems like dunes, mangroves and salt marshes. New development in high-risk zones should be discouraged. 

The document recommends minimising reliance on protection-based measures unless absolutely necessary, reserving such responses for heavily urbanised sites facing significant challenges or as a temporary solution. Instead, the focus should be on the protection of existing coastal ecosystems and promoting restoration in suitable locations to leverage their capacity for containing coastal erosion and mitigating the impacts of extreme climate events.

Innovative strategies 

Some cities are already moving beyond traditional protective infrastructure like seawalls. “Cities are at the forefront of adaptation action and although there is no perfect, one-size-fits-all solution, many cities are turning away from protective infrastructure only (such as seawalls) to instead implement a mix of several typologies of solutions,” says Lebbe, giving examples such as elevated infrastructure, nature-based solutions and planned relocation. 

One example is the 14 municipalities of the Sète Agglopôle Méditerranée in France, which carried out a project including dune restoration, the repositioning of a road, beach nourishment and the deployment of sand-filled geotextile bags. 

Lebbe also points to the actions of the Thames Coromandel District Council in New Zealand, which planned ahead for the next 100 years, and adopted 138 pathways, each for a specific section of the shoreline, that are responsive to change and can be updated as future needs evolve.

Cost of change 

Yet an important question remains: is adaptation prohibitively expensive for some developing world cities? The upfront investment is indeed substantial, but the cost of delayed action is even higher, points out Lebbe. Coastal cities are not only densely populated but also critical economic hubs; most future global GDP growth is centred around cities located in coastal regions. 

One forecast indicates that sea level rise could result in annual damage of as much as 9.3% of global GDP in 2100. In Europe alone, damage is currently estimated at €1bn a year, for a total of €959bn in assets potentially at risk, and it could be as high as €11bn by 2050 and almost €814bn by 2100. 

“The upfront investment needed to kick-start adaptation is expensive for all coastal cities, and even more so for cities in countries with a developing economy. As such, many cities turn to short-term measures or are locked in recovery action,” Lebbe tells bne IntelliNews. 

“However, the cost of delayed action is even starker. Coastal cities are densely populated areas and critical economic hubs, where many communities, activities, infrastructure and lifelines are located.

“Cities will be increasingly burdened by the recovering costs associated with coastal flooding, storms and erosion, and will increasingly require assistance. As costs of adaptation rise and dedicated investments fall far short of needs, enhanced funding from both public and private sources is urgently required and must be directed towards long-term adaptation strategies,” Lebbe adds.