Vanishing coastlines are a major test for government action. For many cities, especially those in nations that have made incremental progress on national climate change policy, and even those like Venice that have grappled with a rise in water levels for decades, the time to act is now.

The International Panel on Climate Change (IPCC) projected in 2007 that global sea levels would rise between 8 inches and 2 feet over the next century. But thanks to persistently high air and sea temperatures over the past six years, glaciers are melting, polar ice caps are shrinking, and ice is being lost from the continental sheets of Greenland and West Antarctica at a faster rate than anticipated. Combining these new developments with the expected thermal expansion, scientists writing for Environmental Research Letters anticipate that global sea levels will rise between 12 inches and 3 feet over the next century—a 60 percent increase over the IPCC model.

That means the coastlines around more than two-thirds of the world’s largest megacities and the sprawl that surrounds them are disappearing much faster than predicted. With millions of urbanites’ security at risk, the consequences of not taking preventive measures go far beyond a sinking Piazza San Marco. Warmer, higher oceans dramatically increase the risk of frequent extreme weather events, damaging floods, and storm surges. Recent storms like Hurricane Sandy on America’s East Coast, with damages totaling over $50 billion for the entire region, and the 2008 Cyclone Nargis in Myanmar, with a death toll that climbed to nearly 140,000 lives, demonstrate the varied and damaging repercussions of sea-level rise all too clearly. Residences, transportation infrastructure, schools, hospitals, industry, and commercial areas, among other valuable urban assets, will face billions of dollars in climate-related damages over the coming decades.

Cities at Economic and Ecological Risk

From Ephesus, Turkey, to Mumbai, India, urban settlements along the sea have been important concentrations of cultural, economic, and population growth for millennia. Today, some of the world’s largest megacities and suburbs, with growing populations of more than 10 million, are also those most vulnerable to sea-level rise. Over the next half century, urban coastal communities around the world will face a new reality of dangerously amplified security risks, loss of life, and economic destruction from climate-change-induced flooding and storm surges.

Kolkata, India, for instance, is expected to contain more than 14 million people in locations vulnerable to rising sea levels and increased flooding by 2070, a sevenfold increase over its exposed population of 1.9 million today. Sea-level rise will jeopardize not only the homes and livelihoods of those 14 million people but also—and perhaps most importantly—their basic safety.

But Kolkata is not the exception—it’s the norm. Most of the top ten port cities with the largest number of people exposed to coastal flooding are growing and industrializing Asian cities (see table 1). Collectively, they are home to a total of nearly 66.4 million people and have combined future exposed assets of more than $19 trillion (see table 2).

Rising sea levels threaten some of the world's largest megacities. With billions of dollars and the security of millions of people at risk, the time to act is now.

Rising sea levels threaten some of the world's largest megacities. With billions of dollars and the security of millions of people at risk, the time to act is now.

With 100 cities generating 25 percent of global GDP, a number that the McKinsey Global Institute anticipates will grow to at least 35 percent by 2025, sea-level rise not only threatens the productivity of many huge cities it also jeopardizes the health and stability of the entire world market. A joint report from the World Wildlife Fund and Allianz SE determined that a midcentury global sea-level rise of 20 inches, with an additional 6 inches in some localized areas along the northeast U.S. coast, could jeopardize assets worth close to $7.4 trillion. This figure only accounts for the assets located in one region of a single country. Imagine the figure for assets exposed across the United States, or, more dauntingly, worldwide.

Planning for Environmental Protection and Economic Sustainability

To help stave off these potentially devastating outcomes, coastal cities and communities should align comprehensive climate protection with economic development strategies. New York City, one of the world’s largest economic engines, is doing just that. PlaNYC began in 2007 as an economic development initiative, but when it became clear that the city would experience significant future impacts from climate change, the plan was transformed. Now it is a cutting-edge example of a city climate plan.

By pursing a climate-protection plan that includes economic goals, PlaNYC was able to overcome the political opposition many cities face when attempting to enact policies to safeguard the climate. To help protect the assets at risk in New York City, PlaNYC laid a framework to coordinate and prioritize the city’s operations and infrastructure investments with the inclusion of climate change estimates and risk assessments. The plan updated codes and standards for flood protection, which had implications for city maps and property insurance, with good results.

Housing developments designed to conform to PlaNYC benchmarks, such as Arverne by the Sea in the Rockaways, Brooklyn, experienced less damage from Hurricane Sandy than older, adjacent developments that were developed before the establishment of such guidelines, according to preliminary studies conducted by staff on the mayor’s Special Initiative for Rebuilding and Resiliency in response to the storm. The elevation of the Rockaway Peninsula is zero feet above sea level, making it vulnerable to flooding. Because PlaNYC anticipated storm surges as a result of more extreme storms, projects developed after the launch of PlaNYC required buildings to be set further away from the beach, built higher off the ground, and only approved if master plans included additional natural barriers, such as sand bars, between the developments and the water.

By contrast, other coastal communities seem to be in a holding pattern. The Chesapeake Bay area in the mid-Atlantic region of the United States is one example. It includes several medium-sized cities (Baltimore, Annapolis, Washington, DC, and the Portsmouth-Norfolk military complex in Tidewater, Virginia) and currently faces sea levels that are rising at twice the speed of the global average. This endangers not only these urban areas but also 66 percent of the region’s commercial fisheries, 90 percent of the Blackwater National Wildlife Refuge, and dozens of other irreplaceable natural resources and wildlife habitats.

Although ad hoc action has been taken to restore beaches in the area, primarily through sand replenishment schemes, these alone are not enough to safeguard both the region’s wildlife and its economy. The Chesapeake Bay area and other politically sluggish coastal communities must enact stronger policies that both foster economic development and protect the climate. In the absence of a broader coastal protection mandate, this type of local action is necessary to secure a financially and economically sound future for coastal communities.

Proactive and Comprehensive Approaches

Broadly speaking, all cities should align comprehensive plans to protect the climate with economic development strategies. But the specifics for each locality will vary. Each needs to develop and implement an adaption strategy customized for its unique experience with sea-level rise. This type of customization is necessary because climate models, satellite data, and hydrographic observations demonstrate that sea levels are not rising uniformly around the world. While some regions may need to adapt to a rise several times as high as the global mean, others may have to adapt to a drop in sea level.

Comprehensive, context-specific coastal planning engages local authorities to advance adaptation measures that respond to local threats and manage the ecological risks that substantial sea-level rise poses to the existing human and natural environment. Comprehensive plans for coastal communities identify economic assets, offer an opportunity to bolster economic development that is aligned with coastal protection, and ultimately secure the financial survival of these communities in the face of future climate risks.

These plans must prepare communities for both current and future climate risks. One way to achieve that is to include sea-level-rise adaptation and mitigation measures in a community’s vision. Sea-level rise, and the extreme weather events it induces, is an immediate but continuously evolving danger that requires both short- and long-term action, including supporting resiliency efforts that individual households and businesses can undertake in the near term and mandating resiliency in infrastructure planning for the long haul.

Getting Information to Consumers

Sea-level rise can be devastating to individual livelihoods, as illustrated by the recent victims of Hurricane Sandy. Distributing practical information to consumers and helping them with implementation is an effective short-term policy to protect community members and their local economy from immediate threats. Such information can help homeowners protect their investments and prepare for emergencies that they may face in the near future. This type of immediate adaptation can help secure community members today while they wait for longer-term policy changes to have an effect.

Harden Up, a website in Queensland, Australia, facilitates such immediate action. It provides practical advice to consumers to make current development, retrofitting, and reconstruction projects as resilient as possible to flooding, inundation, and other effects of rising sea levels. It also provides step-by-step technical assistance along the way. For example, homeowners in flood-prone areas are not only encouraged to build with resilient materials like fiber cement sheets, stone products, steel, hardwood, and glass blocks, they are also shown how to do so. Beyond creating their own plans, participants have also used the portal to share insurance, property, and resilience preparation advice with other vulnerable households. Since the Harden Up project was launched, just under 10,000 coastal households have created disaster-resilient plans to prepare for the current and forthcoming local consequences of climate change.

The Backbone of All Plans: Zoning

Climate-intelligent zoning forms the backbone of all longer-term comprehensive coastal planning. Zoning provides the legal framework to govern the use and future development of coastal land, and overlay zoning allows for special zoning districts based on ecological, economic, or social sensitivity. The use of both zoning and overlay zoning provides the necessary foundation for all other policy and technological tools used in a coastal zone management strategy. Resilient design and building code requirements are then tailored to the land uses set forth in zoning.

Zoning schemes use a strict management system of land-use decisions to control commercial, residential, industrial, and agricultural construction. In Cape Town, South Africa, for instance, each zone is assigned specific regulatory requirements based on land use that include resilient building designs, setbacks that lay out the distance development must be from shorelines, and natural buffers. Additional overlay-zoning regulations based on identified vulnerabilities and floodplains are then superimposed on the baseline plan. Cape Town provides a good example of an effective coastal zone management strategy based on an intelligent, intricate scheme of zoning and overlay-zoning regulations that could be applied to a range of geographic contexts. Further, the city’s plans are updated continually to ensure that they correspond to an evolving physical and socioeconomic environment, which is an effective practice that should be replicated.

This type of strategy requires a proactive government that is willing to plan and implement measures in advance to preemptively protect the region from the negative consequences and hazards of sea-level rise.

Soft Armoring Makes a Hard Difference

Whereas zoning lays the foundation for all protection mechanisms, specifying man-made barriers like seawalls or environmental buffers like wetland protection in comprehensive planning provides additional longer-term physical fortification to coastal economies.

Coastal cities that have long-existing communities and assets in areas that are already eroding, such as Rotterdam in the Netherlands, use both hard- and soft-armoring techniques to enhance flood protection. Hard armoring involves building defensive infrastructure, like engineered seawalls, while soft-armoring strategies include wetland restoration, sand replenishment, and living shorelines. Because hard armor can block sediment from replenishing eroded areas, resulting in dry beaches, severe changes to the marine habitats, and the loss of intertidal areas, the combination of hard- and soft-armoring strategies can lessen negative environmental impacts. Rotterdam combines Maeslantkering, an enormous storm-surge barrier and high-tech water management system, with soft strategies like widening rivers, reinforcing the coastline with sand, and protecting vital wetlands to create a fully integrated network.

The comprehensive Rotterdam Climate Initiative has set the goal of fully climate-proofing the city by 2025, and Rotterdam has embraced water and climate management as a promising economic growth strategy. The city acts as a living laboratory for developing and implementing innovations in climate adaptation with inventions like water plazas and floating buildings.

Plans With Multiple Stakeholders

When planning is directed from a single perspective, like an oil company or a single agency within government, it risks excluding the interests and goals of other stakeholders, leading to the creation of plans that are not as effective as they could be. The participation of different levels of governance, sectors, businesses, and owners of private, at-risk properties is key to providing all the necessary components for a coastal management policy that reflects the viewpoints of every stakeholder group—local and national, public and private.

The U.S. state of Louisiana’s Coastal Master Plan, for example, provides a framework for multilevel governance and attempts to ensure that city plans achieve local goals as much as they conform to national environmental and development regulation. Created by a multidisciplinary commission, the Coastal Master Plan involves local, state, and national governments in the effort to restore Louisiana’s coast. The planning team in Louisiana consists of a variety of public- and private-sector experts, with focus groups for key businesses and industries, such as fisheries, to reflect the range of economic sectors. Such a multilevel governance framework ensures that no interests or goals are being excluded, facilitating the most effective and inclusive results.

Funding for Coastal Cities

Creating coastal cities that are resilient to the effects of sea-level rise requires a significant amount of costly redevelopment as well as the protection of natural areas. A lack of funding is often cited as the biggest barrier to effective coastal management, especially for newly emerging cities in the developing world. With many local economies facing budget cuts, pooling funds from multiple revenue sources is necessary to support the sustainable management of cities’ coastlines. Such funding sources can include state and national governments, international banks and organizations, civil society, and the private sector.

Louisiana’s Coastal Master Plan is again a good example of this approach. It outlines 145 projects that would cost $50 billion over fifty years and pools funding sources for them. Funds come from local sources, a state lockbox, and the federal RESTORE Act, which dedicates 80 percent of all Clean Water Act penalties and fines from the Deepwater Horizon oil spill to environmental and economic recovery projects in the Gulf states. A lockbox guarantees that funds are directed to projects defined by the master plan.

Many developing countries in East Asia, the Middle East, and North Africa do not have sufficient national resources to support local efforts in battling rising sea levels. Cities and states must instead look to public-private partnerships or global-local partnerships. The Strategic Climate Fund through the Climate Investment Funds provides financial assistance and World Bank expertise for coastal communities in Africa, Southeast Asia, and the Caribbean. Within those funds, the Pilot Program for Climate Resilience provides investment and practical assistance to integrate climate risk and resilience into core development planning and implementation. Moroccan coastal communities will begin to use funds and expertise from this source to implement a four-year, $5.2 million integrated coastal management system to meet the challenges of managing the resources of the Mediterranean Sea for long-term sustainability.

In both developed and developing countries, civil society groups and private firms have played an integral role in providing additional technical support, funding, and the capacity to share best practices between continents. Nations should step up to foster such relationships if resources are lacking.

Support at All Levels

Both urban populations and the threat of rising sea levels are growing simultaneously. Coastal cities across the globe cannot afford to endure long debates to produce tangible results. Sea-level rise will act as a threat multiplier in rapidly urbanizing agglomerations, increasing political, economic, religious, demographic, and ethnic tensions by causing land and water to become scarcer.

Cities should develop customized, comprehensive coastal plans to protect the environment and their economic assets of both today and the future. Building on a zoning framework that includes hard constructs like storm-surge barriers as well as soft armors like wetland restoration, such plans identify the actors and lay out the steps for climate and economic protection.

On their own, few localities will be able to produce or afford comprehensive plans and the infrastructure investments they require. Locally led, nationally supported iterative plans are needed from Dhaka to New Orleans that can protect against looming threats. State, federal, and international governance must provide management, funds, and technical assistance to improve resource management and resilience at the coastal-city level. It is on this multidisciplinary, multilevel path that coastal cities will balance sea-level rise with other environmental, economic, social, cultural, and recreational objectives.