The global rise in sea levels is an outcome of the buildup of greenhouse gas emissions that has resulted in a 0.63˚C-increase in median ocean temperatures over the past century. Rising ocean and atmospheric temperatures have resulted in the melting of the polar ice caps and thermal expansion (which causes the volume of water to increase), causing the increase in ocean levels.

Rising sea levels are triggering coastal flooding and erosion as well as the loss of the coastal habitats that provide natural shoreline protection from storm surges. The loss of these habitats increases the number of people at risk.

The rise in sea levels is occurring as the population of Africa’s coastal cities is skyrocketing. Between 2020 and 2030, Africa’s 7 largest coastal cities—Lagos, Luanda, Dar es Salaam, Alexandria, Abidjan, Cape Town, and Casablanca—are projected to grow by 40 percent (48 million people to 69 million) compared with the continent’s overall anticipated increase of 27 percent (1.34 billion to 1.69 billion). Smaller coastal cities may expand even faster: Port Harcourt in Nigeria, for example, is expected to grow 53 percent over this decade. Globally, Africa’s coastal regions are anticipated to experience the highest rates of population growth and urbanization in the world.

This demographic pressure is being driven by the economic significance of Africa’s coastal cities. Africa’s blue economy—comprising ports, fisheries, tourism, and other coastal economic activity—is conservatively projected to grow from $296 billion in 2018 to $405 billion by 2030. Coastal megacities like Lagos and Dar es Salaam power national economies. The GDP of Lagos, for example, is greater than 46 of Africa’s 54 countries.

Africa’s coastal cities serve as the critical gateways to the continent’s vast interior. Disruptions to port cities caused by rising sea levels can have cascading effects on the logistical networks and economies that they support. An estimated 90 percent of Africa’s import and export trade comes through coastal ports.

With a rapidly growing share of Africans living in coastal regions, rising sea levels represent a highly tangible and disruptive impact of global warming on a continent already experiencing rapid population growth and land pressures. In addition to population displacements, rising sea levels will place enormous strain on infrastructure, agriculture, and water access for African citizens, heightening the risk of instability.

Coastal cities not only face the direct threat from rising sea water and storm surges. They also face the unseen threat from groundwater rising, turning urban areas into wetlands. From the erosion of roads and building foundations to backflowing sewers, leeching septic systems, inundated cesspools turned microbe breeding ponds, cities will face myriad infrastructure and public health crises. In Lagos, 50 percent of hospitalized patients suffer from water-borne diseases.

Rising sea levels also threaten coastal residents by contaminating aquifers. Coastal aquifers provide water for drinking and irrigating crops. Coastal aquifers are vulnerable to saltwater intrusion, even from minor rises in sea levels, particularly in the coastal areas of North Africa where groundwater is overexploited to support the growing population and agriculture.

Rising oceans are also behind the increasing incidences of “100-year floods” (having a one percent chance of occurring in any given year). Historically rare, extreme sea level events (the combination of mean sea level, tides, and wave surges) are occurring increasingly frequently, especially in tropical regions. Across large African river basins, the frequency of 100-year flood events is projected to increase to 1 in 40 years at 1.5°C and 2°C global warming, and 1 in 21 years at 4°C warming. Under the business-as-usual model, for some parts of coastal West and East Africa, these extreme outcomes could become annual events.

A Guest Editorial