Africa’s coastlines are facing a rapidly accelerating crisis, with the 2023–2024 El Niño event triggering the most significant sea level surge ever recorded in the region – highlighting a dangerous new reality for the continent’s coastal nations.
In a study published in Communications Earth & Environment, researchers from the department of oceanography at the University of Cape Town (UCT) analysed more than 30 years of satellite data, spanning 1993 to 2024, across the Atlantic Ocean, Indian Ocean, Mediterranean Sea, Red Sea and surrounding waters.
While the global impacts of the 2023–2024 El Niño have been widely documented, its effect on Africa’s sea levels has received far less attention.
Early evidence suggests the event coincided with unusually warm ocean temperatures along almost the entire continent. In some parts of West Africa, sea surface temperatures rose by more than 2°C, they said.
As the study notes, “nearly the entire coastline of Africa experienced anomalously high sea surface temperatures in 2023–2024”.
These conditions were accompanied by elevated sea levels, intensifying storm surges, driving saltwater into freshwater systems and accelerating coastal erosion.
What remained unclear was how much of these extremes can be directly attributed to El Niño and how much reflects other climate systems or the long-term rise in sea levels.
The uncertainty is particularly troubling for Africa, where vulnerability is already high, they say. Limited monitoring infrastructure, sparse tide gauge coverage and a heavy reliance on marine resources leave coastal communities exposed.
The past two years have underscored this risk, with marine heatwaves disrupting fisheries and compounding food and economic insecurity.
The researchers said that Africa’s 38 coastal nations are on the frontline of ocean warming, with parts of the Indian Ocean heating faster than the global average. Without significant emissions cuts, the study warns, the continent risks exceeding 2°C of warming by the end of the century, placing more than 200 million people at risk.
By analysing high-resolution satellite data, they sought to close this gap in understanding, examining how El Niño-driven variability interacts with long-term sea level rise.
They found that regional sea levels have risen by 11.26cm since 1993 — outpacing the global average — and are accelerating at a rate of 0.14mm per year squared, faster than previously documented.
When the long-term trend of rising seas is removed to isolate the effect of natural climate cycles, the 2023–2024 El Niño produced a sea level anomaly of 27mm — the largest on record.
This dwarfs the 1997–1998 El Niño — one of the most powerful climate events of the 20th century — which produced a smaller anomaly of about 19mm.
What made this event extraordinary was not El Niño alone. Multiple climate patterns aligned simultaneously beforehand.
The Indian Ocean Dipole, the Atlantic Niño and the Tropical North Atlantic index all reached record-positive levels, preconditioning the ocean to respond with unusual intensity. This rare convergence amplified the El Niño’s impact far beyond what its strength alone would predict.
The Indian Ocean Dipole is a “see-saw” of ocean temperatures that can warm waters along East Africa. The Atlantic Niño is a similar warming event in the equatorial Atlantic, affecting West African coasts. The Tropical North Atlantic index measures unusually warm water in the tropical North Atlantic, influencing winds and currents.
Dr Franck Ghomsi, the study’s lead researcher and a postdoctoral fellow at the Nansen-Tutu Centre for Marine Environmental Research at UCT, said what is being witnessed is a fundamental shift in how the ocean responds to climate variability.
“The 2023–2024 event interacted with an ocean already preconditioned by multiple climate forces and excessive heat, creating a compound effect that pushed sea levels to heights we have never seen in the satellite record.”
Thermal expansion, or the physical swelling of water as it heats up, accounted for more than 70% of the total rise during the event.
In simple terms, the ocean was experiencing a fever. Typical wind patterns that usually bring cold, nutrient-rich water up from the deep ocean along Africa’s coasts effectively shut down.
This meant hot surface water piled up along the coastline. At the same time, the ocean became highly stratified, or layered, trapping heat near the surface and preventing it from mixing into deeper, cooler waters.
The result was a quadrupling of ocean heat content compared to previous events, creating a feedback loop that locked ever more warmth near the surface and drove sea levels higher.
The study identified a critical turning point around 2009, when sea level rise accelerated by 73%. Before 2009, levels rose at 2.72mm per year; afterwards, that rate surged to 4.70mm per year. The 2023–2024 period alone contributed 2.34cm — roughly one-fifth of all rise recorded since 1993.
The authors warn that this acceleration poses severe risks to Africa’s 38 coastal nations, where more than 15 million people in coastal cities now face heightened flood risk.
Major urban centres, including Lagos, Douala, Accra and Dar es Salaam, are increasingly vulnerable to rising waters, land subsidence and extreme weather.
For Small Island Developing States such as the Seychelles and Comoros, every millimetre of rise threatens infrastructure, freshwater supplies and habitability.
The crisis extends beneath the waves. The suppression of cold, nutrient-rich water that drives sea levels higher also disrupts marine ecosystems. Fisheries that provide food and income for millions of Africans are under increasing stress, threatening biodiversity and food security across West Africa and island communities.
“This research closes a critical knowledge gap regarding African sea levels,” Ghomsi said.
“But knowing the data is only the first step. We must use this information to drive policy, build resilient infrastructure and protect the vulnerable ecosystems and communities that define our continent’s coastline.”
The study provides an integrated perspective on how climate variability and long-term warming combine to shape coastal risk, offering insights that could strengthen early warning systems and support adaptation efforts.
Africa’s coastlines, the researchers stressed, are emerging as early warning indicators of compound climate hazards, where long-term warming and extreme events collide to amplify risk.
They call for expanded ocean monitoring, stronger early warning systems and coordinated regional adaptation strategies in the face of a rapidly changing ocean climate.
From Lagos to Dar es Salaam, major cities are increasingly vulnerable as ocean warming and climate variability combine to intensify sea level rise
