For over three decades, satellites orbiting Earth have measured the height of the ocean surface with remarkable precision. These measurements are crucial because changes in ocean height are one of the clearest indicators of how our planet is responding to climate change. Rising ocean surfaces signal warming temperatures, melting ice and shifting ocean currents.
These all directly affect coastal communities through flooding, erosion and habitat loss. Even a small rise in the baseline sea level means that normal tidal cycles and storm surges reach further inland. This can turn high tides into damaging flood events.
Many people assume ocean levels are uniform, like water sitting flat in a bathtub. In reality, the ocean surface is surprisingly uneven. Winds push water in certain directions. Ocean currents redistribute heat. Temperature differences cause water to expand or contract. Even variations in Earth’s gravity field create bumps and dips in the sea surface. All these factors combine so that sea level can vary by tens of centimetres from one region to another.
When we say sea level has risen, we’re comparing it to a stable reference level, the distance between the satellite and the ocean surface.
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I’m an oceanographer and geophysicist who specialises in these measurements. My research team and I analysed ocean height measurements collected by radar instruments on orbiting satellites from 1993 to 2024, for all waters surrounding Africa.
Our analysis revealed that African seas have risen by approximately 11.26cm since 1993. This process is driven by warming waters and melting ice.
African sea levels are rising by approximately 3.54 millimetres each year, which exceeds the global average of 3.45 mm/yr. Perhaps more troubling is that the pace of rise is speeding up, especially in African waters. This acceleration is a long-term trend driven by ongoing ocean warming and ice sheet melting, and it persists regardless of whether any individual year features an El Niño or a La Niña. The ocean continues to absorb heat and receive meltwater from ice sheets year after year, and it is this relentless accumulation, not any single climate cycle, that drives the long-term acceleration.
Africa’s 38 coastal nations are home to over 200 million people living near the shore. Rising seas threaten these communities with flooding, coastal erosion, and saltwater contamination of drinking water and farmland. Rising and warming seas also disrupt fisheries that millions of Africans depend upon for food and livelihoods.
Dramatic changes
We analysed 32 years of records and isolated the long-term trends from short-term influences like the El Niño weather pattern. We also examined ocean temperature and salinity data from the surface down to 300 metres depth to determine how much of the sea level change was caused by the ocean warming and expanding versus gaining additional water mass.
Our study revealed something remarkable about the 2023 to 2024 period. The El Niño event, which every so often spreads warm water across parts of the Pacific Ocean and alters weather patterns around the world, combined with other climate phenomena. Together, they created the largest sea level spike ever recorded in African waters, reaching an anomaly of 27mm.
The most dramatic changes are occurring in specific regions. The ocean does not respond to warming and climate variability uniformly. Local factors, including the strength and direction of ocean currents, the depth of warm surface layers, the influence of nearby climate patterns like the Indian Ocean Dipole, and the shape of the coastline and seafloor, all combine to make certain areas far more sensitive to change than others.
The Western Indian Ocean, including waters around Mozambique, Madagascar and the Comoros Islands, shows the highest acceleration of sea level rise at 0.16 mm/yr² with a trend of 3.88 mm/yr.
The Eastern Central Atlantic, encompassing the Gulf of Guinea and waters off west African nations like Senegal, Ghana, Nigeria and Cameroon, follows closely at 3.90 mm/yr. These regions are experiencing both the fastest rise and the sharpest acceleration, making them priority areas for monitoring and adaptation.
Impact of El Niño
The western Indian Ocean and the tropical Atlantic were already abnormally warm in 2023-2024, with sea surface temperatures well above their long-term averages. This created a higher baseline from which El Niño could push up temperatures, and therefore sea levels.
Unusual wind patterns suppressed the normal process of upwelling. This is when winds push surface water aside, allowing colder, nutrient-rich water from the deep ocean to rise to the surface. The result was that heat was trapped at the surface instead of being mixed downward and replaced by cooler water. The ocean layers did not mix well.
The result was striking. Thermal expansion alone (warmer water) accounted for over 70% of the exceptional sea level rise during this event, reaching nearly 30mm across the African marine domain. Ocean heat content quadrupled compared to the 2015-2016 El Niño.
The 2023-2024 period contributed 2.34cm of rise, representing 19% of the total increase since 1993 in just two years.
Because sea levels have been steadily climbing for decades, the starting point before each new extreme event is already higher than it used to be. The Western Indian Ocean surged by 3.87cm in one year alone – nearly one third of its total rise since 1993.
What drives rising sea levels
Two main factors drive sea level rise globally. First, as ocean water warms, it expands. Second, melting glaciers and ice sheets in Greenland and Antarctica add water mass to the oceans. Both are consequences of human caused climate change.
This rise is not a natural cycle. While sea levels have fluctuated throughout Earth’s history, the current rate of rise is far faster than anything seen in thousands of years, driven by the burning of fossil fuels and the resulting buildup of greenhouse gases in the atmosphere.
The human cost of rising seas
Major cities face mounting dangers. Lagos, with over 20 million residents, sits on low lying land increasingly vulnerable to flooding. Dar es Salaam in Tanzania faces similar risks. Small island developing states like the Comoros and Seychelles are particularly exposed.
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The “normal” water level today is centimetres higher than it was 30 years ago. Each new event builds on an ocean that is already swollen from decades of warming.
And when upwelling doesn’t happen, fish populations decline and the communities that depend on them lose food and income.
What needs to happen next
Addressing this crisis requires action on multiple fronts. Most fundamentally, global carbon emissions must be drastically reduced to slow ocean warming. Without achieving carbon neutrality by mid century, Africa risks exceeding 2°C of warming by 2100.
Adaptation is equally urgent. African nations need expanded ocean monitoring networks to track changes and provide early warnings. Coasts need protection through sea walls, restored mangroves and improved drainage.
The West Africa Coastal Areas Management Program, a World Bank supported regional effort, is a promising model. It aims to help countries manage erosion, flooding and pollution through investments in infrastructure, nature based solutions, and policy coordination.
Protecting Africa’s coasts requires combining oceanographic science with community level planning to build resilience against an uncertain ocean future.
Franck Ghomsi, Postdoctoral Fellow, Nansen Tutu Centre, University of Cape Town