The study, published Dec. 15 in the journal Communications Earth & Environment, found that sea levels across the continent have risen four times faster since 2010, on average, than they had in the 1990s. The primary reason was additional water mass from polar melt, rather than other phenomena that can cause sea-level rise, the authors found.
The impacts include flooding, erosion of coastal land, displacement of coastal communities and intrusion of salty seawater into freshwater drinking sources.
People in Africa are responsible for only a tiny proportion of human-caused global warming and yet face severe effects from the resulting sea-level rise, said Ghomsi, who is from Cameroon, calling this a “climate injustice.”
He said that emissions from countries in the Global North are having a “huge impact” on countries in the Global South, including in Africa.
The current era of measuring sea-level rise began in the early 1990s with advancements in satellite altimetry, in which radar or laser pulses are bounced off the ocean’s surface. With knowledge of the satellite’s position and the time it takes for the signal to travel back, scientists can estimate sea levels.
This is one of the first studies to look at the sea-level situation for Africa as a whole, covering the oceans that surround the continent. Ghomsi and his co-authors primarily used altimetry data, as local field data are lacking. For example, there are very few long-standing, well-calibrated tide gauges located on the continent, he said. Tide gauges measure water level against a benchmark.
The authors found that the mean sea level in Africa rose by roughly 10.2 cm (4 inches) from 1993-2023, the study period. That figure is comparable to the global one, yet the trends in Africa are particularly alarming, they found. After a moderate uptick in the early 2000s, a notable acceleration occurred around 2010, with the vast majority of the sea-level rise in the study period occurring after that year.
The continent’s waters reached their highest-to-date mean sea level in 2023 following a major rise related to an El Niño ocean warming event. The event continued into 2024 and the prior year’s was eclipsed, according to a narrower study led by Ghomsi that was published Jan. 19.
El Niño warming events arise every few years as part of a cycle that starts in the Pacific Ocean and drives weather patterns around the world.
Spikes during El Niño years are nothing new, but the underlying conditions have changed. For example, there was a spike in 1997-98 that was “dramatic but temporary, sitting on top of a very weak underlying trend”.
The 2013 to 2023 decade shows 4.34 mm [millimeters of sea-level rise, or 0.2 inches] per year. That is not a spike that goes away. That is the new baseline.”
A Guest Editorial