The Mediterranean is a sea as deeply wounded as it is paradisiacal — a Caribbean lapping the shores of Europe and Africa. Yet this seemingly idyllic image turns into a postcard of tragedy as unprecedented storms and marine heatwaves bring death to the coasts and seabeds of the Mare Nostrum. The temperature of its waters signals a fever. The Ocean Summit in Nice is being held overlooking waters as overheated as the geopolitical polarization surrounding their preservation.
In addition to being one of the most polluted seas in the world (albeit unevenly), it is also the fastest-warming sea on the planet. Just at the start of this summer, temperatures are already 2°C above what would be considered normal. “We’ve pumped in the energy equivalent of thousands of atomic bombs, and now we’re seeing it in the [weather] extremes of recent years,” explains physicist and climate data analyst Dominic Royé (MBG-CSIC). “It may come back at us.” A preview of what’s in store for other regions?
For now, the impact on human health is already measurable: tropical nights (with lows above 20°C) and torrid nights (above 25°C) are surging. “They’re becoming more frequent in coastal areas due to the overheated sea.” The Mediterranean is losing its ability to cool down overnight. “This affects health: loss of sleep, higher mortality risk, and reduced wellbeing,” notes Royé, who has worked on studies linking temperature and public health.
Unrelenting Heat for 20 Years: Fuel for What’s to Come
So far, the extreme temperatures recorded in Mediterranean waters have already fueled (though not solely caused) one of Europe’s worst weather disasters: the deadly flash flood in Valencia in October 2024. An event in a region familiar with floods — but this was its first true flash flood, a term that made headlines after the unprecedented downpours in Central Europe in 2021.
Heat is also catastrophic for biodiversity. A hot sea doesn’t just kill what lives in it — it threatens those who live near it. Unfortunately, that’s starting to feel close to home. Some countries are years ahead in preparation.
“The ocean — and its seas — regulate Earth’s climate. I always say that without the oceans, there would be no climate,” says Anna Cabré (University of Pennsylvania), drawing from her dual expertise in oceanography and cosmology. “The Mediterranean has it all,” she adds. A nearly enclosed sea under intense human pressure, yet showing a temperature rise that reflects a global trend.
The Mediterranean Coral Reef Succumbs to Heat and Pollution
Diego Kersting (IATS-CSIC) has spent years diving among Mediterranean coral. “It’s heartbreaking for me to see this now.” He has observed how coral reefs near the Columbretes Islands, off the coast of Castelló, have experienced alarming die-offs after marine heatwaves. They are also suffering from plastic and microplastic pollution.
“A coral that takes 200 years to grow can die in a single hot summer… and recovery is nearly impossible
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For him — and many other experts — the Mediterranean is, with all due caution, “a natural laboratory for studying the impacts of climate change on marine ecosystems.” And he offers a warning ahead of this UNOC3 summit. In his experience, protection alone is sometimes not enough. The Columbretes are a marine reserve, “yet we see degradation even in protected areas: it’s worrying and disheartening.” The corals he grew up with are suffering.
This reef is also a hotspot for microplastic pollution — up to 6,000 particles per kilo of sediment. “It’s outrageous.” Heat makes the situation even worse. According to Joaquim Rovira, a chemical researcher at Rovira i Virgili University and an expert on some of the most microplastic-polluted beaches, “Mediterranean currents are altered by heat: they carry pollutants from Barcelona to Tarragona,” for example.
Cabré believes the Mediterranean has particularities that make it hard to generalize from, but still: “It’s a warning to the world — it shows how dense coastal populations worsen the impacts.” The global trend of living near the coast comes with risks when facing seas that are neglected, overheated, and rising.
- The Solutions? For Cabré, there’s a clear one: “Minimize carbon dioxide emissions.” It’s a global problem, even if its effects vary locally. She’s skeptical about the idea that the sea can save us by absorbing CO₂, since “its capacity is what it is — and that won’t change.”
For Dominic Royé, adaptation is crucial. The massive coastal population around the Mediterranean calls for cities that are livable and “mitigate the urban heat island effect,” capable of withstanding more extreme weather (including early warning systems), exacerbated by a warming sea.
