The impact of climate change on the oceans, and consequently on our lives, is growing ever heavier. The latest data, still provisional, from the European monitoring service Copernicus indicate that the average temperature at the ocean surface exceeded 21 degrees Celsius on Tuesday 31 March. This is nearly 0.5 degrees higher than the average for the period between 1992 and 2022.

Average surface water temperature 0.5 degrees above the 1992–2022 period

Figures from the National Oceanic and Atmospheric Administration (NOAA) appear to be in line: the US agency reports a value of 21.12 degrees Celsius, just below the all-time record set at the end of March 2024, when temperatures reached 21.16 degrees. The figure is 0.57 degrees above the 1991–2020 average.

Commenting on the data to the French daily Le Monde, Météo France oceanographer Thibault Guinaldo observed: "These figures show that we have now reached exceptionally high levels on a global scale." This is especially true in certain areas of the South Atlantic, the Gulf of Mexico and the tropical seas. In some cases, for example to the north-east of the European continent, anomalies of as much as 1.5 degrees Celsius have been recorded.

Ben Noll ✓ @BenNollWeather

𝕏

Somewhere on Earth, the ocean is always warm enough to fuel a hurricane.

This animation shows how that energy shifts around the globe throughout the year.

Red areas mark waters above 80˚F (26.5˚C), the approximate threshold needed for storms to form.

♥ 242💬 7 4 apr 2026 · Apri su X →

This means, among other things, fuel to power extreme weather events — such as those that struck Emilia-Romagna or Valencia in recent years, to cite just two examples. Likewise, the Caribbean and Pacific coasts face the threat of increasingly powerful hurricanes and typhoons, exactly as happened recently in Jamaica.

In 2026, the oceans could still be feeling the heat absorbed in previous years

Furthermore, as Mongabay recalls, "the world's oceans absorb nearly 90 per cent of the excess heat trapped by greenhouse gases in the atmosphere, making this absorption the primary mechanism driving the rise in sea surface temperature. The consequences of ocean warming extend far beyond temperature itself, not only intensifying extreme weather events but altering marine ecosystems and modifying large-scale ocean circulation".

A further factor is a kind of vicious cycle known as the thermal inertia of the oceans — namely the fact that, following prolonged heatwaves, the waters continue to feel the effects of what came before. In other words, conditions from previous seasons create a set of "preconditions" capable of influencing the near future. And bearing in mind that 2025 was the third warmest year on record for the oceans, right after the records of 2024 and 2023, it becomes clear how extreme levels could easily be reached again in the current year. Particularly high temperatures have, after all, been recorded since the start of the year.

The Mediterranean risks a tropicalisation effect

To this already alarming picture, we must unfortunately add the possible return of El Niño in the coming months — the natural phenomenon consisting of the warming of the surface temperature of the south-central and eastern Pacific Ocean. Should it return, the data could prove even more negative than expected, contributing to altering the layers of warm and cold water and affecting their mixing. For a sea like the Mediterranean, the risk is a tropicalisation effect — something we have already experienced firsthand during recent summers, most recently off the coast of Egypt.