by Edison Barbieri, Luca Fiorani https://www.cittanuova.it/loceano-non-dimentica-nove-anni-di-record-di-calore/
A major new scientific analysis shows that the world’s oceans reached the highest level of accumulated heat in recorded history in 2025, marking the ninth consecutive year of record-breaking ocean warmth — a trend that underscores the growing intensity of the climate crisis and its far-reaching consequences.
Scientists from more than 70 research institutions worldwide contributed to this assessment, published in the journal Advances in Atmospheric Sciences. The study synthesised data from multiple global observation systems, producing a comprehensive picture of how the oceans continue to absorb heat at unprecedented rates.
The upper 2,000 metres of the ocean — which act as the primary reservoir for excess heat in the Earth system — stored an estimated 23 zettajoules of additional energy in 2025 compared with the previous year. To put this in perspective, that is an extraordinary amount of energy — one zettajoule is enough to boil nearly 30 billion Olympic-sized swimming pools.
Scientists emphasise that ocean heat content is one of the most reliable indicators of long-term climate change, because water absorbs and retains heat far more effectively than the atmosphere. In fact, more than 90% of the excess heat trapped by greenhouse gases ends up in the oceans, making them the climate system’s main heat sink.
Compared with past decades, the rate at which the ocean absorbs heat has accelerated sharply. Between the late 1950s and the early 1980s, the increase in ocean heat content averaged less than 3 zettajoules per year. In recent years, that rate has climbed to 11–13 zettajoules annually, meaning the oceans are warming more than three times faster than they did just a few decades ago.
This growing heat reservoir has real and urgent consequences:
Extreme weather events. Warmer oceans fuel greater evaporation and carry more moisture into the atmosphere, intensifying rainfall and flooding, as well as strengthening storms and tropical cyclones.
Rising sea levels. As seawater warms, it expands — a process that contributes significantly to global sea-level rise and places coastal communities at increasing risk.
Ecosystem disruption. Certain regions, such as the North Atlantic and the Mediterranean, are experiencing additional stresses like higher salinity, oxygen loss, and acidification, all of which can undermine marine life and biodiversity.
Interestingly, while the deep ocean hit a new heat record, surface sea temperatures in 2025 were slightly lower than in 2024 due to the transient influence of La Niña, a climate pattern that can temporarily cool ocean surfaces. However, this surface “dip” does not change the long-term trend of ocean warming; it merely masks deeper heat accumulation.
Scientists are clear: these ongoing ocean heat records will continue as long as net greenhouse gas emissions remain high. The study calls for expanded global observation systems to better monitor ocean conditions and inform climate policy.
Photo di Roxanne Desgagnés su Unsplash