©Unsplash
The oceans absorb almost all the heat generated by human activity. In 2025, this silent role has reached a new tipping point.
According to a scientific study published in Advances in Atmospheric Sciences, in 2025, the planet's oceans accumulated more heat than in any other year ever measured.
The most reliable thermometer of the climate crisis
Unlike air temperature, which is subject to fluctuations linked to climatic phenomena such as El Niño and La Niña, the heat accumulated in the oceans tells the underlying story of the climate system. The measurements, based on data collected by buoys, satellites and oceanographic instruments, focus on the top 2,000 meters of water, where most of the excess energy is absorbed.
"Every year the planet warms: setting new records has become a new record," John Abraham, a climatologist at the University of St Thomas and co-author of the study, told the Guardian newspaper. "Global warming is ocean warming. If you want to know how much the Earth has already warmed, the answer lies in the oceans."
More heat, more disasters
In detail, the study quantifies the increase in heat accumulated by the oceans in 2025 at almost 23 zettajoules compared with the previous year. To illustrate this order of magnitude, the researchers explain that the heat absorbed annually by the oceans is more than 200 times greater than the electricity consumed worldwide by mankind.
The analysis also shows that the rate of ocean warming has accelerated considerably over the past two decades: Today, the oceans are warming more than twice as much as the average during the second half of the 20th century, a sign of a persistent energy imbalance that is not being corrected. This is a sign of a persistent energy imbalance that remains uncompensated even during "cooler" climatic phases, such as the recent transition of the La Niña climate cycle.
This excess energy does not remain confined to the subsurface. On the contrary, it fuels increasingly violent meteorological phenomena. Hurricanes and typhoons are becoming more intense, rainfall more extreme and flooding more frequent. Ocean heat also contributes to sea-level rise, thanks to the thermal expansion of water, endangering billions of people living in coastal areas.
Another direct effect is the increase and prolongation of marine heat waves, which wreak havoc on marine ecosystems (...) with consequences for fishing and food security.
From Antarctica to the Mediterranean
Ocean warming is uneven. By 2025, the areas most affected include the tropical and southern Atlantic, the North Pacific and the Southern Ocean. Basins closer to Europe are also undergoing rapid change. The North Atlantic and Mediterranean are not only warmer, but also saltier, more acidic and less oxygenated. According to the researchers, this is a profound transformation in the state of the ocean, making the ecosystems and human activities that depend on it increasingly vulnerable.
Analyses indicate that the oceans could be at their warmest temperature for at least a thousand years, with an unprecedented rate of warming over the last two thousand years.
The unknown, concludes John Abraham, is not scientific but human: it all depends on how quickly we can reduce the emissions that make the sea the planet's largest and most dangerous heat reservoir.
Source: Advances in Atmospheric Sciences
(©GreenMe.it 2026/Managing editor: Julie Morgan - The Press Junction/Pic: Unsplash)