The world's oceans, a new record for warming

The global ocean absorbed more heat in 2025 than in any other year since modern measurements began in 1960, according to a new analysis published in the scientific journal Advances in Atmospheric Science, cited by Live Science. The data confirms an alarming trend: for the ninth consecutive year, the heat content of the oceans reached a record level. The world's oceans play a key role in regulating the climate, absorbing more than 90% of the excess heat generated by global warming. That is why their warming is considered by climatologists one of the most reliable indicators of long-term climate change. As the atmosphere warms, much of the additional thermal energy is transferred to the oceans. This accumulation of heat directly influences atmospheric circulation, global precipitation patterns, and the frequency of marine heat waves, phenomena with major impacts on ecosystems and human societies. Ocean temperatures also affect the intensity of tropical storms and the stability of regional climates, which is why scientists are closely monitoring the evolution of these parameters.

• Two ways to measure a warming ocean

Researchers use several methods to assess ocean warming. One of the best-known is the global annual average sea surface temperature, which reflects the temperature of the top few meters of water. In 2025, this temperature was the third highest ever recorded, about 0.5°C above the 1981-2010 average, according to data cited by Live Science. Another metric, considered even more relevant for assessing climate change, is the ocean heat content, which measures the total thermal energy stored in water masses globally. This is expressed in zettajoules, a unit equivalent to one sextillion joules. To calculate the heat content of the oceans in 2025, the study authors analyzed observational data down to a depth of 2,000 meters, the level at which most heat is absorbed. The information comes from several international institutions, including the US National Oceanic and Atmospheric Administration (NOAA), the European Union's Copernicus Climate Change Service and the Chinese Academy of Sciences. The conclusion is unequivocal: in 2025, the oceans absorbed an additional 23 zettajoules of thermal energy, breaking the previous record and marking the longest series of consecutive years with maximum values in the history of observations. "Last year was a crazy warming year, a real crazy one," said John Abraham, a researcher at the University of St. Thomas in Minnesota and co-author of the study. To illustrate the magnitude of this energy surplus, scientists point out that 23 zettajoules per year is equivalent to the energy of 12 Hiroshima-sized atomic bombs exploding in the ocean every second.

• Ocean regions under extreme pressure

The increase in 2025 represents a significant jump from the previous year, when the oceans absorbed about 16 zettajoules of thermal energy. The hottest regions identified last year were the tropical and southern Atlantic, the Mediterranean Sea, the North Indian Ocean, and the Southern Ocean. According to the authors, this data provides "direct evidence that the climate system is in thermal imbalance and continues to accumulate heat.”

• Direct consequences: more violent storms and extreme rainfall

A warmer ocean favors the intensification of the hydrological cycle, leading to more abundant global precipitation and stronger tropical storms. In the past year, rising ocean temperatures have likely contributed to the amplification of extreme weather events, such as Hurricane Melissa in Jamaica and Cuba, severe monsoon rains in Pakistan, and flooding in the Central Mississippi Valley, Live Science notes.