New Delhi, Jan 9 (PTI) Heat stored in Earth's oceans broke records in 2025, with energy in the upper two kilometres increasing by an estimated 23 zettajoules -- roughly 200 times the world's electrical
energy consumption in 2023, according to a study.
Thirty three per cent of the world's ocean expanse reached the top three warmest values since modern measurements began, an international team of researchers, led by the Chinese Academy of Sciences said.
Water expands due to a rise in ocean heat, driving a sea level increase around the world. The extra heat in oceans also intensifies extreme weather by increasing heat and moisture in the atmosphere, they added.
Oceans can be expected to continue breaking records until the world reaches net zero greenhouse gas emissions, the team said.
"The ocean is the hottest on record. We're looking at creating a very different planet -- do we really want to do that?" said Kevin Trenberth, an honorary academic at New Zealand's University of Auckland and co-author of the study published in the journal Advances in Atmospheric Science.
Datasets including those maintained at the Chinese Academy of Sciences and the US' National Oceanic and Atmospheric Administration (NOAA) were analysed.
"The results show that the global ocean continued to warm in 2025, with the upper 2,000 metres OHC (ocean heat content) reaching the highest value ever observed, despite a prevailing weak La Nina state throughout the year," the authors wrote.
The world's weather and climate patterns are driven by the El Nino-Southern Oscillation (ENSO) phenomenon, of which El Nino and La Nina form the 'warm' and 'cool' cycles -- El Nino is related with an increase in temperatures and rainfall, and La Nina with opposite effects.
"The global ocean gained approximately 23 ZJ (zettajoules) of heat relative to 2024, with about 33 per cent of the global ocean area reaching the top three warmest values in their historical records," they said.
The tropical and south Atlantic, Mediterranean Sea, North Indian, and Southern oceans were among the regions that saw a record-high in heat stored in 2025.
Globally, the average sea-surface temperature was 0.12 degrees Celsius lower than that in 2024, but still was the third warmest on record, the study found. PTI KRS KRS SHS
SHS
