New study shows unprecedented energy stored in seas in 2025

A comprehensive study published in the journal Advances in Atmospheric Science has revealed that the world’s oceans absorbed an astounding 23 zettajoules of additional heat in 2025, equivalent to roughly 23 sextillion joules. Scientists say that is comparable to detonating 12 Hiroshima‑sized atomic bombs each day for a year or boiling two billion Olympic swimming pools. The research, involving more than fifty scientists and reported on January 9 by Wired, marks the eighth consecutive year that ocean heat content has set a record. Oceans absorb more than 90% of the excess heat trapped by greenhouse gases, making them crucial buffers for the planet’s climate.

The team used ship‑based measurements, satellite data, temperature models and the Argo float network—a fleet of more than 3,500 robotic buoys that dive to depths of 2,000 metres—to estimate how much heat was sequestered. Although 2024 saw a strong El Niño that briefly elevated surface temperatures, 2025’s La Niña conditions meant surface waters were cooler than average. Even so, heat continued to accumulate deeper in the ocean at an unprecedented rate. Zeke Hausfather, a climate scientist at Berkeley Earth and co‑author of the study, noted that deep‑water warming is a more reliable indicator of long‑term climate trends than surface temperatures because it reflects the total energy imbalance in the Earth system.

Heat hides deep, but consequences ripple outward

Understanding ocean heat content is critical because it drives a host of extreme weather events and long‑term environmental changes. Warm water fuels hurricanes, typhoons and marine heat waves; it also causes seawater to expand, contributing to sea‑level rise. John Abraham, a thermal sciences professor involved in the research, said the record heat means that storms can draw on more energy, making them larger and more destructive. Prolonged warming also stresses marine ecosystems such as coral reefs, which are already suffering from bleaching events and biodiversity loss.

The study’s authors warn that the rapid accumulation of heat underscores the urgency of reducing greenhouse‑gas emissions. While individuals can make small changes to their carbon footprints, the researchers argue that systemic shifts in energy production, transportation and land use are needed to slow warming. Policies aimed at phasing out fossil fuels, protecting forests and investing in renewable energy could help limit the energy entering the oceans. Failure to act risks pushing marine systems beyond their capacity to adapt, with consequences for fisheries, weather stability and the millions of people living in coastal communities.

Policymakers will find the study’s conclusions sobering. 2025 was already the hottest year on record for global surface temperatures, and the unprecedented heat stored in the oceans suggests that upcoming years may bring even more extreme conditions. The ocean functions like a giant heat battery, delaying the full effect of greenhouse warming on land but guaranteeing that extra energy will return to the atmosphere eventually. Scientists call for increased investment in monitoring equipment and climate models to improve predictions of how ocean heat will influence hurricanes, precipitation patterns and droughts. More accurate forecasts could give communities time to prepare for hazards and adapt infrastructure.

Public awareness of the ocean’s role in climate change remains limited, even though marine warming affects everything from seafood supplies to coastal property values. Some experts worry that people may become complacent because surface temperatures fluctuate, masking the true extent of heat sequestered below. By highlighting the enormous energy being absorbed, the study aims to energise climate conversations and galvanise support for ambitious emissions cuts. As Hausfather puts it, ocean heat content is “the most reliable thermometer we have for the planet,” and it is telling us that time is running out to avert the worst impacts of global warming.