The Oceans Just Keep Getting Hotter

New York: Since 2018, a group of researchers has been studying how much heat the oceans are taking in. In 2025, the oceans absorbed 23 zettajoules of heat, breaking records for the eighth year in a row. This number is much higher than the 16 zettajoules from 2024.

A joule measures energy, and one zettajoule equals one sextillion joules. To help understand this, John Abraham, a scientist, said this amount of heat is like 12 Hiroshima bombs exploding in the ocean. This year’s increase shows how the oceans are the largest heat absorber on Earth.

While some heat warms the ocean’s surface, most of it goes deeper. Measurements usually only show surface temperatures, so the oceans’ true warming isn’t completely clear. Zeke Hausfather, another researcher, explained that if oceans were shallow, they would warm faster like land. But the deep currents cause slower warming on the surface.