The world’s oceans absorbed colossal amounts of heat in 2025, setting yet another new record and fuelling more extreme weather, scientists have reported.

More than 90% of the heat trapped by humanity’s carbon pollution is taken up by the oceans. This makes ocean heat one of the starkest indicators of the relentless march of the climate crisis, which will only end when emissions fall to zero. Almost every year since the start of the millennium has set a new ocean heat record.

This extra heat makes the hurricanes and typhoons hitting coastal communities more intense, causes heavier downpours of rain and greater flooding, and results in longer marine heatwaves, which decimate life in the seas. The rising heat is also a major driver of sea level rise via the thermal expansion of seawater, threatening billions of people.

Reliable ocean temperature measurements stretch back to the mid-20th century, but it is likely the oceans are at their hottest for at least 1,000 years and heating faster than at any time in the past 2,000 years.