The world’s oceans have reached their highest recorded temperatures for June, surpassing previous peaks seen during the 2023–24 El Niño period.Average sea surface temperatures are now just under 21°C across tropical and temperate regions, compared with around 19.6°C before widespread industrialisation in the 19th century.

This rise reflects the vast amount of energy trapped by greenhouse gases, with more than 90% of excess heat from human emissions absorbed by the oceans.In 2025 alone, the additional ocean heat was equivalent to about 12 Hiroshima-scale nuclear explosions occurring every second throughout the year.

Scientists warn that current conditions resemble climates last seen around 120,000 years ago, although the change has occurred over just a century due to human activity.

This heat is not confined to the oceans: warmer seas fuel stronger cyclones, increased atmospheric humidity, heavier rainfall and more intense heatwaves over land.A developing El Niño in the tropical Pacific is expected to amplify these effects, with sea surface temperatures already about 1.24°C above average in large regions and subsurface waters more than 6°C warmer than normal.Regional impacts are already visible.Parts of the Mediterranean are up to 6°C above average and the North Sea up to 3°C warmer.

Europe is experiencing extreme heat, while El Niño conditions typically bring dry weather to Australia and Southeast Asia and wetter extremes to western South America.

Marine heatwaves threaten ecosystems such as coral reefs and seagrass beds, while forecasts suggest 2026 could surpass current records as ocean heat continues to surface.

Scientists emphasise the importance of sustained climate monitoring and forecasting to help manage escalating risks, alongside long-term emissions reductions to stabilise the climate system.