The world’s oceans are the hottest on record for June—and El Niño is set to turn up the heat even more

The world’s oceans are the hottest on record for June, pushing past records set during the 2023–24 El Niño years.

Right now, the average sea surface temperature is just under 21°C across the world’s tropical and temperate oceans. Before widespread industrialization in 1870, the temperature was about 19.6°C.

That may not sound like a big difference. But heating the world’s oceans this much requires a truly enormous amount of energy. Of all the extra heat trapped by greenhouse gases from burning coal, gas and oil, more than 90% has gone into the world’s oceans.

As a result, the oceans are getting rapidly warmer. In 2025, the heat added was the equivalent of about 12 Hiroshima-scale nuclear bombs exploding every second of every day.

To find a climate analog comparable to what’s happening now in the oceans, we would have to go back around 120,000 years to before the last ice age. Back then, slow shifts in Earth’s orbit led it to heat up gradually over thousands of years. Humans have accomplished a similar result in a little over a century.

But the heat in the ocean doesn’t just stay there. Hotter oceans fuel stronger cyclones, a more humid atmosphere, more intense rainfall and more heat in air masses over the seas, which can in turn make heat waves over land more likely and more intense.

The El Niño forming in the tropical Pacific right now is likely to be a big one. As it develops, we can expect to see warmer temperatures and extreme events such as marine heat waves in the western Indian, tropical Atlantic and eastern Pacific oceans.

Where are the hotspots on land and in the ocean?

Europe is sweltering through a record-breaking heat wave. The oceans surrounding the region and in enclosed seas are also exceptionally hot.

Parts of the Mediterranean are up to 6°C hotter than the long-term average.

Parts of the North Sea are up to 3°C warmer than average.

The forming El Niño has led to sea surface temperatures about 1.24°C warmer than average across a large area of the central eastern Pacific.

There’s much more heat below the surface as well. Subsurface conditions in the eastern Pacific are more than 6°C above average.

A typical El Niño lasts about a year. The full effect on atmospheric heat becomes clearest toward the end of the cycle. That means while we can expect 2026 to be very hot—perhaps a new record—next year is very likely to be even hotter, as ocean heat is moved back to the surface. We saw this during El Niño events over 2023–24 and 2015–16.

Steady ocean warming coupled with longer-lasting and more intense marine heat waves poses huge threats to marine ecosystems such as coral reefs, seagrass meadows and coastal reefs. Research on the 2023–24 El Niño and the warm 2024 year showed widespread impacts.

From oceans to land

What happens in the oceans doesn’t stay there.

In June 2023, a record-breaking marine heat wave broke previous temperature records across the North Atlantic Ocean. Soon afterward, large areas of Europe were hit by intense heat waves, while extreme rains triggered deadly floods in Spain and severe wildfires broke out around the Mediterranean.

Rising ocean temperatures have many consequences.

A warmer ocean is less able to cool the land over summer. Warmer oceans also lead to more evaporation, boosting humidity and fueling more intense and more sudden extreme rain and floods. These can have devastating consequences.

During El Niño events, there’s a clear geographical pattern. The regions we expect to be warmer or cooler during an El Niño roughly reflect where we are more or less likely to get marine heat waves and more intense tropical cyclones.

Typical cyclone areas such as the western Indian Ocean could see stronger cyclones dumping heavier rainfall when they hit land. El Niño tends to bring extreme rain and floods to western South America and dry conditions over parts of Australia and Southeast Asia.

Can we prepare?

We are gaining a better understanding of how big climate drivers like El Niño shape weather and how to use ocean data from around the world to develop better seasonal forecasts authorities can use to prepare.

Over the past two years, we have improved our ability to forecast marine heat waves three to four months ahead in Australia, the United States and other regions. Forecasts give marine authorities a chance to act early by reducing allowable fishery catches and beginning conservation efforts for vulnerable species.

This early success in ocean forecasting may be short-lived. The current U.S. administration last year slashed funding for climate data-gathering networks and has worked to dismantle the National Center for Atmospheric Research.

This year, the administration announced it would end funding for a key ocean monitoring network before backing down.

Ongoing collection of ocean data is crucial for ocean and land forecasts. If they are weakened or discontinued, we could face the challenge of dealing with worsening climate impacts blind.

Ending the measuring of climate change won’t stop it from happening. The only way to keep climate change from steadily worsening is to reach net zero as soon as humanly possible. Until then, we must use forecasts to prepare for what we can’t avoid.

Who’s behind this story?

Gaby Clark

MA in English, copy editor since 2021 with experience in higher education and health content. Dedicated to trustworthy science news.

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Andrew Zinin

Master’s in physics with research experience. Long-time science news enthusiast. Plays key role in Science X’s editorial success.

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This article is republished from The Conversation under a Creative Commons license. Read the original article.