Ocean Temperatures Reach Record Highs as El Niño Adds to Climate Pressure

The world’s oceans are hotter than ever recorded, according to new data. Scientists say human-caused climate change and the growing El Niño weather phenomenon are driving temperatures higher.

Average sea surface temperatures outside the polar regions reached 21.1C (70F) on Saturday, according to figures from the European Copernicus Climate Change Service.

That is slightly above the previous record of 21.09C, recorded in March 2024. It is also far above the average temperature for this time of year.

Oceans reach record temperatures

The latest figures are particularly concerning because global ocean temperatures usually reach their annual peak in March or April.

This happens at the end of summer in the southern hemisphere. August is therefore an unusual time for global ocean temperatures to reach a record high.

The southern hemisphere contains more ocean than the northern hemisphere. As a result, it has a greater influence on global average sea temperatures.

The Copernicus data is based on temperatures measured 10m (32ft 10in) below the surface. Measurements from buoys, ships and satellites are combined to produce a global estimate.

The margin above the previous record is currently very small. Scientists also warn that all global temperature estimates contain some uncertainty.

However, the timing of the record is raising concern.

“This record is another clear signal of an ocean under growing stress,” said Dr Samantha Burgess, deputy director of Copernicus.

“El Niño is adding heat to the system, but it is doing so on top of decades of human-driven warming,” she added.

El Niño is adding more heat

Scientists are particularly concerned because ocean temperatures are already extremely high while El Niño is still some way from its expected peak.

El Niño is a natural climate phenomenon that brings unusually warm water to the surface of the eastern and central tropical Pacific Ocean.

When warmer water covers such a large area, global average temperatures typically increase as well.

El Niño is expected to continue strengthening until around Christmas. Scientists have warned that the current event could become one of the strongest in centuries.

That could push ocean temperatures even higher.

“The fact that we are already breaking records is an early indicator of how strong the El Niño is becoming,” said Dr Jeremy Grist, senior research fellow at the National Oceanography Centre in Southampton.

“All things being equal we might expect the ocean temperature record to be broken again in March [or] April 2027,” he added.

UK and European seas are also unusually warm

The extreme ocean temperatures are not limited to the Pacific.

Waters around the UK and Europe are also exceptionally warm, despite being far from the main area affected by El Niño.

The western English Channel has experienced almost continuous marine heatwave conditions for more than three years. Temperatures peaked at 7C above normal in July, according to Prof Tim Smyth, director of science at Plymouth Marine Laboratory.

“This is unprecedented,” he added.

Scientists say the widespread nature of the warming is an important warning sign.

It shows how human-caused climate change is increasingly affecting oceans around the world.

Why are warmer oceans a problem?

The world’s oceans absorb more than 90% of the excess heat trapped by greenhouse gas emissions from human activities. Most of these emissions come from burning fossil fuels.

As the oceans warm, the consequences can extend far beyond the marine environment.

“The latest Copernicus data reinforce the troubling upward trend in ocean temperatures,” said Smyth.

Warmer seas can help fuel more extreme weather. They provide storms with additional moisture and energy, potentially making them stronger.

In some coastal areas, warmer seas can also intensify heatwaves on land by reducing the cooling effect of sea breezes.

Rising seas and greater coastal flood risk

Ocean warming also contributes to rising sea levels.

Warmer water expands as it heats up. This process, known as thermal expansion, increases the volume of seawater and contributes to global sea-level rise.

Higher sea levels increase the risk of coastal flooding, particularly during storms and extreme weather events.

This puts coastal communities, habitats and infrastructure under greater pressure.

Marine life faces growing pressure

Extreme ocean heat can also have serious consequences for marine ecosystems.

Coral reefs are particularly vulnerable to prolonged periods of unusually warm water. Marine heatwaves can disrupt habitats and put additional stress on wildlife.

The effects can also spread through marine food webs, affecting species that depend on particular temperatures and habitats.

The increasing frequency of marine heatwaves is already “putting increasing pressure on marine ecosystems and the communities that depend on them”, Burgess said.

Climate change and El Niño are creating a dangerous combination

The current record highlights the interaction between natural climate patterns and long-term human-caused warming.

El Niño can temporarily push global temperatures higher. However, it is occurring against a backdrop of decades of rising ocean temperatures caused by climate change.

With El Niño expected to strengthen further, scientists will be watching ocean temperatures closely over the coming months.

The latest record is therefore more than a single temperature measurement. It is another warning that the world’s oceans are under increasing pressure from a warming climate.

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