Mysterious ‘warm blob’ breaks records in the North Pacific Ocean

North Pacific waters have had their hottest summer on record, according to BBC analysis of a mysterious marine heatwave that has baffled climate scientists.

Sea surface temperatures between July and September were 0.25C above the previous high of 2022; This is a huge increase in an area roughly ten times the size of the Mediterranean.

Although climate change is known to increase marine heat waves, scientists are trying to explain why the North Pacific has been so hot for so long.

But some researchers believe all that extra warmth in the so-called “warm drop” could have the opposite effect in the UK, possibly leading to a colder start to winter.

“There is definitely something unusual going on in the North Pacific,” said Zeke Hausfather, a climate scientist at Berkeley Earth, a research group in the US.

He added that such a jump in temperature in such a large region was “quite remarkable.”

BBC analyzed the data European Copernicus climate service To calculate average temperatures between July and September in a large region of the North Pacific sometimes known as the “warm drop.”

The region extends from the east coast of Asia to the west coast of North America, the same region used previously. scientific studies.

The figures show that not only has the region warmed rapidly in the last few decades, but the year 2025 is also significantly higher than in recent years.

It’s no surprise that the seas are warming. Global warming from humanity’s emissions of carbon dioxide and other gases has already tripled the number of days of extreme heat in the oceans globally. research published earlier this year.

But temperatures have been even higher than most climate models (computer simulations that take humanity’s carbon emissions into account) predict.

Analysis of these models Berkeley World group It suggests that the sea temperatures observed in the North Pacific in August have less than a 1% chance of occurring in any given year.

Natural weather variability is also thought to be part of the reason. For example, this summer saw weaker than normal winds. This means more of the heat from the summer sun can remain at the sea surface rather than mixing with the colder waters below.

But according to Dr Hausfather, this can only go so far in explaining exceptional circumstances.

“This is definitely not just natural variability,” he said. “There’s something else going on here.”

An interesting idea is that a recent change in transportation fuels may be contributing to warming. Before 2020, dirty motor oil produced large amounts of sulfur dioxide, a gas harmful to human health.

But this sulfur also created tiny, Sun-reflecting particles in the atmosphere, known as aerosols, that helped control rising temperatures.

Therefore, eliminating the cooling effect in shipping hotspots such as the North Pacific could reveal the full impact of human-caused warming.

“Sulfur appears to be the leading candidate for causing warming in the region,” Dr Hausfather said.

Other research suggests Efforts to reduce air pollution in Chinese cities are also playing a role in warming the Pacific, he said.

While this polluted air does a job similar to transportation by reflecting sunlight, cleaning it up could have unintended consequences, such as further warming of the ocean.

The marine heatwave in the North Pacific has already had consequences for weather conditions on both sides of the Pacific; probably increased very high summer temperatures in Japan and South Korea and storms in the United States.

“We saw extreme storms in California because warm ocean waters in the Pacific provide heat and moisture,” said Amanda Maycock, professor of climate dynamics at the University of Leeds.

“In particular, there are what we call atmospheric rivers… air bands that contain very high amounts of moisture that feed into them from ocean waters,” he added.

“So if we have warm ocean waters … then they can bring a lot of moisture onto land, which then falls as rain or can precipitate as snow in the winter.”

Long-term weather forecasts are always difficult, but extreme temperatures in the North Pacific have the potential to affect the UK and Europe in the coming months.

This is due to relationships between weather in different parts of the world, known as teleconnections.

“Although the current warm conditions are located in the northern Pacific Ocean, they can create wave movements in the atmosphere that could change weather patterns towards the North Atlantic and Europe,” Prof Maycock said.

“This may favor high pressure conditions over the continent, which brings us more influence from the Arctic where we have colder air,” he added.

“This could spread across Europe and bring us colder weather in early winter.”

Since this is a complex area of ​​science, a cooler outcome is by no means certain. Many other weather patterns also influence UK winters, which are generally becoming milder with climate change.

Warm weather in the North Pacific appears to have different effects later in the winter, favoring milder and wetter conditions in some parts of Europe.

Another factor to bring into the mix is ​​what’s happening further south in the eastern tropical Pacific.

Surface waters there are unusually cold; This is a classic sign of a weather event. La Niña.

La Niña and its warmer sister, El Niño, are natural patterns. research published this week He underlined that global warming may affect the fluctuations between them.

Weak La Niña conditions are expected to continue for the next few months, according to the US science agency NOAA.

All else being equal, La Niña generally increases the risk of a cold start to winter in the UK, but also increases the chances of a mild ending. Met Office says.

“These two drivers in the north and tropical Pacific will move together this winter,” Prof Maycock said.

“But since La Niña is quite weak this year, extreme warmth in the northern Pacific may be more important in predicting next winter.”

Additional reporting by Muskeen Liddar and Libby Rogers