Mysterious ‘hot blob’ breaks records in North Pacific Ocean

North Pacific waters have experienced 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 more than 0.25°C higher than the previous 2022 record, a sharp increase over an area roughly ten times the size of the Mediterranean.

While climate change is known to make marine heatwaves more likely, scientists have struggled to explain why the North Pacific has been so warm for so long.

But all that extra heat in the so-called ‘warm blob’ could have the opposite effect in the UK, perhaps making a colder start to winter more likely, some researchers believe.

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

Such a rise in temperatures across such a large region is “quite remarkable,” he added.

The BBC analyzed data from the European climate service Copernicus to calculate average temperatures between July and September over a large area of ​​the North Pacific, sometimes known as the “hot blob”.

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

The figures show that not only has the region warmed rapidly over the past two decades, but by 2025 it will also be significantly warmer than in recent years.

That the seas are warming is no surprise. Global warming, caused by human emissions of carbon dioxide and other gases, has already tripled the number of days of extreme heat in the world’s oceans, according to a study published earlier this year.

But temperatures were even higher than most climate models – computer simulations that take into account humanity’s carbon emissions – predicted.

Analysis of these models by the Berkeley Earth group suggests that the sea temperatures observed in the North Pacific in August had less than a 1% chance of occurring in a single year.

Natural weather variability is thought to be partly responsible. This summer, for example, the winds have been weaker than usual. This means that more heat from the summer sun can stay on the sea surface, rather than being mixed with the cooler waters below.

But that can’t explain the exceptional conditions far enough, according to Dr. Hausfather.

“It’s certainly not just natural variability,” he said. “There’s something else going on here too.”

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

But this sulfur also formed tiny sun-reflecting particles in the atmosphere, called aerosols, which helped contain rising temperatures.

So removing this cooling effect in shipping hotspots like the North Pacific could reveal the full impact of human-caused warming.

“It appears that sulfur is the leading candidate for this warming in the region,” Dr. Hausfather said.

Other research suggests that efforts to reduce air pollution in Chinese cities have also played a role in warming the Pacific.

This dirty air did a similar job as transportation by reflecting sunlight, while cleaning it up could have had the unintended consequence of allowing increased ocean warming.

The marine heatwave hitting the North Pacific has already impacted weather on both sides of the Pacific, likely increasing very high summer temperatures in Japan and South Korea, as well as storms in the United States.

“In California, we have seen intense thunderstorms because the warm waters of the Pacific oceans provide heat and humidity,” said Amanda Maycock, professor of climate dynamics at the University of Leeds.

“In particular, there are things that we call atmospheric rivers…bands of air that contain very large amounts of moisture that feed in from ocean waters,” she added.

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

Long-term weather forecasting is always difficult, but extreme heat in the North Pacific could also affect the UK and Europe in the coming months.

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

“Although the current warm conditions are in the North Pacific, they may generate wave movements in the atmosphere that could change our weather downstream in the North Atlantic and Europe,” Professor Maycock said.

“This may tend to favor high pressure conditions over the continent, which brings us more influence from the Arctic, where the air is colder,” she added.

“This may be attracted to Europe and bring us colder weather as winter begins.”

A colder outcome is by no means certain, as this is a complex area of ​​science. Several other weather conditions also affect British winters, which are generally becoming milder with climate change.

And a warm North Pacific appears to have different effects later in winter, favoring milder, wetter conditions in parts of Europe.

Another factor to consider is what’s happening further south in the eastern tropical Pacific.

There, the surface waters are unusually cool – a classic sign of the weather phenomenon known as La Niña.

La Niña and its warm sibling, El Niño, are natural phenomena, although research published this week highlighted that global warming could itself impact fluctuations between them.

Weak La Niña conditions are expected to persist over the coming months, according to NOAA, the US science agency.

All things being equal, La Niña generally increases the risk of a cold start to the UK’s winter, but also brings a greater chance of a mild end, according to the Met Office.

“These two drivers from the North and Tropical Pacific will act together this winter,” Professor Maycock said.

“But because La Niña is quite weak this year, extreme heat in the North Pacific may be more important in predicting the coming winter.”

Additional reporting by Muskeen Liddar and Libby Rogers