Computer Simulations Show Nightmare Atlantic Current Shutdown Less Likely This Century

The sun rises over the Atlantic Ocean as a bird flies in Lido Beach, New York, US, February 26, 2025. (Reuters)
The sun rises over the Atlantic Ocean as a bird flies in Lido Beach, New York, US, February 26, 2025. (Reuters)
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Computer Simulations Show Nightmare Atlantic Current Shutdown Less Likely This Century

The sun rises over the Atlantic Ocean as a bird flies in Lido Beach, New York, US, February 26, 2025. (Reuters)
The sun rises over the Atlantic Ocean as a bird flies in Lido Beach, New York, US, February 26, 2025. (Reuters)

The nightmare scenario of Atlantic Ocean currents collapsing, with weather running amok and putting Europe in a deep freeze, looks unlikely this century, a new study concludes.

In recent years, studies have raised the alarm about the slowing and potential abrupt shutdown of the Atlantic end of the ocean conveyor belt system. It transports rising warm water north and sinking cool water south and is a key factor in global weather systems.

A possible climate change-triggered shutdown of what's called the Atlantic Meridional Overturning Circulation or AMOC could play havoc with global rain patterns, dramatically cool Europe while warming the rest of the world and goose sea levels on America's East Coast, scientists predict.

It's the scenario behind the 2004 fictionalized disaster movie “The Day After Tomorrow,” which portrays a world where climate change sparks massive storms, flooding and an ice age.

Scientists at the United Kingdom's Met Office and the University of Exeter used simulations from 34 different computer models of extreme climate change scenarios to see if the AMOC would collapse this century, according to a study in Wednesday's journal Nature. No simulation showed a total shutdown before 2100, said lead author Jonathan Baker, an oceanographer at the Met Office.

It could happen later, though, he said. The currents have collapsed in the distant past.

Still, the computer simulations should be “reassuring" to people, Baker said.

“But this is no greenlight for complacency,” Baker warned. “The AMOC is very likely to weaken this century and that brings its own major climate impacts.”

The Atlantic current flows because warm water cools as it reaches the Arctic, forming sea ice. That leaves salt behind, causing the remaining water to become more dense, sinking and pulled southward. But as climate change warms the world and more fresh water flows into the Arctic from the melting Greenland ice sheet, the Arctic engine behind the ocean conveyor belt slows down. Previous studies predict it stopping altogether with one of them saying it could happen within a few decades.

But Baker said the computer models and basic physics predict that a second motor kicks in along the Southern Ocean that surrounds Antarctica. The winds there pull the water back up to the surface, called upwelling, where it warms, Baker said. It's not as strong, but it will likely keep the current system alive, but weakened, through the year 2100, he said.

Baker's focus on the pulling up of water from the deep instead of just concentrating on the sinking is new and makes sense, providing a counterpoint to the studies saying collapse is imminent, said Oregon State University climate scientist Andreas Schmittner, who wasn't part of the research.

Those Southern Ocean winds pulling the deep water up act “like a powerful pump keeps the AMOC running even in the extreme climate change scenarios,” Baker said.

As the AMOC weakens, a weak Pacific version of it will likely develop to compensate a bit, the computer models predicted.

If the AMOC weakens but not fully collapses, many of the same impacts — including crop losses and changes in fish stock — likely will still happen, but not the big headline one of Europe going into a deep freeze, Baker said.

Scientists measure the AMOC strength in a unit called Sverdrups. The AMOC is now around 17 Sverdrups, down two from about 2004 with a trend of about 0.8 decline per decade, scientists said.

One of the debates in the scientific world is the definition of an AMOC shutdown. Baker uses zero, but other scientists who have been warning about the shutdown implications, use about 5 Sverdrups. Three of Baker's 34 computer models went below 5 Sverdrups, but not to zero.

That's why Levke Caesar and Stefan Rahmstorf, physicists at the Potsdam Institute for Climate Research and authors of an alarming 2018 study about potential shutdown, said this new work doesn't contradict theirs. It's more a matter of definitions.

“An AMOC collapse does not have to mean 0 (Sverdrups) overturning and even if you would want to follow that definition one has to say that such a strong AMOC weakening comes with a lot (of) impacts,” Caesar wrote in an email. “The models show a severe AMOC weakening that would come with severe consequences.”



Bull Sharks Linger in Warming Sydney Waters

A man watches large waves on Bondi Beach in Sydney on July 2, 2025, as large swells and high winds hit the east coast of Australia. (Photo by SAEED KHAN / AFP)
A man watches large waves on Bondi Beach in Sydney on July 2, 2025, as large swells and high winds hit the east coast of Australia. (Photo by SAEED KHAN / AFP)
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Bull Sharks Linger in Warming Sydney Waters

A man watches large waves on Bondi Beach in Sydney on July 2, 2025, as large swells and high winds hit the east coast of Australia. (Photo by SAEED KHAN / AFP)
A man watches large waves on Bondi Beach in Sydney on July 2, 2025, as large swells and high winds hit the east coast of Australia. (Photo by SAEED KHAN / AFP)

Bull sharks are lingering off Sydney's beaches for longer periods each year as oceans warm, researchers said Friday, predicting they may one day stay all year.

The predators are migratory, swimming north in winter when Sydney's long-term ocean temperatures dip below 19 degrees Celsius (66 degrees Fahrenheit) to bask in the balmier waters off Queensland.

A team of scientists looked at 15 years of acoustic tracking of 92 tagged migratory sharks in an area including Bondi Beach and Sydney Harbour.

Records show the sharks now spend an average of 15 days longer off Sydney's coast in summer than they did in 2009, said James Cook University researcher Nicolas Lubitz.

"If they're staying longer, it means that people and prey animals have a longer window of overlap with them."

Shark attacks are rare in ocean-loving Australia, and most serious bites are from three species: bull sharks, great whites, and tiger sharks, according to a national database.

There have been more than 1,200 shark incidents around Australia since 1791, of which over 250 resulted in death.

Researchers found an average warming of 0.57C in Bondi for the October-May period between 2006 and 2024, said the study published in the peer-reviewed journal Science of The Total Environment.

Over a longer period, remotely sensed summer sea-surface temperatures in the area rose an average 0.67C between 1982 and 2024, they said.

"If this trend persists, which it likely will, it just means that these animals are going to spend more and more time towards their seasonal distributional limit, which currently is southern and central New South Wales," Lubitz said.

"So it could be that a few decades from now, maybe bull sharks are present year-round in waters off Sydney," he added.

"While the chances of a shark bite, and shark bites in Australia in general, remain low, it just means that people have to be more aware of an increased window of bull shark presence in coastal waters off Sydney."

Climate change could also change breeding patterns, Lubitz said, with early evidence indicating juvenile sharks were appearing in rivers further south.

There was some evidence as well that summer habitats for great whites, which prefer colder waters, were decreasing in northern New South Wales and Queensland, he said.

Tagged sharks trigger an alarm when they swim within range of a network of receivers dotted around parts of the Australian coast, giving people real-time warnings on a mobile app of their presence at key locations.