How Worried Should You Be About a Key Atlantic Current Collapsing?

How Worried Should You Be About a Key Atlantic Current Collapsing?

The Day After Tomorrow gets invoked often in climate discourse, but then, we keep having extreme events that seem to mimic the movie. The latest example is a new study, published Thursday in Nature Climate Change, that sounds the alarm about “early-warning signals” the Atlantic Meridional Overturning Circulation could collapse.

Known as the AMOC to scientists, it’s a crucial global current that scientists have been worrying about for years. The new paper suggests that climate change has basically thrown the stability of the AMOC into jeopardy, and that the system is now at “a point close to a critical transition.” It’s hardly the only concern when it comes to climate change — have you looked out your window lately? — but its collapse has grave implications for the world.

At first thought, a change in the speed of an ocean current doesn’t seem that worrisome. We are, after all, facing rampant fires, floods, heat, and soaring sea levels all over the world — can’t the ocean currents just hang out for a little bit while we try and figure out the rest of our shit? But the AMOC is actually crucially important to weather around the globe. It helps shepherd warm water from the tropics to the North Atlantic, which keeps Europe temperate for its latitude and otherwise ensures that weather around the world stays Normal.

The AMOC is so important, in fact, that its wellbeing is considered a key climate “tipping point.” Scientists have been keeping an eye on the AMOC because, worryingly, it appears that climate change is having an unwelcome impact. The Greenland ice sheet is melting, resulting in a large pool of cold freshwater in the North Atlantic that essentially acts as a roadblock to the current.

That’s what makes this new study so troubling. Previous studies of the AMOC have largely relied on data from the past few decades. The new study analyses historic temperature and salinity data stretching back to the 19th century as well as the more recent data and climate models. Together, they all suggest that the AMOC is losing strength and is more susceptible to major changes that could knock it off its course.

So… what’s the takeaway for regular people here? Do we need to prepare for the ocean’s conveyor belt to suddenly stop and change weather as we know it within our lifetimes? Will Dennis Quaid shepherd us all into the New York Public Library to save us from a monster wave of storm surge?

The paper crucially includes no prediction for when the AMOC could go awry, but it does suggest that the current is losing strength to resist any major changes. According to the latest climate models, an AMOC collapse by 2100 is pretty unlikely — not impossible, but it’s probably not going to happen.

“Yes, a collapse could happen during our lifetime, but it is impossible to give a probability because our models are not good enough to trust their future projections in a quantitative sense,” Sybren Drijfhout, an oceanographer at University of Southampton and affiliated with the Royal Netherlands Meteorological Institute who has studied the AMOC, said in an email. He also noted that “both previous media reports and, to a lesser extent the manuscript itself, tend to make too strong claims and tend to neglect various reservations that should have been made.”

Among the issues he noted were that the paper looks at “fingerprints” of the AMOC and not the circulation itself, fingerprints that could be reflecting changes to other parts of the climate system such as the North Atlantic Oscillation. He added that, while the signals the paper looks at seem to line up with AMOC collapse, they don’t necessarily “PREDICT such a collapse.”

What’s more, the prospect of crossing this AMOC “tipping point” threshold isn’t as dire as reaching other tipping points, because slowing the ocean’s circulatory system takes place over decades, not years. In other words, even if we pass the first point of no return, there’s theoretically time to fix it by getting temperatures under control before it completely collapses. Other recent research shows the planet would have to warm upwards roughly 4 degrees Celsius for the AMOC to cross the tipping point threshold, but it could theoretically come back.

“If we were to cross the AMOC tipping point threshold, then there is still the possibility with fast climate mitigation that a complete collapse could still be prevented,” Paul Ritchie, a postdoc at the University of Exeter who studies tipping points and led that other research, said in an email. With that in mind, there are other more pressing climate matters that can occupy our anxious minds.

Ritchie said that he’s more worried about reaching crisis points in other systems that “work on much faster timescales.” Another paper put out last year shows that some key ecosystems we rely on, like the Amazon, could collapse suddenly in the coming decades if we continue to push them too hard via the climate crisis and deforestation.

“Some tipping elements work on much faster timescales, such as monsoons and the Amazon rainforest, which may be decades or only years, and for these faster tipping elements there is less chance to prevent the irreversible change once over the threshold,” Ritchie said. “So, I’m possibly more concerned about crossing a fast-onset tipping threshold, such as the Amazon rainforest, as there would be little chance to prevent large-scale dieback (which would amplify global warming further) if we were to cross that particular threshold.”

But that doesn’t mean that we shouldn’t be at least think about what happens if the AMOC were to collapse. Drijfhout said the new study is a “very interesting and societally disturbing paper with an important message that cries out for further research to corroborate these yet preliminary results.”

“The consequences of a collapse would be significant, and therefore we should still be worried about it, even if the probability might be low,” Ritchie said. “I see it similar to the chances of a house fire: the probability is very low, but we still install smoke detectors to keep us safe.”

Frankly, when it comes to our present climate, the alarms are already ringing pretty loudly. We don’t need any more warnings to know that fossil fuel use must be wound down.

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