The day after tomorrow it is often invoked in climatic discourse, but we still have extreme events that seem to mimic film. The latest example is new study, published Thursday in the journal Nature Climate Change, which sounds alarming because of the “early warning signal” Atlantic meridional circulation could crash.
Known to scientists as AMOC, it is a key global current that scientists have cared about for years. The new paper suggests that climate change has fundamentally jeopardized the stability of the AMOC and that the system is now “at a point close to a critical transition.” That’s not the only concern about climate change –have you been looking out the window lately?– but its collapse has serious consequences for the world.
At first glance, the change in the speed of the ocean current does not seem to worrying. After all, we are facing huge fires, floods, heat and high sea levels all over the world – can’t ocean currents just linger a bit while trying to figure out the rest of our shit? But AMOC is actually crucial for time around the world. It helps the shepherd warm water from the tropics to the North Atlantic, which keeps Europe moderate for its latitude and otherwise ensures that weather around the world remains normal.
The AMOC is so important, in fact, that its well-being is considered a key climate “milestone.” Scientists have been wary of AMOC because, worryingly, climate change appears to have an unintended impact. Greenland the ice sheet is melting, resulting in a large pool of cold fresh water in the North Atlantic that essentially acts as a roadblock.
This is what makes this new study so worrying. Previous AMOC studies have largely relied on data from recent decades. The new study analyzes historical data on temperature and salinity dating back to the 19th century, as well as more recent data and climate models. All together they suggest that the AMOC is losing strength and is more susceptible to major changes that could knock it off 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 that the planet would have to warm up approximately 7.2 degrees Fahrenheit (4 degrees Celsius) for the AMOC to cross the milestone threshold, but could theoretically return.
“If we were to cross the threshold of the AMOC milestone, there is still the possibility, with rapid climate mitigation, that a complete collapse could still be prevented,” said Paul Ritchie, a postdoctoral fellow at the University of Exeter who studied the research milestones. With that in mind, there are other more pressing climate issues that can occupy our anxious minds.
Ritchie said that he was more worried about reaching crisis points in other systems that “work on much faster deadlines”. One more paper came out last year shows that some of the key ecosystems we rely on, such as the Amazon, could suddenly collapse in the coming decades if we continue to push them too hard through the climate crisis and deforestation.
“Some rollover elements operate at much faster timescales, such as monsoons and the Amazon rainforest, which can take decades or just years, and these faster rollover elements are less likely to prevent irreversible changes once the threshold is crossed,” Ritchie said. “So I’m probably more concerned about crossing a rapid rollover threshold, like the Amazon rainforest, because there would be little chance of preventing a large-scale decline (which would further boost global warming) if we crossed a certain threshold. “
But that doesn’t mean we shouldn’t at least think about what will happen if the AMOC crashes. Drijfhout said the new study was “very interesting and socially disturbing work with an important message calling for further research to confirm these but preliminary results”.
“The consequences of the collapse would be significant, so we should still be concerned about it, even if the probability was small,” Ritchie said. “I see it’s similar to the chances of a house fire: the probability is very small, but we’re still installing smoke detectors to make sure.”
Honestly, when it comes to our current climate, alarms are already ringing quite loudly. We do not need additional warnings to know that the use of fossil fuels must be reduced.