In The Day After Tomorrow, the warming of the planet causes the Atlantic meridional overturning circulation (AMOC), the formal name for the overall system of Atlantic Ocean currents, to effectively collapse—inducing a new ice age upon the planet.
The writers of the movie may have taken dramatic liberties with climatological research to imagine such an outcome—after all, they had to find a reason for Dennis Quaid to make a dangerous trek across a newly formed glacier around New York City to save Jake Gyllenhaal.
But the collapse of AMOC isn’t impossible. In fact, we're rapidly reaching a tipping point, thanks to climate change, according to a new study published Tuesday in Nature Communications that predicts it could collapse by the middle of the century, possibly even as early as 2025.
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“It calls for immediate action,” Peter Ditlevsen, a climate researcher at the University of Copenhagen and a co-author of the new study, told The Daily Beast. “With the worrisome finding, some research will need to deal with more climate model based assessments of regional climate changes with a collapse of the AMOC.”
The ocean currents that comprise AMOC work like conveyor belts to carry warm water from the southern latitudes into the North Atlantic. Heat from the south causes colder, saltier water in the north (which is heavier) to sink. (The Pacific Ocean lacks the same kind of salinity, and it’s the reason water around Alaska tends to be colder than in Scandinavia, even though they share the same latitude.)
But AMOC can be shut down if too much fresh water is added to the ocean, which reduces its salinity. Ocean waters become less heavy, which basically causes the AMOC currents to turn “off.” That infusion of freshwater could come from the melting of ice sheets, increased river runoff, and increased precipitation—all things that are driven by climate change.
Ditlevsen and his co-author ran their study by looking at sea surface temperature data of the North Atlantic stretching back to 1870, which can help tell us about the historical stability of AMOC. After running new analyses, they came to conclude that AMOC is getting more unstable over time. Mechanisms that maintain regularity are falling apart.
The authors’ analyses suggest AMOC will collapse sometime between 2025 and 2095—likely in the middle of the century, but they warn it may happen sooner. Such an event would likely lead to rapid rises in sea levels, and a sharp decrease in temperatures across the Northern Hemisphere. Severe storm events would likely follow.
The new study is very alarming—if you buy into its findings. And there is some skepticism among other scientists. The latest report from the U.N.’s Intergovernmental Panel on Climate Change said it was unlikely that AMOC would collapse based on current climate models. And New Scientist reports several other experts have cautioned that uncertainties make it difficult to pinpoint when the AMOC tipping point will occur (something Ditlevsen himself conceded).
Still, the IPCC has been criticized again and again for pulling its punches and moderating its conclusions in the face of political pressure. And most experts have observed that climate change has blown past most predictions made in the past.
The good news is that this is all reversible—“if you react to it quickly enough,” said Ditlevsen.
Once we cross the tipping point, it will be several decades before a full collapse of AMOC begins, and that’s a moment where greenhouse gas concentrations can still be brought down to prevent the worst case scenarios from unfolding.
That doesn’t mean there should be any reason to not to act. “It is not going to be The Day After Tomorrow, but we do not really have analogies for the collapse, as it happened last more than 12,000 years ago,” warned Ditlevsen.
