Run AMOC
Reading Time: 4 minutesA Key Plot Point From The Day After Tomorrow Is Set to Come True. Yes, It’s Freaky., A study says that an ocean current will ‘collapse,’ adding to our climate chaos. Here’s what that means, and what you can do., AMOC: What to know about the ocean current p
The bad climate news keeps coming: A new study adds to the evidence that the Atlantic Ocean’s critical system of currents will eventually collapse in response to melting ice sheets in Greenland (thanks, global warming). These currents shuttle water—and along with the water, heat—between the poles, influencing climate around the world. It would be a pretty big problem if the system, called the Atlantic Meridional Overturning Circulation (or AMOC for short), stopped working.
You might be wondering how worried you should be. Let’s get into it.
If the AMOC is so important, why hadn’t I heard of it before now?
You have, actually! The AMOC collapses in the movie The Day After Tomorrow. And the famous Gulf Stream is one of the currents that contributes to the AMOC. It moves warm water from the Gulf of Mexico up toward Europe, which is why Western Europe experiences a relatively milder climate than the same latitude in North America.
And what exactly is it doing?
The AMOC ‘is like the thermostat of the earth,’ says oceanographer René van Westen of Utrecht University in the Netherlands, who led the new Science Advances study. It helps keep global temperatures from going too far to one extreme or another. Our atmosphere, which is just ‘tootling around doing its thing,’ is directly affected by the surface temperature of the ocean, says Lynne Talley, a world expert on ocean circulation at Scripps Institution of Oceanography. And that is affected by the water moving around in the depths.
OK, so ocean water is always flowing around like this, transporting heat and regulating temperature … how?
Ocean circulation is driven by density differences, which depend on the salinity and the temperature of the water. Cold, salty water is heavier than warm, fresh water. When flowing water reaches Greenland, it becomes very cold and salty, causing it to sink and flow south, where the water warms and rises closer to the surface again. Van Westen compares the process to a conveyor belt going around and around.
Changing the salinity of the water messes up the way the water flows. That’s why the melting of the Greenland ice sheets is a big problem: It’s injecting a ton of freshwater into the ocean far north, where the water is usually very salty. The more freshwater, the weaker the circulation—not to mention that atmospheric temperatures are also increasing, which also makes water lighter. The new study shows that if the density dynamics change enough, the conveyor belt will eventually stop moving, aka ‘collapse.’ That means it won’t transport any water, saline, or heat across the globe.
So what happens to the global climate if it collapses? It won’t be a total Day After Tomorrow situation. Right?
If AMOC collapses, heat will linger in the Southern Hemisphere, warming South America and Australia and causing Western Europe to cool down. Things definitely won’t happen as fast as they do in the movie, or be as dramatic. For example, it will take about 100 years for temperatures to decrease 5 to 10 degrees Celsius in Western Europe.
While it might sound nice that some areas would cool down, it will get too cold in many places. For instance, in Bergen, Norway, measurements for the month of February show as much as a 35-degree decline per century, which is ‘really crazy,’ says van Westen. Talley doesn’t foresee the cooling to cause an ice age as it did in The Day After Tomorrow—'[global] warming will not bring an ice age!’ she says—but the decline will be significant.
In addition, the sea level will rise up to a meter in some places, says van Westen; the East Coast of the U.S. will be particularly affected. And there will be less precipitation in Western Europe, which will have massive impacts on agriculture there. ‘You cannot adapt to this,’ noted Peter Ditlevsen, an ice climate researcher at the University of Copenhagen, to Inside Climate News. ‘There’s some studies of what happens to agriculture in Great Britain, and it becomes like trying to grow potatoes in northern Norway.’
Are we already seeing problems with the AMOC, or is this like an all-or-nothing thing?
Since the 1950s, AMOC’s circulation strength has decreased by somewhere between 10 and 15 percent, says van Westen. But as long as the water hasn’t freshened too much from glacier melt, the conveyor belt will ‘keep on cranking,’ says Talley. Van Westen’s recent study found that once there’s enough fresh water input, the slow decline that’s been happening will drop off like a cliff, and AMOC will essentially grind to a halt.
How do scientists even know what’s going on with currents deep in the ocean?
A huge effort has been in place for decades to monitor changes in the AMOC. It’s extremely expensive to maintain, says Talley, but worth it to understand what’s happening in the ocean. Since 2004, the AMOC flow has been continuously recorded by instruments deployed near the Florida Strait in the Atlantic Ocean, in a program called the RAPID-MOCHA array. Meanwhile, a fleet of 4,000 floats around the world—named Argo, after Jason’s ship in Greek mythology — measures temperature and salinity in the upper part of the ocean, while satellites measure wind. All of this information can then be used in computer simulations to calculate what might happen with the current in the future.
OK, the million-dollar question: When will the AMOC collapse happen?
It’s a million-dollar question for a reason. No one really knows, but scientists are trying to figure that out. A 2023 paper proposes that it could happen any time between 2025 and 2095, but other scientists are skeptical that we can home in that specifically.
Well that’s terrifying! What do I do with this information?!
It is pretty alarming. ‘I hope that not everybody is panicking,’ says van Westen. ‘But I also hope that people take the climate crisis really seriously.’ The solution is, as we know well, reducing greenhouse emissions, which will decrease both atmospheric warming and the speed of glacier melt. And while these changes really need to happen at the political and public policy level, he thinks it’s important to remember that individual actions do matter, too. ‘All the small contributions will help.’
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