When a vital Atlantic Ocean current might collapse is so important that it needs to be figured out

Climate tipping point for the Arctic Ocean Current: Why Copenhagen needs more brakes on the train, and what we need to do now to reduce fossil fuel emissions

The amount of density on this planet is very important. A conveyor belt of ocean warm water heads north from the tropics to the far north in the Atlantic. That makes it denser, so it sinks and heads back south, finishing the loop. The system of currents called the AMOC moves 15 millioncubic meters of water per second.

This century is more likely to be weakened by the AMOC. That could cause some of the same impacts as a collapse, if not more so. It will take more time than shown by some studies, because of the normal fluctuations in the current.

That’s a tipping point that would come much sooner than anyone thought. “We got scared by our own results,” says Susanne Ditlevsen, a statistician at the University of Copenhagen and coauthor of the new paper. We checked and checked, and I think they’re right. Of course, we might be wrong, and I hope we are.” The scientific community is divided over how quickly the AMOC might decline and how best to figure that out.

Scientists know this conveyor belt has collapsed in the past. Around 12,000 years ago, temperatures around Greenland suddenly dropped by about 18 degrees Fahrenheit. That shift is attributed to a sudden shutdown of the AMOC — and demonstrates the potential impact of such a climate tipping point.

Ditlevsen did her team’s calculation by using measurements of Atlantic sea surface temperatures as a proxy for the AMOC. The readings went back to the 1870s because of measures taken by ship crews. This meant researchers could compare temperatures before and after the start of the wide-scale burning of fossil fuels and the ensuing changes to the climate.

“It’s a worrisome result,” says Peter Ditlevsen, professor of climate physics at the University of Copenhagen in Denmark and an author of the study. “It calls for quite immediate actions. We need to reduce emissions. There are more brakes on the train.

Why it’s so important to figure out when an Atlantic ocean current might be too cold: Why does it matter when the AMOC collapses?

Milder winters in Europe are largely thanks to an influx of heat from the AMOC. Warm water from the equator travels up the East Coast of the US before crossing to Europe. That is where water cools down, releasing heat into the atmosphere.

“In Scandinavia, we have a sort of pleasant, mild climate,” Ditlevsen says. If you compare the latitude of Alaska to that of the U.S., you’ll see it’s much colder.

The salty water is heavier than the cold one, causing it to sink near the world’s largest island. The ocean current flows south along the ocean floor in a similar way to a conveyor belt.

There is broad consensus on the potential consequences, despite researchers differing on the timing of the collapse. The collapse of the AMOC could have repercussions all over the planet. Temperatures in Europe could fall, while heat in the tropics would rise, exacerbating climate change that’s already occurring.

Rainfall could decrease across the Sahel region of Africa, threatening crop production for millions of people. Scientists have found that subtle changes in Atlantic currents can have significant effects on marine life, such as threatening North Atlantic right whales.

It’s going to have an effect on agriculture. It’s going to affect disease in the central region. It’s going to affect mass migration.”

Source: https://www.npr.org/2023/07/27/1190519762/why-its-so-important-to-figure-out-when-a-vital-atlantic-ocean-current-might-col

Foukal’s study of the polar vortex distribution in the Arctic, Greenland, and Antarctica: Evidence for a complete collapse or no complete collapse?

Foukal says this most recent study relies on temperature records from a small part of the system and doesn’t simulate what would happen to the entire current itself. It’s crucial to understand the cause of a collapse to estimate the timing, but Ditlevsen’s study doesn’t address that.

A similar thing could happen again, as humans continue to heat the atmosphere by burning fossil fuels. Ice in the Arctic and Greenland’s ice sheets are melting at an increasing pace, also adding fresh water to the Atlantic. But Foukal says researchers are still trying to determine whether that would be enough to cause a complete collapse.