The Engine that drives our Oceans is Slowing down

The collapse of the Atlantic Meridional Overturning Circulation (AMOC)—the conveyor belt engine that drives our oceans—could happen as soon as 2100, according to a study from Utrecht University published last month in the journal Science Advances.

And while the world may not suffer a fatal flash freeze like in the 2004 action flick The Day After Tomorrow, an AMOC breakdown would probably reduce average air temperatures in the Northern Hemisphere by around 40 degrees Fahrenheit or more, spelling out disaster for life on our planet.

But last year, a brother-sister science team in Denmark made their own prediction about the tipping point. Their model found that the AMOC could shut down as early as 2025 (though the duo says it’s more likely to happen toward the middle of the century).

The controversial study, published in Nature Communications in June 2023, sparked a media frenzy and a sizable amount of backlash.

If correct, either of those studies’ findings would mean catastrophic consequences for our climate. But why do the two studies arrive at such drastically different timelines for the AMOC’s demise, and which conclusion is more credible?

The Atlantic Meridional Overturning Circulation is a branch of the Ocean Conveyor, a global circulation system in the world’s oceans that moves warm water from the Southern Hemisphere to the Northern Hemisphere and returns the cold water back again; it impacts temperatures at the surface, resulting in the climates we now recognize around the globe.

It moves ten times more water every second than all of the world’s rivers combined, and yet it may take one drop of water 1,000 years to travel the whole route.

In the Atlantic, the branch of the Ocean Conveyer known as the AMOC is important to this system because it hosts the beating heart of the system known as the Greenland Pump.

Water moves up from the Southern Hemisphere of the United States, across the Atlantic, and up to Greenland via the Gulf Stream, which is partly driven by ocean currents like the AMOC and partly by the wind and the movement of Earth.

As the Gulf Stream travels, some of it evaporates, releasing warmth into the air and cooling the water. The water is now not only cooler, but saltier, because of the evaporation.

In the past, some of it would freeze when it hit the cold temperatures of Greenland, and the remaining salty water would sink down and begin traveling south, again, toward the equator.

That’s the pump; it moves in the AMOC like a heartbeat moves blood through the circulatory system.

But that circulation has begun to slow. As Greenland warms due to climate change, less water is freezing and the existing ice is melting faster than expected, dumping fresh, cold Arctic water into the salty water.

Without so much heavy, salty water moving to the bottom and heading south, the pump is now weaker. If the amount of fresh water hits a tipping point, it could stop working altogether.

The AMOC hasn’t shut down for 12,000 years. But when it shut down in the past, it preceded dramatic climate changes.

If it does so again, it could drop temperatures in the Northern Hemisphere, raise sea levels, interrupt rain flows, and cause droughts, famine, and other disasters.

They knew that because, since the 1950’s, scientists have been drilling down into Greenland’s ice and pulling up ice plugs of roughly 3–24 feet in length and five inches in diameter that tell the story of the climate when each of those layers of ice formed.

They have drilled all the way down into the land below the ice, some 1,500 feet. Scientists can read Greenland’s climate history in those ice cores in the same way you can read the rings of a tree.

They can read it from bubbles of gas in ice frozen thousands of years ago that reveal information about the greenhouse gases in the atmosphere at the time. They can read it from the chemical composition of organisms trapped in the ice.

Through reading these ice cores, paleo climatologists can see clearly when the AMOC broke down in the past, and how dramatic climate shifts always followed.

Compared to the robustness of the Utrecht University team’s models, the Ditlevsens’ model seems rather simple. On the other hand, without having to focus on so many factors, they may be better able to focus more on what matters.

Guessing wrong, and postponing action, at any rate, seems riskier than guessing wrong and acting more quickly.

Oceans getting more Acidic since the Industrial Revolution

The collapse of the AMOC has huge implications, and we can’t just sit back and say, ‘I don’t know, maybe we’re wrong.

We hope we’re wrong. But I don’t think we’re wrong. The more data we collect and the more we work on the model, the more confident we are in our results. And we have to stop fossil fuel usage and greenhouse gas emissions if we want to stop this.

Yahoo / ABC Flash Point News 2024.