Is the Amoc running Amok? Will Europe freeze?

Breakfast With Bwana 

This is a story about climate change… sort of. And about responsible journalism… sort of.

By Anil Madan

The other day, I was listening to news headlines on the radio. After that brief interlude, a somewhat breathless reporter described what seemed a catastrophic disruption in AMOC, the Atlantic Meridional Overturning Circulation. He declaimed with a certain level of alarm and anxiety that the salinity of the waters about the Gulf Stream is decreasing because of Arctic ice melt and that this is leading to a slowing of the Gulf Stream. Eventually, this will lead to extreme cold in the north Atlantic, so Ireland, England, the Scandinavian countries, indeed, all of Europe is at risk.

I was intrigued, not the least by the physics underlying this amazing circulation, so I decided to see what I could find. And, of course, I was curious about just how imminent this English deep freeze is.

What is this AMOC? Meridional refers to something of or related to the south and relating to a meridian. “Overturning” in this case refers to the flow of water from the north to the south and back at different levels in the ocean.

The National Oceanic and Atmospheric Administration’s (NOAA) website explains it thus:

“The ocean’s water is constantly circulated by currents. Tidal currents occur close to shore and are influenced by the sun and moon. Surface currents are influenced by the wind. However, other, much slower currents that occur from the surface to the seafloor are driven by changes in the saltiness and ocean temperature, a process called. thermohaline circulation. These currents are carried in a large ‘global conveyor belt,’ which includes the AMOC.

“The AMOC circulates water from north to south and back in a long cycle within the Atlantic Ocean. This circulation brings warmth to various parts of the globe and also carries nutrients necessary to sustain ocean life.

“The circulation process begins as warm water near the surface moves toward the poles (such as the Gulf Stream in the North Atlantic), where it cools and forms sea ice. As this ice forms, salt is left behind in the ocean water. Due to the large amount of salt in the water, it becomes denser, sinks down, and is carried southwards in the depths below. Eventually, the water gets pulled back up towards the surface and warms up in a process called upwelling, completing the cycle.”

 Why should this cause us any concern? Well, as a few hysterical articles explained, this circulation of water plays a significant role in our climate. The AMOC uses the flow of water to transfer heat from the warmer tropics to colder northern latitudes. The Gulf Stream, for example, is well known to help maintain milder temperatures over the British isles and Europe than land at comparable latitudes farther west in the Atlantic Ocean, such as Newfoundland or Labrador which are significantly cooler.

This illustration from the NOAA Goddard Space Flight Center Scientific Visualization Studio shows how this fascinating flow spreads across the earth.

 What triggered a flurry of articles was a recent paper in Science Advances titled: ‘Physics-based early warning signal shows that AMOC is on tipping course’.

In reporting on this paper, an article on Vox.com raised this dire specter: “But not only would temperatures in Europe plummet, the change would trigger a climate tipping point, generating cascading effects around the world. There would be more than two feet of extra sea level rise in North America. The Southern Hemisphere could grow warmer, potentially further destabilizing Antarctica’s ice sheets. In the Amazon rainforest, some parts would get rainier and others would dry out. Wildlife would suffer too, as essential nutrients for marine life would not as readily reach the Northern Atlantic.”

The paper in Science Advances did not describe any urgency to the problem. Indeed, it is difficult to figure whether the authors claim to have modeled anything accurate. They write that “most 150-year time windows do not provide an accurate estimate of the tipping point.”

When I read more, I came across this on the NOAA website: “The entire circulation cycle of the AMOC, and the global conveyor belt, is quite slow. It takes an estimated 1,000 years for a parcel (any given cubic meter) of water to complete its journey along the belt. Even though the whole process is slow on its own, there is some evidence that the AMOC is slowing down further.”

The Woods Hole Oceanographic Institute publishes Oceanus, a journal that discusses matters relating to the oceans and their effect on planet earth. An article last August on this AMOC collapse involved a discussion with three scientists. Each said words to this effect: “I don’t know if the AMOC is reaching a tipping point.” Some pointed out that there are prognostications of a tipping point being reached between 2025 and 2095, but others that it is highly unlikely over the next century.

The most striking point to me is that direct measurements of AMOC have been made only since 2004. Yes, twenty years. We do not know what we do not know. But what is clear is that we do not know a lot.

For now, go with the flow.

 Cheerz…
Bwana

Mauritius Times ePaper Friday 22 March 2024