AMOC - What it is and Why You Should Care

AMOC stands for Atlantic Meridional Overturning Circulation. It's slowing down significantly, and people in the know are pretty worried about it. 

According to Professor Stefan Rahmstorf, AMOC is "a near-surface northward flow along the Atlantic, from the far south up to the high north. There the water gives off its heat to the atmosphere, sinks down, and returns south at a 2-3 km depth." Here's a schematic animation from NASA, titled, The Thermohaline Circulation aka The Great Ocean Conveyor Belt:

"The AMOC is part of the global overturning circulation driven by density differences. It supplies the deeper waters with oxygen. Schematic from my 2002 Nature article; yellow dots is where the water sinks into the deep." 

"Both a cold blob in the ocean and the excessive warming along the American coast are a telltale 'fingerprint' pattern of an AMOC slowdown. . . . The high-resolution climate model predicts this fingerprint in a CO2 scenario. The observed temperature trend since 1870 shows it. And so do the Copernicus satellite data. . . . Let's look at the same results in another way. These use very different methods: Nutrient content in the water, sediment grain sizes where the deep southward return flow passes, etc. They give rather consistent results: the AMOC is now at its weakest in a millennium."

"The climate system has a number of 'tipping elements' (subsystems with tipping points). Here's a nice overview from Germany's national science academy Leopoldina."

"The possible AMOC tipping point was first described in a very simple feedback model by Henry Stommel in Tellus 1961. The northern Atlantic is rather salty because of the AMOC, and the AMOC words because it's rather salty there (and the water thus dense enough to sink). Wally Broecker called this feedback a 'chicken and egg situation' and famously warned about 'unpleasant surprises' in Nature 1987. . . . As far as I know, this behaviour is robust across all models where it has been tested. The tipping point is real, but models differ greatly how close we are. . . . But the models don't expect it to appear already now."

"Did I talk about impacts yet? Consequences of an AMOC breakdown would be disastrous. Not just cooling (left below), but also major shifts in tropical rainfall belts (right), here from the recent OECD report on Climate Tipping Points. 

Also major dynamic sea level changes on top of the global rise due to warming and ice melt (Levermann et al., 2005). Plus reduced ocean CO2 uptake, ecosystem disruption, loss of oxygen in the deeper ocean, extreme weather events. . . . Two weeks ago I gave the introductory keynote for a two-day AMOC session at the IUGG Conference in Berlin, and here is my conclusion slide.

Even though it is uncertain exactly how close we are to tipping points, the consequences would be so serious that we must try to absolutely minimize the risk. It's one more reason to stick to the Paris 1.5°C goal. The latest IPCC report has sent out a clear warning. 

And finally, the OECD Climate Tipping Points Report also states it very clearly. Don't take my word for it. I really hope that those playing down tipping point risks have studied the evidence carefully enough to know what they are talking about."

This past week I listened to a show on CBC about how climate change is affecting people's vacations, and many people said they're just starting to think they might change how they do things, fewer plane rides, and more vacations closer to home. It's great, for sure, but how are people just hearing about this now?? It's so hard for us to recognize dangers until they're right in our face. We like to think we're better than other mammals, but I'm not seeing many signs that's true.