Is the weather running AMOC in Ireland

November 1, 2024

Part 2

In the March 1, 2024 issue of the ieBLOG section of www.irishenvironment.com we wrote about the nature and, and to  a limited extent, the impacts of the Atlantic Meridional Overturning Circulation (AMOC).  In this issue (November 2024) we explore that issue further through the talk by Stefan Rahmstorf of the Earth system analysis department at the Potsdam Institute for Climate Impact Research in Germany on the the workings and risks from the AMOC.  We also republish an Open Letter by Climate Scientists to the Nordic Council of Ministers, calling for the closer attention of the Council and others to the serious risks of major ocean circulation change in the Atlantic. In his talk Professor Rahmstorf mentions in passing that Ireland and Scotland will experience changes to their weather and environment.

In a recent interview, Rahmstorf explores some of the likely outcomes in Ireland and Scotland, and Europe in general, if the AMOC continues to weaken or even collapses, sooner rather than later.  Below are excerpts of that discussion:

BT [Ben Turner]: So what would climates around the North Atlantic look like if AMOC were to collapse? What regions would be the worst affected?

SR [Stefan Rahmstorf]: There would be many impacts. The most immediate one that people probably already know about is the cooling around the northern Atlantic, which is already there in the form of the cold blob. It’s also in the air temperature around that region, it’s the only part of the world that has not warmed, but has been getting colder, in the last 100 years.

So we already have the symptom there, but when the AMOC really gets much weaker still and collapses, then the cold blob would expand and cover land areas as well — like Ireland, Scotland, Scandinavia, Iceland, they would likely get several degrees colder and also drier.

That would then enhance the temperature contrast across Europe, because Southern Europe would still be warm and Northern Europe would be cool. These temperature differences drive extreme weather events, bringing a lot more variability and storms. The sea level would also rise by up to half a meter [1.6 feet] in the northern Atlantic in addition to the global average rise that is happening anyway.

There would also be an effect on ocean carbon dioxide uptake. Currently, the ocean takes up 25% of our CO2 emissions just by gas exchange at the sea surface. The ocean can do that because a lot of that CO2 is then transported to the deep ocean by the AMOC. If the overturning circulation stops, that CO2 will stay near the surface and quickly equilibrate with the atmosphere. That would make it [C02 concentrations] rise faster in the atmosphere.

The AMOC also transports oxygen into the deep ocean. This is also bad news [if this process stops], because if you get an oxygen-depleted ocean it would disrupt the entire web of life in the northern Atlantic, and that would disrupt fisheries.

A map of the ocean currents in the Atlantic. (Image credit: Peter Hermes Furian via Shutterstock)

BT: That paints a very strange picture of our future climate — things being colder around the northern Atlantic, warmer to the south, and there being a lot more CO2 in the atmosphere. What impacts will that combination have globally?

SR: We’d see the whole Northern Hemisphere cool compared to what it would be with just global warming [acting alone]. Although it wouldn’t exactly cool [outright], climate change would counteract that effect in most places, except around the North Atlantic.

In the Southern Hemisphere, greenhouse warming would get worse. There would be a shift in the tropical rainfall belts. We know from paleoclimate records that these Heinrich events, for example, have caused major drought problems in parts around the tropics and in other areas. You would also get flooding from tropical rainfalls shifting to places where people and infrastructure are not used to it.

In terms of more detail, there are surprisingly few studies on that so far. We mostly know from paleoclimate data how drastic and worldwide these changes are, even reaching as far as New Zealand, which is as removed from the North Atlantic as you can possibly get.

From Ben Turner, ‘We don’t really consider it low probability anymore’: Collapse of key Atlantic current could have catastrophic impacts, says oceanographer Stefan Rahmstorf,” Live Science bit.ly/40peSxI

See also, Guidance for Met Éireann forecasters on impact for Ireland from possible collapse of the Atlantic Meridional Overturning Circulation (AMOC).   https://bit.ly/40n62k0