Are you ready for real disaster news? If the warming currents in the North Atlantic weaken or collapse, Ireland, England, and North Europe will become stormy and cold, even as the world warms. A collapse of the ocean system known as “AMOC” has happened before. New study: destabilization could come again soon, even this decade. Hear it straight from author Susanne Ditlevsen, followed by analysis, including by Stefan Rahmstorf.
There has been a lot of sensational, overblown reporting about an AMOC collapse, starting with the science-fiction movie “The Day After Tomorrow”. In this program you hear directly from an author of a new study in Nature Communications, Professor Susanne Ditlevsen.
All this comes in a time of unprecedented climate chaos. Extreme super-events are piling on, popping up around the world in the same week. Slovenia was just wrecked by extreme rain, with floods expected to pour into Croatia. As I record this, the UK is bracing for a life-threatening storm system. A forest fire on the Hawaiian Island of Maui just burned down a tourist town with at least a half dozen dead.
Three months worth of rain fall on Northern China in 40 hours, flooding Beijing as never before. That was just a blip in the news but will take years to recover.
Iranians are used to high heat, but the whole country was ordered to shut down for two days to save lives in an extreme heat event. Six hundred scouts needed medical treatment for heat exhaustion (and COVID) in a big international camp-out in South Korea. Japan was lashed with record heat and dangerous storms at the same time.
Almost unreported, there was a winter heat wave in South America. Temperatures over 100 degrees, 37 C were reported in Chile, some record heat reaching high up into the Andes. For perspective, the start of August in the Southern Hemisphere is like the beginning of February in the North. It should be cold. High heat has never come this early. The weather has gone insane.
But don’t think an ocean circulation collapse could be a good thing for the UK, Europe or anywhere else. A bit later I examine sources explaining the real impacts. Right now, let’s get to the news about WHEN the North Atlantic Meridional Overturning Circulation – AMOC – could change to a state not seen on Earth for at least 12,000 years.
AMOC COLLAPSE – SOONER THAN YOU THINK
– SUZANNE DITLEVSEN
If the warming currents in the North Atlantic weaken or collapse, Ireland, England, and Northern Europe will become hard places to live. Northern forests and agriculture around the world would be affected. A collapse of the ocean system known as “AMOC” has happened before. Now scientists worry that destabilization could come again soon, even in this decade.
On July 25th, the journal Nature Communications published a paper called “Warning of a forthcoming collapse of the Atlantic meridional overturning circulation”. The authors are Peter and Susanne Ditlevsen. Co-author Susanne is Professor of Mathematics at the University of Copenhagen in Denmark.
“In this work, we show that a transition of the AMOC is most likely to occur around 2025-2095 (95% confidence interval).”
Professor Suzanne Ditlevsen (Photo by Lars Svankjær)
Susanne Ditlevsen is not a climate scientist per se, but a respected Professor of Mathematics. I think there is a tendency to discount the value of mathematical models. But then we remember the atomic bomb began in the world of math and that got very real. Her co-author and brother Peter Ditlevsen is a climate scientist running a center called :”Tipping Points and the Earth System” (TiPES) at the Niels Bohr Institute in Copenhagen.
The TiPES group just released a new study on July 12, 2023, suggesting “Huge tipping events dominated the evolution of the climate system”. The title of the peer-reviewed paper is: A punctuated equilibrium analysis of the climate evolution of cenozoic exhibits a hierarchy of abrupt transitions.” Find it here.
There is still a lot of scientific discussion about what could be a world-changing event if AMOC shifts state. For example in a 2022 paper, scientists Feng He and Peter Clark revisited the freshwater forcing of the Atlantic Meridional Overturning Circulation and found, quote: “The important result is that the AMOC appears to be less sensitive to freshwater forcing than has long been thought, according to both the data and model.”
The Ditlevsens’ paper does not depend on increasing meltwater or drivers, but the stability of bifurcating systems in general. By the way, UK senior scientist Tim Palmer sees possible advantages to a weakening of the overturning circulation. It might slow ice loss and sea level rise for the rest of the world. But it sounds like that comes at tremendous cost for north Europe.
In a new paper, not yet published, Johannes Lohmann and colleagues propose intermediate steps between the currently known AMOC and a much lower quasi-stable state. But these changes of state are also “abrupt”. So the north Atlantic current may go down in steps, or could it collapse to a new low state precipitously. Lohmann and colleagues are looking for “early warning signs” of system collapse.
WE KNOW AMOC IS WEAKENING
A series of papers have documented the Atlantic Meridional Overturning Circulation is weakening. For example see “Observed fingerprint of a weakening Atlantic ocean overturning circulation”, with Stefan Rahmstorf and led by Levke Caesar. Radio Ecoshock covered that in with Dr. Levke in my March 31, 2021 show “The Decade After Tomorrow”.
Our Radio Ecoshock guest Johannes Lohmann discovered the RATE of change can bring tipping points sooner than simple calculations would suggest. He uses the weakening of AMOC as his case study. Find that in my Radio Ecoshock show posted March 17, 2021 “This Future Doesn’t Work”.
A HELPFUL TERM FOR THIS INTERVIEW: SADDLE NODE BIFURCATION
“In the mathematical area of bifurcation theory a saddle-node bifurcation, tangential bifurcation or fold bifurcation is a local bifurcation in which two fixed points (or equilibria) of a dynamical system collide and annihilate each other.”
WHAT WILL HAPPEN WHEN AMOC COLLAPSES?
As you heard from Susanne Ditlevsen, it is difficult to predict what will happen if the AMOC changes to a very weak state and moves southward. We can’t rely on data from previous AMOC shifts during the ice ages – because humans are now warming the world at a never-before-seen pace. All this combines into something very different and very new. That is not good news for an ecological system that depends on certain conditions on land and in the sea.
Let’s take the UK for example. If you just look at IPCC projections and other models, it looks like the UK would be a good place to survive global warming. By 2080, southern Britain would be hotter but bearable with periodic droughts. Scotland would be warmer, but that might feel good. The Scottish Highlands would get wetter. As James Lovelock pointed out, the sea around the UK would help protect it from temperature extremes developing over land masses like Russia, China, and North America. Lovely.
But if the AMOC shuts down things don’t go so well. Many sources suggest the average UK temperatures would drop by 3.4 degrees C, about 6 degrees Fahrenheit. Other experts suggest it could be even colder, up to 5 degrees C. A 2021 report by the OECD says:
“Europe and North America would experience a drop of 3°C – 8°C and 1°C – 3°C respectively. In the southern hemisphere, there is little predicted temperature change, but strong disruptions to precipitation patterns in the tropics.”
Winters would be much colder. We can barely imagine that while the rest of the world suffers through long-lasting heat waves.
IT’S THE RAIN, NOT THE COLD
But the real blow for the UK after AMOC collapse is not temperature but changing rain. Paul Ritchie and his co-authors studied this for their 2020 paper “Shifts in national land use and food production in Great Britain after a climate tipping point.”
They say: “We show that economic and land-use impacts of such a tipping point are likely to include widespread cessation of arable farming with losses of agricultural output that are an order of magnitude larger than the impacts of climate change without an AMOC collapse.”
In fact, Ritchie et al found the amount of arable land in the UK would drop from the current 32% to around 7%. That is disaster and an end to any dreams of the UK having the security of it’s own food. The authors say that 7% figure could be boosted higher by irrigation, but there are limits to the amount of irrigation water available.
So the AMOC collapse is as much about changes in precipitation as temperatures. The media leaves this out.
PLANETARY PRECIPITATION CHANGES
One major institutions took a stab at predicting impacts of an AMOC collapse. The Organization for Economic Co-operation and Development (OECD) is composed of 37 democracies. In 2021, the OECD published a report called “Climate Tipping Points”. The OECD study found rainfall over Siberia would fall so low that boreal forests would convert to savanna grass lands or bush land. Meanwhile the extra water vapor in the atmosphere due to heating would fall heavily on the Canadian boreal forest.
Scientists worry the AMOC collapse impacts on precipitation patterns could change water distribution in the atmosphere over the whole planet. For example, after AMOC collapse, the speed of Amazon conversion from forests to grass/shrubs might go faster. The memory in human civilization has never experienced this new state of the ocean. We just don’t know what could happen.
In studies of the AMOC among other tipping points, scientists say that ocean tipping point could be a mediator in triggering others. The OECD report says, quote:
“In addition, this work further identifies the West Antarctic and the Greenland ice sheets as “initiators of tipping cascades” and the AMOC as the “mediator transmitting cascades” concluding that the polar ice sheets are of particular importance for the stability of the climate system as a whole.”
AMOC COLLAPSE DISASTER FOR MONSOONS AND FOOD IN TROPICS
But the AMOC collapse is a disaster that spreads to people and agriculture in the global South. The OECD says:
“Monsoon systems are likely to also be affected by a potential collapse or slowdown of the AMOC. Analysis by the OECD (2021) finds that West Africa will experience the largest decreases in rainfall on the planet under global warming scenarios. The shutdown of the AMOC will exacerbate this effect, disrupting the African monsoon and leading to further reduction in precipitation that can in turn, cause widespread drought over much of the region. A collapse of the AMOC would also lead to the weakening of the Indian summer monsoon which could lead to more frequent droughts with potentially detrimental impacts on Indian farmers’ rice harvests.”
THE EXETER AMOC TALK BY STEFAN RAHMSTORF
In this Radio Ecoshock show, I play a clip from a presentation by the German oceanographer Stefan Rahmstorf. It was recorded at the University of Exeter in November 2022.
Recently Rahmstorf says he had to revise his thinking on how soon an AMOC state change could arrive. Along with the IPCC, he though the collapse is very unlikely to arrive during this century. But due to at least three new studies, Rahmstorf changed his mind. He now agrees that, on our current high emissions path, this vital ocean circulation system could fall apart during the next decades. He revised his position post at RealClimate.org.
In that post, Rahmstorf adds:
“Another study, this time using 312 paleoclimatic proxy data series going back a millennium, is Michel et al. 2022. They argue to have found a ”robust estimate, as it is based on sufficiently long observations, that the Atlantic Multidecadal Variability may now be approaching a tipping point after which the Atlantic current system might undergo a critical transition.”
He addresses the new Ditlevsen paper on the BBC, July 26, 2023. I play a clip on the show.
SORTING OUT FACTS VERSUS MYTHS
Let’s sort out AMOC facts from myths. First of all, as Sabine Hossfelder says on YouTube, the Gulf Stream is not going to stop. AMOC is driven not by winds but by differences in heat and salt content. The Gulf Stream is partly driven by the rotation of the Earth, which is not affected by climate change.
1. AMOC IS NOT THE GULF STREAM
There is massive confusion about names and how the system works. Because so many people have heard of the Gulf Stream, the media and a few scientists talk as though the Gulf Stream and AMOC are the same thing. They are not.
But it’s not easy. People in Scotland calling the Atlantic current the Gulf Stream, even though the Gulf Stream technically ends when it mixes into northern waters around Labrador and up the sides of Greenland. As I understand it, the Gulf Stream does operate to move heat and water from the Tropics toward the Pole. No doubt it is part of the global ocean system called “The Great Conveyor Belt.”
When you sail east from the United States, say from Virginia heading toward the Caribbean, not far out to sea it becomes difficult to sail south. Ships encounter a steady flow of water, running up to 5 nautical miles per hour, going north. In a small boat that only goes 5 knots, you would stay in the same place with the engine running full power or sailing at top speed. Eventually further East, you are out of the Gulf Stream and can more easily sail south.
The AMOC is not a single identifiable current like that. It is a distributed system with a lot of different sub-currents curling around in the ocean. But there is a known general direction to the over-all flow. The AMOC is more that a current. Being an overturning circulation, ocean water becomes heavier with salt in the north and sinks to the bottom. From there it flows in a counter current around 2,000 meters, says 6,000 feet, below the surface. That cold bottom current goes all the way to Antarctica. AMOC is part of the pump that keeps sea water circulating between the Poles.
That is AMOC myth number One: it is not the same as the Gulf Stream. While AMOC can shift to a very weak state, called an “off-state” by experts, the Gulf Stream is driven by other factors including the rotation of the Earth, and will not stop even during rapid climate change. At least that’s what we think so far.
2. EUROPE WILL NOT EXPERIENCE ANOTHER ICE AGE IN TWO YEARS
Some people get a lot of clicks, Youtube views and Re_X’s by picking the worst possible outcome and exaggerating that.
The UK may get bad winter storms, like the amazing snow dump of 1952. But again, snow storms point to warmer weather, not extreme cold. When the air is really cold, like minus 30 or 40 on either temperature scale, that air cannot hold much water vapor. Heavy snow is less likely during extreme cold. Every northern Canadian grew up with the phrase “it’s too cold to snow”. Real temperature is what matters.
In a generally warming world, the worst predicted upon AMOC collapse is around 5 degrees C. average cooling in the UK, with 2 or 3 degrees more likely. The coldest days would likely be colder. Leaving changes in precipitation aside, just that much cooling with rearrange wild plant and animal survival in the United Kingdom (and Ireland), and the instability could wipe out crops in some seasons. A lot of buildings in the UK are not ready for a colder climate, being poorly insulated. Energy bills would go up, driving even more warming in the rest of the world.
Stefan Rahmsdorf suggests after the AMOC tipping point is passed, it might take two or three decades to fully expand the impacts, to cool the UK and north Europe as much as it can, not to mention harsh impacts on coastal Norway. But then, perhaps a century or two later, continued warming of the planet would overcome the AMOC collapse cooling. Dear old London would begin to warm again, long after the country has been completely rearranged by the ocean current collapse.
Nobody with any expertise in climate science believes the UK will become anything like the Ice Age. Manchester will not be covered by a glacier a mile thick.
3. IS AMOC OR THE GULF STREAM KEEPING UK AND EUROPE WARM?
Now we get to a tough question, still debated by some scientists: is AMOC or the Gulf Stream keeping UK and Europe warm? Almost everyone, including many top scientists say yes it is. But maybe not. This dispute is important, because if true, northern Europe may not be so heavily impacted by an AMOC shut-down.
Richard Seager is a climate scientist at Lamont Doherty Earth Observatory. Educated in the UK, he’s a Professor of Ocean and Climate Physics at Columbia. Seager is definitely not a fringe climate denier. But Professor Seager says the UK and North Europe are warmer than expected for their latitude not because of the Gulf Stream or any ocean current. Here is his explanation in a post called “Climate mythology: The Gulf Stream, European climate and Abrupt Change”:
Dr. Richard Seager, Lamont Doherty Earth Observatory.
“Using observations and climate models we found that, at the latitudes of Europe, the atmospheric heat transport exceeds that of the ocean by several fold. In winter it may even by an order of magnitude greater. Thus it is the atmosphere, not the ocean, that does the lion’s share of the work ameliorating winter climates in the extratropics. We also found that the seasonal absorption and release of heat by the ocean has a much larger impact on regional climates than does the movement of heat by ocean currents.
Seasonal storage and release accounts for half the winter temperature difference across the North Atlantic Ocean. But the 500 pound gorilla in how regional climates are determined around the Atlantic turned out to be the Rocky Mountains. Because of the need to conserve angular momentum, as air flows from the west across the mountains it is forced to first turn south and then to turn north further downstream. As such the mountains force cold air south into eastern North America and warm air north into western Europe. This waviness in the flow is responsible for the other half of the temperature difference across the North Atlantic Ocean.”
Saying “ocean heat transport contributes a small warming across the basin” Richard Seager suggests a slowdown of the Gulf Stream would: “introduce a modest cooling tendency.” If true, that would be great news for our UK listeners. But it does not address an increase in storminess and storm strength, or the large drop in precipitation for European agriculture and other global impacts.
Seager has published several papers in support of his insistence that atmospheric changes dominate over ocean current influences like AMOC. He does not say the UK and North Europe will not cool, just not as much as predicted by ocean modelers. It shows the level of uncertainty about what will really happen when the Atlantic Overturning goes into its off state. Personally I think the OECD scientists are well aware of atmospheric science and probably took these factors raised by Seager into account – and still found dangerous cooling for Europe in the waters ahead. But I am not an expert.
Seager’s peer-reviewed paper on this is “Is the Gulf Stream responsible for Europe’s mild winters?”
3. MYTH THREE: THE AMOC OPERATES ALONE
The third myth is that AMOC operates alone, as a separate system of the ocean. I raised this with Susanne Ditlevsen in our interview. We know AMOC is one end of a huge system of ocean water running from Pole to Pole. The Southern Ocean Overturning Circulation is the other end. As we learned in my April 2023 interview with Australia’s Dr. Matthew England, the southern pump is failing too. He told us the surface to deep water exchange there has already tipped.
As Western media gorged on Donald Trump news, climate activist Bill McKibben said this southern ocean change is the biggest story on the planet. You can download my interview with lead author Dr. England here.
We understand why whole teams of European scientists, and I include the UK, are working hard on what could happen to the AMOC. They examine every influence, satellite data and every report from the past. But as Ditlevsen said, they do not appear to add in the weakened pump at the other end of the system, in Antarctica and the Southern Ocean. We need a whole system approach.
Weakening overturning in the Southern Ocean could be an added significant reason why the Atlantic overturning system has already dropped by at least 15%. How big a factor is it? Will that drive a state shift in AMOC even sooner? We all need to know. I hope to see published research on this question.
Wrapping up, remember the AMOC collapsing by 2025 is a “rare possibility”, at the bottom end of a 75 year bracket of possible timing. The date of this doom-like huge scale ocean shift is likely determined by the rate humans continue to dump carbon dioxide and other greenhouse gases into the atmosphere. A miracle of climate action might stall the AMOC shift by a century or two. Maybe that would be enough time to find a solution.
Personally, I don’t see any signs of that miracle. We are going in reverse, funding new oil, gas and coal, and burning more than ever while slashing down the forest carbon sinks. You know all the bad news. My guess, for what it is worth: anyone under the age of 40 has a good chance of being alive to witness the biggest shift since civilization began: the Atlantic Meridional Overturning Circulation will collapse into it’s alternate weak state. Then we enter the “find out” phase. From what we see dimly, we produce a time of trials, dragging the rest of living things along with us.
NEXT WEEK ON RADIO ECOSHOCK
Next week on Radio Ecoshock, we revisit the eternal question: is it too late? This 2009 radio special is called “Enjoy Yourself, It’s Later Than You Think”, with clips from James Lovelock, Derrick Jensen, James Hansen and more, including a few tunes. Listen in.
I’m Alex Smith. Thank you for hanging out in this changing current, and caring about our world.
At the end of this week’s program, you hear the song “Enjoy Yourself (It’s Later Than You Think)” – Guy Lombardo (Canadian 1950).