Perhaps, this blog spends too much time talking about the atmosphere, so to make amends today, let’s see what is happening to the temperature of the ocean surface. And see whether anything unusual is going on. Let’s start with yesterday’s sea surface temperatures around North America (below). Sorry, it is all in °C. Keep in mind that 10°C is roughly 50F, 20°C is around 68F, and 30°C is approximately 86F.
The eastern Pacific near the West Coast is cold (about 50F), with central California’s waters a bit cooler than ours. You must head to the southern tip of the Baja Peninsula to find the water warm enough for comfortable swimming.
The East Coast is a study in contrasts. The water off of New England is crazy cold (dropping below 7C), while the uber-warm Gulf Stream is found along the west coast of Florida, moves past the Carolinas, and then heads northeastward into the Atlantic.
There is a HUGE temperate contrast between the Gulf Stream current and the cold water of the Northeast. A blow-up of the sea surface temperatures off the Northwest really shows the amazing horizontal temperature changes north of the Gulf Stream
Look closely and you will waves in the interface between warm and cold water in the Atlantic and a fascinating loop in the warm water over the Gulf of Mexico (first image above). Very warm water over the Caribbean and west of Central America
Your next question is probably: is the current pattern of sea surface temperature unusual?
To evaluate this, the next map shows the difference between yesterday’s sea surface temperature and normal conditions (also called the SST anomaly).
Pretty close to normal off the Northwest coast. A few degrees colder than normal for California’s coastal waters. And near normal on Mexico’s west coast. Most of the Gulf and Atlantic coast is slightly above normal. Temperature is cooler than normal north of the Gulf Stream, which suggests that the Gulf Stream is south of its normal position by a hundred miles or so.
The biggest sea surface temperature story is what is happening in the tropical Pacific. Last year, a strong El Nino brought MUCH warmer than normal sea surface temperatures from South America, westward into the central Pacific.
But something major has happened. The tropical Pacific surface waters are rapidly cooling, resulting in cooler than normal waters in many locations (see map, with arrows showing you some of the coolest spots).
El Nino is dead. Long live La Nina, its frigid cousin!
The Atlantic Meridional Overturning Circulation (AMOC) is one of Earth’s major ocean circulation systems—it redistributes heat on our planet and is a key driver of climate variability. There is a northward transport of heat throughout the Atlantic, comprising one quarter of the global heat flux (reaching a maximum of 1.3PW at 25°N).
Figur 1. AMOC is the Atlantic section of the global Meridional Overturning Circulation (MOC). One part of it is the Gulf stream, that transports heat northwards from the tropics.
The heat transport is a balance of the northward flux of the warm Gulf Stream, Ekman pumping, and southward fluxes of cooler thermocline, and cold North Atlantic deep water. The circulation is completed after a very long time as the deep waters rise to the surface again in the Southern Ocean. The turnover period of AMOC is many hundreds of years.
Forecasts of cascading tipping points
Several studies have found evidence that both the Gulf stream and the AMOC have weakened during the last 40 years or so.[1][2][3] One highly publicized report warns that a continued weakening would have “severe impacts” and increase the risk of “cascading problems” for other major Earth systems, “such as the Antarctic ice sheet, tropical monsoon systems and Amazon rainforest” – see the figure below illustrating the major climate crisis teleconnections related to AMOC.[4] Climate crise effects would occur in many other areas as well. Stormier weather, more floods, collapsed plankton production, and widespread oxygen death in the oceans (anoxia) are forecast. The issue of AMOC’s whereabouts is therefore of great interest.
Figur 2. AMOC is a centerpiece in the cascades of tipping points thought up by alarmist researchers.[4]
What the IPCC says
The IPCC AR6 report highlights AMOC as a main building block in the climate and that it potentially is one of the most important ‘tipping points’.[5] Over the years, the IPCC has had dramatic projections for the AMOC. In the latest climate report (AR6) they claim that the AMOC currently is at its weakest for the last 1600 years and forecast a dramatic future decline.
Figur 3. AMOC-flow anomalies according to IPCC model simulations. The thick grey and black lines are the history as simulated by the two latest model generations. The colored lines are forecasts from the models according to selected emissions scenarios. Flows are in Sverdrups (Sv, million cubic meters per second). Source: AR6 WG1 fig. 9.10, which is taken from [3]
The IPCC claims that AMOC is “very likely” to weaken over the 21st century under all emission scenarios.[ch 4.3.2.3] An almost monotonous reduction by 25 to 50 percent in 2100 is predicted, depending on which scenario is chosen.
IPCC only has “medium confidence” that there will not be an “abrupt collapse” before 2100. If it collapsed, the world’s weather patterns would be dramatically impacted.
The revised history neatly fits the narrative that a decline in the AMOC is mainly caused by increased levels of greenhouse gases, i.e., that it is caused by anthropogenic global warming (AGW).
…but no decline seen in recent data from the Atlantic
Recently, we got an update from the measuring stations called RAPID, which directly measure the various flows that together constitute AMOC. RAPID measures AMOC at a series of stations, located at 26.5 N. The flows are measured in the Gulf Stream, another part is the Ekman transport, and finally the southbound return flow of different layers of cold water. These three components together form AMOC, see the red time series in the figure below (copied from the RAPID website).
Figur 4. Readings of the AMOC flows in Sverdrups (Sv). (A)MOC is the red curve with a flow of 16.8 ±4.6Sv. It comprises the Gulf stream (green, 31.3 ±3.1 Sv), the Ekman transport (black, 3.7 ±3.5 Sv), and the cold, deep southbound flow (lila, -18.2 ±3.4 Sv). The latest data are up until March 2022. Source: RAPID.
As can be seen from the figure, the AMOC did have a certain decrease at the very beginning of the RAPID measurement period, from 2004 until 2010, but after that AMOC is trend-stable. The Gulf stream shows a slight decrease, in line with the above-mentioned research, whereas the other components are stable. Volatility is also stable over time within a fairly large short-term variability.
Data collected directly in the Atlantic Ocean thus do not provide any support for the IPCC’s forecasts of an ongoing collapse of the AMOC.
IPCC’s forecasts disputed by field research
In recent years, a number of research reports have been published that put the IPCC forecasts into question.[6][7] Some of the researchers behind RAPID write that they can’t find any signs of a weakening AMOC during the last 30 years.[6] This is the very period where the revised history from IPCC claims there is a steep decline, due to their climate models. Reality vs. fiction.
The researchers write that AMOC rather seems to be “a decadal oscillation, which is superimposed on a multidecadal cycle”. Paleoclimatic records also show distinct multidecadal variability of the AMOC.
Which are then the dominant feedbacks and their associated timescales in AMOC’s natural variability? Is AMOC variability periodic, or quasi-periodic? The timescales, as well as the mechanisms behind these natural variations remain unexplained. This is no wonder, given the current’s extended turnaround time (100’s of years). The IPCC itself is not too sure about the state of the AMOC: “Given the large discrepancy between modelled and reconstructed AMOC in the twentieth century and the uncertainty over the realism of the 20th century modelled AMOC response (Section 3.5.4.1), we have low confidence in both.” (p. 9-32)
Summing up
The model makers have managed to create an impression of a steeper decline in the AMOC from 1990 and onwards by manipulating the models from the CMIP5 to the CMIP6 model generations. This manipulation of the history fits the climate crisis narrative that a decline in the AMOC is caused by greenhouse gas emissions and AGW.
The IPCC is not too convinced and gives a “low confidence” to the models. This doesn’t stop the IPCC from forecasting a sharp and monotonous decrease of the AMOC as “very likely“. They promote a climate crisis narrative entirely built on models they themselves give a low confidence rating.
The issue of natural variability is pertinent to all discussions on the AMOC, but remains unresolved. This doesn’t stop the IPCC from giving the primary role in AMOC developments to the effects of greenhouse gas emissions and AGW.
The empirical data on the water flows in the various strands of the AMOC in the Atlantic show no decline in the last 30 years. The AMOC is stable and doesn’t show any sign of decline.
References
[1] Robust Weakening of the Gulf Stream During the Past Four Decades Observed in the Florida Straits, Piecuch and Beal, 2023, https://doi.org/10.1029/2023GL105170
[2] Observation-based early-warning signals for a collapse of the Atlantic Meridional Overturning Circulation, Niklas Boers, Nature 2021, https://doi.org/10.1038/s41558-021-01097-4
[4] Exceeding 1.5°C global warming could trigger multiple climate tipping points, Armstrong McKay and 5 co-authors, Science 2022, https://doi.org/10.1126/science.abn7950
[6] A 30-year reconstruction of the Atlantic meridional overturning circulation shows no decline, Worthington and 5 co-authors, 2021, https://doi.org/10.5194/os-17-285-2021
[7] A stable Atlantic Meridional Overturning Circulation in a changing North Atlantic Ocean since the 1990s, Fu and 4 co-authors, Science 2022, https://doi.org/10.1126/sciadv.abc7836
Gabriel Oxenstierna is a PhD at Stockholm University and one of the Clintel signatories.
The lead and co-author have clearly different views on this: Lead author: “While we can definitively say this weakening is happening, we are unable to say to what extent it is related to climate change or whether it is a natural variation.” Co-author: “It saddens me to acknowledge, from our study and so many others, and from recent record-breaking headlines, that even the remotest parts of the ocean are now in the grip of our addiction to fossil fuels.” What have headlines got to do with science research? – – – The Gulf Stream transport of water through the Florida Strait has slowed by 4% over the past four decades, with a 99% certainty that this weakening is more than expected from random chance, according to a new study.
The Gulf Stream — which is a major ocean current off the U.S. East Coast and a part of the North Atlantic Ocean circulation — plays an important role in weather and climate, and a weakening could have significant implications, says Science Daily.
“We conclude with a high degree of confidence that Gulf Stream transport has indeed slowed by about 4% in the past 40 years, the first conclusive, unambiguous observational evidence that this ocean current has undergone significant change in the recent past,” states the journal article, “Robust weakening of the Gulf Stream during the past four decades observed in the Florida Straits,” published in Geophysical Research Letters.
The Florida Straits, located between the Florida Keys, Cuba, and The Bahamas, has been the site of many ocean observation campaigns dating to the 1980s and earlier. “This significant trend has emerged from the dataset only over the past ten years, the first unequivocal evidence for a recent multidecadal decline in this climate-relevant component of ocean circulation.”
The Gulf Stream affects regional weather, climate, and coastal conditions, including European surface air temperature and precipitation, coastal sea level along the Southeastern U.S., and North Atlantic hurricane activity. “Understanding past Gulf Stream changes is important for interpreting observed changes and predicting future trends in extreme events including droughts, floods, heatwaves, and storms,” according to the article.
“Determining trends in Gulf Stream transport is also relevant for clarifying whether elements of the large-scale North Atlantic circulation have changed, and determining how the ocean is feeding back on climate.”
“This is the strongest, most definitive evidence we have of the weakening of this climatically-relevant ocean current,” said Chris Piecuch, a physical oceanographer with the Woods Hole Oceanographic Institution, who is lead author of this study.
The paper does not conclude whether the Gulf Stream weakening is due to climate change or to natural factors, stating that future studies should try to identify the cause of the weakening.
“While we can definitively say this weakening is happening, we are unable to say to what extent it is related to climate change or whether it is a natural variation,” Piecuch said. “We can see similar weakening indicated in climate models, but for this paper we were not able to put together the observational evidence that would really allow us to pinpoint the cause of the observed decline.” . . . The study builds on many earlier studies to quantify long-term change in Gulf Stream transport. While the weakening found in the current study is consistent with hypotheses from many previous studies, Piecuch noted that the current study is “water-tight” and is “the first unequivocal evidence of a decline.”
Piecuch said that the finding of definitive evidence of the weakening of the Gulf Stream transport of water “is a testament to long-term ocean observing and the importance of sustaining long ocean records.”
The current study, which is part of a bigger six-year project funded by the National Science Foundation to make new measurements of the Gulf Stream at the Florida Straits, emphasizes the importance of having long-term observations, he said. “The more subtle that the change is that you are looking at, the longer is the observational record that you need to be able to tease that subtle change out of an observational time series.”
“Be very worried: Gulf Stream collapse could spark global chaos by 2025” announced the New York Post. “A crucial system of ocean currents is heading for a collapse that ‘would affect every person on the planet” noted CNN in the U.S. and repeated CTV News here in Canada.
One can only imagine how those already stricken with climate anxiety internalized this seemingly apocalyptic news as temperature records were being shattered across the globe.
This latest alarmist rhetoric provides a textbook example of how not to communicate climate science. These headlines do nothing to raise public awareness, let alone influence public policy to support climate solutions.
This is also not the first time such headlines have emerged. Back in 1998, the Atlantic Monthly published an article raising the alarm that global “warming could lead, paradoxically, to drastic cooling—a catastrophe that could threaten the survival of civilization.”
In 2002, editorials in the New York Times and Discover magazine offered the prediction of a forthcoming collapse of deep water formation in the North Atlantic, which would lead to the next ice age.
Building on the unfounded assertions in these earlier stories, BBC Horizon televised a 2003 documentary titled “The Big Chill,” and in 2004 Fortune magazine published “The Pentagon’s Weather Nightmare,” piling on where previous articles left off.
Seeing the opportunity for an exciting disaster movie, Hollywood stepped up to created The Day After Tomorrow in which every known law of thermodynamics was ever so creatively violated.
The latest series of alarmist headlines may not have fixated on an impending ice age, but they still suggest the Atlantic meridional overturning circulation could collapse by 2025. This is an outrageous claim at best and a completely irresponsible pronouncement at worst.
The sweetspot of climate communications strikes an optomistic tone while reinforcing that change is possible. Credit: Andrew Weaver
The Intergovernmental Panel on Climate Change has been assessing the likelihood of a cessation of deep-water formation in the North Atlantic for decades. In fact, I was on the writing team of the 2007 4th Assessment Report where we concluded that:
“It is very likely that the Atlantic Ocean Meridional Overturning Circulation (MOC) will slow down during the course of the 21st century. It is very unlikely that the MOC will undergo a large abrupt transition during the course of the 21st century.”
The 6th assessment report went further to conclude that:
“There is no observational evidence of a trend in the Atlantic Meridional Overturning Circulation (AMOC), based on the decade-long record of the complete AMOC and longer records of individual AMOC components.”
Understanding climate optimism
Hannah Ritchie, the deputy editor and lead researcher at Our World in Data and a senior researcher at the Oxford Martin School, recently penned an article for Vox where she proposed an elegant framework for how people see the world and their ability to facilitate change.
Ritchie’s framework lumped people into four general categories based on combinations of those who are optimistic and those who are pessimistic about the future, as well as those who believe and those who don’t believe that we have agency to shape the future based on today’s decisions and actions.
Ritchie persuasively argued that more people located in the green “optimistic and changeable” box are what is needed to advance climate solutions. Those positioned elsewhere are not effective in advancing such solutions.
More importantly, rather than instilling a sense of optimism that global warming is a solvable problem, the extreme behavior (fear mongering or civil disobedience) of the “pessimistic changeable” group (such as many within the Extinction Rebellion movement), often does nothing more than drive the public towards the “pessimistic not changeable” group.
A responsibility to communicate, responsibly
Unfortunately, extremely low probability, and often poorly understood tipping point scenarios, often end up being misinterpreted as likely and imminent climate events.
In many cases, the nuances of scientific uncertainty, particularly around the differences between hypothesis posing and hypothesis testing, are lost on the lay reader when a study goes viral across social media. This is only amplified in situations where scientists make statements where creative license is taken with speculative possibilities. Possibilities that reader-starved journalists are only too happy to play up in clickbait headlines.
Through independent research and the writing of IPCC reports, the climate science community operates from a position of privilege in the public discourse of climate change science, its impacts and solutions.
Climate scientists have agency in the advancement of climate solutions, and with that agency comes a responsibility to avoid sensationalism. By not tempering their speech, they risk further ratcheting up the rhetoric with nothing to offer in terms of overall solutions or risk reduction.
A review of the Guardian’s habitual Gulf Stream misreporting.
Is there no loyalty among climate extremists? The Guardian makes a mistake about the fundamental difference between the Gulf Stream and the Atlantic Meridional Overturning Circulation (AMOC) and suddenly everyone is on its case, some accusing it of sloppy reporting, others demanding a correction of its fake news, (which didn’t come.) To be fair it wasn’t just the Guardian – the BBC, CNN and others also got it wrong.
The Gulf Stream – which brings warm water to North West Europe – is not the same as the AMOC. They are two fundamentally different currents. Unless the Earth ceases to be a globe, ceases to have oceans and ceases to turn – something that even the Guardian hasn’t yet alarmed us about – the Gulf Stream will be with us.
The AMOC is important for climate because it is the large-scale overturning motion in the Atlantic. It has demonstrated instabilities in the past, especially during the last Ice Age due to large influxes of fresh water. It has weakened over at least the past 100 years, possibly the last thousand years. Some believe this weakening, or at least its most recent activity, is due to human influence, but that is mostly conjecture as we do not understand the decadal and centennial natural variability of the AMOC, let alone longer-term ocean cycles. Standard climate models maintain that the risk of the AMOC collapsing is small.
It’s not as though the Guardian hasn’t been fighting on the alarmist front using ocean currents many, many time before.
Last year it told us that we are on the brink, or may even have passed, five ‘disastrous’ tipping points; the collapse of Greenland’s ice cap, the melting of permafrost, changes to the great northern forests, the loss of mountain glaciers and of course, the collapse of the AMOC.
Two years ago the same journalist told us the same story … that ‘scientists had spotted warning signs of Gulf Stream collapse’ – again confusing the Gulf Stream with the AMOC.
The tipping points also make another appearance as they may have been crossed two years previously.
The same journalist got the Gulf Stream and the AMOC mixed up 2018, saying that the Gulf Stream was at its weakest in 1600 years. He added that it threw into question alarmist predictions of a looming catastrophic collapse as it would take centuries to occur. The Guardian claimed that it was now 15% weaker than it was around 400 AD, and humans were responsible for a significant part of that weakening.
The latest surge in the Guardian’s habitual Gulf Stream misreporting was based on two Danish researcher who announced a sharp weakening of ocean currents around the North Atlantic, predicting “a collapse of the AMOC to occur around mid-century under the current scenario of future emissions,” or even as soon as two year time.
This research was not based on climate models but based on so-called instability research in which a system, in this case the AMOC, exhibits instability and more variability just before it reaches a so-called tipping point and transitions to a new state.
Given the lack of understanding of its current dynamics and its past variability, the public would be well advised to take worst case predictions with a pinch of salt.
Atlantic Meridional Overturning Circulation (AMOC). Red colours indicate warm, shallow currents and blue colours indicate cold, deep return flows. Modified from Church, 2007, A change in circulation? Science, 317(5840), 908–909. doi:10.1126/science.1147796
Leave it to CNN to jump the shark with scary claims Excerpts in italics with my bolds.
A new study published Tuesday in the journal Nature, found that the Atlantic Meridional Overturning Current – of which the Gulf Stream is a part – could collapse around the middle of the century, or even as early as 2025.
Scientists uninvolved with this study told CNN the exact tipping point for the critical system is uncertain, and that measurements of the currents have so far showed little trend or change. But they agreed these results are alarming and provide new evidence that the tipping point could occur sooner than previously thought.
Yike! Shades of Day After Tomorrow
Scientists Admonish Against Going Over the Top
Fortunately knowledgable experts in the area have weighed with context and perspective at Science Media Centre
Of course some commented as cheerleaders, but many cautioned against exaggeration and speculation. The RAPID programme (see diagram at top) measures daily flows of water at several depths between the North Atlantic and Arctic oceans, and its scientific coordinator, Prof Meric Srokosz, National Oceanography Centre, University of Southampton, said:
While the possible collapse of the AMOC with significant climatic impacts is a concern, providing a warning of its collapse is problematic as a long set of observations is required. In this paper the warning depends on using proxy AMOC data (here based on sea surface temperature, SST) as direct continuous AMOC measurements are only available since 2004. The warning comes from applying statistical techniques to a long time series (over a century) of proxy AMOC data, but the warning is only as good as the proxy data are in representing the true AMOC. So, this warning needs to be treated with caution as there is no consensus as to which proxies can accurately capture the behaviour of the AMOC over the long term.”
Prof Penny Holliday, Head of Marine Physics and Ocean Circulation at the National Oceanography Centre, and Principal Investigator for OSNAP, an international programme researching AMOC processes, variability and impacts, said:
“Confidence in the validity of the conclusions are undermined by our knowledge that sea surface temperature of the North Atlantic subpolar gyre is not a clear indicator of the state of the AMOC, and that there is no evidence that the AMOC has dramatically weakened in the past 50-75 years. A collapse of the AMOC would profoundly impact every person on Earth but this study overstates the certainly in the likelihood of it taking place within the next few years.”
Does the press release accurately reflect the science?
“On the whole it does – the title of the paper is more sensational than the actual statements within it, and the press release does make that clear. However there are two statements that are not accurate as follows:
‘The strength of the AMOC has only been monitored continuously since 2004 and these observations have shown AMOC to be weakening’
“This is stated in the paper but it is not correct information. The observations since 2004 show that the AMOC goes through fluctuations of being in a stronger or weaker state that last for about 10 years. The observations since 2004 show the subtropical AMOC getting slower from 2004 to 2012, but gradually becoming stronger since then. The only data from AMOC observations shown in the paper are from 5 sparse ship surveys and are used out of context – the authors use them to argue for a severe decline in the AMOC, but that interpretation has long been discredited in the scientific literature (including in the reference they cite for it).
‘The authors found early warning signals of a critical transition of the AMOC system and suggest that it could shut down or collapse as early as 2025 and no later than 2095.’
“This is not quite as the paper states. In the paper the time period of potential collapse depends on choices they have made in how they construct the time series of sea surface temperature which they use as evidence for change. They present three versions of the temperature records, and the three resulting model predictions suggests a collapse is ‘likely’ at any time from 2024 to 2180. The 2025-2095 is the period of time their statistical model predicts that a full or partial collapse is most likely.
How does this work fit with the existing evidence?
“The conclusions are different to the consensus derived from climate projections as described by the IPCC AR6 assessment. The averaged AMOC projections from climate models under all the IPCC emissions scenarios all show an AMOC decline, but not a collapse (a “high confidence” conclusion). Some individual climate model runs do show a future collapse in the AMOC, so the possibility cannot be entirely ruled out.
Are there any important limitations to be aware of?
“There are some questionable assertions and decisions in the methods as follows. The authors state confidently that the sea surface temperature (SST) of the North Atlantic subpolar gyre can be used as a proxy for the strength of the AMOC. The validity of an SST proxy for AMOC strength is a matter of ongoing scientific debate however, because it is based on model behaviour and is not proven using real-world data.
There is solid evidence that there is no such clear relationship, especially on timescales of less than 30 years.
“I believe the authors have overstated the pattern of subpolar North Atlantic SST change by subtracting two (and three) times the global mean surface temperature trend. This is not the usual approach for highlighting North Atlantic regional temperature trend (instead it is more usual to subtract just 1 x the global trend). The choice means that some of the SST data they use in the statistical model has exaggerated decline since the 1970s when the global SST began to sharply rise. In the version of the statistical model for which the global mean SST trend is removed, the predicted likely time of a partial or complete collapse becomes later and over a wider window of time.
“As mentioned above, the actual observations of AMOC since 2004 have long-since discredited the evidence that the authors are using to validate their modified SST temperature record. The 5 data points they show in the paper were collected several years apart by ship surveys, and it is well known and well established that they give a highly misleading impression of AMOC decline. All the observational evidence we have shows no evidence of dramatic decline in the AMOC over the past 50-75 years.
How uncertain are the uncertainties?
“The authors say that the model’s 95% confidence interval is 2025-2095. This is a measure of statistical uncertainty and they state in the discussion that they cannot rule out slowing rather than a collapse, as well as listing other reservations and caveats. Because of the limitations of their use of modified SST as a proxy for AMOC, the uncertainty in the stated message in the title and abstract is high.
What are the implications in the real world?
“The potential for the AMOC system of currents to collapse under global warming is a high impact, low likelihood scenario, and policymakers and planners do need to be aware of it. NOC and international partners are investing in ongoing observations of the AMOC in order to determine how closely changes in AMOC contribute to changes in SST and consequential climate and social and economic impacts on people. The strength of the out-of-sight ocean currents of the AMOC has surprisingly direct impacts on food, water and energy security, infrastructure risk, biodiversity, and human health. The paper demonstrates that decades of observations are needed to be able to detect a major tipping point in the AMOC, and the authors call for continued measurements of these great Atlantic ocean currents for long enough to do so.
Prof. Dr. Jochem Marotzke, Director of the Department Ocean in the Earth System, Max-Planck-Institute for Meteorology, Hamburg, Germany, said:
“The work provides no reason to change the assessment of the 6th IPCC Assessment Report: ‘There is medium confidence that there will be no abrupt collapse before 2100′. The statement so confidently made in this paper that collapse will occur in the 21st century has feet of clay. The maths are solid, but the starting point is highly dubious: the essential equation – marked with (1) in the paper – relies on the simplified models representing bifurcation – i.e. AMOC collapse – also being correct. But the more comprehensive models do not show this very bifurcation. In this respect, the paper does not live up to its self-imposed claim: ‘The strategy is to infer the evolution of the AMOC solely on observed changes in mean, variance and autocorrelation.’
The interpretation relies to an enormous extent on the authors’ theoretical understanding being correct, and there are huge doubts about that.
“It must be added that there is considerable doubt as to whether surface temperature measurements are a valid proxy for the AMOC. Again, the paper addresses these uncertainties inadequately.
“When reporting about this study, it is important to include the key aspects in which this paper fails to include the scientific uncertainties.
Prof Niklas Boers, Professor of Earth System Modelling at the Technical University of Munich, said:
“I do not agree with the outcome of this study. While the qualitative statement that the AMOC has been losing stability in the course of the last century is true and supported by the data, uncertainties are too high to reliably estimate a time of tipping. In particular, the uncertainties in the heavily oversimplified model assumptions by the authors are too high. Moreover, the uncertainties in the underlying datasets are huge and would make the extrapolation carried out by the authors far too uncertain to actually report a year or even a decade for the AMOC tipping.”
Fig. 1. Schematic of the major warm (red to yellow) and cold (blue to purple) water pathways in the NASPG (North Atlantic subpolar gyre ) credit: H. Furey, Woods Hole Oceanographic Institution): Denmark Strait (DS), Faroe Bank Channel (FBC), East and West Greenland Currents (EGC and WGC, respectively), NAC, DSO, and ISO.
The Gulf Stream system could collapse as soon as 2025, a new study suggests. The shutting down of the vital ocean currents, called the Atlantic Meridional Overturning Circulation (Amoc) by scientists, would bring catastrophic climate impacts.
The new analysis estimates a timescale for the collapse of between 2025 and 2095, with a central estimate of 2050, if global carbon emissions are not reduced. Evidence from past collapses indicate changes of temperature of 10C in a few decades, although these occurred during ice ages.
“I think we should be very worried,” said Prof Peter Ditlevsen, at the University of Copenhagen in Denmark, and who led the new study. “This would be a very, very large change. The Amoc has not been shut off for 12,000 years.”
The Atlantic meridional overturning circulation (AMOC) is a major tipping element in the climate system and a future collapse would have severe impacts on the climate in the North Atlantic region. In recent years weakening in circulation has been reported, but assessments by the Intergovernmental Panel on Climate Change (IPCC), based on the Climate Model Intercomparison Project (CMIP) model simulations suggest that a full collapse is unlikely within the 21st century. Tipping to an undesired state in the climate is, however, a growing concern with increasing greenhouse gas concentrations. Predictions based on observations rely on detecting early-warning signals, primarily an increase in variance (loss of resilience) and increased autocorrelation (critical slowing down), which have recently been reported for the AMOC. Here we provide statistical significance and data-driven estimators for the time of tipping. We estimate a collapse of the AMOC to occur around mid-century under the current scenario of future emissions.
If the AMOC collapse occurred it would likely be really bad, temperatures in Europe and North America could plunge, and Europe and North America would likely experience ice age like conditions which could last hundreds, or even thousands of years.
An AMOC collapse is believed to have caused the Younger Dryas, an abrupt return to Northern Hemisphere ice age conditions which occurred 12,900 years ago, which lasted over a thousand years.
An AMOC collapse is believed to have caused the Younger Dryas, an abrupt return to Northern Hemisphere ice age conditions which occurred 12,900 years ago, which lasted over a thousand years.
The scientists in the body of the study above admit continuous monitoring of the AMOC only started in 2004, which seems a pretty short baseline to make long term forecasts. But there have been other attempts to reconstruct the recent history of the AMOC, which have produced far less conclusive results.
The evolution of the North Atlantic Meridional Overturning Circulation since 1980
The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the climate through its transport of heat in the North Atlantic Ocean. Decadal changes in the AMOC, whether through internal variability or anthropogenically forced weakening, therefore have wide-ranging impacts. In this Review, we synthesize the understanding of contemporary decadal variability in the AMOC, bringing together evidence from observations, ocean reanalyses, forced models and AMOC proxies. Since 1980, there is evidence for periods of strengthening and weakening, although the magnitudes of change (5–25%) are uncertain. In the subpolar North Atlantic, the AMOC strengthened until the mid-1990s and then weakened until the early 2010s, with some evidence of a strengthening thereafter; these changes are probably linked to buoyancy forcing related to the North Atlantic Oscillation. In the subtropics, there is some evidence of the AMOC strengthening from 2001 to 2005 and strong evidence of a weakening from 2005 to 2014. Such large interannual and decadal variability complicates the detection of ongoing long-term trends, but does not preclude a weakening associated with anthropogenic warming. Research priorities include developing robust and sustainable solutions for the long-term monitoring of the AMOC, observation–modelling collaborations to improve the representation of processes in the North Atlantic and better ways to distinguish anthropogenic weakening from internal variability. The Atlantic Meridional Overturning Circulation (AMOC) has a key role in the climate system. This Review documents AMOC variability since 1980, revealing periods of decadal-scale weakening and strengthening that differ between the subpolar and subtropical regions.
One thing which is missing from today’s forecasts of imminent AMOC collapse is a large body of fresh water which could be the potential trigger for the collapse. The Younger Dryas collapse in Northern Hemisphere temperatures was believed to have been caused by disruption to ocean currents which occurred when a gigantic glacial lake sitting on the North American and Canadian ice sheet abruptly discharged thousands of cubic miles of water into the Atlantic Ocean, though there is evidence a lot of fresh water may have ended up in the Arctic Ocean.
Identification of Younger Dryas outburst flood path from Lake Agassiz to the Arctic Ocean
The melting Laurentide Ice Sheet discharged thousands of cubic kilometres of fresh water each year into surrounding oceans, at times suppressing the Atlantic meridional overturning circulation and triggering abrupt climate change1,2,3,4. Understanding the physical mechanisms leading to events such as the Younger Dryas cold interval requires identification of the paths and timing of the freshwater discharges. Although Broecker et al. hypothesized in 1989 that an outburst from glacial Lake Agassiz triggered the Younger Dryas 1, specific evidence has so far proved elusive, leading Broecker to conclude in 2006 that “our inability to identify the path taken by the flood is disconcerting”2. Here we identify the missing flood path—evident from gravels and a regional erosion surface—running through the Mackenzie River system in the Canadian Arctic Coastal Plain. Our modelling of the isostatically adjusted surface in the upstream Fort McMurray region, and a slight revision of the ice margin at this time, allows Lake Agassiz to spill into the Mackenzie drainage basin. From optically stimulated luminescence dating we have determined the approximate age of this Mackenzie River flood into the Arctic Ocean to be shortly after 13,000 years ago, near the start of the Younger Dryas. We attribute to this flood a boulder terrace near Fort McMurray with calibrated radiocarbon dates of over 11,500 years ago. A large flood into the Arctic Ocean at the start of the Younger Dryas leads us to reject the widespread view that Agassiz overflow at this time was solely eastward into the North Atlantic Ocean.
If say the Greenland Ice Sheet were to form a gigantic glacial lake comparable to Lake Agassiz, that would be a major cause for concern. Such a lake could potentially deliver a devastating impulse of fresh water to the far North, potentially triggering a replay of the environmental catastrophe which some believe caused the Younger Dryas mini ice age.
But to my knowledge, no similar glacial lake exists in today’s world.
In the absence of a credible source of a fresh water impulse on the scale of Lake Agassiz, the lack of clear understanding of exactly what happened 12,900 years ago, short evidential baselines, and the absence of firm observational evidence of a looming AMOC collapse, lets say I’m not about to lose sleep over claims we are approaching an imminent major climate tipping point.
For more information on climate uncertainties and risks, click here.
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Global warming, climate change, all these things are just a dream come true for politicians. I deal with evidence and not with frightening computer models because the seeker after truth does not put his faith in any consensus. The road to the truth is long and hard, but this is the road we must follow. People who describe the unprecedented comfort and ease of modern life as a climate disaster, in my opinion have no idea what a real problem is.
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