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New studies confirm weakening of the Gulf Stream circulation (AMOC)

Filed under: — stefan @ 17 September 2020

Many of the earlier predictions of climate research have now become reality. The world is getting warmer, sea levels are rising faster and faster, and more frequent heat waves, extreme rainfall, devastating wildfires and more severe tropical storms are affecting many millions of people. Now there is growing evidence that another climate forecast is already coming true: the Gulf Stream system in the Atlantic is apparently weakening, with consequences for Europe too.

The gigantic overturning circulation of the Atlantic water (dubbed AMOC) moves almost 20 million cubic meters of water per second – almost a hundred times the Amazon flow. Warm surface water flows to the north and returns to the south as a cold deep current. This means an enormous heat transport – more than a million gigawatts, almost one hundred times the energy consumption of mankind. This heat is released into the air in the northern Atlantic and has a lasting effect on our climate.

But since the 1980s, climate researchers have been warning of a weakening or even a cessation of this flow as a result of global warming. In 1987, the famous US oceanographer Wally Broecker titled an article in the scientific journal Nature “Unpleasant surprises in the greenhouse”. Even Hollywood took up the subject in 2004 in the film “The Day After Tomorrow” by the German director Roland Emmerich. However, there were no measurement data that could prove an ongoing slowdown.

Only since 2004 has there been continuous monitoring at 26°N in the Atlantic (RAPID project). Although the data show a weakening of the current system, the measurement series is still too short to distinguish a possible climate trend from decadal variability. For the longer-term development of the Gulf Stream system, we must therefore rely on indirect evidence.

A long-term AMOC weakening should lead to a cooling in the northern Atlantic. Such a regional cooling in the middle of global warming has been predicted by climate models for a long time. And indeed, the evaluation of data on sea surface temperatures shows that the northern Atlantic is the only region of the world that has escaped global warming and has even cooled down since the 19th century (see graph). In addition, one can see a particularly strong warming off the North American coast, which according to model simulations is part of the characteristic “fingerprint” of a weakening of the Gulf Stream circulation.

Diagram of the Gulf Stream system with the warm surface current and the cold deep current. The actual Gulf Stream off the US coast is a part of this more comprehensive circulation system. The color shading shows the measured temperature trend since the late 19th century. This diagram is based on Caesar et al., Nature 2018 and first appeared in the Washington Post.

This fingerprint is regarded as important evidence, and not least because of this, the Intergovernmental Panel on Climate Change (IPCC) stated for the first time a year ago in the Summary for Policy Makers of its Special Report on the Oceans:

 “Observations, both in situ (2004–2017) and based on sea surface temperature reconstructions, indicate that the Atlantic Meridional Overturning Circulation (AMOC) has weakened relative to 1850–1900.”

New studies support long-term weakening

Two new studies now provide further independent evidence of this weakening. In August a paper by Christopher Piecuch of the Woods Hole Oceanographic Institution on the Florida Current – the part of the Gulf Stream system along the Florida coast – was published. Although continuous measurements of the current have only been available since 1982, Piecuch was able to reconstruct the strength of the Florida Current over the last 110 years from measurements of the sea level difference between the two sides of the current. To do so, he used 46 tide gauge stations in Florida and the Caribbean as well as a simple physical principle: the Coriolis force deflects currents in the northern hemisphere to the right, so that the water on the right side of a current stands higher than on the left. The stronger the current, the greater the difference in sea level. Comparison with measurements since 1982 shows that the method works reliably.

The result: the Florida current has weakened significantly since 1909 and in the last twenty years has probably been as weak as never before. Piecuch’s calculations also show that the resulting reduction of heat transport is sufficient to explain the ‘cold blob’ in the northern Atlantic.

This Monday, in Nature Climate Change a further study appeared, of researchers of Peking University and Ohio State University (Chenyu Zhu and Zhengyu Liu). For the first time, their paper provides evidence for an AMOC slowdown based on data from outside the North Atlantic. Model simulations show that a weakening of the AMOC leads to an accumulation of salt in the subtropical South Atlantic. This is due to the fact that strong evaporation in this region constantly increases the salinity, while the upper branch of the ocean circulation drains the salty water northwards, continually bringing in less salty water from the south. When this current weakens, the water in this region becomes saltier. This is exactly what the measured data show, in accordance with computer simulations. The authors speak of a “salinity fingerprint” of the weakening Atlantic circulation.

Video animation of ocean currents in the CM2.6 climate model of the Geophysical Fluid Dynamics Lab in Princeton:

In addition to these oceanographic measurements, a number of studies with sediment data indicate that the Gulf Stream circulation is now weaker than it has been for at least a millennium.

These current changes also affect Europe, because the ‘cold blob’ out in the Atlantic also influences the weather. It sounds paradoxical when you think of the shock frost scenario of the Hollywood blockbuster The Day After Tomorrow: but British researchers found that in summer the jet stream in the atmosphere likes to take a route around the south side of the cold blob – this then brings warm winds from the southwest into Europe, leading to heat waves there, as in the summer of 2015. Another study found a decrease in summer precipitation in northern Europe and stronger winter storms. What exactly the further consequences will be is the subject of current research.

However, the latest generation (CMIP6) of climate models shows one thing: if we continue to heat up our planet, the AMOC will weaken further – by 34 to 45% by 2100. This could bring us dangerously close to the tipping point at which the flow becomes unstable.

This article appeared originally in German in Der Spiegel: Das Golfstromsystem macht schlapp

269 Responses to “New studies confirm weakening of the Gulf Stream circulation (AMOC)”

  1. 251
    nigelj says:

    I am a layperson, but I do have a copy of my old physical geography text “Atmosphere, Weather and Climate” Barry and Chorley, 1971 edition, reprinted 1975, and the chapter on climate change makes no mention of some consensus view that cooling was coming, or anything like that, It did not even mention one study predicting cooling. If there was a consensus of some sort they would have mentioned it.It did discuss all the various related issues. I do realise this is near the middle of the flat period of temperatures, and things might have changed a bit subsequently, but it gives some indication to that point.

    The whole thing was obviously just media hype based on the views of a minority of scientists, amply demonstrated by the research study by Peterson 2008 which has never been adequately rebuted. I might pay attention if the denialists actually published a study, but we all know its not going to happen because they have nothing of substance to add.

  2. 252
    Al Bundy says:

    vic: I never claimed “an overwhelming scientific consensus” for cooling or anything else. All I did was post some excerpts

    AB: Ah, the “I’m not a perv/racist/denier/whatever. I just retweeted a perv/racist/denier/whatever” defense!

    It’s true that folks repeat stuff not only to support, but alternatively to ridicule via parody. But somehow I don’t see you on Stephen Colbert’s level…

    And I was there, too. I never heard anything remotely resembling what you describe. I kept hearing: “If humans weren’t here the planet would probably be heading into a glaciation, but human GHG emissions will at least lessen it, might prevent it, and might result in an increase in global temperatures. We just don’t know.”

    That was quite quickly replaced with, “Things are going to warm up. Now we have to figure out how much and what that means to the biosphere.”

    I am rather mystified that you think that you have a point. There was a question. Folks squabbled and postured and pontificated. Those who were wrong either died or pretended they were really always right, I mean, if you look at it properly.

    That’s what humans do.

    If your point is that folks act like people always have, then Whoop Dee Doo.

    If your point is that since people squabble today the dead losers of yesteryear who you agree with must have been right then no, it means you are as useful as a dead loser.

  3. 253
    John Pollack says:

    Victor @247 “Please learn to read before letting your assumptions run away with you. I never claimed ‘an overwhelming scientific consensus’ for cooling or anything else. All I did was post some excerpts from an article by Angus McFarlane. He’s the one who made the claim, not I. I have no idea whether or not there was ever a “scientific consensus” for cooling, nor do I care.”

    Apparently, we live by different rules. When I post something under my name, I consider myself responsible for it, whether it’s a weather forecast, or a quote from somebody else. If I disagree with part of what I am quoting from them, I believe that I am responsible for either making it clear that I disagree with that particular part, or, if feasible, not including it at all. So, the way I see it, if you quote somebody without comment, you agree with the quote. If you don’t, then make the disagreement clear, or don’t post it. Otherwise, it’s your opinion, too.
    If you didn’t care whether there was ever a scientific consensus for cooling or not, why post the quote.

    I don’t find it respectful or scientifically oriented to post things that you don’t care about, and then expect other people to figure out which part of the quoted rubbish you actually agree with. I do consider it telling that when you are actually called out on the content you post, you chose to blame it on the person you were quoting. Scientists retract statements when they make a mistake, as I did when I said that my dismissal of the numerical modelers as part of the “Wisconsin school” was unjustified, and later proved quite wrong.

  4. 254

    V 247: Clearly many climate scientists expressed alarm over the possibility that the global cooling trend so evident at the time was going to continue indefinitely

    BPL: What part of “there was never a consensus behind a global cooling crisis” do you not understand?

  5. 255
    MA Rodger says:

    With apologies to those who feel brevety is a blessing, which it is. But this is about crap always being halfway to the sea before the cork can be pulled from the disinfectant bottle.

    Victor Grauer of Pittsburgh PA,
    How long now have you been trolling up & down the comment threads of RealClimate? Six years!! Six years older and you’re not a single day wiser.

    Let us review your latest foray out from under your bridge and down this comment thread.

    @27 you ask our the author of the OP (HINT – who is a working climatologist) how a tiny one degree increase in global average temperature can be considered responsible for such dramatic fire, flood and storm while also bringing drought and melted ice cap: what science can explain how all this results from a simple one degree increase when the poles are many tens of degrees colder than the tropics? Oh and Victor, you do remember not to forget to include in all this the weakened AMOC which is the topic of discussion.
    Now this cannot be trolling because Victor Grauer of Pittsburgh PA isn’t a troll.

    @52&53 you make no attempt to engage with the resulting sarky criticism except to return like-with-like. Trollishly you deny making an argument and say you are too lazy to lift a finger for yourself.

    @74 (& @134) you appear incapable of understanding the word “warming” seemingly interpreting it to be equivalent to the word ‘warm’. Of course, while trolls are not to good with our language as they speak trollish, Victor Grauer of Pittsburgh PA isn’t a troll. He is plain stupid, too stupid to string an argument together as he admits @87 although he has forgotten this @97 when he vainly attempts such a feat, three-times. And @99 we get what is perhaps the Vicky Pollard response. And while you do better @117, perhaps, Victor, you need to pay more attention to Little Britain if you wish to employ such a stratagem.

    Then with things going a bit quiet on this particular theme, @141 we have a couple of disparate references nonchalantly lobbed into the thread for some reason, although obviously not an act of trolling, or part of an argument as Victor Grauer of Pittsburgh PA isn’t a troll and doesn’t do ‘argument’.

    And we could continue with longer passages of trollish nonsense presented @165&173 but there isn’t a great deal of point as @179&191 it is evident there has been zero progress since the apparently-trollish position set out @27 and we’re thus back where we started. (I say ‘apparently’ as Victor Grauer of Pittsburgh PA isn’t a troll, ‘apparently’.)

    @201 (although not @208&209&212) there is a sign of some less-than-trollish argument when the troll-blather is followed by a pack of denialist blather; accusations of climate alarmist blaming everything on temperature and increasing CO2 levels when we have seen temperature changes before. (Note that Victor Grauer of Pittsburgh PA isn’t a denier because he insisted he wasn’t one 6 years ago, although would a denier be aware of being in denial?)

    ……

    Then a complete change of suject is inserted into the thread. Hey, could it be about the AMOC & the topic of the thread?
    Don’t be daft! Of course not. Trolls don’t do ‘topic’ although Victor Grauer of Pittsburgh PA isn’t a troll, ‘apparently’.

    @211 we are treated to the ‘but back in the 1970s science said we would soon be freezing to death’ argument. Some obscure 1974 CIA document comfirms this, a document so important that the swivel-eyed Tory Spectator writes it up 35 years later.
    And of course, we all miss the point as Victor Grauer of Pittsburgh PA (who isn’t a troll, ‘apparently’) shows @222. The CIA document is “not just some media hype, concocted by journalists looking for an alarming story.” The drought, famine and flood of AGW is also shown to happen with global cooling. And there was a “consensus” on this (reportedly at a meeting in San Diego in 1974), just like there is today with AGW. And that means … go and figure it out yourselves.

    And we still miss the point as Victor Grauer of Pittsburgh PA (who isn’t a troll, ‘apparently’) shows @225. The point with the CIA document is it apparently shows official cooling alarmism in the 1970s that is an exact mirror to todays AGW alarmism. (So presumably as Victor Grauer of Pittsburgh PA who isn’t a troll, ‘apparently’, is saying of both 1970s cooling alarmism & today’s AGW alarmism – both are wrong.)
    Perhaps to reinforce this, @241 we are treated to a piece of denialist nonsense from 2019 that purports to show a scientific consensus for global cooling in the 1960s & 1970s. And if that were inadequate, @244 we are treated to a list of media reports from the 1970s about an impending global cooling.

    …….

    So what of the argument set out by Victor Grauer of Pittsburgh PA (who isn’t a troll, ‘apparently’)? What is it the old fool has been trying to say all this time?
    @247 we are led to believe the 1970s cooling concensus is not afterall part of it. Nor is the “mirror image” of the 1970s cooling with today’s AGW. Instead they are just “strikingly similar” in that “many climate scientists expressed alarm” over 1970s cooling as today alarm is expressed over AGW.

    So….

    There is perhaps an argument that the likes of the skyrocketeers have more press coverage that they merit (just a the cool-men of the 1970s). But where does that lead? Perhaps no further than to the adage that “Empty barrels make more noise.”

  6. 256
    Dan says:

    re: 247 and the global cooling myth. Read and learn (that last part may be hard given your history and apparent inability to comprehend science and the scientific method):
    http://www.realclimate.org/index.php/archives/2005/01/the-global-cooling-myth/

  7. 257
    Victor says:

    nigelj: Its a list of media hype and misinformation.

    V: Precisely. My point exactly. Media hype and misinformation — then AND now.

    n: When they say things like “scientists say” gullible people like Victor clearly think this means there’s a consensus or something.

    V: I never said there was a consensus. Stop assuming. Learn to read. The media are still basing their claims on what “scientists say.”

    n: But when you read the detail, or check their claims, it is just a small number of “scientists saying” these things, not the majority.

    V: Then as now. Typically what we now see are similarly alarming reports based on some “study” or other. Or do you really think today’s journalists in each case take a survey to determine whether the “findings” they so breathlessly report were supported by a consensus?

  8. 258
    Susan Anderson says:

    re anti-fact, anti-reality propagandists and distractionalists, who were first discredited by the likes of Socrates, and whose tactics were ably deconstructed by Schopenhauer in 1896:
    http://www.mnei.nl/schopenhauer/38-stratagems.htm

    I repeat:

    Better to remain silent and be thought a fool than to speak and to remove all doubt

    And to the rest, point by point debunking of this garbage validates and encourages it.

  9. 259

    Hey, if anybody needs an example of the increasingly popular “false equivalence,” Victor can hook you up. (#257, but you probably knew that.)

  10. 260
    jgnfld says:

    Re.: “…(that last part may be hard given your history and apparent inability to comprehend science and the scientific method)”

    Scientific method???, hell vic has shown on many occasions he doesn’t understand the meaning and interpretation of something so easy and basic as r=z’z/n

  11. 261
    John Pollack says:

    Victor @226 “I referenced it for one reason only: it holds up a mirror to the rampant climate change alarmism we now see all around us. What we see in that 1974 report comes so close to the hysteria of today that I initially assumed it must be a hoax, a deliberately contrived satire. Only it’s not.”

    John: What’s news to you is very old stuff to me, and a lot of other people on this board.

    Victor @247 “As for my status as a ‘troll,’ echoed endlessly by so many of the true believers posting here, my comments have invariably been on-topic, scientifically oriented and respectful.”

    John: And just how respectful and scientifically oriented is referring to concern about abrupt climate change as “hysteria?” You are telling us that we’re the equivalent of women who are letting our emotions run away with us and making a scene because of our possession of a uterus. I suppose that makes those of us identifying as male as “girly-men.” A gratuitous, trollish insult, for sure!

    As for “alarmism” : alarms have their purpose, and this is one. When your house is filling up with smoke, an alarm should get your attention and alert you to danger. There sure was a lot of smoke from the western U.S. this summer. In fact, one could see it in satellite pictures all the way over the Atlantic Ocean at times. As a forecaster, it was my job to raise an alarm about dangerous weather conditions. Nevertheless, there were people killed each year because they drove around barriers and into deep water. A climate alarm is entirely appropriate now, and it ought to keep blaring because humans aren’t doing nearly enough to avert large-scale disasters.

    Victor @226 (with affirmation by KW @243) “I also found it instructive to learn that so many climate scientists back then managed to attribute disasters such as drought, famine, flooding, and heavy rainfall to falling temperatures, in contrast to the climate scientists of today who attribute the same assortment of calamities to rising temperatures. The name of the game is: confirmation bias.”

    John: I already commented on this @240. Abrupt climate change causes a fairly similar set of disasters, whether it’s cooling or warming. (Notable exceptions are hurricanes and sea level rise for warming.) Agricultural failures, droughts, and flood are at risk either way. The locations may change, but the risks are similar.

    Here’s an analogy. We’re seated at a nice dinner party, starting the meal. Then, we notice four burly guys getting ready to give our rug a yank on the west side. The alarmists among us start yelling. “Stop! You’re going to make a big mess! You’ll spill the soup and the drinks, and break the plates. People will fall over and get hurt. Their dress clothes will be ruined.” The men go away, and the meal continues. The scientists in the group discuss how much of a yank it would take to actually spill all the stuff, knock the plates off, and topple people out of chairs. They work out approximate acceleration limits before varying levels of damage ensue. Toward the end of the meal, seven burly men show up to give the rug a yank on the east side. The scientists yell “Stop! You’re going to make a big mess. You’ll produce too much acceleration, and knock off the drinks and the china. People will topple over in their chairs, and get hurt. Their clothes will get ruined. The legs might even break off the table, and come down on people’s feet.” Victor and KW say “You scientists are just a bunch of alarmists. You predicted just about the same thing at the beginning of the meal, and nothing bad happened. Now you want us to believe that there will be the same type of disaster when the situation is totally opposite. It’s confirmation bias, and shows that you’re in denial of your own fallibility.”

  12. 262
    nigelj says:

    Victor @257 .

    “V: Precisely. My point exactly. Media hype and misinformation — then AND now.”

    n: There is one big difference you are overlooking. We have the IPCC now, a large global body that reviews the science. They even have sceptics who are reviewers for balance. Our media have accurately reported the findings of the IPCC. They know its easy for the public to google the IPCC studies so its not so easy for the media to just make stuff up. History moves on but you are not taking this into account.

    n: When they say things like “scientists say” gullible people like Victor clearly think this means there’s a consensus or something.

    V: I never said there was a consensus. Stop assuming. Learn to read. The media are still basing their claims on what “scientists say.”

    n: I didnt say you said there was a consensus. I said its obvious you agreed there was a consensus because all your rhetoric support the idea there was a consensus. You can pretend you have no position, but its just a pretense. You know it, and I know it.

    n: But when you read the detail, or check their claims, it is just a small number of “scientists saying” these things, not the majority.

    V: Then as now. Typically what we now see are similarly alarming reports based on some “study” or other. Or do you really think today’s journalists in each case take a survey to determine whether the “findings” they so breathlessly report were supported by a consensus?

    n: Wrong. At least 90% of climate scientists agree we are warming the climate according to numerous polls of scientists and studies of the papers they produce, and these have been published in peer reviewed journals so cannot be lightly dismissed.

    The studies include: Verheggen et al., 2014, Powell, 2013, John Cook et al., 2013, Farnsworth and Lichter, 2011, Anderegg, Prall, Harold, and Schneider, 2010, Doran and Kendall Zimmerman, 2009, Bray and von Storch, 2008, Oreskes, 2004, Bray and von Storch, 2003. One of these studies might be wrong, but its very unlikely they are all wrong. But you will treat this as something else inconvenient to sweep under the carpet. Refer:

    https://en.wikipedia.org/wiki/Surveys_of_scientists%27_views_on_climate_change

  13. 263
    Victor says:

    250 nigelj says:

    “No sorry, Victor is way off topic. The article is about the gulf stream slowing and Victor is talking about the general effects of warming and also alleged 1970s ice age predictions.”

    V: I was responding to Stefan’s claim that “Many of the earlier predictions of climate research have now become reality. The world is getting warmer, sea levels are rising faster and faster, and more frequent heat waves, extreme rainfall, devastating wildfires and more severe tropical storms are affecting many millions of people.” See above. I invoked those old “ice age” scares as they so closely mirror the alarmism of today, as exemplified by Stefan’s post. The certainties expressed in that CIA report are particularly apt in the light of Stefan’s confident proclamations.

    n: And his idea of trolling is wrong. Internet trolls are people who make inflammatory claims and this fits Victor perfectly.

    V: I don’t make inflammatory claims, I question them.

  14. 264

    KW 243: I think Victor draws a very valid comparison between the ’70s and now

    BPL: That says more about you than about Victor’s comparison.

  15. 265
    Ray Ladbury says:

    Weaktor@257
    And Jesus fricking wept! Dude, this is not a matter of the “media” distorting the conclusions of various studies. Read the fucking science!!! It is unequivocal.

  16. 266
    Victor says:

    re #255. I want to thank my biggest fan, MA Rodger, for providing such a complete, thorough (and amusing) summary of the points I’ve been making, not only on this thread, but during the entire six years (according to his count) since I made my debut on this forum. He seems to have carefully studied every single comment I’ve produced during that time, including those banished to the bore hole. I’m impressed. And touched. Seems like he knows me better than I know myself.

    Fascinating to see how his simplistic overview is riddled with insults and empty rhetoric in place of argument. Especially amusing is the “witty” take-off on Marc Antony’s famous speech in praise of Caesar: “Victor Grauer of Pittsburgh PA (who isn’t a troll, ‘apparently’)” — “Brutus is an honorable man. So are they all honorable men.”

    Honorable men indeed.

  17. 267
    nigelj says:

    Susan Anderson @258

    “re anti-fact, anti-reality propagandists and distractionalists, who were first discredited by the likes of Socrates, and whose tactics were ably deconstructed by Schopenhauer in 1896:”

    Thanks that list, its a cracking good read. For me this one sums it up best: “When your opponent uses an argument that is superficial, refute it by setting forth its superficial character. But it is better to meet the opponent with a counter argument that is just as superficial, and so dispose of him or her. For it is with victory that your are concerned, and not with truth.”

    Yep, its about victory, scoring points, a cheap thrill, not the truth. But winning debates does not always win the political election or truly win over the audience deep down. Rhetorical trickery works with the morons and politicians bases, but I suspect less so with astute people and undecided voters. This tricky style of debate is essentially based on deceptions of various kinds. Its kind of dirty. I’m no saint, but I just cant bring myself to use it very much. Victor is good with the empty rhetorical points scoring trickery. He uses it as a substitute for any real understanding of the issues.

    “And to the rest, point by point debunking of this garbage validates and encourages it.”

    There is indeed a risk of doing that, however if the denialists drivel is left unchallenged, there could be a risk it gains traction with the public (who can be gullible). By analogy, try going to court and not defending yourself and see how things go. Clever lawyers will destroy you, and you will loose badly.

    So in terms of dealing with denialists we have a ‘conundrum’ or a ‘dilemma’. I tend to think the best solution to responding to denialists is mostly a short, facts based response with one single link to the relevant science, and avoid engaging them in discussion. BUT on this website and this particular old thread, I doubt vast hordes of the general public are reading the comments, so a bit of discussion is entertaining and informative (MAR above is a classic example). So maybe just chill out a bit.

  18. 268
    Al Bundy says:

    John Pollack: Abrupt climate change causes a fairly similar set of disasters, whether it’s cooling or warming. (Notable exceptions are hurricanes and sea level rise for warming.) Agricultural failures, droughts, and flood are at risk either way. The locations may change, but the risks are similar.

    AB: Yep. And beyond the Global Means, if Georgia and Arizona swap rainfall, then even though no global change has occurred animals, plants, farmers, and regular people get scrawed.

    Biomes grow in place. Dirt grows in place. Systems grow in place. Techniques grow in place. Swapping stuff around is a grand way to initiate a Great Dying…

  19. 269
    Killian says:

    Susan Anderson: And to the rest, point by point debunking of this garbage validates and encourages it.

    They have been told for a very long time. As you can see, they are as addicted to their feeling superior and imagining they are protecting the world from evil, all while encouraging it by repetition, as victor, et al. are to their lying and ideologies.

    They will not give it up, or even slow down, and thus a solid 50-75% (rough guess) of these forums is denialist bullshit.

    Sad.