Study: There is no real evidence for a diminishing trend of the Atlantic Meridional Overturning Circulation

Topographic map of the Nordic Seas and subpolar basins with schematic circulation of surface currents (solid curves) and deep currents (dashed curves) that form a portion of the Atlantic meridional overturning circulation. Colors of curves indicate approximate temperatures. Source: R. Curry, Woods Hole Oceanographic Institution/Science/USGCRP.

Topographic map of the Nordic Seas and subpolar basins with schematic circulation of surface currents (solid curves) and deep currents (dashed curves) that form a portion of the Atlantic meridional overturning circulation. Colors of curves indicate approximate temperatures. Source: R. Curry, Woods Hole Oceanographic Institution/Science/USGCRP.

This paper was just published today in the Journal of Ocean Engineering and Science. It seems to be definitive refutation of Mann and Rahmstorf’s claims, and quells the alarm bells that climate proponents have been ringing for years, not just in Mannian science that’s been refuted time and again, but in Hollywood movies like The Day After Tomorrow. Doom and Gloom just isn’t happening when you look at the real-world data whereas Rahmstorf and Mann prefer to use computer models. In an email from the lead author Albert Parker, he noted:

[The AMOC is] apparently quite stable and not following the anthropogenic CO2 emissions

I’ll say:

amo_timeseries_1856-present-1[1]

The paper:

There is no real evidence for a diminishing trend of the Atlantic Meridional Overturning Circulation

A. Parker, C.D. Ollier

Abstract

The Atlantic Meridional Overturning Circulation (AMOC) is part of the great ocean “conveyor belt” that circulates heat around the globe. Since the early 2000s, ocean sensors have started to monitor the AMOC, but the measurements are still far from accurate and the time window does not permit the separation of short term variability from a longer term trend. Other works have claimed that global warming is slowing down the AMOC, based on models and proxies of temperatures. Some other observations demonstrate a stable circulation of the oceans. By using tide gauge data complementing recent satellite and ocean sensor observations, the stability of the AMOC is shown to go back to 1860. It is concluded that no available information has the due accuracy and time coverage to show a clear trend outside the inter-annual and multi-decadal variability in the direction of increasing or decreasing strength over the last decades.

Introduction

The Atlantic Meridional Overturning Circulation (AMOC) is a critical part of the Earth’s climate system transporting heat from the tropics and Southern Hemisphere toward the North Atlantic. The recent period of monitoring with ocean sensors cover is very short and does not permit the separation of short term variability from long term trends [3], [13],[17], [4], [16] and [18].

A recent study by Rahmstorf et al. [12] claims, based on models and proxies, that global warming is slowing down the circulation of the ocean. They say that their computational maps of temperature patterns over the 20th century show a significant area of cooling in the Northern Atlantic near Greenland and suggest that this cooling may be due to a reduction in the AMOC over the 20th century and especially after 1970. They believe the AMOC weakness after 1975 is an unprecedented event in the past millennium. They claim that further melting could contribute to further weakening of the AMOC.

The models and proxies of Rahmstorf et al. [12] predict the overturning circulation is slowing down as the greenhouse gases warm the planet and the melting ice adds freshwater to the ocean, but actual observations so far as Willis [18] and Rossby et al.[13] show no signs of any slowdown in the circulation.

(a) Values of the AMOCSSH and the AMOCMSL over the time window 1993 to 2014. (b) Extended AMOCMSL spanning more than 150 years. The AMOCSSH and the AMOCMSL well correlate each other. Over the time window 1856 to 2014, the AMOCMSL has a reducing trend of –0.82•10-2 Sv/year. Over the time window 1910 to 2014, the trend of the AMOCMSL is opposite of growing +0.24•10-2 Sv/year. The AMOCMSL drastically reduces over the last 10 years, but this is only the effect of the variability. This result demonstrates the significant stability of the AMOC merely subject to significant seasonal, inter-annual and multi-decadal variability. The AMOCMSL result exhibits a significant similarity in terms of positive and negative phases with the global temperature reconstructions as GISS temp. (c) Amplitude vs. period from the Fast Fourier Transform (FFT) of the detrended MSL of The Battery (NY) and Brest. (d) Amplitude vs. period from the Fast Fourier Transform (FFT) of the AMOCMSL. A quasi 60-years oscillation is evident in all the time series.

(a) Values of the AMOCSSH and the AMOCMSL over the time window 1993 to 2014. (b) Extended AMOCMSL spanning more than 150 years. The AMOCSSH and the AMOCMSL well correlate each other. Over the time window 1856 to 2014, the AMOCMSL has a reducing trend of –0.82•10-2 Sv/year. Over the time window 1910 to 2014, the trend of the AMOCMSL is opposite of growing +0.24•10-2 Sv/year. The AMOCMSL drastically reduces over the last 10 years, but this is only the effect of the variability. This result demonstrates the significant stability of the AMOC merely subject to significant seasonal, inter-annual and multi-decadal variability. The AMOCMSL result exhibits a significant similarity in terms of positive and negative phases with the global temperature reconstructions as GISS temp. (c) Amplitude vs. period from the Fast Fourier Transform (FFT) of the detrended MSL of The Battery (NY) and Brest. (d) Amplitude vs. period from the Fast Fourier Transform (FFT) of the AMOCMSL. A quasi 60-years oscillation is evident in all the time series.

Conclusions

Every approach proposed so far for the AMOC has indices that may or may not represent the long term trend in the AMOC depurated of the variability. Every approach interprets changes in the indices as supporting either no AMOC slowdown or a clear evidence for a slowdown. Either may be right or wrong, but they cannot both be right. Here we argue that there is no unquestionable evidence of any change in the AMOC signal if not variability.

The long-term sea level variations along the east coast of North America appear to be different north and south of Cape Hatteras. And the differences in north-south sea level change can be argued to reflect changes in the AMOC which then adjust the sea surface temperature (SST) patterns that make up the Atlantic Multi Decadal Oscillation (AMO). A stronger AMOC should lead to warmer temperatures in the Atlantic marking a positive AMO so the AMOC and AMO should be linked. Long-term AMO oscillations then argue for an oscillating AMOC over the past 50 years without a long-term trend.

There is no reliable measure of the AMOC direct or based on proxies that covers a sufficient time window to show a clear trend beyond inter-annual and multi-decadal variability. Claims of strengthening or reducing of the AMOC are therefore pure speculation

Significance

Our paper discusses the limits of all the indices and studies proposed so far for the AMOC, also introducing a novel long term index based on tide gauge results that is integrated with the recent satellite observations of sea surface height and temperature, salinity and velocity from profiling buoys. The paper concludes that there is no undoubtable evidence of a weakening or strengthening of the AMOC, as no index returns an accurate measure of the AMOC strength over a time window long enough to clear the longer term trend of the multi-decadal variability. The most likely pattern is oscillatory about a longer term trend not sufficiently well delineated.

Full paper, open source is here: http://www.sciencedirect.com/science/article/pii/S246801331500008X

57 thoughts on “Study: There is no real evidence for a diminishing trend of the Atlantic Meridional Overturning Circulation

  1. What is an non-Nobel Prize liar Tree Ring Nature Trickster, data hiding, FOI obfuscater (Michael Mann) doing talking about Atlantic circulation?

    • I forgot, malicious law suitor, and fatso… (in reference to the referenced paper Mann and Rahmstorf …not this one)

    • A little known fact is that Michelle Manners (Michael E. Mann) wrote his doctoral dissertation on ocean currents and the Atlantic Decadal Oscillation.

      • ok, that explains the ocean part, thanks, but what about, lying, obfuscating, Nobelling, nature tricking, and being a malicious fatso?… with a creepy gotee.

    • They’ve just said, “Nothing to see here”. They’re not going to turn around and say, “but give us a grant anyway.”

      The research necessary to answer the question involves filling the North Atlantic with Argo buoys and waiting a hundred years.

  2. Noticeable in the ice charts that this year there is less ice around Svalbard than usual. As the North Atlantic is cooler than normal, it’s strange as to where the heat is coming from.

    • Think ‘wind’. Several weeks of consistent wind will move ice around quite a bit. Sometimes, it packs the ice into the central Arctic, and sometimes usheres it out. This looks like a ‘pack it in’ year, but the overall ice volume is increasing for the last few years.

    • Where is the heat coming from ?.
      SW asia thanks to unusual blocking over Russia. This winter the blocking highs over Russia have extended far to the south then normal. Which has allowed the transport of warm air from SW Asia to push north up into the Arctic. Warming up western asia along the way. This warm southern wind would have aided melting and also would have pushed to ice northwards as well..

  3. Clear, concise, and definitive. “Pure speculation”! My favorite part. Except that I doubt anything done by Rahmsdorf or Mann can be pure.

  4. Now this IS something. Finally a paper that reports a continued null hypothesis (no evidence of a trend in current indices). Very rare indeed. That it got published by journals that much prefer sexier result is amazing.

    • It appears to coincide with the magnetic field of the sun. Correlation is not causation, but it might be a place to go hunt. The bottom of the AMO cycle in 1970s and 1910 were in phase with a relative decline in sunspots, etc. Of course, it might not have anything to do with them. Any oscillator will oscillate at its resonant frequency if you pump energy at it to some degree.

      • An abrupt slowdown of Atlantic Meridional Overturning Circulation during 1915–1935 induced by solar forcing in a coupled GCM

        http://www.clim-past-discuss.net/10/2519/2014/cpd-10-2519-2014.html

        “Abstract. In this study, we explore an abrupt change of Atlantic Meridional Overturning Circulation (AMOC) apparent in the historical run simulated by the second version of the Flexible Global Ocean–Atmosphere–Land System model – Spectral Version 2 (FGOALS-s2). The abrupt change is noted during the period from 1915 to 1935, in which the maximal AMOC value is weakened beyond 6 Sv (1 Sv = 106 m3 s−1). The abrupt signal first occurs at high latitudes (north of 46° N), then shifts gradually to middle latitudes (∼35° N) three to seven years later. The weakened AMOC can be explained in the following. The weak total solar irradiance (TSI) during early twentieth century decreases pole-to-equator temperature gradient in the upper stratosphere. The North polar vortex is weakened, which forces a negative North Atlantic Oscillation (NAO) phase during 1905–1914. The negative phase of NAO induces anomalous easterly winds in 50–70° N belts, which decrease the release of heat fluxes from ocean to atmosphere and induce surface warming over these regions. Through the surface ice–albedo feedback, the warming may lead to continuously melting sea ice in Baffin Bay and Davis Strait, which results in freshwater accumulation. This can lead to salinity and density reductions and then an abrupt slowdown of AMOC. Moreover, due to increased TSI after 1914, the enhanced Atlantic northward ocean heat transport from low to high latitudes induces an abrupt warming of sea surface temperature or upper ocean temperature in mid–high latitudes, which can also weaken the AMOC. The abrupt change of AMOC also appears in the PiControl run, which is associated with the lasting negative NAO phases due to natural variability.”
        More people should try it.

  5. Mann & Rahmstorf, amok catastrophe modellers and proxy jockeys whose theories keep going awry in the face of real science.

    I wonder what exciting fantasy climate theories they’ll come up with data they’ll torture and try to do away with next?

  6. And the AMO is in decline, perhaps for decades. That means northern hemisphere sea ice extent will move gradually back to the 1970s levels and annual changes when a coming ice age was in fashion. So therefore in about 20 years we will look back and conclude scientists and observers forgot how to read long term cycles of note. It will be called the Dark Ages of Cycle Recognition. Those pushing enlightenment at that point had better treed lightly and use carefully chosen words to state the obvious.

    • Let’s just call it the Dark Ages of Climate Science so that it covers everything currently going on. :) Seems like a perfect term for sooooo many aspects of it.

  7. Hansen’s new paper hi lights the AMOC disruptions promoted by Rahmstorf. This refutation will kick a major leg out of the catastrophe-mongering.

  8. Hopefully this paper will help to end the myth that the North Atlantic Drift is the cause of europe’s mild winters and the shutting down of the current will cause a ice age.

    • @taxed – it almost certainly is the cause of (western) Europe’s mild winters. That’s why there are palm trees growing at 58° north – same latitude as the non-vanishing polar bears at Churchill. The myth is that it’s about to shut down. It will at some point, when the present interglacial decides it’s had enough, but that is (a) in the future and (b) entirely out of our control, as this study nicely shows.

      • Smart Rock
        The cause of NW europe’s mild is the warm air flow from the mid Atlantic.
        ln December the UK had its warmist December on record even though the northern Atlantic was cool during this time. So Atlantic SST’s did not do a lot of cooling there. What will take europe into a ice age is increases in blocking patterns over the Greenland/northern europe area. Which will turn the warm SW air flow north towards Greenland or south towards southern europe. Leaving northern europe more expose to cold air coming from the north or east.
        You could say that there was a risk that this blocking would slow down the current due to blocking the movement of the prevailing winds which drive the current so aiding with the cooling. But even if this was the case. lt would be one of the effects of the cooling not the cause of it.

    • Actually, when that current does change salinity and runs shallower, that will trigger the next glaciation. It doesn’t shut down, it just doesn’t dump as much heat as it plunges into the deeps.

  9. The paper referenced by footnote 10 of the post paper is well worth a separate read and highlight. It pulls together a number observational threads to conclude Arctic summer sea ice extent has a ~ 60 year quasioscillatiion, and that the ice was likely begun a ~30 year recovery phase. That torpedos AGW Arctic amplification and ‘Arctic ice is going to disappear’ meme. Satellite coverage roughly coincided with the most recent ice peak in this quasioscillation. Thats gunna hurt the warmunists badly in a few years.

  10. A recent study by Rahmstorf et al. [12] claims, based on models and proxies, that global warming is slowing down the circulation of the ocean. They say that their computational maps of temperature patterns over the 20th century show a significant area of cooling in the Northern Atlantic near Greenland and suggest that this cooling may be due to a reduction in the AMOC over the 20th century and especially after 1970.

    Yet again we hear that warming causes cooling. Only in Oceania can this kind of “truth” exist. “Ignorance is strength.”

    • GTL,

      Exactamundo, compadre.

      Ocean circulation has nothing to do with CO2. Circulation is an effect of coriolis, and thermodynamics, as entropy tends to move everything toward the same temperature.

      It happens in a glass beaker, too. There are currents when there is a temperature differential — with or without CO2 present.

    • GTL….” Yet again we hear that warming causes cooling. Only in Oceania can this kind of “truth” exist. “Ignorance is strength.”……

      Well, why do you think Canada is so COLD ? It’s because us Canadian males are so HOT !!! LOL

    • You know….when you think about it…technically, warming DOES cause cooling….when two things in contact with each other are different temperatures, one of them warms and the other cools as it gives it’s warmth to the other….so….if “their computational maps of temperature patterns over the 20th century show a significant area of cooling in the Northern Atlantic near Greenland and suggest that this cooling may be due to a reduction in the AMOC over the 20th century and especially after 1970.” then something else SHOULD be warming to that same degree….right? And that means….duh..duh..duuuuuuuuuuuuuuh….we have MORE missing warming hiding somewhere folks! (you know…maybe we should start checking the “math” used to calculate that whole “amount of Sun’s energy coming in vs amount of energy escaping to space” thing??? Because maybe there’s really nothing missing after all….)

      So, if the Sun’s energy isn’t changing enough to cause that cooling, or the tilt of the Earth on it’s axis, or everyone in Greenland is leaving their fridge doors open…and we know it’s NOT the AMOC now….maybe it’s the additional CO2!! :) But if they don’t know what is causing this mysterious cooling…and they have to rely on PURE SPECULATION to even come close to answering the question, then it’s not hard to make the leap to the idea that anything else they have “suggested” might also be pure speculation as well.

      • In a warmist world, where heat can be transferred from CO2 in the atmosphere to the deep oceans without warming the water in between, I suspect speculation runs rampant.

    • Part of the problem with the Warmists is that they have to have an emergency to build their “15 minutes of fame” careers on. Multi decadal oscillations just don’t cut it, let alone natural ones. As far as I can see the phenomena described as “global warming” is almost entirely observed in the Northern hemisphere. With no evidence of any change in the Atlantic oscillation, the default assumption has to be we are in the midst of a normal cycle.

  11. “A stronger AMOC should lead to warmer temperatures in the Atlantic marking a positive AMO so the AMOC and AMO should be linked.”

    The reverse, a slower MOC leads to a warm AMO. driven by increased negative Arctic & North Atlantic Oscillation since the mid 1990’s, while more CO2 is modeled to increase positive AO/NAO. The faster MOC with a cold AMO is well obvious in the mid 1970’s, so it is now slower.
    Here you can see the slow MOC events occur during strong negative AO/NAO episodes both ends of 2010, mid 2012, and March 2013 (click on graph):
    http://www.rapid.ac.uk/

    • And this what should be driving it, strong solar wind +NAO and -AMO. and weaker solar wind -NAO and +AMO:

  12. There are real-world (ocean-going) oceanographers who look to actual data for confirmation/negation of hypotheses, and then there are academic (office-bound) ones who never look beyond their computer print-outs. Not hard to tell where Rahmstorf and the alarmists belong.

  13. This winter has shown how its the weather that has most impact on the european temps rather then this current. The northern Atlantic has been cool though out this winter, but that has not stopped the UK having a very mild winter. lts the blocking off of the mild SW air flow is the cause of climate cooling in europe, not the slowing down of this current. The temperature changes within europe itself during the rather prove this. For at times NW europe almost become as warm as the present, but NW Russia remained in the ice age. Other times things went the other way.
    lts hard to see how this would have happened if the slowing of this current was the cause of the ice age.

  14. The only way as l see it that warming can cause cooling is if it causes the weather patterns to become more static just to the south of the Arctic circle. Because given time these static patterns would cause climate cooling in the NH.

  15. Interesting clash between Hansen and Mann regarding the final version of Hansen’s multi-author paper of doom. http://www.atmos-chem-phys.net/16/3761/2016/acp-16-3761-2016.pdf

    Michael Mann, a Penn State university climate scientist familiar with the original study, commented, “Near as I can tell, the issues that caused me concern originally still remain in the revised manuscript. Namely, the projected amounts of meltwater seem unphysically large, and the ocean component of their model doesn’t resolve key wind-driven current systems (e.g. the Gulf Stream) which help transport heat poleward. That makes northern hemisphere temperatures in their study too sensitive to changes in the Atlantic meridional overturning ocean circulation,”</blockquote

    http://www.heraldonline.com/news/article67758027.html

  16. Definitely a slow deconstruction of the past 25 years alarmist science is going on. More proof of the CO2 CAGW thing ending with a whimper. Politicos seem to have what they need anyway so they are still moving ahead, the real science never having been of any interest.

  17. I wonder how the Warmists will treat this paper? Ignore it? Attack the authors? Attack the journal it’s puiblished in?

  18. Doesn’t this paper also raise even more questions about the validity of Hansen et al (2016) “we are all going to drown” paper pumped by Gillis in the NYT?

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