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Models versus observations: AMOC edition

15 Nov 2023 | Science Notes

The Atlantic Meridional Overturning Circulation or AMOC, which we have mentioned previously including in our Pentagon Crystal Ball video, and which is better known as the “Gulf Stream” (though technically the part that hauls warm water from the Caribbean to Europe is only part of the AMOC system) has been a thorn in the side of climate modelers for a long time. It’s the sort of massive and influential component of the climate system that they really need to be able to get right if they are going to claim that the science is settled and they know what will happen to it over the next century. But they don’t get it right, and as a new study shows, the more they tweak the models, if anything the worse they get.

A new study (h/t NoTricksZone) by a pair of scientists from Ireland and Germany comparing climate model simulations of the AMOC over the post-1950 period demonstrates that, well, let’s let the authors tell us:

“We show that both the magnitude of the trend in the AMOC over different time periods and often even the sign of the trend differs between observations and climate model ensemble mean, with the magnitude of the trend difference becoming even greater when looking at the CMIP6 ensemble compared to CMIP5.”

“CMIP6” refers to the latest climate models and “CMIP5” refers to the ones before. The authors go on:

“Comparing the models’ AMOC evolution to the observational data (figure 3, lower panel), we find that neither the CMIP5 nor the CMIP6 ensemble mean are successful at representing the observational AMOC data... Overall, we find that the various AMOC reconstructions based on observational data have discrepancies but agree with each other better than with the multi-model ensemble means. While, for the post-2004 period the sign of the trend suggested by the CMIP ensemble means agrees with the one found in the observational evidence, it is off for the earlier time periods with the CMIP models suggesting an overall strengthening from 1957 to 1992 but a weakening from 1993 to 2004 and the observational data suggesting the opposite. It is also interesting to note that the CMIP6 ensemble mean tends to show greater discrepancies with the observations than the CMIP5 ensemble mean.”

So over the past 70 years there was a long weakening of the AMOC while the models said it should be strengthening. Then there was a weakening from 1993 until the middle of the past decade when the models said it should be strengthening. Other than that minor malfunction over pretty much the whole period in question, though, the models are working great.

The failure of models to get the AMOC right doesn’t necessarily mean the future will involve less warming than expected. The authors point out that maybe the weakening AMOC, by cooling Europe a bit, suppressed some warming and if the AMOC strengthens in the future instead of weakening like the models say it’s going to, that could lead to even more warming. It just means the models are no use at all in predicting the future because they can’t even explain the past.

Which does surely raise the question why the IPCC says it has such high confidence in them. Can it be that they tell it what it wants to hear?

“We finish with a pessimistic statement: if it is not possible to reconcile climate models and observations of the AMOC in the historical period, then we believe the statements about future confidence about AMOC evolution should be revised. Low confidence in the past should mean lower confidence for the future! The IPCC AR6 report ranks it as very likely that the AMOC will decline in a changing climate. But, if these models cannot reproduce past variations, why should we be so confident about their ability to predict the future?”

Why indeed? And if they know the models can’t get the AMOC right, yet the IPCC declares high confidence in their projections for that one phenomenon, why should we believe any of their projections including those that involve unreliable estimates of a series of interlocking systems?

2 comments on “Models versus observations: AMOC edition”

  1. It is truly amazing to see grown men and women of science treat climate models as if they were REAL data.

    One paper in Nature, "Globally resolved surface temperatures since the Last Glacial Maximum," Osman, Tierney, et al. (2021), mixed models with real data to draw conclusions about the past.

    Reminds me of Mann's "Hockey Stick."

    We know that the AMOC, thermohaline circulation shut down for 1,300 years, and rather abruptly, at that. What is equally amazing is the speed with which the Younger Dryas ended -- warming as much as 10C in as little as 10 years in some places. Comparing this to the UN IPCC's scare story of 3C/100 years, the warming at the end of the YD was 33x as fast! Oops! (Doesn't this destroy the Warming Alarmists' "alarm?")

    The cause of the YD is still in question, but the likeliest culprit was a massive spill of less dense, cold, fresh water from a lake which had formed in the middle of the Laurentide (North America) ice sheet. That freshwater cap on the North Atlantic, continually fed by ongoing ice sheet melt, may have kept the AMOC from restarting for 1,300 years.

    What could have stirred up the North Atlantic sufficiently to allow AMOC to restart?

    The end of the YD has been nominally dated to 9620 BC. Here are some other items dated to about the same time:
    * Volcanic debris in the GISP2 ice core for 9620.77 BC and tapering off over the next two years.
    * A sudden, 2-meter (or more) drop in sea levels worldwide (Fairbanks, 1987).
    * A genetic split dated to about 10,000 BC between mtDNA haplogroup X into two groups separated by the Atlantic Ocean -- Sioux and Ojibwe in North America, and Basques and Druze in Eurasia.
    * Plato's story of the demise of a large, island empire which threatened the rest of humanity -- a massive, overnight tectonic collapse.

    All of these data points correlate strongly with other facts, including data in linguistics and geology.

    While it seems "standard" for modern scientists to ridicule any talk of Atlantis, the incredibly amazing thing is: No one has ever disproven Atlantis. The topic was merely dismissed, because "everybody knows." Sounds like the madness of Warming Alarmists.

    To show you how bad this madness has become, one professional historian discovered structures off the coast of an island in the Bahamas. He asked an archaeology professor in Florida to investigate, but the man refused because Bimini in the Bahamas was associated with Atlantis and he did not want to ruin his career. (Groan!) If extraordinary claims require extraordinary evidence, but egos are so wound up they'll never look at that extraordinary evidence, then science is Broken! Stabbed in the heart by the "Everybody Knows" syndrome.

    Mission: Atlantis (hardcover, paperback, ebook)
    Dumb Genius: How intelligence is sometimes its own worst enemy (hardcover, paperback, ebook)

  2. Guess it is really just what weather should be. The earth turns, creates winds and currents. It has buffer after buffer to maintain it's normal state. From atmosphere to biology with all the physics and chemistry interactions to solar influence while sitting on a nuclear furnace and taking into account only a micro second of the earths evolution, they pretend to predict anything. The arrogance of man expounds.

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