Is the Antarctic-driven abyssal ocean overturning doomed in 2050?

by Frank Bosse

Probably not, in spite of the recent headlines.

A recent article in Nature Abyssal ocean overturning slowdown and warming driven by Antarctic meltwater by England et al. (hereafter E23) caused quite a stir in the media.  The BBC wrote:Antarctic Ocean currents heading for collapse – report.

E23 built a model to describe the formation and behavior of abyssal water masses around Antarctica.  The Antarctic abyssal waters are important due to its impact on the overturning circulation (AOC) – the lower cell of the Meridional Overturning Curculation (MOC) – which overturns heat, freshwater, oxygen, carbon and nutrients in the abyssal ocean.  The AOC directly influences warming and the availability of nutrients to support marine life near the surface of the ocean.

Here is a schematic of the global MOC:

Screen Shot 2023-04-11 at 1.36.58 PM

Fig.1.: The global MOC, a reproduction of Fig.1 of Marshall / Speer (2012).  The Antarctic Bottom Water (AABW) is shown on the left side in descending blue arrows.

E23 concludes:

“In particular, a net slowdown of the abyssal ocean overturning circulation of just over 40% is projected to occur by 205”

According to E23, this would also have some impact on the Atlantic Meridional Overturning Circulation (AMOC), which is responsible for the vast majority of the northward heat transport on earth:

“As the meltwater release from Greenland and Antarctica increases over time, the AABW overturning and AMOC strength both weaken by 2050.” (AMOC by 19% shows Fig. 2).

The cause is the additional meltwater from the Antarctic ice shelves, which has a widespread impact on the Antarctic Bottom Water (AABW):

“First, the projected addition of Antarctic meltwater causes an anomalous freshening . . . which produces fresher and less dense AABW, and eventually reduced AABW volume, after the 2030s.”

The key figure of E23:

Screen Shot 2023-04-11 at 1.38.05 PM

Fig.2: A reproduction of Fig. 3a, b in E23. The Antarctic melting will lead to a reduction under the influence of the anthropogenic forcing (aka “Climate Crisis”) of the AABW of 42% (a) in 2050, shown in red. In black: without this forcing.

In Fig. 2 (b) the AMOC shows a robust downward trend over 2004-2020; this is not the case in the observations of “Rapid” at 26.5N;  there is much internal variability, with a dip in 2010 and thereafter a slightly recovery.

Screen Shot 2023-04-11 at 1.39.15 PM

Figure:  Observations of the AMOC 2004 to 2020 of “Rapid” at 26,5°N:  Source.

Let’s now have a look how the authors calculated the melting up to 2050, which is a crucial input of the described model for the AABW. From the Methods section of E23:

“…and the multi-model ensemble mean of CMIP6 models under a high- anthropogenic-emissions scenario, Shared Socioeconomic Pathway 5-8.5 (SSP5-8.5), for the future climate component from 2020 until 2050.”

In a twitter thread the lead author stated (and provided a “SharedIt” link to read the full paper, thanks for this):

“…our projections were run under a ‘business as usual’ scenario. Deep and urgent emissions reductions will give us a chance of avoiding an ocean overturning collapse.”

Is SSP5-8.5 (or RCP 8.5 in IPCC AR5) “Business as usual”? Not so, stated this comment, also in “Nature”:

“Stop using the worst-case scenario for climate warming as the most likely outcome”.

Its projections of future greenhouse gas emissions are generally acknowledged to be unrealistic even on pessimistic assumptions.

Furthermore: is the Multi -Model Ensemble mean (MME) of the CMIP6-models appropriate for this approach? No, the MME mean is skewed high owing to a high climate sensitivity due to some models running much too hot. Gavin Schmidt:

“The default behavior in the community has to move away from considering the raw model ensemble mean as meaningful.”

This leads to an urgent need of a discussion of the choice of SPS5-8.5 and the CMIP6 ensemble mean in E23. Unfortunately the paper doesn’t do this, so I will do it in this blog post.

What effect does the choice of the projected temperatures in the Antarctic for 2020 to 2050 have, which in turn influences the expected melting?

With the help of the KNMI Climate explorer I investigated the expected trends, first for the settings used in E23:

Screen Shot 2023-04-11 at 1.41.56 PM

Fig.3: The linear temperature trends in and around Antarctica for SPS5-8.5 and the MMM of the CMIP6’s, as it was estimated in E23.

In comparison, the not-so-skewed CMIP5’s MME mean for the more likely RCP4.5 scenario:

Screen Shot 2023-04-11 at 1.42.41 PM

Fig.4: The linear temperature trends for RCP4.5 in and around Antarctica.

Note that the trend slopes in the crucial melting areas of the western Antarctic (including the Ross Sea and the Weddell Sea) are nearly 50% steeper in the Fig. 3 than in Fig. 4. This results in a warming in this area from 2020 to 2050 of 0.6 K (Fig.4) based on RCP 4.5 and the CMIP5 MME mean; in Fig. 3 it results in 1.3 K based on SSP5-8.5 and the CMIP6 MME mean.

However, these are climate model simulation results. Let’s compare the spatially resolved linear trends of grid cells for the area 60°S to 90°S in the time span 1990 to 2021, virtually the same length as the 30 years long time span 2020 to 2050 in E23 for the observations (GISS) and the “not so hot case” of Fig.4:

Screen Shot 2023-04-11 at 1.43.47 PM

Fig.5: The spatial trend slopes of the gridded data for the CMIP5 models with the scenario RCP 4.5 (left) and observations, GISS (right) for the time span 1990-2021 (“Hindcast”)

Not only do the simulations warm far too quickly in Antarctica and its environs over the last 30 years,
but the modeled warming is poorly correlated with observed warming in most grid cells (Fig.5)

In wide and crucial areas for the forming of the AABW especially on the coastlines (with the exception of the Ross Sea on the bottom) the observed and modelled trends are quite different – in the observations the trends are near zero.

The more realistic scenario CMIP5 RCP4.5 shows a twice as fast warming in the Antarctic (60°S-90°S) as the observations, and the CMIP 6-SSP5-8.5 mean scenario shows an almost 3 times faster warming in the “hindcast” period 1990 to 2021 despite the fact that there is relatively little difference in greenhouse gas emissions and changes in other drivers of climate change between the SSP5-8.5 and RCP4.5 scenarios and observations during that period.

In the light uncertainty of the spatial resolved trends in the observations, I use the relation of the trends of the entire Antarctic region, estimating that the warming bias in models will persist to 2050. This would lead to an additional warming of only 0.3K for 2020 to 2050 in the Western Arctic, 23% of the estimation in E23.


Neither the sole warming scenario nor the multi model CMIP6 ensemble mean used by E23 to estimate the melting in Antarctica up to 2050 is appropriate. The resulting MME mean heavily overestimates the likely surface warming and hence the melting, making it “not meaningful” (see Gavin Schmidt’s citation) as input for the AABW-model used in E23.

For the crucial regions, the trend slopes 1990 to 2021 in the observations are only about one third of the simulations used by E23. Moreover, projected future greenhouse gas emissions and levels are unrealistically high in SSP5-8.5 scenario used by E23. This suggests that future surface warming in and around Antarctica is likely to be far lower than E23 assumes, which in turn means ice melting and hence the slowing of the abyssal ocean overturning would be much less than E23 projects.

E23 moreover concluded that the ocean freshening due to melting near parts of the western Antarctic (namely Ross Sea and Weddell Sea) will lead to the described reduction of the AABW within 30 years to 2050. I had a look at the observational “Argo” data, provided by the “Marine Atlas”. Until December 2021 there is no trend in the salinity data, here shown for the average 0-2000 m depth in the Weddell Sea:

Screen Shot 2023-04-11 at 1.46.41 PM

Fig. 6: “Argo” observations of the ocean salinity near the Weddell Sea. In the area of the Ross Sea, there is also no trend (not shown) . The figure was generated with the “Marine Atlas”.

The problems with this paper are: reliance on the implausible SSP5-8.5 emissions scenario, use of the CMIP6 multi-model ensemble mean which is running too hot, and failure to critically evaluate the model simulations using recent observations.  Further failures by Nature’s review and editorial process, combined with uncritical and amplified media promotion,  have unnecessarily confused the science and public.

Acknowledgement: I thank Nic Lewis for very helpful comments on earlier draft versions.

41 responses to “Is the Antarctic-driven abyssal ocean overturning doomed in 2050?

  1. There is no empirical evidence for this Antarctic ocean conveyor shut down. In fact, the southern ocean is absorbing huge amounts of carbon, more than previously estimated, which could only happen if downwelling was robust.

    Also, it’s been shown that the Antarctic overturning circulation is a lot more variable than previously supposed.

    • I wish she was coming back permanently! I miss her on the show so much. She and Jackson were so great together and brought out really interesting facets of each other’s characters. Would love to see them get back together (though I don’t think it’s going to happen) here⇢⇢⇢►

    • I wish she was coming back permanently! I miss her on the show so much. She and Jackson were so great together and brought out really interesting facets of each other’s characters. Would love to see them get back together (though I don’t think it’s going to happen) here⇢⇢⇢►

  2. Joe - the non climate scientist

    My apologies for not having a chance to read the article in detail, though how does the geothermal activity (primarily in west antarctica) factor into the equation.

    fwiw, numerous commentators on the activists / “scientific” websites make mention that the geothermal activity as near zero effect.
    thanks for any insight

  3. Is that red spot on the GISS actual data from the records of Vostok? I did not think the satellite data from UAH (SoPol) showed anywhere that warming. I also note they show the big red spot where they have no observational data.
    Turtles all the way down, I think.

    • Chris, the CMIP’s calculate the surface temperatures, not the temperatures of the lower troposphere as ist does UAH. Using different timeseries would lead to an apples to oranges comparison. For your information the trends in the grid cells for UAH, also 1990-2021:
      Thanks for your interest.

      • Yes I know Frank there is a difference between the way the two sets of temperatures are measured, but I also know the distance between the inland temperature measurement points is vast 1000 km or more. The GISS data map has detail in areas where there are no measurements, like west of the Transantarctic Range, where-as round Vostokj, they more correctly show it just as boxes with no smoothing. There is good data for South Pole, but that in all data sets, that is just shown as the circle

      • Chris, I know that all spatially resolved data have an uncertainty especially in the AA region due to some “holes” in obs. Threfore I used the trends of the whole region 90S-60S to evaluate the model trends vs. the obs. trends. Do you agree that this is the best way to avoid some bias?

      • thecliffclavenoffinance

        CMIPS make projections based on arssumptions and other programming by humans.

        Projections of the future climate are data free
        There are no data for the future climate

        Climate computer games are based on theories and assumptions made by humans.

        But humans have never been able to make accurate long term climate predictions.

        Therefore, no human could program a computer to make an accurate long term climate prediction.

        The so called climate models are not models of the climate of this planet. They are not CAPABLE OF MAKING ACCURATE LONG TERM CLIMATE PREDICTIONS. Because detailed knowledge of EVERY climate change variable does not exist.

        And even if such great knowledge did exist, there is no logical reason to assume the climate in 100 years could EVER be predicted … (Just like the precipitation in London 365 days from today can’t be predicted — and that’s only one variable, for one location, in one year, not all climate variables for the whole planet in 100 years).

        Climate models are just computer games — climate astrology. — mainly used to scare people about the future climate.

        No human today knows whether the global average temperature will be warmer, or colder, 100 years from now.

      • Frank
        I don’t disagree with what you have done. I am pointing out that the data is very sparse for the modellers to make all their grand pronouncements. You have shown that, comparing the models to what actual data there is. Your final paragraph sums it up well though may be too kind to them.

  4. That “paper” looks like the result of requesting a new “emergency” publication to reinforce the the “crisis”. The headlines have been working overtime lately as “they” are not going to give up their “beanstalk”.

  5. As far as I can see, the paper’s assertions are based on the lower density of fresh water vs. salt and the increase of fresh water injection into the ocean from melting glaciers/polar ice.
    What is not the least bit clear is what the effect of relative densities are on overturning as opposed to other effects like temperature gradients. In theory, there should be almost no abyssal overturning because colder water is less dense than warmer water. And yet there is still abyssal overturning.
    As with all of the other models in the climate field – it seems this computer model needs to be deeply scrutinized and calibrated vs. reality before any conclusions should be based on its outputs.

  6. thecliffclavenoffinance

    Antarctica has not warmed from more CO2 in the atmosphere since decwnt measurements began in the 1970s.

    Most of Antarctica cools from more CO2 in the atmosphere primarily because of a permanent temperature inversion.

    There has been some local warming of some ice shelfs and the tiny peninsula, due to underseas volcanoes. The locations of local warming near known underseas volcanoes are in a pattern that could not have been caused by CO2.

    The claimed slight decline of the total Antarctica ice mass is too small to be taken seriously — within a reasonable margin of error for the estimate.

    The bottom line is:
    Antartica is NOT melting and will NOT melt from atmospheric CO2 enrichment. That is the primary reason NOAA tide gauges do not reflect an acceleration of the global very long term relative sea level trend.

    All of these important facts are missing from this article.

  7. More important than RCP choice, the big problem is the high sensitivity, particularly in the interior of the continent where the GHE is inverted in the real world due to the high altitude and latitude and no source of heat for surface warming.

    While 8.5 isn’t plausible, on the short-medium term 7 is reasonable since slow development in Africa cannot be expected to continue.

    • aaron: The inverted CO2 effect is localised in the high elevation parts of the eastern AA for single months. However, increasing CO2 leads to warming also in the AA, see . I also compared the obs. GMST with SSP 2-4.5 and the mean of the CMIP5’s: for 1990…2022 the MMM shows a 17% steeper trend globaly than the obs.(GISS).
      Thanks for your interest.

      • thecliffclavenoffinance

        Air temperature inversions are common features in Antarctica, especially in most of the interior, where they are observed nearly year-round.

        Strong inversions frequently occur in the Arctic winter,

  8. Climate science these days seems to revolve around: ‘Promise to do some modelling which will give the funder’s desired outcome, namely ‘dangerous climate change’ over whatever time period is deemed most preferred by the funders’.

    This study clearly had as its objective to create a modelling system which would project a slowing of AMOC, with claimed horrendous consequences.

    Proper science does not have a political outcome in mind, it devises testable hypotheses and then ensures that the measurements made to test the hypotheses are free from unintended anomalies.

    Science is rapidly becoming like medicine, an unreliable, unprincipled market place of computer-generated modelling scenarios for sale.

  9. I found out that the link to the BBC-report was broken in the main text, sorry fot this. The working link:

  10. The BBC and Nature are ‘skating on thin ice’ yet again with this alarmist story . . mind you, anyone on thin ice should be alarmed!

  11. As lare as Oct. ’22 a dry winter was predicted for California…

    • Much like the anti-vax memes – myth and misinformation continue no matter how many times scientific investigation disproves the claims of the catastrophists. So now, penguins are stranded on floating blocks of ice instead of polar bears.

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  17. Bill Fabrizio

    Thanks, Frank.

  18. UAH 6.0 tropospheric warming trend has been confirmed by a new method in a new paper. Meaning what? The climate models are running too hot, that’s what.

    In their new paper Zou and his co-authors rebuilt the STAR series based on a new empirical method for removing time-of-day observation drift and a more stable method of merging satellite records. Now STAR agrees with the UAH series very closely — in fact it has a slightly smaller warming trend. The old STAR series had a mid-troposphere warming trend of 0.16 degrees Celsius per decade, but it’s now 0.09 degrees per decade, compared to 0.1 in UAH and 0.14 in RSS. For the troposphere as a whole they estimate a warming trend of 0.14 C/decade.

  19. The outdoors THERMOMETER doesn’t measure the outdoors air temperature!

    The outdoors thermometers measure the outdoors TEMPERATURE, so we knew what to put on to get dressed accordingly to the outdoors temperature.

    The outdoors thermometers give us some very valuable information about the outdoors thermal conditions (is outside the house cold or it is warm).
    By experience we know what to put on according to the outdoors measured temperature.

    The outdoors thermometers do not measure the actual air temperature. It is impossible for an outdoor thermometer to measure the outdoors air temperature.

    Indoors the enclosed air is in thermal equilibrium with surrounding it walls. Thus the indoors temperature thermometer measures we rightly consider as the air temperature too.

    When thermometer measures outdoors temperature, the outdoors air temperature is not in thermal equilibrium with its surroundings.

    Thus it is impossible to measure the outdoors air temperature with thermometer.

    Air is a thin medium, also air is known to be a good insulator. Even in the shade thermometer is subjected to the surroundings solar energy reflection or/and the surroundings IR energy emission.

    When indoors thermometer (in a room) we remove the air from the room, the readings on thermometer will not change.

    On the airless Moon, in shade, thermometer will read a temperature.

    Conclusively, when we put a thermometer out of the window, thermometer doesn’t measure the air temperature.


    • Frank Bosse presents a readily understandable analysis of a paper that was published without intrinsic errors but that is misleading in its results and probably its intent. Frank shows how an interested party outside the field of climate science can with some creativity and a bent for analysis use publicly available data and information to put in proper prospective papers like E23.

      It is too bad that media types do not avail themselves to analysis of the likes of Frank’s. This lack of media analysis probably owes more to intent than ignorance.

      • Ken, thanks for your kind words. I think it’s a little “over the top” to demand that some media do their own analysis before starting it’s “loudspeakers”. And it’s my impression that there is much “copy’n paste” at work because stories in different media were very similiar. To identify the “patient zero” who was the source of this stir was not the target of my post, however finding it could be useful. Some media are “click-bitches” looking for hot stuff. The qualtity controll of this stuff would be indeed responsible when it comes to “climate anxiety” in the public with some negative impact on the societies. I’m afraid we still have a long way to go to establish such an instrument.

  20. This id eee oh see doesn’t even make sense from the Church of Climate Doomers’ perspective. Has some snail virus hijacked Germany’s collective brain?

    At 10 p.m. on Saturday, the Isar-2 nuclear plant near Munich will begin winding down its power generation in steps of 10 megawatts per minute.

    After about 45 minutes, it will drop to 30% capacity and automatically sever from the national electricity grid. The other two plants still in operation, Neckarwestheim-2 and Emsland, will by then be in the midst of a similar process. By midnight, all three will be offline, ending Germany’s tumultuous six-decade reliance on nuclear energy.
    EnBW AG’s Neckarwestheim-2 Plant Ahead Of Germany Shuttering Its Nuclear Power Station
    The Neckarwestheim 2 nuclear plant on April 7.
    Photographer: Alex Kraus/Bloomberg

    When the three plants, which collectively provided Germany with 6% of its power last year, finally shut off, Europe’s largest economy will face an unprecedented challenge: securing its energy supply without nuclear or Russian natural gas, and with renewables expanding at a slower pace than needed.

  21. The EU’s ESG debacle continues.

    The EU Commission’s latest clarifications also seek to address the long-outstanding issue of how to define a sustainable investment. The EU’s failure to date to provide clear parameters around such a key ESG concept has drawn criticism amid concerns of greenwashing.

    The Commission said it won’t impose minimum thresholds and instead leave it to market participants to demonstrate that their claims are fair. At the same time, it warned that the disclosure framework requires “increased responsibility” on the part of market participants.

    But that could end up being costly for clients.

    “For investors, the lack of explicit regulatory standards increases the time and effort required to identify financial products that both meet their sustainability preferences and protect them from greenwashing,” Stephan Kippe, an analyst at Commerzbank Research, said in a note.

  22. While Germany inexplicably shuts down three of their nuclear reactors, Finland cranks up a 1.6 gW one.

    The 1,600-megawatt plant sitting on a rocky island that juts into the Baltic Sea on Finland’s west coast entered regular operation in the early hours of Sunday. Olkiluoto-3 is the first new atomic reactor in the Nordic countries since the mid-1980s, and the first in its home nation in more than four decades. About 30% of Finland’s electricity will now be produced on Olkiluoto.

    Generating emission-free power for homes and businesses, the start coincides with a nuclear revival in Europe and the diversification of supplies away from Russia. France is among the leaders, just as the continent’s economic powerhouse, Germany, on Saturday disconnected its remaining three reactors from the grid to exit the technology altogether.

    “We have seen this shift from many European countries to double down on energy security and ensure domestic supply after the invasion of Ukraine, and this new reactor will help a long way for Finland to achieve this,” said Fabian Skarboe Ronningen, a senior analyst at Rystad Energy AS.

  23. Frank: Given that this was published in Nature, you’d think that the peer reviewers would have considered some of the issues you have brought up.

    I might add that observations of Antarctic Sea Ice extent have until recently showed ice increasing, while models show it decreasing. One paper discussion this problem shows that natural variability in sea ice extent in model simulations much greater that the current forced response. I’m not sure how important sea ice extent is to deep water formation, however.

    • Hi namesake… I don’t think that anybody at “Nature” considered anything. I thought about a comment on Nature’s website, however I dismissed this idea. Why? The ideas of the piece and the sole considered SSP made it clear, that there is a fundamental problem, not only with this piece. One can’t discuss with frogs when it comes to the drainage of moores.
      re Arctic Ice: Grace found a decline between 2002 and 2019, your cited paper points to much IV and in the result it’s hard to distinguish between IV and forcing, as usual. One more reason to take the model output of the mean ( which is indeed the pure forcing) with a grain of salt and to take care when transforming this to the real world. Unfortunately this was not done in the cited piece.
      best Frank