Atlantic reversal


From Eurekalert: Earth’s climate change 20,000 years ago reversed the circulation of the Atlantic Ocean

Global warming today could have similar effects on ocean currents and could accelerate climate change

The Atlantic Ocean circulation (termed meridional overturning circulation, MOC) is an important component of the climate system. Warm currents, such as the Gulf Stream, transport energy from the tropics to the subpolar North Atlantic and influence regional weather and climate patterns. Once they arrive in the North the currents cool, their waters sink and with them they transfer carbon from the atmosphere to the abyss. These processes are important for climate but the way the Atlantic MOC responds to climate change is not well known yet.

An international team of investigators under the leadership of two researchers from the UAB now demonstrates the response of the Atlantic MOC to climate change in the past. The new research results will be published on 4 November 2010 in the international front-line journal NATURE. The research project was led by Rainer Zahn (ICREA researcher) and Pere Masque, both of the UAB at the Institut de Ciència i Tecnologia Ambientals (ICTA) and Department of Physics. With collaborators at the universities of Seville, Oxford and Cardiff (UK) they investigated the distribution of isotopes in the Atlantic Ocean that are generated from the natural decay of uranium in seawater and are distributed with the flow of deep waters across the Atlantic basin. The young investigator Cesar Negre studied the natural abundance of these isotopes in the seafloor sediments 2.5 km deep in the South Atlantic and achieved a PhD degree in the Environmental Science and Technology doctoral programme at ICTA.

The study shows that the ocean circulation was very different in the past and that there was a period when the flow of deep waters in the Atlantic was reversed. This happened when the climate of the North Atlantic region was substantially colder and deep convection was weakened. At that time the balance of seawater density between the North and South Atlantic was shifted in such a way that deep water convection was stronger in the South Polar Ocean. Recent computer models simulate a reversal of the deep Atlantic circulation under such conditions while it is only now with the new data generated by UAB scientists and their colleagues from Seville and the UK that the details of the circulation reversal become apparent. This situation occurred during the ice age 20,000 years ago.

Although this was far back in time the results are relevant for our climate today and in the near future. The new study shows that the Atlantic MOC in the past was very sensitive to changes in the salt balance of Atlantic Ocean currents. Similar changes in seawater salt concentration are expected to occur in the North Atlantic in the course of climate warming over the next 100 years. Therefore the data to be published in Nature offer the climate modelling community the opportunity to calibrate their models and improve their capacity to predict reliably future ocean and climate changes.

###

The research has been funded by the Spanish Ministry for Science and Innovation (MICINN).

======================================

This is just the usual press release with no link to the paper and no real scientific details to go with it, allowing compliant media minds to reprint it without questioning it. I’ll be interested to find out how they determined this reversal. If anybody locates a copy of the paper, please leave a note in comments.

I also think this headline could be true:

Atlantic Ocean ocean current reversal 20,000 years ago changed the Earth’s climate.

- Anthony

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80 Responses to Atlantic reversal

  1. Myron Mesecke says:

    I also think this headline could be true:
    Atlantic Ocean ocean current reversal 20,000 years ago changed the Earth’s climate.

    But that headline would admit that what the ocean’s do have an effect on the climate and they can’t go around saying that!

  2. John Kehr says:

    This is a very interesting piece of information. The Greenland ice cores are full of rapid and significant changes in temperature that correspond to the meltwater pulses that happened during the warming phase from glacial to interglacial.

    The same signal shows up throughout the entire NGRIP record. Such reversals or at least circulation shutdowns might happen more frequently than we think. I will have to follow up on this one.

    Theinconvenientskeptic.com

  3. mkelly says:

    Several monthes ago I watched a National Geographic on the Sahara Desert showing fossils of crocs, clams, etc at various locations. It was shown that every 20,000 years the Sahara goes through a complete reversal from desert to a land of lakes and running rivers. It has done so several times and was last green 10000 or so years ago. They used layered sediment of dust off the coast of Africa to separate out desert from green eras. No mention of global warming or reversal of Atlantic currents.

  4. Dougmanxx says:

    ” Recent computer models simulate a reversal of the deep Atlantic circulation under such conditions while it is only now with the new data generated by UAB scientists and their colleagues from Seville and the UK that the details of the circulation reversal become apparent.”

    If it happened in a computer, it must be true!

  5. Pascvaks says:

    There is little doubt that the Global Ocean Conveyor was different at different times in geological history. Will be interesting to see the actual data (not simulations).

  6. Mark Cooper says:

    Sounds dodgy to me- did they mean that before 20k YBP the current flowed in the opposite direction!?

    I guess they never saw this report from Nasa then:

    http://www.jpl.nasa.gov/news/news.cfm?release=2010-101

  7. exNOAAman says:

    Perhaps this is related? (Seen in Erosion Control Magazine yesterday)
    link: http://www.erosioncontrol.com/the-latest/ieca-university-partners.aspx
    Based more on melting glaciers, but similar idea for Atlantic flow.

    quote: These Megafloods entered the Gulf, rapidly raising the water level and forcing the overflow out through the many smaller Florida/Cuba Straits. This Glacial overflow then spread across the lower lying area known as the Bahama Mega-Bank. 12,000yrs. ago, (with sea levels at least 300 ft. lower than today) the Bahama Mega-Bank was an exposed land mass larger than present day Florida.

  8. Jarmo says:

    The timeframe fits the known facts.

    Here is a useful page about deglaciation and the potential causes:

    http://web.me.com/uriarte/Earths_Climate/10._Deglaciation.html

  9. TomRude says:

    Talking about the tail that wags the dog…

  10. John Kehr says:

    Doug,

    I am also skeptical about models as what you put in determines what you get out. In this case it is clear that meltwater pulses change things in Greenland. The signiture of that shows up frequently. This matches the observations.

    It also helps show that orbital changes drive the climate. It is win for skeptics even if they don’t think so.

  11. John Game says:

    Here is the reference: Nature 468, 84-88 (4 November 2010)

  12. kadaka (KD Knoebel) says:

    Nature paywall:
    Reversed flow of Atlantic deep water during the Last Glacial Maximum
    Has abstract. Snippet:

    Nutrient-based proxies (1, 2) and recent model simulations (3) indicate that during the Last Glacial Maximum the convective activity in the North Atlantic Ocean was much weaker than at present. In contrast, rate-sensitive radiogenic 231Pa/230Th isotope ratios from the North Atlantic have been interpreted to indicate only minor changes in MOC strength (4, 5, 6). Here we show that the basin-scale abyssal circulation of the Atlantic Ocean was probably reversed during the Last Glacial Maximum and was dominated by northward water flow from the Southern Ocean. These conclusions are based on new high-resolution data from the South Atlantic Ocean that establish the basin-scale north to south gradient in 231Pa/230Th, and thus the direction of the deep ocean circulation.

    And other similar things where the assistance of anna v, Pamela Gray, E.M. Smith and the like is appreciated for translation and digestion.

    Journal reference was found in the Science Daily post of the press release.

  13. Wind Rider says:

    So, we’ve got basic data points collection, and the employment of extrapolations of same, to feed a computer model, from which an ‘interesting’ result is found.

    Ok. Congrats on the PhD thesis.

    A nice tidbit for the crowd that doesn’t handle the concept of change (in the midst of a constantly active and cyclic system) to begin squalling that we’re all going to die horrid deaths no later than next Wednesday or Thursday if we don’t enact Plan Z immediately, or am I reading too much into it?

  14. tarpon says:

    And to think all this happened in the last glacial ice age. Conditions far different from current.

    Just jumps out at you — “might it happen during every glaciation event”…. Why not?

    And then why would you think the warm cycle would produce the same result. Not likely ehhh.

  15. It’s worse than we thought.

    Man’s excessive use of fossil fuels (Al Gore’s use excepted) must have CAUSED the reversal 20,000 years ago. After all, don’t the ice core studies demonstrate CO2 causing an increase of global temperature 500 to 800 years BEFORE natural increases in the level of CO2. Imagine how much more powerful anthropomorphic increases in CO2 are – perhaps orders of magnitude more powerful! What? You say an effect can’t happen before it’s cause? You are clearly a denier.

    According to post modern science, cause and effect is an old fashion idea held by flat earthers and other such troglodytes. All you need to do is run a computer simulation and you create the past, present, and future without regard to anything outside of the computer. Next, you can assert “the science is settled” and get to call anyone who does not agree a “denier” or worse. Finally, you get to tax and regulate the deniers into extinction and get to feel good because you are saving the planet.

  16. Enneagram says:

    Something happened not 20,000 years ago but 10,000 thousand of years ago: Tradition say there was a big continent there…and, of course, that changed it all!.
    Then, anyone of us here at WUWT can assure it, it happened that, on that ill fated continent, a group of people who called themselves the GREENS of the GAIA FOLLOWERS, or those who congregated in a then well known society, formed in Rome, called “The Club of Rome” where its members held the idea that the majority of mankind should be expeditiously sent to beyond the frontiers of the river of the death, so as they, the “chosen ones”, God’s favorites, could reestablish the Garden of Eden and live for ever, without those nasty and dirty working loving people .
    Thus they managed to invent a new way to extract the energy from the Sun, however, as they all were sons and daughters of Mommy and Daddy, they ignored there were Laws in Nature which could not be interfered as it would risk the existent itself of the Planet or the portion of it where these laws would be violated. This new portentous and big, really gigantic fashioned “gadget”, was a big building with the shape of a pyramid, having on its most highest extreme a gem “crystal”, of a beautiful reddish color, then known as Ruby, which transmuted the sun’s rays into useful power, destined to power with inexhaustible energy their “Garden of Eden”. But….what really happened afterwards we all know it.
    The problem is that in recent times, it seems that several of the then members of those secret societies, have reincarnated and are equally and stubbornly pursued to achieve their unforgotten and most stupid and contrary to universal laws, foolishness.

  17. Nuke says:

    Another model. Models are great at expressing an hypothesis, but do not prove it.

    How about some real data that can support or disprove the hypothesis instead?

  18. Espen says:

    20000 years ago the last glaciation was still going strong, so the climate was very different and less stable: Climate during a glaciation is unstable climate. Climate during an interglacial is stable climate. Still these scare stories – that AGW may cause similar “disruptions” – pop up again and again.

  19. Mike says:

    “This is just the usual press release with no link to the paper and no real scientific details to go with it, allowing compliant media minds to reprint it without questioning it. I’ll be interested to find out how they determined this reversal. If anybody locates a copy of the paper, please leave a note in comments.”

    Go to the nearest university library and look it up.

  20. Peter Ward says:

    “The study shows that the ocean circulation was very different in the past and that there was a period when the flow of deep waters in the Atlantic was reversed. This happened when the climate of the North Atlantic region was substantially colder…”

    So if the (currently warming) north pole gets colder again we get global warming, while the warming pole proves… global warming! I love theories that can never be falsified.

  21. Bill Yarber says:

    Mark

    Thanks for article. Interesting that MOC appears to have increased in speed from ’93 to ’09. Did the speed increase because the Earth warmed, or the opposite? Just like temp vs. CO2 concentrations, cause and effect can be hard to determine.

    Bill

  22. Enneagram says:

    Wind Rider says:
    November 4, 2010 at 8:12 am
    A story that Discovery, History,etc. and all the pathological and thanatophilic media will air ASAP for sure !

  23. GaryM says:

    Is it just me, or does

    “The young investigator Cesar Negre studied the natural abundance of these isotopes in the seafloor sediments 2.5 km deep in the South Atlantic and achieved a PhD degree in the Environmental Science and Technology doctoral programme at ICTA.”

    sound familiar? Wasn’t Mann a “young investigator” whose discovery of the hockey stick was in the course of getting his PhD?

    A more detailed description of the paper seems to be here.

    http://news.yahoo.com/s/livescience/20101103/sc_livescience/atlanticoceanswatersreverseddirectionstudyfinds

    “To reach these conclusions, scientists investigated a pillar of sediment roughly 128 feet (39 meters) long, extracted from the seafloor by use of a ship off the coast of the tip of Africa under about 8,000 feet (2,440 m) of water.”

    I’m no scientist, so maybe the scientists here can explain: if this is an accurate description, can you really determine something on this scale from “a” (presumably single) pillar (apparently the ocean equivalenty of an ice core?)?

  24. Enneagram says:

    Bill Yarber says:
    November 4, 2010 at 9:05 am
    The “speed of the earth” what you call it is the Length of the Day=LOD, and its changes are absolutely cyclical and related to gravity/electromagnetic fields, so linked to sun’s activity.
    See pdf #8th page 50, where you, comfortably siited, will see a scientific temperatues’ forecast to the year 2100, made of course by a real scientist.
    Professor Leonid B. Klyashtorin, of the Federal Institute for Fisheries and Oceanography, Moscow, Russian Federation (e-mail: Klyashtorin@mtu-net.ru)

    ftp://ftp.fao.org/docrep/fao/005/y2787e/

    Document Archive: y2787e08.pdf pp.50
    which shows a low at the year 2020, the same as WUWT regular, M.Vukcevic’s extrapolation of Sun’s polar fields:
    http://www.vukcevic.talktalk.net/PF.gif

  25. Peter Taylor says:

    The relevance of this for climate change is not obvious to me. If you look at the NGRIP ice-cores in Greenland for the depth of the ice-age – say, between 50,000 and 30,000BP you can see 10 major cycles affecting the temperature at the surface of the ice-mass, and hence reflective of what is happening in the North Atlantic. The warming phase is very sudden and about 3C in magnitude. Then there is a gradual decline before the next cycle. One could average the cycle out at about 2000 years, but the pattern is obvious to the eye – a quasi-Fibonacci spiral series with each warm phase about half the duration of the previous – 8:5:3:1. It is as regular as a heartbeat, but then breaks down as the ice-age nears its end, with a much larger and still very steep rise at about 12,000BP.

    Whatever causes these changes, I would think that the abyssal flow is a consequence, not a part of the cause. The abyssal currents already flow north in the eastern part of the basin, and south in the western, and the last time I looked at oceanographic models – which was some time ago in the 1980s’s when the UK was dumping radioactive waste off the Azores, the waters moved north and then turned south with no interchange with the surface. The northern zone is marked by downwelling of the Arctic waters which are cold and salty and this appears to entrain some of the Gulf Stream waters – but I am not convinced that this process affects the heat budget that much. The heat budget of the North Atlantic is much more likely dominated by the wind patterns, especially the tracking of low pressure heat extracting cyclones, and by the cloud cover that is induced, with the westerlies then taking that warmth to Europe.

    We know that periodically during the more stable Holocene, there is a regular roughly 1000 year shift (but again, you can discern an 8:5:3:2:1 pattern and one where we are at the end of….with each peak being lower and the trough deeper (leaving out the big swings of the Younger Dryas because the transition from ice-age to Holocene involved some rapid oscillations and unusual events). And some research shows that the last such trough (Little Ice Age) coincided with low solar activity and shifts in the jetstream (as we have seen recently also). The jetstream directs the tracking of the cyclones.

    When this shift occurs, high pressure builds over the Arctic (sending anticyclones across from Canada through Greenland to Fennoscandinavia) and the down-draught from these blocks the westerly air current and brings Arctic snows and deep frosts to Northern Europe. There are knock on effects across Eurasia into Mongolia and China. All of which are very bad news for food production – globally, the world relies on these regions for its current grain surplus.

    Under these shifting wind regimes, the Gulf Stream, which is a surface current and wind-driven will flatten across the mid-Atantic and the North Atlantic will cool. This pattern may affect the deep water abyssal currents and perhaps this is the cause of the reversal of flow (they are very slow anyway) – but it is not clear from the news so far whether this reversal is a one-time unusual event toward the end of the ice-age. The shifts bring rain and storms to Iberia and cloudy cooler Mediterranean weather.

    So – with the dominant driver being the jetstream, ‘global warming’ would have to cause that to move south, when the models predict it will move north. And in actuality, it now looks as if after 0.5 C of warming, it is still capable of moving south when the Sun’s UV output is low.

  26. Katherine says:

    To those complaining about modelling “yet again,” the team “investigated the distribution of isotopes in the Atlantic Ocean that are generated from the natural decay of uranium in seawater and are distributed with the flow of deep waters across the Atlantic basin…. Cesar Negre studied the natural abundance of these isotopes in the seafloor sediments 2.5 km deep in the South Atlantic….” That sounds like “real data” to me, not modelling.

    The connection to modelling seems to come in at “Therefore the data to be published in Nature offer the climate modelling community the opportunity to calibrate their models and improve their capacity to predict reliably future ocean and climate changes.” Emphasis added. Correct me if I’m wrong, but it seems they’re saying, “Here’s real data. Check your models against it.” Isn’t this a Good Thing?

  27. kadaka (KD Knoebel) says:

    This page yields the following links for the study (as well as others for that issue of Nature):

    First paragraph
    Full text
    PDF
    Editor’s summary

    I don’t know which are good or what they’ll yield, since as of this writing all they are giving me is nature.com technical errors. Their servers are crashing, apparently.

  28. pat says:

    Same question. You know that ocean currents were reverse of the present because?

  29. Bob Tisdale says:

    Wasn’t able to find a free preprint. But let’s see. The title of the paper is “Reversed flow of Atlantic deep water during the Last Glacial Maximum.” The press release above states, “The study shows that the ocean circulation was very different in the past and that there was a period when the flow of deep waters in the Atlantic was reversed. This happened when the climate of the North Atlantic region was substantially colder and deep convection was weakened. At that time the balance of seawater density between the North and South Atlantic was shifted in such a way that deep water convection was stronger in the South Polar Ocean.”

    Anything else that might be in the paper about changes in MOC during a warming period would then appear to be computer-modelled speculation.

  30. Mike Haseler says:

    As soon as I read “Gulf stream” it was immediately obvious this article was being very liberal with its terminology. The Gulf stream is the current from the Gulf of Mexico and it virtually disappears before it becomes the North Atlantic drift.

    Both currents follow prevailing winds: the Gulf stream follows equatorial winds pushing into the Gulf of mexico which is then squeezed out like toothpaste between Cuba and Florida. The North Atlantic drift follows the SW trade winds that predominate in the North Atlantic.

    Whilst I can’t be bothered to read an article which can’t even get basic things like nomenclature correct, I suspect it is this old chestnut of the Arctic current which is a very small current which is thought to be driven by evaporation and increasing salinity in the Arctic ocean … a current which is … I forget but 1/2000 of the North Atlantic drift in size springs to mind.

    So basically, this whole “gulf stream” current thing is a great con. Rename a minuscule current going into the Arctic that never goes anywhere near the Gulf the: “gulf stream”, and then (probably correctly) say this current varies …. and then use the confusion over name to suggest the whole of the trade-wind driven current will switch off even though it’s driven by the trade winds which no one is suggesting is affected by global warming (but I could be wrong … perhaps mann even now has a paper … how mankind is stopping the world spinning)

  31. rbateman says:

    20,000 years is just about the average length for the Interglacials of the last 3-4 Ice Ages. They can also be as long as 30,000 and as short as 10,000 years, implying two circulations out-of-synch. Is the other one in the Pacific?

  32. Enneagram says:

    kadaka (KD Knoebel) says:
    November 4, 2010 at 9:39 am
    Tomorrow we’ll see them, Fridays are for cartoons here in WUWT.

  33. Charles Higley says:

    “Therefore the data to be published in Nature offer the climate modelling community the opportunity to calibrate their models and improve their capacity to predict reliably future ocean and climate changes.”

    Like this is going to happen. Tuning a broken instrument does not fix it – it will always sound bad.

  34. Dave Springer says:

    This can’t be right. Climate doesn’t change without anthropogenic CO2 emissions.

  35. davidmhoffer says:

    Summary:

    o it was much colder 20,000 years ago
    o it got steadily warmer since then
    o glaciers melted and current reversed direction
    o the climate was affected by the current reversal

    DUH!

    The climate has been warming for 20,000 years causing some current to change direction thus affecting the climate. Wow. Good thing all those processes stopped so that we could measure how we are affecting the climate to hundredths of a degree.

  36. Tenuc says:

    Yet more cargo cult science from our climatologists!

    There are a couple of if’s here, and they are big if’s – (the use of a single proxy of) “radiogenic 231Pa/230Th isotope ratios from the North Atlantic have been interpreted to indicate only minor changes in MOC strength. Here we show that the basin-scale abyssal circulation of the Atlantic Ocean was probably reversed during the Last Glacial Maximum and was dominated by northward water flow from the Southern Ocean. “

    Even if it did happen, the geography of the global, planetary orbit, solar radiation and a million other things have change over the last 20,000y. Why should this possible even be relevant to today?

    Finally, even if it turns out to have significance, is it not more likely that the possible reversal happened because of the glaciation and the researcher is confusing cause and effect?

    No wonder the general public no longer believe in climate science – from the press release, this paper would seem to be a FAIL.

  37. Mike says:

    @ GaryM

    Other cores are discussed in the paper.

  38. Anything is possible says:

    Re-inventing the wheel with all this…..

    Paleo-climatologists were proposing over 30 years ago that the Gulfstream was much weaker, and positioned further south, setting up a cold sub-polar gyre in the North Atlantic, during previous glaciations.

    It was further proposed that a catastrophic outflow of freshwater melt into the North Atlantic from the disintegration of the Laurentide Ice Sheet again shut off the Gulfstream, causing European climate to regress into the cool phase known as the “Younger Dryas” (c.11K BP) which lasted about 1000 years.

    Has the scientific community become so obsessed with the “CO2 causes everything” mantra, that anything which proposes otherwise is viewed as new and revolutionary science, even if the theories have been long-established?

    Sheesh…….

  39. Enneagram says:

    Instead we would hope to see an IPCC reversal for the sake of humanity and for avoiding what will be a probable world conflict because of climate insanity/

  40. vukcevic says:

    John Kehr says: November 4, 2010 at 7:19 am
    The same signal shows up throughout the entire NGRIP record.

    Hi John
    I would not, for time being, put to much money on the NGRIP record. I have mentioned it few times, but everyone ignored it except for Dr. Judith Curry who responded:
    curryja | October 31, 2010 at 2:11 pm
    I’ll flag this to look at later, I’m not all that familiar with this issue but it looks important
    http://judithcurry.com/2010/10/29/uncertainty-and-the-ipcc-ar5/
    Here is reason:
    The 10Be deposits count matches pretty well the Central England temperatures.
    http://www.vukcevic.talktalk.net/CET&10Be.htm
    For more details see my post:
    http://wattsupwiththat.com/2010/11/03/a-profile-of-dr-judith-curry/#comment-523164

  41. tty says:

    “Here we show that the basin-scale abyssal circulation of the Atlantic Ocean was probably reversed during the Last Glacial Maximum and was dominated by northward water flow from the Southern Ocean. ”

    If this is correct there must have been a major upwelling zone somewhere in the North Atlantic. The North Atlantic was closed to the north during the glaciation since there was no Bering Strait.

  42. George E. Smith says:

    Well I don’t see how that’s possible; no not the reversal; but that affecting the Climate. Water is water; and one piece of water is just like another so why would movement affect anything ?

    But speaking of current reversal; I seem to have a vague recollection that back in the 2007-2008 time frame when there was talk of the “PDO switching to its cold phase”, I read some sort of non-peer reviewed science literature; or it could have been a T&V or radio bulletin that implied; at least that is how I interpreted it; that the direction of rotation of the current in the Arctic Ocean had actually reversed.

    Does that make any sense; and do you arctic experts know if something like that did happen; I would expand the time scale to maybe 2006-2009.

    I don’t make this stuff up; but I can be prone to misinterpreting what was said; but some story like that caught my interest back when that PDO went cold.

    So Does the direction of Arctic Ocean circulation affect these cyclic events; perhaps I should add does maybe the Ocean cycle like say PDO cause an arctic ocean reversal.

    I’ve always believed that the Gulf Stream would keep flowing, so long as the earth kept rotating; even to the point of wanting to reverse the earth rotation direction so we could get a warm gulf stream up the California Coast; and get rid of all those crummy salmon; and replace them with Tuna, Mahi-mahi, and other tropical game fishes.

    So did I just dream about the AO reversing its rotation or does that really happen ?

  43. John F. Hultquist says:

    This study adds to the information. That’s nice.
    20,000 years ago Earth had a much different appearance with lower ocean surface, exposed continential shelves, much ice-covered land in the Northern Hemisphere, lots of dust [ look up loess: Example: http://adsabs.harvard.edu/abs/2002AGUFM.H22B0899S ], and a few other issues.

    I mention the dust because of the recent post about soot and the Greenland ice melting:
    http://wattsupwiththat.com/2010/11/03/greenland-ground-zero-for-global-soot-warming/

    – – – – – – – Mike says: at 9:00 am
    Go to the nearest university library and look it up.

    Subscribers usually get copies a few weeks before publication date, so as this is a November issue someone likely has it. A university library is another thing all together. Depending on policy, staffing, and unknowns a new issue may be a bit slower to appear in the reading room.

  44. Bill Illis says:

    The ocean conveyor system one sees on the internet is a cartoon. The real ocean does not operate in one big free-flowing belt.

    The currents are driven by the prevailing winds and the shapes of the continents.

    Water generally flows from the hot equator to the cold poles, but it travels westward along the equator first and then piles up on the eastern side of the continents and then is directed north-or-south by the shape of the continent (more accurately by the shape of the mid-depth continental shelves).

    When the warmer water reaches the mid-latitudes, the prevailing winds shift to eastward and the ocean currents are dragged along on eastward on their eventual journey to either the poles or to getting recycled equator-ward again by the shape of the continents on their western side.

    So, the direction of the conveyor(s) could be changed if we reversed the rotation of the Earth, made the poles warmer than the equator or changed the shape of the continents. Easy.

  45. woodNfish says:

    This is just the usual press release with no link to the paper and no real scientific details to go with it, allowing compliant media minds to reprint it without questioning it.

    The media wouldn’t question this nonsense even if it had the paper and data attached.

  46. John F. Hultquist says:

    tty says: at 11:01 am
    The North Atlantic was closed to the north during the glaciation since there was no Bering Strait.

    Please read Mike Haseler’s comment at 9:51.

    Then give us an update.

  47. John from CA says:

    Influence of Bering Strait flow and North Atlantic circulation on glacial sea-level changes
    http://www.cgd.ucar.edu/ccr/publications/ngeo729.pdf

    “As the rise of the boreal summer solar radiation above the mean of the past 130 kyr lags the ESL rise, solar radiation changes alone cannot explain the timing of the ESL oscillations observed at the beginning of the last glacial. However, these early ESL minima were all characterized by a closed—or nearly closed—Bering Strait. We propose and demonstrate that this nearly closed Bering Strait had an important role, leading to the ESL rise after those minima through modulation of the MOC strength. We show that the subsequent surface climate changes and the associated albedo–climate feedback processes provide the necessary conditions to initialize the melting of the ice sheets and produce an ESL rise.”

    “The opening of the Bering Strait may also have wider implications on climate. For example, a recent study23 suggests that abrupt climate change events evident in the Greenland ice core record between 70 and 11 kyr bp (ref. 30) may be related to the closing of the Bering Strait. Although the Bering Strait itself may not directly control the surface climate change, the effect of the strait on the transport of the fresh Pacific water into the Arctic and North Atlantic does influence the MOC strength, and consequently can modulate Earth’s climate. Therefore, climate changes and the Bering Strait may well have been intimately linked throughout the Late Pleistocene ice age.”

  48. M White says:

    If the atmosphere was cooled and liquified then added to the worlds oceans, I’d be interested to know what fraction of the combined volume the atmosphere would be?

    I can’t see it beeing much. This is why I would say it is the Oceans that have the biggest effect on our climate.

    This statement just seems stupid “Global warming today could have similar effects on ocean currents and could accelerate climate change”

  49. William says:

    Interglacials have in the past lasted roughly 12,000 years, not 20,000 years as stated above. The past interglacials have ended abruptly.

    http://en.wikipedia.org/wiki/Ice_age

    “It was conventional wisdom that “the typical interglacial period lasts about 12,000 years,”…

    The wikipedia article was written by the AGW fan club and states that this interglacial period could last longer, ignoring the fact that past interglacial periods ended abruptly, due to some unknown forcing change. (i.e. A prediction of what will happen in the future requires an understand of what caused the past paleo climatic changes.)

    As I have stated the paleo data shows there have been geomagnetic excursions at the same time as the termination of past interglacial periods. There is also an increase in volcanic activity at the time of the geomagnetic excursions. It appears the same forcing function causes the glacial period to end, the cyclic abrupt Bond events, and the end of the interglacial period. As Bond noted in his paper there are cosmogenic isotope changes at all of the Bond events including the Younger Dryas abrupt climate change that occurred 12,800 years ago. Bond tracked 22 of the cycles and found that they have a periodicity of 1470 years.

    The geomagnetic field strengthens by a factor of 3 to 5 during the interglacial period. In the last 10 years, geomagnetic specialists have found “geomagnetic jerks” (abrupt changes in the inclination of the geomagnetic field and geomagnetic excursion appear to be occuring cyclically. What appears to drive the changes, is an interruption to the solar sunspot mechanism. (One theory for sunspot creation has the ropes that form sunspots created at the solar tachocline, which is the interface of radiative zone and the convection zone. The large planets move the sun and certain specific motions of the sun by the planets disturbs the tachocline such that sunspots are not produced. That explains the cyclic nature of the affects on the earth.)

    When the sunspot cycle restarts there are very large CMEs that affects the geomagnetic field. The affects depend on the eccentricity of the earth’s orbit and the hemisphere where the strike occurs. The affects are also depend on the earth’s tilt. The South Atlantic geomagnetic anomaly appears to be evidence of the most recent strike.

  50. John from CA says:

    M White says:
    November 4, 2010 at 11:42 am
    If the atmosphere was cooled and liquified then added to the worlds oceans, I’d be interested to know what fraction of the combined volume the atmosphere would be?

    I can’t see it being much. This is why I would say it is the Oceans that have the biggest effect on our climate.

    This statement just seems stupid “Global warming today could have similar effects on ocean currents and could accelerate climate change”

    ========

    Stability of the Atlantic meridional overturning circulation in a zonally-averaged ocean model: the effects of freshwater flux, wind stress, and diapycnal diffusivity
    Draft, 17 January 2010
    http://earth.geology.yale.edu/~avf5/publications_pdf/SevellecFedorov.AMOC.2D.2010.pdf

    “78 Although these results are typically reproduced by other models, the details of the simulations such as the amount of freshwater needed for the collapse of the AMOC, the magnitude of climatic impacts, or the role of the winds over the Southern Ocean vary from one model to the next. As a result, the 21st century projections for AMOC changes summarized in the IPCC AR4 reveal a strong discrepancy between coupled models. These issues bring about several important questions: How do we test the models? Which factors determine the sensitivity of the AMOC to the freshwater and other forcings in a given model? What is the relative importance of different processes in bringing deep water from depths back to the surface? To answer these questions we need to look at what determines ocean thermal structure and the properties of ocean meridional overturning.”

    “120 The stability of the overturning circulation subject to a steady freshwater forcing has been a subject of numerous studies, starting with a box model by Stommel (1961) who showed the existence of multiple-equilibria in the system with a bistable regime. That is, a regime with two types of stable steady-state solutions – a strong circulation corresponding to the active AMOC (the on-state) and a weak circulation with the collapsed AMOC (the off-state). These results have been confirmed by direct integrations of zonally-averaged models (Stocker and Mysak, 1992; Schmittner and Weaver, 2001; Ganopolski and Rahmstorf, 2001), ocean GCMs (Rahmstorf, 2000; Hofmann and Rahmstorf, 2009; Prange et al., 2003; Nof et al., 2007), and intermediate complexity coupled models (Rahmstorf et al., 2005). Similarly, the so-called continuation techniques find AMOC steady-states in ocean GCMs without the need to use time integrations (e.g. Weijer et al., 2003; Dijkstra and Weijer, 2003).”

  51. Enneagram says:

    A prediction of what will happen in the future requires an understand of what caused the past paleo climatic changes.
    Or, to know how it works the world. It was always known, as traditional symbols show, until some chose to forget and others said it was for us impossible to know (Agnosticism, a movement to govern upon people thanks to people’s ignorance). See
    http://www.scribd.com/doc/40514613/Unified-Field-Explained-8

  52. Enneagram says:

    I forgot to cite William says:
    November 4, 2010 at 11:47 am

  53. Brego says:

    Re: M White says:
    November 4, 2010 at 11:42 am

    “If the atmosphere was cooled and liquified then added to the worlds oceans, I’d be interested to know what fraction of the combined volume the atmosphere would be?”

    The troposphere averages ~18 mm/M^2 of precipitable water relative to the surface. If this water was instantly condensed and added to the ocean only, it would add 23.4 mm of depth to the ocean. The average depth of the ocean is 3790 M (although estimates vary widely and it is actually unknown). The water from the troposphere would equal ~6.2 millionths of the combined volume.

  54. Kitefreak says:

    “the way the Atlantic MOC responds to climate change is not well known yet.”

    That’s as far as I need to read this article.

  55. John from CA says:

    OT — Its official, this is going to end badly (Ice Age):

    Counteracting Global Warming: A Good Idea?
    November 4, 2010 by doncorrigan
    http://into-nature.com/2010/11/04/counteracting-global-warming-a-good-idea/

    Some climates scientists and geo-engineers say America’s political system is too dysfunctional to ever address long-term problems like global warming.”

    Therefore, technologists in other countries are exploring ways to lower the earth’s temperatures. One plan involves aerosoling tiny, reflective particles into our skies to deflect the sun’s heat. Another has robotic ships shooting salt water into ocean clouds to deflect sun heat and to stabilize planet temperatures.”

    These technologies are now being developed in the European Union, China and Canada. Lest you think this is all a sci-fi pipe dream, David Keith of an environmental systems group in Calgary said plans are well along for the new technology, and a major investor is Bill Gates.”

  56. Earle Williams says:

    This can be explained with one word.

    No, not plastics

    I'm surprised it hasn't come up before. Prior comments have alluded to it, but nothing quite has the impact. Nothing quite explains just how significantly mankind's emissions have altered or will alter the earth's climate.

    What is that one word?

    Chronoconnections

    ;-)

  57. Will Crump says:

    Peter Taylor:

    The science daily article predicted that the reversal would happen again within 100 years, but it was not convincing to me.

    Any insight?

    The article indicated a reversal that occurred 20,000 years ago is expected to occur again in the next 100 years, but the explanation of why was not convincing. The abstract did not say anything about a change over the next 100 years. The change is predicted in a model due to sea water salt concentrations, but the reversal 20,000 years ago occurred when the climate of the North Atlantic region was substantially colder and deep convection was weakened. It is not clear that current conditions over the next 100 years will be the same as they were 20,000 years ago

    The Science Daily article claimed the study was relevant because:

    “The study shows that there was a period when the flow of deep waters in the Atlantic was reversed. The results are relevant for the near future since similar changes are expected to occur in the course of climate warming over the next 100 years.”

    Later in the article:

    “The study shows that the ocean circulation was very different in the past and that there was a period when the flow of deep waters in the Atlantic was reversed. This happened when the climate of the North Atlantic region was substantially colder and deep convection was weakened. At that time the balance of seawater density between the North and South Atlantic was shifted in such a way that deep water convection was stronger in the South Polar Ocean. Recent computer models simulate a reversal of the deep Atlantic circulation under such conditions while it is only now with the new data generated by UAB scientists and their colleagues from Seville and the UK that the details of the circulation reversal become apparent.

    This situation occurred during the ice age 20,000 years ago. Although this was far back in time the results are relevant for our climate today and in the near future. The new study shows that the Atlantic MOC in the past was very sensitive to changes in the salt balance of Atlantic Ocean currents. Similar changes in seawater salt concentration are expected to occur in the North Atlantic in the course of climate warming over the next 100 years. Therefore the data to be published in Nature offer the climate modelling community the opportunity to calibrate their models and improve their capacity to predict reliably future ocean and climate changes.”

  58. Arno Arrak says:

    This is all computer modeling you need to take with a grain of salt. I have never heard anything good about climate models and expect this to be more of the same. They apparently had some studies of reaction products of uranium disintegration from the ocean floor and decided to model how they got there. What we need to know is not what happened during the ice age but what happened at the turn of the twentieth century. That is the time when the reorganization of the North Atlantic current system started bringing warm water to the north and melting the Arctic. That, and not some greenhouse effect is why sea ice is diminishing.

  59. DesertYote says:

    William
    November 4, 2010 at 11:47 am

    Interglacials have in the past lasted roughly 12,000 years, not 20,000 years as stated above. The past interglacials have ended abruptly.
    ##
    That means the next ice age starts the day before, the day after tomorrow!
    Darn, I was kinda hope’n that it might get a little bit warmer ‘fore the next big freeze. Seems like we never quite made it out of the last one.

  60. kadaka (KD Knoebel) says:

    More info on the study:
    http://www.nature.com/nature/journal/v468/n7320/abs/nature09508.html

    Looks like “everything but the main text.” Abstract, Author info (Affiliations, Contributions), and, most important:

    1. Supplementary Information (767K)
    The file contains a brief introduction on 231Pa/230Th as a water flow-rate proxy, Supplementary Figures 1-3 with legends, the data from the Agulhas Plateau and the equatorial Atlantic which help to interpret the MD02-2594 record; the equations used for the calculation of 231Pa/230Th ratios. The file also contains Supplementary Table 1 and additional references.

    Note: File is labeled PDF, downloads fine, my non-Adobe viewer identifies the actual file within the PDF as a Microsoft Word document. Looks nice and informative.

    Wow, peer-reviewed published climate science literature with freely-available data and equations, provided up front. Who didn’t get the memo? ;-)

  61. Lee Kington says:

    William says:
    November 4, 2010 at 11:47 am
    Interglacials have in the past lasted roughly 12,000 years, not 20,000 years as stated above. The past interglacials have ended abruptly.

    The span of an interglacial (the warm period) may deviate from the factors and events which create and end them. In other words; a change which starts the warming toward the interglacial will begin long before the warmth of an interglacial is reached.

    During the depths of the last glacial period several relatively minor warming events occurred. The last one, the one that warmed all the way into the holocene began about 18,000 years ago. The possibility the warming was due, to some extent, by a major change in oceanic circulation which started changing 20,000 years ago (2,000 years prior to evident warming) is quite real.

    Allow me to go back to the 18,000 year figure for a moment, a reason why I refer to it. Interglacials are periods of non-exact time span just like the glacial cycles. “Average” periods of durations are what is generally cited. I view the calibration, sequencing, a bit different. Present day temperatures are pretty much at the lower end of interglacial temps. Using the temps of the LIA as the ‘crossover’ point; with each interglacial the span from when the final warming during the depths of glaciation started to the time when the following interglacial ended is consistently roughly 18,000 years. The period it takes to warm up into an interglacial will vary, the period from the interglacial maximum to the re-entry into glacial may vary. However, the total time span of 18,000 years is quite constant.

    Why it that important (to me anyway)? Since the duration of the interglacials vary considerably, and the duration from interglacial maximum to re-entry into glacial varies considerably one cannot, by standard sequencing, determine at what point in the holocene we are at. When will it end?

    The Milankovitch cycles certainly play a large role, but, are not enough to explain the glaciation periods in full. Entry into glaciation is very difficult to correlate with the cycles. The numbers just don’t add up to establish a proper accounting. Hence, other factors must be involved. Oceanic circulation is a likely candidate for at least one of, if not one of the major, factors. Those are events which will occur with or without any influence by man.

    The holocene has been an interglacial with a relatively stable climate in comparison to others. This may be, to my interpretation, due to the Younger-Dryas. Despite the obvious impacts it seems, again to me, that the Younger-Dryas mitigated / retarded some of the interglacial warming which would have otherwise occurred. With the Holocene climatic optimum being relatively cool the climate, rather than dropping right off, dropped slightly and then essentially stabilized. Man has been spoiled by the graces of nature…. for now. The true general climate of earth is not as gracious a host to man as we have become accustomed to.

    I did an article on that quite some time ago. It was poorly done I must admit. Perhaps it is time to revisit the topic and generate one of better quality.

  62. Louis Hooffstetter says:

    Earle Williams says: “Chronoconnections”

    Enlighten us Earle. Google is no help. What’s up with Chronoconnections?

  63. Ian W says:

    ““The study shows that the ocean circulation was very different in the past and that there was a period when the flow of deep waters in the Atlantic was reversed. This happened when the climate of the North Atlantic region was substantially colder and deep convection was weakened.”

    Talk about a statement of the blindingly obvious. 20,000bp was in the middle of the last ice age. So yes – the climate of the North Atlantic Region was substantially colder. Indeed it was cold to the level that the polar ice sheet extended South to New York and covered UK. An Arctic ice sheet of this extent might just alter almost all the prevailing winds, the North Atlantic Drift and the MOC – is this a surprise to anyone?

  64. HR says:

    How can this be?

    There is no mention of CO2 in connection to research about climate change. These guys must have it wrong. Antony I think you’re right to suggest an alternative title. It’s generally the speculation that goes beyond the data that angers me most.

    It certainly looks like system variability as a driver of climate could be an option. I’d be interested how AGW theory explained climate change 20,000 years ago.

    To partly answer my own question here’s something from the Geological Society’s recent document on the subject.

    “How did levels of CO2 in the atmosphere change during the ice age?

    The atmosphere of the past 800,000 years can be sampled from air bubbles trapped in Antarctic ice cores. The concentrations of CO2 and other gases in these bubbles follow closely the pattern of rising and falling temperature between glacial and interglacial periods. For example CO2 levels varied from an average of 180 ppm (parts per million) in glacial maxima to around 280 ppm during interglacials. During warmings from glacial to interglacial, temperature and CO2 rose together for several thousand years, although the best estimate from the end of the last glacial is that the temperature probably started to rise a few centuries before the CO2 showed any reaction. Palaeoclimatologists think that initial warming driven by changes in the Earth’s orbit and axial tilt eventually caused CO2 to be released from the warming ocean and thus, via positive feedback, to reinforce the temperature rise already in train28. Additional positive feedback reinforcing the temperature rise
    5
    would have come from increased water vapour evaporated from the warmer ocean, water being another greenhouse gas, along with a decrease in sea ice, and eventually in the size of the northern hemisphere ice sheets, resulting in less reflection of solar energy back into space.”

  65. Earle Williams says:


    Louis Hooffstetter says:
    November 4, 2010 at 4:47 pm
    Earle Williams says: “Chronoconnections”

    Enlighten us Earle. Google is no help. What’s up with Chronoconnections?

    Louis,

    You may be aware of the concept of teleconnections, where a cause and effect are seperated by distance. This distance is sufficient that absent the presumed teleconnection the two would appear to be unrelated.

    Now you are ready to understand the concept of chronconnections. Cause and effect that are seperated by time. Chronoconnections, being a post-normal creation of climate science, are not constrained by the quaint notion that time flows in but one direction. Such notions are relics of the fossilized “empricial” science hegemony.

    So it is now crystal clear how the unprecedented man-made CO2 pollution of the last two centuries is chronoconnected to the Atlantic reversal circa 20,000 years BCE in a causal fashion.

  66. Earle Williams says:

    Bah, try to be clever and you mispell “empirical”!

    ;-)

  67. Lee Kington says:

    Espen says:
    November 4, 2010 at 8:58 am
    20000 years ago the last glaciation was still going strong, so the climate was very different and less stable: Climate during a glaciation is unstable climate. Climate during an interglacial is stable climate. Still these scare stories – that AGW may cause similar “disruptions” – pop up again and again.

    I must disagree, in part. 20,000 years ago was just a tic in geologic time (about 2,000 years) prior to the warming event which resulted in warming into the holocene. In essence, the last glacial period was ending.

    Stable vs non-stable climate as related to glacial and interglacial periods. I would tend to say that one (interglacial) is warmer and one (glacial) is colder. Though storm tracks and events may differ the climate during the two is ever changing and at about the same or similar rates.

    The Holocene, our interglacial, has indeed been one of relatively consistent climate when compared to other interglacials. Man has been fortunate. The stability of the Holocene may be due to the Younger-Dryas interrupting the warming toward the interglacial (Holocene) maximum. With the climate not attaining the warmth it otherwise would have, dynamics changed, and the climate of the Holocene stabilized. Had it not been for the Younger-Dryas the temperature trend for the Holocene may have been more of an up and down spike.

    Had the Holocene climatic maximum been 1.5 to 3 C warmer than it was the climate today could very well have been quite different. It is ‘possible’ that the only reason we are not clearly dropping into the next glacial period presently is due to the low temperatures of the maximum.

    That said, the transition from interglacial to glacial has been stated by some to be a period of great variability, turbulence, and unpredictability of climate. That does, in a way, make sense due to the fact that numerous elements of climate dynamics would be changing. When I look at a marked difference in how the Arctic and Antarctic are behaving in contrast to other geologically recent times of similar global temperatures, and I note various changes in temperature trend patterns, it is evident (to me) that the nature of our climate is changing. Climate is always changing, the nature of it, how it is behaving now appears to be undergoing a change. A change that many may be misinterpreting.

    Why would they be misinterpreting? Because they are trying to make a seven layer cake with only 2 ingredients.

    Now I wait for a supporter of CAGW to state that increased warming at the time of the Holocene Climatic Optimum could not result in cooling or more rapid cooling.

  68. Pamela Gray says:

    To add to the discussion: Changes in oceanic currents, as well as changes in the temperature of those currents (and I am talking about the overturning currents) can be impacted by sudden influx of fresh water. This occurs when climate warms. The paradox is the abruptness of fossil evidence of this change. While the climate may warm slowly, the sudden change in currents happens because of sudden breaks in continental ice jams (think state-sized and bigger). We aren’t talking about an ice jam that suddenly breaks and releases river-sized flows. We are talking about huge ice jams that have kept great-lakes sized and bigger ponds at bay. Till that is, the ice jam breaks. It doesn’t take forever for that fresh, low-salt water to reach the ocean. And the breaks tend to occur fairly close to each other even though the ice jams may be on different continents. That’s a lot of fresh water suddenly flowing into the ocean.

  69. pkatt says:

    If continents weren’t in the same positions 20,000 years ago so why would we expect the ocean currents to flow the way they do today? Heck tomorrow a massive upheaval under the ocean might change the currents. Seems a whole lot more likely a cause to me then a painfully slow infusion of fresh water in salt water. Nature does slow very well, its catastrophic that it changes for.

  70. UK Sceptic says:

    They do not understand the process but they can model it? Haven’t we already travelled down this cul-de-sac?

  71. Lee Kington says:

    RE:
    pkatt says:
    November 4, 2010 at 10:31 pm

    Certainly geographic changes affect both ocean and atmospheric currents. Even our cities with their tall buildings, change in thermals, etc. most likely have some (albeit minor) influence. Continental drift, for the most part, however is a slow (very slow) process. Australia is moving north at what?….. 1/4 inch per year or about 418 feet over 20,000 years. Would that alter currents slightly? Yes. Enough to generate noticeable and attributable change?

    There is another influence over time. Sea level and coastlines. It is cited that the sea level around Australia was more than 350 feet lower 20,000 years ago. Sydney, rather than being a coastal port, would have been about 15 miles inland. Most, if not all of the present Australian coast would be far inland. Hence the change in currents due to geographics between then and now would be much more significant due to sea level rather than 418 feet of drift. Lower sea levels would also mean that subsurface geographic features could / would have greater influence on currents and climate.

    At least, those are my thoughts on the matter.

  72. Bill Illis says:

    Having looked into this more, they are talking about the deep, deep ocean circulation, not the surface currents.

    In the Atlantic, Antarctica produces the densest, coldest water and this dominates the flow at the very bottom of the Atlantic. It doesn’t really flow too far though and kind-of just reaches an equilbium point at about 30N, two-thirds up the Atlantic.

    The North Atlantic deep water is next in density and dominates the mid-deep ocean flow. Because this flow can continue on and enter other deep ocean flows thoughout the planet (and mix in with other mid-depth deep water around Antarctica), it can flow by Africa etc.

    http://web.me.com/uriarte/Earths_Climate/Appendix_4._Ocean_currents_files/p237.jpg

    http://www.clivar.org/organization/southern/images/lumpkin.jpg

    I think this study is just saying the Antarctic deep water also dominated the mid-depth flow. It wouldn’t make much difference anyway – it is not going anywhere. Wally Broeker outlined how this circulation would probably change decades ago already although this chart is not quite what this study says occurred.

    http://oceanworld.tamu.edu/resources/oceanography-book/Images/nao-en_33957.jpg

  73. Peter Taylor says:

    Will Crump – you ask for any insights on the current reversal –

    There are two factors that ‘warming’ might induce: warmer surface waters in the North Atlantic zone of downwelling; and freshening of the North Atlantic due to either glacial melt or increased river flows in the Arctic Basin.

    As far as I can tell, the warm surface waters get entrained in the downwelling of the much colder Arctic bottom water, and do not constitute a major part of the larger conveyor system – rather, the North Atlantic gyre accumulates warm water to about 200m depth, and I think this warm water pool is periodically diminished/enhanced by differential heat transfer to the atmosphere (something I put forward in the ‘Ocean Cycles’ chapter in ‘Chill’.).

    With regard to freshening – this was reported by Dickson et al in 2002:

    Dickson B. et.al. (2002) Rapid Freshening of the Deep North Atlantic Ocean Over the Past Four Decades Nature 416, April 25, 2002.

    but this trend appears to have reversed:
    Hátún H. et al (2005) Influence of the Atlantic Subpolar Gyre on the Thermohaline Circulation Science 309: 1841-1844

    Likewise, the slowing down of the THC reported by:
    Bryden H.L. et al.,( 2005). Slowing of the Atlantic meridional overturning circulation at 25ºN. Nature 438, 655-657.

    is not regarded as consistent:

    Knight J.R., et al., (2005). A signature of persistent natural thermohaline circulation cycles in observed climate. Geophysical Research Letters 32, doi:10.1029/2005GL024233.

    And so, despite the warming and freshening of the North Atlantic in recent decades, the THC has both slowed down and speeded up. The expectation from sediment data is that the bottom deepwater circulation speeds up during warm periods, yet the recent major warm period in the North Atlantic coincided with a slowing down.

    We should note that it takes the bottom water about 30 years to move 1000km. So measurements taken at different parts of the Atlantic – such as Norwegian data on the downwelling zone, and Bryden’s data further south, are not rally going to inform us of the true dynamic.

  74. Will Crump says:

    Thanks Peter Taylor

  75. Tim Clark says:

    Peter Taylor says:November 5, 2010 at 8:23 am
    There are two factors that ‘warming’ might induce: warmer surface waters in the North Atlantic zone of downwelling; and freshening of the North Atlantic due to either glacial melt or increased river flows in the Arctic Basin.

    It requires more precipitation to have more streamflow. More precipitation requires more evaporation/condensation from the ocean, which increases the salt content. More clouds take heat to the tropopause and reflect sunlight.
    Warmer surface waters increase evaporation/precipitation increasing net deposition of snow/ice reducing net glacial ice loss.

    Doesn’t add up.

  76. Peter Taylor says:

    Tim Clark:

    I’d be the first to agree it doesn’t add up! But if data are accurate, then there was a freshening in the North Atlantic (recently ceased) and the sea surface area south of Greenland has got warmer and still is. Both of these could theoretically slow the THC.

    As to the wider picture – there is data on increased glacial melt and run-off from Siberian rivers; a 14% increase in cloudiness in the Arctic Basin; and during the positive phase of the PDO increased precipitation (and warmth) in Alaska; but during this same period of about 25 years, global cloud cover decreased by about 4%.

    So warmer seas globally seem to have produced less cloud globally (or vice versa – more likely!).

    Personally, I think the tracking of cyclones and anticyclones influenced by the jetstream is key to understanding northern hemisphere dynamics – when solar UV flux was high from 1980-2003, the jetstream moved northward and the polar vortex was tight, when the Sun’s reduced its flux and extended that reduction for a year or more, the jetstream shifted south and the polar vortex expanded.

    Charles Perry has published work suggesting that oceanic warm water pools create feedback via warm rising air that affects the jetstream – for example, a warm North Pacific during positive PDO, and perhaps therefore also during a warm North Atlantic during a positive AMO. I am not convinced of the potential of this feedback.

    If you look at the jetstream right now, it is massively kinked and the kinks do not appear to correlate with SSTs – I still do not know what causes these kinks.

    Take a look at:

    http://www.squall.sfsu.edu/crws/jetstream.html

    I would suggest that the contortions of the jetstream initiate cyclonic vortices and somehow also direct the anticyclone centres too. A more northerly jet will dump more rainfall in Fennoscandinavia and Siberia from the North Atlantic, and more in Alaska from the North Pacific. Greenland ice melt may be due to warmer seas.

    It will be interesting to see what happens this winter, with the solar flux still relatively low – and a negative AMO with high pressure systems in the sub-Arctic, the jet should flatten and run due west-east into Iberia with a repeat of the devastating floods of last winter (especially in the Sierra Nevada). Sediment studies from southern Spain show this happened last during the Little Ice Age.

    The problem is that globalised average data don’t provide much of a guide as to what happens in the two key regions of the northern Pacific and northern Atlantic – which I am convinced actually drive the long term cycles such as MWP/LIA and the shorter 60-70 year cycles such as the 1945-1975 cool period (now known NOT to be due to industrial aerosols – see my chapter on ‘natural cycles’ in ‘Chill’ for references).

  77. LightRain says:

    “Global warming today could have similar effects on ocean currents and could accelerate climate change”

    And 20,000 years ago what caused the temperatures to rise similar to today?

  78. Pamela Gray says:

    pkatt, 20,000 years ago, the continents were in the same position they are now. One of the potentially major differences would have been in Antarctica. The southern tip of South America nearly bridges with Antarctica (the sea floor there has a mountainous ridge). The massively thick floating sea ice may have touched the bottom of that narrow channel thus diverting the circumpolar Antarctic current into the Atlantic Ocean. That diversion would have significantly cooled the Atlantic. It would be an easy guess that this will happen again. I think the cyclical Milankovitch Antarctic ice buildup (and thus the diversion of that cold current into the Atlantic basin) is what cools the Atlantic enough to allow a growing ice cap in the Arctic. Hence the onset of an ice age. Just my musings.

  79. phlogiston says:

    Bill Yarber
    Nov 4, 9:05 am

    I have a hunch baased on Arctic sea temperatures that the strength of the MOC (and of an impotant component of the MOC – the gulf stream) oscillates with the AMO.

    Thus we should see MOC strength coming back down soon.

Comments are closed.