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Global warming and ocean heat content

Filed under: — gavin @ 3 October 2011

The connection between global warming and the changes in ocean heat content has long been a subject of discussion in climate science. This was explicitly discussed in Hansen et al, 1997 where they predicted that over the last few decades of the 20th Century, there should have been a significant increase in ocean heat content (OHC). Note that at the time, there had not been any observational estimate of that change (the first was in 2000 (Levitus et al, 2000)), giving yet another example of a successful climate model prediction. At RC, we have tracked the issue multiple times e.g. 2005, 2008 and 2010. Over the last few months, though, there have been a number of new papers on this connection that provide some interesting perspective on the issue which will certainly continue as the CMIP5 models start to get analysed.

The most recent paper was a new study from NCAR out last week that looked into what happens to OHC in models when there are occasional 10 year periods with no trends in global surface temperatures (Meehl et al, 2011).

It is well-known (or at least it should be) that simulations for late 20th C and early 21st Century do not produce monotonically increasing temperatures at the annual or decadal time-scale. For the models used in AR4, the decadal trends expected under estimates of present day forcings are roughly N(0.2,0.14) (i.e. a Gaussian distribution centered on 0.2 ºC/decade with a standard deviation of ~0.14ºC/decade. This implies that one would expect an 8% probability of getting surface temperature trends less than zero in any one decade.

The Meehl et al study looked at the changes in ocean heat content during these occasional decades and compared that to the changes seen in other decades with positive surface trends. What they found was that decades with cooling surface temperatures consistently had higher-than-average increases in ocean heat content. This makes perfect sense if there is internal decadal variability in the fluxes that connect the deeper ocean to the surface ocean (which of course there is). An anomalous downward heat flux reduces the ocean surface temperature (and hence global surface temperature), which generates an anomalous heat flux into the ocean from the atmosphere (because the flux into the ocean is related to the difference between atmospheric and ocean temperature). And this of course increases total OHC.

A related study from the UK Met. Office looked at the relationship between the ocean heat content changes in the top 700m and the total ocean heat content change in models (Palmer et al, 2011). They found that (unsurprisingly) there is more variability in the top 700m than in the whole ocean. This is important to quantify because we have better estimates of the upper ocean OHC change than we do of changes in the whole ocean. Observational studies indicate that the below-700m increases are not negligible – but they are poorly characterised (von Schuckmann et al, 2009). The Palmer study indicates that the uncertainty on the decadal total OHC change is about 0.15 W/m2 if one only knows the OHC change for the top 700m.

So what can we infer about the real world from these tests? First, we can conclude that we are looking at the right quantities. Total OHC changes are a good measure of the overall radiative imbalance. Second, there is likely to be a systematic issue if we only look at the 0-700m change – this is a noisy estimate of the total OHC change. Third, if the forcings are close to what we expect, we should anticipate that the deeper ocean (below 700m) is taking up some of the slack. There are of course shorter term sources of variability that also impact these measures (OHC changes associated with ENSO, solar irradiance variability over the solar cycle) which complicate the situation.

Two further points have come in comment threads recently that are related to this. The first is whether the changes in deep ocean heat content have any direct impact other than damping the surface response to the ongoing radiative imbalance. The deep ocean is really massive and even for the large changes in OHC we are discussing the impact on the deep temperature is small (I would guess less than 0.1 deg C or so). This is unlikely to have much of a direct impact on the deep biosphere. Neither is this heat going to come back out from the deep ocean any time soon (the notion that this heat is the warming that is ‘in the pipeline’ is erroneous). Rather, these measures are important for what they tell us about the TOA radiative imbalance and it is that which is important for future warming.

The second point is related to a posting by Roger Pielke Sr last week, who claimed that the Meehl et al paper ‘torpedoed’ the use of the surface temperature anomaly as a useful metric of global warming. This is odd in a number of respects. First, the surface temperature records are the longest climate records we have from direct measurements and have been independently replicated by multiple independent groups. I’m not aware of anyone who has ever thought that surface temperatures tell us everything there is to know about climate change, but nonetheless in practical terms global warming has for years been defined as the rise in this metric. It is certainly useful to look at the total heat content anomaly (as best as it can be estimated), but the difficulties in assembling such a metric and extending it back in time more than a few decades preclude it from supplanting the surface temperatures in this respect.

Overall, I think these studies show how we can use climate models to their best advantage. By looking at relationships between key quantities – those that can be observed in the real world and those that are important for predictions – we can use the models to interpret what we are measuring in the real world. For these cases the inferences are not particularly surprising, but it is important that they be quantified. Note that the assumption here is akin to acknowledging that since the real world is more complicated than the (imperfect) models, inferences in the real world should at least be shown to work in the models before you confidently apply them to reality.

However, it is the case that none of these studies prove that these effects are happening in the real world – they are merely suggestive of what we might strongly expect.


References

  1. S. Levitus, "Warming of the World Ocean", Science, vol. 287, pp. 2225-2229, 2000. http://dx.doi.org/10.1126/science.287.5461.2225
  2. G.A. Meehl, J.M. Arblaster, J.T. Fasullo, A. Hu, and K.E. Trenberth, "Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods", Nature Climate change, vol. 1, pp. 360-364, 2011. http://dx.doi.org/10.1038/nclimate1229
  3. M.D. Palmer, D.J. McNeall, and N.J. Dunstone, "Importance of the deep ocean for estimating decadal changes in Earth's radiation balance", Geophysical Research Letters, vol. 38, pp. n/a-n/a, 2011. http://dx.doi.org/10.1029/2011GL047835
  4. K. von Schuckmann, F. Gaillard, and P. Le Traon, "Global hydrographic variability patterns during 2003–2008", J. Geophys. Res., vol. 114, 2009. http://dx.doi.org/10.1029/2008JC005237

283 Responses to “Global warming and ocean heat content”

  1. 101
    Bob Loblaw says:

    Re: 78 and 90.

    There is a smidgeon of truth in the idea that temperature anomalies are related to heat fluxes, but it is a lot more complex than Dr. Pielke seems to assume. In the lower atmosphere (a few metres height), with which I am most familiar, one method of measuring the heat flux is called “eddy correlation” or “eddy covariance”, and involves the simultaneous measurement of both temperature and vertical velocity. Basically, each upward or downward puff and it’s heat content (temperature X heat capacity) is measured, and the average of the cross-product over time is the flux. You can also measure evaporation if you have humidity measurements, or the flux of any other gas if you have its concentration.

    In the lower atmosphere, you need readings at least several times per second, and very fast-reacting sensors. The usual suspects are sonic anemometry and fine-wire thermocouples (e.g., less than a thousand of an inch), and IR absorption measurements for gas concentrations. Developed as a research tool in the 1960s (IIRC), you can now buy these off-the-shelf (e.g., Campbell Scientific CSAT3 3-D Sonic Anemometer).

    To have a value representative of a larger area, You need to make sure your mean vertical velocity is zero, or you’re in a plume or zone of descending air. Otherwise, you’d need a lot of spatial sampling to average things out.

    In the ocean, the same principles would apply. Temporal sampling would be a lot less (you need to sample the turbulence), but zones of rising or descending water would be a problem. I doubt that current ocean temperature monitoring systems are designed to do this, but if someone familiar with Argo thinks it can be done, feel free to argue the case. In the absence of a demonstration that it is possible, I’ll side with the idea that ocean temperature anomalies are just temperature anomalies.

  2. 102
    MapleLeaf says:

    This may be OT, but Roger senior did introduce the issue of the global temperature records. Roger senior on is trying to claim that the EPA and Tom Karl misled people. I suggest he look up the official meaning of “collect”. But I digress. In reality on his blog (that he links us to abovee) he goes much further than that, his picture of Pinocchio (with a very long nose) at the top of the post strongly suggests that he is accusing Karl and/or the EPA of lying. I find that inflammatory rhetoric by Roger senior (some might say defamatory) very inappropriate and not at all constructive. What is more it is hypocritical given his recent (and very vociferous) laments about scientists calling out Spencer and Christy and other ‘skeptics’ on their very real misleading comments and errors.

  3. 103
    Brian Dodge says:

    “I submit that the Hadley global SST fits the bill as well as anything … There has been no net warming since 1997 – 14 years with CO2 up 7% and no net warming. ( Check the actual data at the Hadley center)” Norman Page — 7 Oct 2011 @ 12:32 PM

    Okey dokey. (data from http://www.cru.uea.ac.uk/cru/data/temperature/hadsst2gl.txt OLS fits by http://www.woodfortrees.org/data/hadsst2gl/from:xxxx/trend/ where xxxx is year)

    1992 #Least squares trend line; slope = 0.0139042 per year
    1993 #Least squares trend line; slope = 0.0122811 per year
    1994 #Least squares trend line; slope = 0.0101578 per year
    1995 #Least squares trend line; slope = 0.00802613 per year
    1996 #Least squares trend line; slope = 0.00630044 per year
    1997 #Least squares trend line; slope = 0.0015432 per year —- cherry pick, but still positive
    1998 #Least squares trend line; slope = 0.000656129 per year —- sweeter (but positive) cherry
    1999 #Least squares trend line; slope = 0.00558789 per year
    2000 #Least squares trend line; slope = 0.0015527 per year
    2001 #Least squares trend line; slope = -0.00482041 per year —- still sweeter cherries(FINALLY, a real live negative trend), but only ten year noise dominated trend

    1981 #Least squares trend line; slope = 0.0137489 per year —- 30 year climatological trend – compare trend from 1992.

    How’s that pie coming?

    I find that the scariest metric does come from the ocean – the Arctic ocean -http://www.woodfortrees.org/plot/nsidc-seaice-n/from:1979.6/every:12. The slope triples after 1995.

    I submit that given the signal to noise, there’s no significant difference in using UAH, HadCRUT, or HadSST.

  4. 104
    Hank Roberts says:

    Perhaps a new term is needed, one that includes the deep ocean and the upper surface of the Earth:

    “… 200 meters deep. Much deeper and the temperature differences become too minute to pick up …. that depth allows them to take measurements that go back about 500 years ….

    ‘… those measurements tell us the Earth is warming faster than we previously thought.’”

    There’s good precedent for doing this:

    http://e360.yale.edu/feature/living_in_the_anthropocene_toward_a_new_global_ethos/2363/

    “Nobel Prize-winning scientist Paul Crutzen first suggested we were living in the “Anthropocene,” a new geological epoch in which humans had altered the planet…. Crutzen and a coauthor explain why adopting this term could help ….”

    http://www.analects-ink.com/mission/Confucius_Rectification.html

    “If language is not correct, then what is said is not what is meant; if what is said is not what is meant, then what must be done remains undone; if this remains undone, morals and art will deteriorate; if justice goes astray, the people will stand about in helpless confusion. Hence there must be no arbitrariness in what is said. This matters above everything.”

  5. 105
    Hank Roberts says:

    Maybe “Climate System Change” to include stratospheric cooling?

  6. 106

    Bob Loblaw – The temperature changes can be integrated across a vertical layer (e.g. the upper 700 meters of the ocean) and in time (e.g. over a year) to diagnose the flux divergence of heat within this layer over the selected time period. We do not need direct measurements of the fluxes to do this.

    We can express this change in heat in units of Joules which can be converted to an average heating rate in Watts per meter squared over this time period.

  7. 107
  8. 108
    Rob Painting says:

    Bob Irvine @ 91 – “Your answer was that colder water has a lower expansion coefficient and therefore the same amount of energy would cause less thermal expansion if it were to find it’s way to the deep oceans.”

    No Bob, you just made that up. Scroll back over the comments if you like – you started off on that tangent. My initial response to you was that La Nina/El Nino causes huge exchanges of water mass between land and ocean. That’s the main reason why CO2 uptake by land-based vegetation fluctuates greatly between ENSO episodes – El Nino induced global drying of the land surface is harmful to plants.

    Bob -“Song and Colberg support my position”

    No Bob. Here’s the Song & Colberg (2011) paper. They simply reinforce what has been explained to you above – short term sea level fluctuations are due to exchanges taking place in the upper ocean, but the long-term rise in sea level (due to thermal expansion) can only be explained by deep ocean warming. Which is why they write:

    “In summary, we have proposed a plausible hypothesis that deep ocean warming may have contributed up to one‐third of the observed altimetry SLR”

    Again – this is not inconsistent with the modeling in Meehl (2011) – surface heat exchange altering global surface temperatures, but the deep ocean steadily accumulating heat.

    Bob – “the inescapable conclusion is that the earth’s heat content is increasing much more slowly than all the models predict.”

    Bob, have you forgotten that Meehl (2011) is based on a climate model? These hiatus decades are not a new feature in climate models either.

  9. 109
    bibsir says:

    Another reason to use surface temperature as the measure for global warming is because that is what is melting glaciers, will change weather, cause species extinction etc.

  10. 110
    Bob Loblaw says:

    Re: 106

    Yes, that is correct, Roger. You can get flux divergence from that, but as you clearly admit, you do not get the actual flux at either the top or bottom of the layer. You are confusing the two issues by using the term “average heating rate” – you are getting the average difference between the two heating rates (heat going in or out the top, and heat going in or out the bottom of the layer). Mathematically, there are an infinite number of pairs of top/bottom fluxes that will give you the same result – the only mathematical constraint on their values is that the difference match the change in storage that you have calculated. So, your methodology is a complete failure at determining an actual flux value at either the top or the bottom of the layer. The value that you calculate does not even need to be anywhere close to the magnitude of either flux (and doesn’t even have to be of the same sign). e.g., 101-100=1, 11-10=1, (-49)-(-50)=1, etc.

    Note: in the description above, I am intentionally leaving things in a one-dimensional frame, thinking of the ocean as an infinite layer. Of course, in the real world, we’re working in 3-D, and Roger’s change in storage is actually the result of flux divergence in three directions – horizontal times 2, and vertical. This does not make it a simpler problem. For a given change in heat storage for the volume of water in question, there are now six fluxes that can be changing to affect the result.

    If we do the 3-D calculation for the entire ocean, then we can reasonably assume that the fluxes at the horizontal edges are zero, and then we get no horizontal flux divergence. This brings us back to the relatively simple 1-D case above, but guess what? We’ve just reframed our calculation back to “total change in ocean heat content” for whatever layer thickness we have chosen. It is not a flux calculation.

  11. 111
    Hank Roberts says:

    > e.g … upper 700 meters

    But some of the recently warmed water goes to the depths; some is near the surface. The depth distinguishing one from the other vary across the ocean basins:

    “Oldest water is at intermediate depths
    Surface = youngest
    Deep = newly ventilated”

    http://www.clas.ufl.edu/users/eemartin/GLY307411/lectures/8.%20Deep%20Ocean%20Circulation.ppt

  12. 112
    norman page says:

    @ 95 Response
    Gavin in my first post – 80 I said “This is obviously a short term on which to base predictions but in the context of declining solar activity – to the extent of a possible Dalton or Maunder minimum and the negative phase of the Pacific Decadal Oscillation a global 20 – 30 year cooling spell is more likely than a warming trend.”
    If all there was was the short term 2003 – 2011 trend I would agree that any predictions would be fragile – but the impotant point is the association of this trend with the PDO ( google Easterbrook PDO ) and with the sharp drop in solar magnetic field strength in 2004. The sun is really in uncharted territory – solar science is in the process of total upheaval.
    Incidentally your first graphs (anything different)didnt include the SST data but the Hadcrut three is close enough.
    As to cherry picking – all analyses of time series are inevitably cherry picked one way or another – I have given perfectly valid reasons for picking 2003 as an inflection point.I’m very willing to test my predictions over time and I’ll check out your Intrade suggestion – maybe the odds will look better than the stock market at the moment.

  13. 113

    Bob Loblaw – The flux divergence of heat is what produces the temperature change. Thus we can use the observed temperature change to compute the flux divergence of heat. The difference in the flux at the surface minus any flux out at the bottom of the layer (or if you integrate to the bottom of the ocean where you can assume a zero flux) is the flux divergence. We do this kind of calculation all the time in atmospheric and ocean boundary layer stidies.

  14. 114
    David B. Benson says:

    Hank Roberts @111 — Great slideshow. Thank you.

  15. 115
    sidd says:

    Prof. Pielke writes on the 8th of October, 2011 at 2:24 PM:

    “The temperature changes can be integrated across a vertical layer (e.g. the upper 700 meters of the ocean) and in time (e.g. over a year) to diagnose the flux divergence of heat within this layer over the selected time period. We do not need direct measurements of the fluxes to do this.”

    why does the calculation not also depend on the integration of velocities ? is the assumption that the vertical mass flux across the 700m depth average to zero ?

    sidd

  16. 116
    MapleLeaf says:

    Roger senior @113 writes.

    Thus we can use the observed temperature change [I'm assuming he means from Argo floats] to compute the flux divergence of heat.

    Gavin, please correct me if I am wrong, but would doing that not require a fixed array observation system? The Argo floats are drifting and thus do not measure temperature at the same depth over a continuous period of time, and to calculate the fluxes one would require accurate measurements, not time and distance interpolated values. So might one be able to calculate the fluxes using data from a fixed array like TAO/TRITON? But that would limit the analysis to the tropical Pacific.

    Go here and select “T-Depth Anomalies – Equatorial Pacific”, the animation there seems to show positive sub-surface temperature anomalies working their way down to almost 500 m over the western tropical Pacific. Or am I barking up the wrong tree?

    Either way, instead of telling others what they should/could be doing, why is Roger senior not actually doing the research on this issue himself?

  17. 117
    Ken Lambert says:

    Mapleleaf #116

    I have thought for some time that the only way to get an accurate OHC would be to have a fixed array of sensors at all depths globally reporting at the same instant in time. This would be a very large undertaking.

    In that way Time 1 and Time 2 differences could give weekly, monthly, yearly snapshots of the global oceans which would detect OHC changes accurately.

    Argo is the current best we have, but I do not know how closely its data comes to a ‘gold standard’ of a fixed array, considering the drifting floats might not sample the same pixel of ocean at Time 2 as Time 1, and how reporting time differences are handled.

  18. 118
    Ray Ladbury says:

    Ken Lambert,
    I don’t think it is quite as difficult as you posit. The timescales for energy changes in the 0-700m top portion of the oceans are much longer than those of the atmosphere, while the scale for the deep oceans is hundreds of years or longer. Things ain’t changing that fast. Likewise on spatial scales, the deep ocean currents are remarkably stable. Yes, it’s a big project, but most of the data would be pretty boring.

  19. 119
    ldavidcooke says:

    RE:117

    Hey Ken,

    Try the TAO/Triton data display time series plots. Choose your freq., change to one variable for 10 data sites, choose your data sites (be aware some have not the history others do), choose your variable, then choose your data window. This covers the equatorial range in the Pacific. For the Atlantic find the PIRITA data set.

    If you are interested you can query the 60skyrad data set at arm.gov to try to get an estimate of the W. Pac. “goes-inter”. Using the refs. above suggests the downwelling potential in the top 300m.

    If you can find the Lidar/RPS sea surface scans you might be able to pick out a Sodium value in an attempt to derive a surface salinity value. Though I have not seen it yet, I am sure there have to be several papers addressing the volume of evaporation ratio to salinity values. Hence, you can then derive the wv and latient heat (specific heat?) transfered to the atmosphere. What is left is the radiant balance already being monitored by several EOS remote systems. This should help point out the verticle flow.

    To get a fuller picture you would need to track the horizontal movement as well. Ocean currents are a big help and are available today from several sources.

    The loss of the GLORY APS based system is the biggest hole in the measure, IMHO. Its replacement being low on the priority list is a shame, if we intend to be more empirical then theoritical in the near future. It’s replacement is unlikely to fly before I will…

    Cheers!
    Dave Cooke

  20. 120
    Bob Loblaw says:

    Re: 113

    Yes, Roger, we agree on that. To put it in strict mathematical terms, if T=temperature, t=time, C=volumetric heat capacity, and z=depth (we’ll stick to the 1-D case), and F=flux (well, flux density, in W/m^2), then we get:

    C*dT/dt = -(dF/dz)

    The left side is the rate of change of heat content, and the right side is the flux divergence (change in flux with depth). You can integrate between two depths to get a total for the layer, and the fluxes of importance are the top and bottom of the layer. (Note: I really should have partial derivatives in the above equation – being new here, I’m just not sure how to stick in a curly d in this text box)

    …but referring to the change in ocean heat content as “flux divergence” doesn’t make it some magical new thing – it is just a rearrangement of the above equation. Remember, in comment #78 you said:

    the downward movement of heat would be seen in positive temperature anomalies as they move towards lower depth. Similarly, if this heat were to re-emerge, we would also see it as the anomalies move upwards.

    ….and this simply isn’t true with the limited data from something like Argo. A positive temperature anomaly (increasing temperature) is nothing more than an increase in heat content for that layer, and it can be the result of increasing flux in at the top, or decreasing flux out at the bottom, or even decreasing flux at the top combined with a greater decrease at the bottom, etc. Or, it can just be cool water being replaced by warmer water in terms of ocean currents – from any direction (not just downward). In order to be able to determine that an increase in temperature is associated with an increased downward heat flux, you need the sort of detailed temperature and vertical velocity data that I mentioned in my first comment about eddy correlation techniques.

    When you increase the range of integration to be the entire ocean, so that the flux at the bottom is zero, then you get the case where an increase in mean ocean temperature (or, to rephrase it, an increase in total ocean heat content) can be interpreted as an increase in the global mean flux of heat into the ocean at the surface…

    …but then all you are saying is that total ocean heat content went up because more heat went in at the surface. This is not revolutionary science, and putting bells and whistles on it by calling it “flux divergence” or talking about “integration” doesn’t change that. And just because you can make that statement about surface fluxes when you integrate over the entire ocean, that does not mean that you can make an analagous statement about a single point in the ocean when its temperature rises or falls.

    Changes in temperature tell you changes in heat content, which tells you that something has changed in terms of net flux or ocean currents, but you don’t get any details about the individual fluxes themselves unless you have more information tan just temperature.

    So please don’t reiterate for yet another time that change in ocean heat content tells us about flux divergence, because we agree on that. It’s your claim in #78 about positive temperature anomalies indicating downward movement of heat (and vice versa) that you need to try to defend.

  21. 121
    David Lewis says:

    Regarding Gavin’s response to comment #3: I can’t understand why you say there is no contradiction between Hansen’s ideas and those advanced by Meehl and others at NCAR. If you could explain in more detail it would be greatly appreciated.

    Eg on page 35 of Hansen et.al. Earth’s Energy Imbalance and Implications, there is a republished Trenberth’s “Missing Energy” diagram (the one that originally appeared in Trenberth’s “Tracking Earth’s Energy” Perspectives piece in 16 April 2010 Science).

    On that same page 35, Hansen writes this about Trenberth’s ideas: “the slowdown of ocean heat uptake, together with satellite radiation budget observations, led to a perception that Earth’s energy budget is not closed (Trenberth 2009, Trenberth and Fasullo 2010), as summarized in Fig 19A. However, our calculated energy imbalance is consistent with observations (Fig 19b), implying there is no missing energy in recent years”.

    Hansen appears to be making the case, in Earth’s Energy Imbalance and Implications, that “most” state of the art climate models send too much heat into the deep ocean and therefore respond to climate forcings too slowly. He cites a personal communication with Romanou and Marshall who in a “paper in preparation” appear to have traced CFCs moving slower than models assume into the deep Southern Ocean. He imagines into existence a model that produces a result closer to the way he thinks the real world actually is, and using a climate response function he assumes this imaginary model has, finds that it calculates an energy imbalance very close to his idea of what current observations are, i.e. around 0.6 W/m2 which he believes might come out to 0.75 W/m2 if the data set had a complete solar cycle in it. He says the GISS model says the energy imbalance right now should be 1 W/m2.

    He says in his GISS luncheon talk explaining these ideas (on Youtube here http://www.youtube.com/watch?v=5EV3zKjwC9Y&noredirect=1 ) that he is working with other scientists to try to come up with a more realistic ocean for the GISS model so that he will have an actual model calculation to back up his idea rather than the dreamed up model he discusses in the paper. This dreamed up model that responds to climate forcings more quickly implies, he says in the abstract to the paper, a more powerful negative aerosol forcing, which he says is -1.6 W/m2. As far as I can tell his submission to the IPCC AR4 assumed aerosol negative forcing to be less powerful, maybe -1.4 W/m2. He says “most” other modellers use -1.0 W/m2 for aerosols.

    It seems clear as crystal that he doesn’t think there is any “missing energy” to account for, he thinks current models send too much heat into the ocean, and, as he wrote in his 2010 Global Surface Temperature Change paper “we conclude that there has been no reduction in the global warming trend of 0.15°C– 0.20°C per decade that began in the late 1970s.

    It seems at least some of the talk about ten year trends with no rise in the global average surface temperature chart can lead to confusion, because of imprecise use of terms. Trenberth’s own AR4 IPCC contribution stated the shortest time period over which the global warming signal emerges from the noise was 25 years. Yet people write as if it is significant that a ten year period starting in 1998 on the global average surface temperature chart, which only describes a tiny part of where the heat is in the planetary system that is warming, doesn’t clearly show a rising signal.

  22. 122

    Bob Loblaw – Regarding

    “positive temperature anomalies indicating downward movement of heat (and vice versa) that you need to try to defend”

    If one analyzes the vertical movement of these temperature anomalies over time (and the temporal and spatial resolution is good enough), the heat flux can be obtained from these plots.

    The total heating/cooling over a period of time of the ocean in Joules can be used to diagnose the time-space integrated heat flux into and out of the ocean in Watts per meter squared. Please see our paper on this

    Pielke Sr., R.A., 2003: Heat storage within the Earth system. Bull. Amer. Meteor. Soc., 84, 331-335.
    http://pielkeclimatesci.wordpress.com/files/2009/10/r-247.pdf

    See also Jim Hansen’s comments in http://pielkeclimatesci.files.wordpress.com/2009/09/1116592hansen.pdf

    [Response: No-one is arguing that one cannot get the net flux into the measured layer (say 0-700m) by measuring the temperature changes over time. I think the open question is whether the anomalous downward heat flux at 700m can be measured with the same fidelity. You seem to be asserting that this it is possible to get a good estimate of this by (presumably) calculating the anomalous diffusion (K dT'/dz) and advective flux (w T' + w' T) (though w' is probably small). I am unaware of any published estimate of these terms evaluated at 700m, but perhaps you might suggest one? NODC has started to produce ocean heat content changes for the 0-2000m layer and that shows large recent increases when compared to 0-700m, but data quality will not be as good as for the upper ocean. - gavin]

  23. 123
    sidd says:

    Mr. Bob Loblaw wrote on the 9th of Oct 2011 at 11:21 AM:

    C*dT/dt = -(dF/dz)

    should not the convective derivative come in here ?

  24. 124
    Bill DiPuccio says:

    Gavin,

    In 2005 you coauthored a paper with James Hansen and Josh Willis (in collaboration with twelve other scientists), on “Earth’s Energy Imbalance: Confirmation and Implications” (Science, 3 June 2005, 1431-35).

    This paper affirmed the critical role of OHC. “Confirmation of the planetary energy imbalance,” you maintained, “can be obtained by measuring the heat content of the ocean, which must be the principal reservoir for excess energy” (1432).

    In that paper you said that GISS model projections had been verified by a solid decade of increasing ocean heat. This was regarded as confirmation of the IPCC’s AGW hypothesis.

    Whatever semantic disagreements you have with Pielke, do you agree with him that OHC is the most robust metric for detecting warming in the climate system?

    [Response: What is this obsession with ranking different metrics? OHC changes are very useful at confirming that the system has been out of energy balance on average for the last few decades. But if you want evidence of warming of the climate system, you can also look at the met station data, the ice data, glacial retreat, SST, NMAT, TLT etc etc. It is precisely because there are some many streams of data that agree that we have confidence that the planet is indeed warming significantly. Any single metric - whether from satellites or Argo - is prone to systematic issues that are sometimes hard to detect, and sometimes hard to fix - therefore reifying any single metric is just foolish. Our understanding of the system comes from a balance of evidence argument, not because any one metric is the best. - gavin]

  25. 125

    Gavin – If the temporal and spatial resolution are sufficient, all that is needed is to monitor the Joules of heat in the upper 700m to follow their upward and downward motion (which is given by the temperatures).

    In the plot that you show of heating down to 2km, do you have evidence that this heat was first in the upper 700m? All you need to do is show this being transported through that layer, and I will be convinced of the robustness of the heating deeper than 700m.

    There is no need to explicitly calculate the fluxes; their net effect (the flux divergence of heat) is accomplished by integrating the mass-weighted temperature anomalies over time. This is presumably what Jim did in the comment he provided.

    [Response: You've lost me. How did heat content increase below 2000m without it passing through the top 700m? (I think we can safely assume that we don't have a coincident increase in undersea geothermal heat flux!). - gavin]

  26. 126
    Hank Roberts says:

    Earlier I suggested “climate system change” for gathering together all the various changes aside from surface temperature.

    Lo, there’s another possible term in that title of Dr. Pielke’s:
    “Heat storage within the Earth system”
    So “Earth system change” would cover the larger volume

    Climate is what people experience; “climate change” is the change in what people experience — and measuring surface temperature is used for that.

    The earth system — the material world — includes the various ocean layers at varying time scales, the borehole temps.

    Someone may have preempted using that term for some other collection of data sets, I realize.

    But I have some hope words can be agreed on, if only by the longterm consensus determined by reading the journals in hindsight.

    The “what were these people talking about, and what were they really measuring” question always has to be asked, reading science papers.

    When I was a teenager, I took Geology 101 from the old textbook before the new ones came out that adopted continental drift, and did some field work with geologists. Back then “synclines” and “anticlines” were explained as caused by accumulation and erosion of material — add or remove enough and the Earth folded. It wasn’t going anywhere, just, you know, folding.

    The measurements, the outcrops, the dip and strike, the type of rock — those are all good data. The explanations … changed.

    This is why scientists define their terms or refer to specific citable definitions. Good habit to get into.

  27. 127
    Bob Loblaw says:

    Re Roger Pielke @ 122 and 125

    Once again, your argument only applies to the simplified case where you have integrated over the entire ocean (in 3-D), because there is only one surface left with a non-zero flux (the ocean-atmosphere interface). Once again, we agree that if it is this specific case that you are referring to, then you are correct. The paper that you refer to, at quick read, only seems to refer to this overall ocean heat storage question – but you may wish to point me to a particular section of that paper if it has particular relevance.

    Perhaps a specific question will help. When you state “the downward movement of heat would be seen in positive temperature anomalies as they move towards lower depth”, are you restricting this statement to the mean global temperature of a particular layer “e.g., 0-700m), or do you intend this to be interpreted in a broader sense – i.e., applicable to local temperatures? Please indicate the spatial and temporal range over which you intend “downward movement of heat” and “temperature anomaly” to apply.

    …but in the mean time, what would be your interpretation of the following thought experiment (numbers made up):

    Global mean surface flux into ocean (downward), 3W/m^2. Global mean flux across 700m depth (downward, lower boundary of 0-700m layer), 2W/m^2. Net rate of 0-700m heat content change, 1W/m^2. Regime changes so that flux at 700m reduces to 1W/m^2. The 0-700m layer will now warm at twice the rate (2W/m^2). Another regime change, and 700 flux increases to 4W/m^2. 0-700m layer now starts cooling, based on net heat content rate of -1W/m^2.

    All fluxes are always downward, yet we see two different heating rates in the 0-700m layer, and one cooling scenario. How does this mesh with your expectation of “temperature anomalies”?

  28. 128
    Bob Loblaw says:

    re sidd @ 123

    Mr. Bob Loblaw wrote on the 9th of Oct 2011 at 11:21 AM:

    C*dT/dt = -(dF/dz)

    should not the convective derivative come in here ?

    I intentionally left the flux definition a bit vague, to avoid that can of worms. In the case of pure conduction (e.g., an opaque solid), you’d be able to express the flux as K*dT/dz, where K is the thermal conductivity, and then the flux divergence is the second derivative of the temperature gradient (assuming constant thermal conductivity).

    In the case of turbulent transfer with zero mean velocity, you can usually get away with a similar expression using temperature gradient, with a turbulent flux transfer coefficient.

    In the case of non-zero mean velocity, you need to account for the flux associated with the mean velocity, too.

    Does that satisfy?

  29. 129
    Bill DiPuccio says:

    Responding to Gavin in 124: “Our understanding of the system comes from a balance of evidence argument, not because any one metric is the best.”

    If 80%-90% of the energy in the climate system is stored in the oceans, then it only makes sense to rank this first since it represents the largest sample. That’s not to say, as you point out, that this metric is without problems. Nor does it mean the other metrics should be ignored.

    But if, for example, the average near surface air temperature declines over several years, but ocean heat increases, then we can conclude that the system’s energy is still increasing even though it has not yet been manifested as sensible heat. If, on the other hand, all metrics are given equal weight, you might draw an entirely different conclusion.

  30. 130
    prokaryotes says:

    Deep ocean heat is rapidly melting Antarctic ice

    Antarctica is disintegrating much faster than almost anybody imagined — see “Nothing in the natural world is lost at an accelerating exponential rate like this glacier.” In 2001, the IPCC “consensus” said neither Greenland nor Antarctica would lose significant mass by 2100. They both already are. As Penn State climatologist Richard Alley said in March 2006, the ice sheets appear to be shrinking “100 years ahead of schedule.”
    http://thinkprogress.org/romm/2010/12/15/207091/deep-ocean-heat-is-rapidly-melting-antarctic-ice-global-warmin/

  31. 131
    prokaryotes says:

    Further…

    Quote

    “In the area I work there is the highest increase in temperatures of anywhere on Earth,” said physical oceanographer Doug Martinson of the Lamont-Doherty Earth Observatory. Martinson has been collecting ocean water heat content data for more than 18 years at Palmer Island, on the western side of the Antarctic Peninsula.
    “Eighty-seven percent of the alpine glaciers are in retreat,” said Martinson of the Western Antarctic Peninsula. “Some of the Adele penguin colonies have already gone extinct.”
    Martinson and his colleagues looked not only at their very detailed and mapped water heat data from the last two decades, but compared them with sketchier data from the past and deep ocean heat content measurements worldwide. All show the same rising trend that is being seen in Antarctica.
    “When I saw that my jaw just dropped,” said Martinson. The most dramatic rise has happened since 1960, he said.

  32. 132

    Gavin – You wrote

    “You’ve lost me. How did heat content increase below 2000m without it passing through the top 700m? (I think we can safely assume that we don’t have a coincident increase in undersea geothermal heat flux!). – gavin]”

    This is precisely my point. We should have seen this heat be transfered through the upper 700 meters. From my understanding, the temporal and spatial resolution in the upper 700m is good enough to see this (but we certainly need colleagues at JPL and elsewhere to tell us if it does not have this accuracy).

    Below 700 meters, however, the reported warming is based on sparser data so the uncertainty in the plot you have shown for those depths is higher. What is the estimated uncertainty? Before accepting it as sufficiently accurate, we also need to look at the heat transfers through the upper 700 meters.

    [Response: I think this is becoming a little repetitive. You have not given anyone a reason to think we can measure absolute downward heat flux at 700m (or elsewhere), nor have you given a reference for anyone performing such a calculation. In my opinion, such an estimate would be extremely difficult and the uncertainties would be so large as to make the attempt much less of a constraint than is required. But regardless of that problem, your request simply doesn't make any sense for a problem dominated by (effective) diffusion. Take an anomalous temperature profile that is linear in z: T'(z) = T0 * (1 - z/700) above 700m and zero below. The downward diffusive flux is constant (K*T0/700) (assuming constant K) and equal to the flux in at the surface. How would you be able to 'see' the heat being transferred? There is no shortcut here!

    As for the error bars on the 0-2000m numbers, these are provided in the data file from NODC, and I've added them to the plot I gave before. - gavin]

  33. 133
    Pete Dunkelberg says:

    @ 127: Actually, ocean heat is sensible heat except when it goes into melting ice.

    @ others: “global warming” historically refers to warming the surface environment doesn’t it? Warming the surface including the sea surface could happen rapidly without the deep or middle ocean having time to warm. This might happen if greenhouse gasses increased very suddenly.

  34. 134
    sidd says:

    Gavin, thanks for the comment on the advective derivative, and the link to the data. For those interested I have plotted the data for the Pacific,Atlantic and Indian Ocean heat content together with the world ocean at
    http://membrane.com/sidd/OHC.png

    I do notice that the dip in world OHC in the 70s does not appear to be reflected in the individual basin breakouts, nor the dip in 1982.

    sidd

  35. 135
    dhogaza says:

    Bill Dipuccio:

    If 80%-90% of the energy in the climate system is stored in the oceans, then it only makes sense to rank this first since it represents the largest sample.

    RPSr. knows that the available data is sparse, so insisting on this metric furthers his delaying tactics and FUD.

    I would personally suggest that the best metric is the one that has the best data, which would be surface temps, by a very, very large margin.

    Of course, one can also say that better data regarding ocean temps would be a very good thing, and maybe, eventually surpass (or be combined with) the surface temps to build a better model of how the globe’s warming.

    But that’s not what RPSr. has suggested. He’s hitched his wagon to the relatively poor ocean data while insisting we should ignore the surface data to build a picture of unwarranted uncertainty.

  36. 136
    dhogaza says:

    Gavin:

    (I think we can safely assume that we don’t have a coincident increase in undersea geothermal heat flux!)

    In the cause of touting uncertainty, one can certainly assume that RPSr’s not going to cave on that possibility, or other possibilities.

    That’s the point, after all … pin the game on uncertainty. He plays the same game Curry does …

  37. 137
    CM says:

    Bob Loblaw #120, re: curly d’s,

    The ∂ symbol should be available with Alt+2202 on Windows, Alt-d on a Mac U.S. keyboard, or (I may screw this up) (ampersand-part-semicolon) right in the html (testing: ∂). Mostly people here just put their math in plain, arbitrary ascii, but if you need display math, RealClimate uses the QuickLatex WordPress plugin, which see.

  38. 138
    CM says:

    Yup, I did screw up; preview wasn’t working. I meant: ∂

  39. 139
    Bob Irvine says:

    Rob Painting #108

    Here is the relavent table from Cazenove & Llovel 2009.

    (1993-2007) (2003-2007)
    1. Observed (3.3+-0.4mm/yr) (2.5+-0.4mm/yr)
    2. THERMAL EXPANSION (1.0+-0.3) (0.25+-0.8)
    3. Glaciers (1.1+-0.25) (1.4+-0.25)
    4. Total Ice Sheets (0.7+-0.2) (1.0+-0.2)
    5. Land Waters (N/A) (-0.2+-0.1)
    6. Sum (2+3+4+5) (2.85+-0.35) (2.45+-0.85)
    7. Observed minus Sum (0.45) (-0.05)

    You can see that Land waters have been allowed for. They were calculated using GRACE measurements of vertical intergrated water column (surface water, soil moisture ,underground water) with some imput from models and local weather.

    The main thrust of this blog article is that the current hiatus in air temperature, upper OHC,and falling sun blocking aerosols (Mishchenco, NASA, supported by global brightening data, 1991-2005) at a time when CO2 has risen can only be explained by the missing energy finding it’s way to the deep ocean.

    This does not fit with the thermal expansion data above which includes the deep ocean. Remember there are large lags in air temp. due to the thermal inertia of the oceans while the OHC has little or no lag due it’s larger heat capacity.

    You make the point that there has been decade long hiatus in OHC in the recent past before continued increase.

    There has only been 2 in the last 60 years and both had no lag and are explained. The 1950′s to 1970′s is explained by industrial aerosols or cosmic rays depending on which side of the fence you sit. The 1980′s hiatus is explained by the El Chichon volcanic eruption. There is no evidence of energy suddenly diverting to the deep oceans during these periods.

    I say again that you need to explain the large drop in thermal expansion of the oceans (OHC) from 1993-2003 to 2003-2007.

    Some points; The sea level rise budget (2003-2007) above is virtually closed adding to confidence in these figures. The total sea level rise matches the sum of it’s parts (Glaciers + Ice Sheets + Thermal expansion + Land Waters).

    There has been 5 El Ninos and 4 La Ninas in the last 13 years of flat air temperatures.

    I agree with you that energy has transfered to the deep ocean during the current hiatus, just not enough as the thermal expansion figures show. I also agree that the oceans may have warmed slightly to 1500m (Von Schuckmann et al).

  40. 140

    Gavin – Your plot did not appear.

    [Response: Fixed. thanks. - gavin]

    On your question regarding heat transfer downward, if the models show warming at depth, why don’t you show plots as to the magnitude of its fluxes over time and space through the upper 700m of the ocean. Then one could look at the observations to see if this flux is there with the same pattern and magnitude as the real world data.

    I assume our disagreement is in the form of these fluxes. If they are diffuse and distributed across the upper oceans, I agree they would be hard to see in the Argo data. However, if this transfer occurs in globs associated with mesoscale and larger ocean circulation features (as suggested in the ECMWF data), we should clearly see this movement of heat.

    [Response: Model estimates of total heat flux through 700m are possible of course, but non-trivial to compute (including effects of the resolved circulation, isopycnal diffusion, and vertical mixing) - though this might well be worth doing for the CMIP5 models. However, I don't have the answers handy. But I have no confidence that the observations will be sufficient to distinguish the anomalous heat flux from the climatological mean with sufficient precision to be helpful. If you think it is, please point to a study that has attempted this. - gavin]

  41. 141
    prokaryotes says:

    Cyclones May Help Fuel Ocean Heat Transfer, Scientists Say

    Tropical cyclones may play a key role in the transfer of ocean heat that should be considered when predicting future climate change, scientists said.

    Storms such as Atlantic hurricanes and Pacific typhoons mix the ocean, forcing warm water down and toward the poles, and cooling the surface by as much as 8 degrees Celsius (14 degrees Fahrenheit), scientists at Purdue University in West Lafayette, Indiana, said today in the journal Nature. About 15 percent of ocean heat transfer may be due to tropical cyclones, they wrote.

    The mechanism identified in the paper may result in a so- called feedback loop, in which increases in temperature ultimately lead to further rises due to a chain reaction, according to Matthew Huber, a co-author of the paper. Understanding that process may help scientists better predict future effects of climate change, he said.

    “If this mixing were included, we hypothesize that models would do a better job of getting tropical ocean temperature correct, and better predict future climate change feedbacks,” Huber said in e-mailed replies to questions. “This may mean accurately predicting severe weather events, like hurricanes, is a necessary prerequisite to understanding future global warming.”

    The trigger for the chain is the warming brought on by increases in greenhouse gases such as carbon dioxide that trap the sun’s energy in the atmosphere. This warming increases cyclone activity, leading to more ocean mixing, Huber said.

    Heat Pump

    “This mixing is also a downward heat pump and might tend to enhance the overturning circulation, transporting slightly more heat to the poles,” Huber said. “This in turn might act to enhance polar amplification of climate change, increasing the global mean warming.”

    At the poles, the increase in warm waters serves to melt sea-ice, which reflects sunlight more than the seawater exposed beneath. This acts to amplify the warming effect, as more of the sun’s energy is absorbed.

    A rise in the average tropical sea-surface temperature of just 0.25 of a degree Celsius could lead to a worldwide increase of 60 percent in the total power let out by cyclones, according to the Purdue research. That temperature gain could also triple the amount of cyclone-induced ocean heat transport, they said.

    The scientists said their findings need to be better reflected in climate models, which currently assume a fixed level of background mixing of tropical waters, without taking into account the more dynamic cyclone-induced process. Inclusion in such models will help make future predictions, Huber said. http://www.bloomberg.com/apps/news?pid=newsarchive&sid=aN0lm0YGSkfs

    [Response: Yes, this is very interesting work, a few years old. There has been some followup work to this in recent years, including some that I have been involved in. This remains a fascinating, but still very uncertain, mechanism. - mike]

  42. 142
    Ray Ladbury says:

    Bill DiPuccio,
    Your recommendation ignores the fact that:
    1)the deep ocean interacts with the surface (where we live) only on very long timescales and fairly weakly
    2)the deep oceans don’t change all that rapidly

    People don’t seem to realize how hard it is to do science in the deep oceans. We know the surface of Mars–and even Venus–better than we know Earth’s surface.

    What we learn from Earth’s paleoclimate is that it is certainly possible to have extended excursions to high temperature (e.g. PETM), so it is unlikely that the deep oceans will save our tuckuses–especially given that we are raising the temperature about 10 times more rapidly than even the PETM rise. I don’t see much to give comfort here.

  43. 143
    Ken Lambert says:

    I hope you don’t mind my quoting Mr Peter who made this rather detailed contribution on SKS in August this year. Would Gavin and Dr Piekle care to comment on the heat transport mechanisn Mr Peter describes?:

    Quote:
    While we are into this OHC thing, some words about how on earth can heat get down to the abyss at all are in order.

    The first thing to note is that the MOC (Meridional Overturning Circulation) is not a heat engine. That is, it does not convert temperature differences into mechanical energy to keep ocean currents moving, but it is the other way around. It depends on some external mechanical energy source to maintain circulation and redistribute heat.

    If a body of fluid in a gravitational field (like the oceans) is both heated and cooled at different places but at the same gravitational potential (e.g. at the surface on low and high latitudes respectively), that would not produce any macroscopic flow whatsoever.

    There are two caveats to this proposition.

    1. Visible light (sunlight) and especially UV can penetrate into the ocean to some depth (a couple of hundred meters at most), so heating in fact happens at a somewhat lower geopotential than cooling, which is restricted to the surface (down to several meters, if waves are taken into account). But it would provide for a very shallow circulation only, not the kind of deep overturning observed. Also, it is worth noting that thermal infrared (“back radiation”) can not penetrate into seawater at all (several mm at most).
    2. There is also heating at depth, by geothermal heat flux, which is about 0.1 W/m2 averaged over the entire seafloor (and 0.04 W/m2 over the continents). In some regions (for example at the boundaries of the Nazca plate, South Eastern Pacific) it can be as high as 0.3 W/m2. This heating happens at the right geopotential (at the bottom), so it does produce overturning, albeit at a much slower rate than observed.

    Needless to say heat conductivity of seawater is so low, that by conduction alone (with no macroscopic flow) it would take ages for heat to get down to the abyss from the surface.

    There are parts of MOC that work as a heat engine indeed. Downwelling of cold saline water in polar regions is such an exception. However, if there were no other processes at work in other regions, the abyss would eventually get saturated with very cold water of high salinity and downwelling would stop altogether. Or rather, it would switch to the much slower rate permitted by geothermal heating alone.

    We should also note this part of the so called thermohaline circulation does not add heat to the abyss, but removes it from there.

    Currently deep water production is restricted to two distinct regions of the oceans. One is where the North Atlantic joins the Arctic ocean, the other is along the Antarctic coastline. In theory it could also happen in the North Pacific, but in fact it does not, for the salinity is too low there and the coastline is not cold enough.

    Details of the physics are somewhat different in the North and the South though. The North Atlantic Drift carries ample quantities of warm, highly saline water into the Arctic ocean (the high salinity is leftover of evaporation), which cools down there and when it gets next to freezing (the most dense state of seawater), it sinks. It is an intermittent process, restricted to “chimneys” (of diameter ~100 km and lifetime of several weeks) in the open ocean. Please note the heat carried to the polar region this way is lost to the atmosphere entirely, the cold saline water sinks to the bottom without it. This heat subsequently is radiated out to space, as that is the only heat reservoir around which is colder (-270°C).

    Antarctica is a special place. No warm current gets near to the continent, so salinity of seawater there is inherently lower than in the Northern Atlantic. On the other hand along the coastline, especially in winter, extremely cold gale force katabatic winds descend from the plateau creating polynyas (open water expanses) by blowing sea ice away.

    High chilly winds coupled with open water provide for vigorous cooling of water masses (because total area of air-sea interface is huge, think of sea spray) and as sea ice starts to form, salinity also increases by brine exclusion. Cold dense water then descends to the abyss along the continental slope. At the underside of great Antarctic ice shelves even super-cooled water is formed. Its potential temperature is below freezing, that is, it only stays fluid because of pressure, it would freeze if raised to the surface.

    In general abyssal water of Antarctic origin is somewhat colder but less salty than its Arctic cousin.

    But still, we need an energy source to keep the engine going. In other words, abyssal waters have to be warmed up and diluted in order to be able to raise somewhere and make room for more cold, dense polar water.

    The process that does exactly that is supposed to be deep turbulent mixing, driven by external mechanical energy sources like tides and winds.

    Tidal forcing is a considerable source of mixing, but it is deterministic and independent of all other forcings on climate. It is also cyclic, not exactly, but close enough. The Metonic cycle (the period the National Tidal Datum Epoch [NTDE] of the U.S. is based on) is 19 years long. Or more precisely it is 235 synodic months which is 1h 38′ longer than 19 tropical years. The nodal cycle of lunar orbit happens to be only slightly shorter than that (18.5996 years).

    It means if one is looking for trends in deep turbulent mixing, it is best to consider multiples of the Metonic cycle. Epochs shorter than that (like 6 years) are to be considered as a last resort only if one does not have data with longer timespan. Even then some caution is in order, to filter out tidal effects on trends as much as possible (the same is true for sea level studies).

    The other source is internal waves excited by winds. One can see that distribution of wind power is extremely uneven on the surface of Earth.

    It is concentrated in three regions, the Southern ocean, the Norh Pacific and the Norh Atlantic. Of these winds in the south are the most intense by far (and surprisingly mild over the continents).

    The only problem remaining is that in the open ocean turbulent mixing is measured to be at least an order of magnitude smaller than needed to maintain the observed flows in MOC.

    The solution seems to be there are narrow regions where topography of the bottom is very complex, like over mid ocean ridges or certain rugged continental slopes where deep turbulent mixing can be up to two, sometimes even three orders of magnitude higher than average. However, these sites are poorly known and most are not even identified yet.

    So, the very energy source driving MOC and making thermohaline downwelling possible is not well constrained. It is also one of the (many) weak points of GCMs (General Circulation Models). This process is represented in them only through parametrization and even if we knew much better the process going on in real oceans, their too coarse resolution could not accommodate to the small scale vigorous and probably intermittent mixing which characterizes it.

    Anyway, the take home message is that MOC (Meridional Overturning Circulation), consequently heat exchange between the surface and abyss is not driven by temperature differences, but external mechanical energy sources.

    Of course winds (unlike tides) are not independent of climate (they are driven by a heat engine, as the atmosphere is mostly heated from below and cooled from above), but in this respect one has to study winds over the southern ocean first (roaring forties & stormy fifties), as according to some estimates up to 80% of deep turbulent mixing happens here (or rather, in restricted sub-regions of it).

    Therefore if one is interested in heat transport to the lower layers of oceans, one should pay close attention to those remote and alien waters.
    End Quote

  44. 144
    ldavidcooke says:

    Hey All,

    Probably OT, when reviewing the NODC OHC in the China Sea 2010 for the JFM period there appeared to be a significant anomaly there to over 500m. Looking at the SRRS NH Analysis for this period the dominate atmospheric condition overhead was a Cut-Off Low series (extending from 850mb-250mb) that orbited the area. If this is validated with significant cloud cover in the area what explaniation would there be for the warm column that also did not affect downstream column warmth?

    It would seem that though there is a slight increase globally, most of the input must have a very short residence at high input levels with diffusion accounting for the small amount of the remaining trend increase. In essence, it would appear there is little in the way of flux inputs below 60 deg. N/S. Is this character to change when the is no longer sea ice at the poles?

    It would seem that equipping future ARGO units with a salinity or ion detection monitor would help in the tracking of flux or residual heat falling through the sea layer depths. This would help separate the likely source of the warming phenomena reveiling if it is resident radiant emission, mixing or low latitude wind driven turn over (keeping in mind that as the SSTs increase the Walker circulation was supposed to decrease). My pardon for interrupting…

    Cheers!
    Dave Cooke

  45. 145
    Paul S says:

    Bob Irvine,

    If you look at the 700m OHC time series posted by Gavin upthread you’ll see a large surge over 2002-2003. I would suggest the main reason for the discrepancy between the 1993-2007 and 2003-2007 thermal expansion figures is that the latter only sees the end of this surge. From a long-term perspective the 1993-2007 figure is larger than expected and the 2003-2007 figure is smaller than expected.

    There has been 5 El Ninos and 4 La Ninas in the last 13 years of flat air temperatures.

    You’re talking about the trend over a time period so it doesn’t matter about the count – what matters is when they happen within the time series and the strength. If the 5 El Ninos were all at the beginning and the 4 La Ninas at the end you would get a strongly negative ENSO index.

    Assuming ‘the last 13 years’ refers to 1998-present I calculated the trend using NOAA’s MEI data and it is negative.

  46. 146
    Hank Roberts says:

    Citing: Ken Lambert’s quote “Mr Peter … on SKS in August” is from: http://www.skepticalscience.com/news.php?p=2&t=106&&n=798#59258
    More from him: http://www.google.com/search?q=Berényi+Péter

  47. 147

    Gavin – You wrote

    “If you think it is, please point to a study that has attempted this”

    I am not aware this has been looked at. I will check with.

  48. 148
    Pete Dunkelberg says:

    Deep ocean mixing:
    a) enough to keep the deep oxygenated overall
    b) not all at the same rate

    Clearly, there are spots of quick descent and quick rise to and from the deep ocean. To what extent is it the same water after a long journey? Can water descend at one pole and rise at the other?

    Particulars – let’s put 1 and 1 together

    Strong export of Antarctic BottomWater east of the Kerguelen plateau
    Y. Fukamachi1*, S. R. Rintoul2,3,4, J. A. Church2,3,4, S. Aoki1, S. Sokolov2,3,4, M. A. Rosenberg4 and M.Wakatsuchi1

    http://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/44116/1/NG3-5_327-331.pdf

    This outgoing current must be matched by an incoming current.
    http://news.discovery.com/earth/antarctica-melting-warming-penguins-101214.html

    Now that the upwelling deep sea water is the clear cause of the melting ice shelf, rather than summer melt water, as had been thought in the past, it’s a question of how winds will change in a warming world and whether they will drive more warm water into the ice shelves.

    “So we have thrown the problem back over the fence to the climate modelers,” said Bindschadler.

    http://blogs.ei.columbia.edu/2010/12/14/deep-ocean-heat-is-melting-antarctic-ice/

    This
    http://www.sciencedirect.com/science/article/pii/S0031018211001799
    may or may not be the corresponding paper still in press.
    Exactly how deep does the deep water that rises under the Pine Island Glacier come from? It must be warmer than it was a few decades ago. How recently did this water descend?

    Evidently some of the cold water that descends to the deep ocean is not as cold as it used to be, and is still not as cold as it used to be when it comes back up. Heat that goes deep is not all lost to the surface environment.

  49. 149
    Rob Grover says:

    LOVE the Gavin-PielkeSr interchange here. Any possibility of Gavin and Pielke partnering to have a regular and constant interaction?

  50. 150
    Pete Dunkelberg says:

    Re 148: see Martinson’s detailed comments here
    http://blogs.ei.columbia.edu/2010/12/14/deep-ocean-heat-is-melting-antarctic-ice/

    Antarctic Circumpolar Current = ACC


    The warm water carrying the heat is Upper Circumpolar Deep Water (UCDW); it is circulated around the Antarctic by the ACC, and because of the proximity of the ACC adjacent to the continental margin in the western Antarctic (and only in this region), this is the water accounting for the ocean heat in both my area along the peninsula and the WAIS melt region. These observations provide support for increased ocean heat observed in my region is the same as that driving accelerated WAIS glacial melt.

    If the deep oceans did warm, we know that there are southward currents that would advect some of this heat to the ACC, and from there to the western Antarctic.

    - Doug Martinson


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