Full-depth OHC

Since my holiday is now over, I thought I might briefly comment on a recent paper by Cheng et al., called Observed and simulated full-depth ocean heat-content
changes for 1970–2005
. John Abraham, one of the authors, has already discussed it in his Guardian article, so I won’t say too much. The basic result is that

The full-depth OHC has increased by 0.74 [0.68, 0.80] x 1022 J yr-1 (0.46Wm-2) and 1.22 [1.16–1.29] x 1022 J yr-1 (0.75Wm-2) for 1970–2005 and 1992–2005, respectively….

Credit: Cheng et al. (2016)

Credit: Cheng et al. (2016)

What’s more interesting, though, is that they compare this with the results from climate models. Although there is a spread in model results, they do find that

the ensemble median has excellent agreement with our observational estimate: 0.68 [0.54–0.82] x 1022 J yr-1 (0.42Wm-2) from 1970 to 2005 and 1.25 [1.10–1.41] x 1022 J yr-1 (0.77Wm-2) from 1992 to 2005.

and, consequently, suggest that

OHC be a fundamental metric for climate model validation and evaluation, especially for forced changes (decadal timescales).

which seems related to something Roger Pielke Sr and I wrote about a while ago.

I think this paper is very interesting, especially as Anthropogenic Global Warming (AGW) is fundamentally about energy; our emission of greenhouse gases (GHGs) drives the system further and further out of energy balance, with most (~93%) of the excess energy going into the oceans. Therefore, as the paper suggests, using Ocean Heat Content (OHC) to assess climate models makes a great deal of sense.

Also, since the energy imbalance is largely driven by the change in forcing and the resulting feedbacks, if the models are doing a reasonable job of representing the change in total energy, then it provides some confidence that estimates for equilibrium climate sensitivity (ECS) are reasonable. The transient climate response (TCR) is maybe less clear, but if the models do a reasonable job of representing the distribution of energy within the system, then it should also provide confidence in TCR estimates. As the table below shows, the models quite closely match the full-depth OHC change, as well as the 0-700m OHC changes.

Credit : Cheng et al. (2016)

Credit : Cheng et al. (2016)

To be clear, though, some models suggest a larger OHC change than has been observed, and some suggest less. As the paper itself says, [t]he CMIP5 models show a large spread in OHC changes, suggesting that some models are not state-of-the-art and require further improvements. However, that the ensemble median is in quite good agreement with the observations provides some confidence that some models are doing pretty well, and that you can at least use the ensemble to assess AGW. Also, this whole process of comparing observations and models is a crucial part of doing research. If we had multiple Earths and a time machine, it could be pretty easy to develop the ideal model. Since we don’t, it’s not easy and takes time, as we both collect more data and develop new methods for analysing the data.

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39 Responses to Full-depth OHC

  1. Pingback: Full-depth OHC | Hypergeometric

  2. Welcome back, Anders. I have been wanting a model/obs comparison for OHC for some time now since that’s where most of the heat is being retained. This is golden.

  3. JCH says:

    Appears to show a slight dip during 1999 – 2001 La Niña event, and a brief leveling during the 2008 La Niña…

  4. Russell says:

    Since 93% of the solar heat gain is going and will continue to go into the hydrosphere, rather more thought should be given to the evolution of water albedo with human action and climate change.

    Modeling indicates that just as emissions of CO2 and NOx impact the radiative equilibrium of the atmosphere above global shipping lanes – a positive GHG forcing , marine albedo changes from both ship wakes and phytoplankton blooms locally and regionally reduce solar heat gain.

  5. I would guess that ship wakes would count as a forcing, while phytoplankton blooms would be a feedback.

  6. izen says:

    Phytoplankton blooms are probably a positive feedback. They increase surface warming by reducing transparency..

  7. BBD says:

    HAMLET
    Do you see yonder cloud that’s almost in shape of a marine algal bloom?

    POLONIUS
    By th’ mass, and ’tis like an albedo change indeed.

    HAMLET
    Methinks it is like a weasel.

    POLONIUS
    It is backed like a weasel.

    HAMLET
    Or like a squirrel.

    POLONIUS
    Very like a squirrel.

  8. Russell says:

    Nay, Polonius- not by the mass , but by the Mie cross section, for In Wittenburg I was taught the number density rules how deep incarnadine we see such creatures dye the sea.

  9. Ethan Allen says:

    Russell sez …

    “Modeling indicates that just as emissions of CO2 and NOx impact the radiative equilibrium of the atmosphere above global shipping lanes – a positive GHG forcing , marine albedo changes from both ship wakes and phytoplankton blooms locally and regionally reduce solar heat gain.”

    So I guess they all (meaning deep draft shipping vessels) shouldn’t do this?

    The Surprising Way Ships’ Wakes Could Help Ease Global Warming
    http://www.huffingtonpost.com/entry/ships-ease-global-warming_us_56b0e2cce4b0655877f73d91

    Can increasing albedo of existing ship wakes reduce climate change?
    http://onlinelibrary.wiley.com/doi/10.1002/2015JD024201/pdf

    Its not like i haven’t been on ~40 deep draft vessels, oh wait, I have.

    Prop wash/ship wake can only raise the local albedo along the ship path.

    So, it is simply not possible for ship wakes creating a net positive GHG forcing. Simple as that.

    But if you have peer reviewed links containing direct albedo measurements from ship wakes
    (before during after passage), please cite here. Because your “ship wakes make the deep blue sea the deep black sea” appears to be an eleventeen on my BS meter. TIA

  10. Raff says:

    A while back there was much discussion of why actual data did not match the CMIP5 average, because there was no reason to expect it to and because there is only one world and other reasons that I thought i understood at the time. Now the data does match the mean and I am confused…. Should I be?

  11. Raff,
    The difference is, I think, that the surface temperature show much more variability than the ocean heat content. Hence, the surface temperatures, on decadal timescales, are probably not necessarily a good indicator of the forced response, while the OHC might be better. Of course, if you have had some kind of pattern of surface warming that has influenced the planetary imbalance, then even the OHC might not be expected to match the ensemble mean/median.

  12. The Very Reverend Jebediah Hypotenuse says:


    Prop wash/ship wake can only raise the local albedo along the ship path.
    So, it is simply not possible for ship wakes creating a net positive GHG forcing. Simple as that.

    Once upon a time, people made similar “it’s impossible” remarks concerning jet contrails.
    https://www.sciencedaily.com/releases/2002/08/020808075457.htm

    There are quite a few ships at sea:
    https://www.shipmap.org/

  13. The Very Reverend Jebediah Hypotenuse says:

    ATTP:

    The difference is, I think, that the surface temperature show much more variability than the ocean heat content. Hence, the surface temperatures, on decadal timescales, are probably not necessarily a good indicator of the forced response, while the OHC might be better.

    There is a third way.
    Borehole temperature profiles can capture a great deal of information about climate…

    https://www.ncdc.noaa.gov/data-access/paleoclimatology-data/datasets/borehole
    https://sites.google.com/site/borehole4climate/borehole/publications

  14. Ethan Allen says:

    Rev,
    I win …


    https://www.google.com/search?q=ship+wake&espv=2&tbm=isch&source=lnt&tbs=isz:l&sa=X&ved=0ahUKEwiHtp6J-ZjOAhXK5iYKHdk0AqQQpwUIFg&dpr=1&biw=1920&bih=1113

    I’m sort of waiting for peer reviewed skip wake albedo references supporting a darkening/absorption/lower albedo of the ocean surface. I found one above that actually supports my POV. Simple as that. That is all.

  15. Ethan Allen says:

    ATTP, I have a somewhat snarky post with perhaps too many image somewhere in attp limbo.

    Another reference that supports my POV …
    Effects of ship wakes on ocean brightness and radiative forcing over ocean
    http://onlinelibrary.wiley.com/doi/10.1029/2011GL048819/full

    “Changes in surface albedo represent one of the main forcing agents that can counteract, to some extent, the positive forcing from increasing greenhouse gas concentrations. Here, we report on enhanced ocean reflectance from ship wakes over the Pacific Ocean near the California coast, where we determined, based on airborne radiation measurements that ship wakes can increase reflected sunlight by more than 100%.”

    This one really is a no brainer. 😦

  16. Willard says:

    We should distinguish “P is impossible to estimate” from “Q is physically impossible.”

  17. BBD says:

    IIRC the climatological effects from contrails and ship tracks (clouds, not wakes) are thought to be relatively small, rather like their relevance to OHC.

  18. The Very Reverend Jebediah Hypotenuse says:

    Rev,
    I win …

    Sure.
    I see now that you are arguing that the forcing would be negative, not that it is impossible.
    My bad.

  19. Ethan Allen says:

    Yes, small number.

    Also I misread Russell’s post, I parsed it all wrong, he’s saying the same thing as I am.

    “Marine albedo changes from both ship wakes and phytoplankton blooms locally and regionally reduce solar heat gain.

    My bad.

  20. The Very Reverend Jebediah Hypotenuse says:

    BBD:

    Dated, and regional, but perhaps relevant enough:
    https://www.sciencedaily.com/releases/2004/04/040428061056.htm?trendmd-shared=0

  21. BBD says:

    Very Rev

    More up to date and supports the NASA study. Glad I don’t fly anymore.

    http://www.nature.com/nclimate/journal/v1/n1/full/nclimate1078.html

    This whole thing is still a squirrel started by Russell to divert away from the implications of the OHC data. Russell likes to think that there is massive uncertainty about climate sensitivity being about 3C (ECS), so he won’t like this result at all.

  22. Willard says:

    More on Al Bedo:

    I blame Al’s brother, Lee.

  23. BBD says:

    Very droll, Willard.

  24. izen says:

    I wonder which has the larger effect, the increased albedo from the ship wake, or the increase in turbulent mixing of surface water and deeper waters in temperature stratified oceans?

    More accurate data on OHC is useful, but perhaps not for judging the accuracy of models. That there is a spread of model results may indicate that those that best match the data are just lucky, not necessarily a better instantiation of the climate.

  25. That there is a spread of model results may indicate that those that best match the data are just lucky, not necessarily a better instantiation of the climate.

    I agree; this is an issue. However, I think we expect the OHC to show less variability than the surface temperatures and so it may be a better way to assess models than surface temperatures. Of course, we really want to assess more than one thing, so I certainly don’t think that OHC alone is enough.

    Having said the above, if the OHC matches some models, then that would either seem to suggest that they’re getting the forcings and feedbacks roughly correct, or that somehow their errors are – by chance – cancelling.

  26. Vinny Burgoo says:

    What a terrific article, Willard. Paraphrase: ‘Such blooms are the new normal because of climate change and political inaction. Well, mostly political inaction – and, to be honest, that’s political inaction about agricultural runoff, sewage and suburbanization, not climate change. But have no doubt: climate change will one day make these existing problems worse, so our implying that political inaction on climate change was to blame and our use of the climactivist buzzphrase ‘new normal’ were wholly justified.’

    (Cross-thread alert: Searching Google Image for ‘spurious framing’ turns up very little except some nice pix of a Martin PBM Mariner seaplane, which, like the Catalina, was used for scooping up water from lakes and coastal waters to dump on wild fires. I saw a Catalina doing that once. Godnose how the pilot managed it. A very hairy manouevre.)

  27. izen says:

    Rather larger than the wakes from ships are ‘ship tracks’ the generation of low level cloud ‘contrails’ from the engine exhaust gasses and particles.
    http://earthobservatory.nasa.gov/IOTD/view.php?id=80203
    Although these are bright clouds with a high albedo these are low level clouds and occur at night as well as during the day. The determination of whether they are a net positive or negative forcing may be difficult. (grin)

  28. BBD says:

    Yes, that’s why I specifically referred to them as ship tracks (clouds not wakes) above.

    * * *

    Vinny, climate change is going to wreak merry havoc with ocean ecosystems as it has done many times before. Trying to drag in ‘climactivism’ and imaginary ‘spurious framing’ is just your denialism showing again.

  29. JCH says:

    Boy howdy… but but but but but but but but but but but…

  30. izen says:

    @-ATTP
    “Having said the above, if the OHC matches some models, then that would either seem to suggest that they’re getting the forcings and feedbacks roughly correct, or that somehow their errors are – by chance – cancelling.”

    I am not familiar with the details of the models used. But if one type of ocean heat diffusion modelling gave consistently close result to the observed data then that correlation might be suggestive of having got the physics right..
    However if most of the models have a much greater spread than the data uncertainty then it is just as likely that the errors are cancelling by chance in the ‘matching the data’ cases.

    @-“However, that the ensemble median is in quite good agreement with the observations provides some confidence that some models are doing pretty well, and that you can at least use the ensemble to assess AGW. ”

    This may suffer from granting climate models a ‘Wisdom of crowds’ skill.

  31. izen,

    But if one type of ocean heat diffusion modelling gave consistently close result to the observed data then that correlation might be suggestive of having got the physics right..

    Yes, this seems reasonable. If the ocean diffusion determines the rate at which energy is transported from the mixed layer (which equilibrates with the atmosphere quite quickly) then if one type of diffusion modelling gave consistently close results it would be suggestive, especially if the surface temperatures (which determines the Planck response) were also a good match.

    This may suffer from granting climate models a ‘Wisdom of crowds’ skill.

    Possibly. I was thinking that if the match is pretty good over a multi-decade timescale, then it might be indicative. However, if there isn’t also a match with the surface temperatures it might suggest that the models are still not getting the forcings and feedback quite right.

  32. > Paraphrase: […]

    Here’s another one, Vinny: “Let’s conflate eradication with creation to pretend that political inaction creates cyanobacteria, and the let’s peddle in the word climactivist.”

    Unless you dispute that warmer and wetter doesn’t imply gooier?

    Thank you for your concern.

  33. izen says:

    @-Willard
    “Unless you dispute that warmer and wetter doesn’t imply gooier?”

    Algae blooms are dependent on nutrients, a stable surface layer and hours of sunlight, rather more than temperature.

  34. Steven,
    Yes, that is quite good. They do have a full response to that if you down the zip file with the updated paper and the responses to the referees.

  35. Willard says:

    > Algae blooms are dependent on nutrients, a stable surface layer and hours of sunlight, rather more than temperature.

    And hours of sunlight have nothing to do with temperature:

    Climate Impacts That Might Affect Algal Blooms:

    Warming water temperature

    Harmful algae usually bloom during the warm summer season or when water temperatures are warmer than usual. Warmer water due to climate change might favor harmful algae in a number of ways:

    • Toxic blue-green algae prefer warmer water.
    • Warmer temperatures prevent water from mixing, allowing algae to grow thicker and faster.
    • Warmer water is easier for small organisms to move through and allows algae to float to the surface faster.
    • Algal blooms absorb sunlight, making water even warmer and promoting more blooms.

    https://www.epa.gov/nutrientpollution/climate-change-and-harmful-algal-blooms

    In other news, blankets don’t really warm.

  36. Steven Mosher says:

    Ya. Dr. Rice I love that aspect of open publishing.
    Funny how the better arguments about a set of findings are in the peer review comments. Not in all cases ,but in enough cases to make the reviewer s comments required reading.

  37. Ken. I am glad our past weblog post is bearing fruit. Your current post is excellent. Roger Sr

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