AGW Observer

Observations of anthropogenic global warming

NODC ocean heat content

Posted by Ari Jokimäki on September 13, 2010

For some years there has been claims that oceans have cooled after 2003. There has been some flaws identified from the measuring equipment. It has been shown that those flaws caused the original appearance of cooling so the latest scientific research doesn’t seem to give support to the claims of cooling in recent years. The widely used Argo-network is under corrections currently and the situation should be more clear in near future. However, the claims of cooling still continue. I’ll take a brief look at the issue.

The cooling that went away

By now this is quite well known story, so I’ll descibe it just briefly. In 2006, Lyman et al. reported that they had found cooling from the world’s oceans after 2003. This of course generated claims among climate change deniers that global warming has stopped even though the authors of the study didn’t thought so. In 2007, Josh Willis, one of the authors of the original study found out that the cooling they had found didn’t seem to be real. There were problems with some Argo floats and expendable bathythermographs (XBT’s) which both were causing an apparent cooling effect to the data. When the bad Argo floats were excluded and XBT-problem was corrected for, the cooling was no more. [whole story here]

There is also a study from von Schuckmann et al. (2009) suggesting that oceans have actually warmed after 2003 (or 2004 as the current round of claims seem to be). More references on ocean temperatures and on this ocean heat content problem are given in the end of this article.

NODC – the go to place for recent claims

Despite the situation described above, the claims of ocean cooling continue. In some online discussions and blogs I have seen NOAA’s National Oceanographic Data Center (NODC) being used as the source showing that oceans have cooled after 2003 or 2004. As it’s NOAA website, it has authority and therefore seems to be credible reference for backing up the claims. I’m not going to argue that NODC is not credible resource but I’m going to show why it’s not currently the best place to study the issue.

The data in NODC is from their world ocean database, and it is described here. The chapter 6.6 there discusses data problems. Let’s see what it says about the problem Willis identified:

A large number of SOLO floats with FSI CTD packages deployed in the Atlantic Ocean between 2003 and 2006 were found to have a pressure offset problem due to a software error. This error caused pressures to be paired with the temperature measurements from the next lower level, creating the illusion of a cooling ocean. Once the problem was found, a list of such floats was compiled. An effort was made to correct the problem, successful in some floats, not in others. All data from all these problem floats are included in WOD09.

(Bolding mine.) So, this problem causes apparent cooling and the data from problem floats is included. Another problem is also described there:

More recently, in early 2009, a problem with the Druck pressure sensor has been found (J. Willis and D. Roemmich, minutes of 10th meeting of International Argo Steering Team). This problem causes pressure sensor drift after deployment. Deployment of new floats was halted temporarily, until the pressure sensor design could be altered. Already deployed APEX floats are being monitored closely for sensor drift. The full extent of this problem is not yet apparent.

It seems that there are even more problematic Argo floats included in the NODC data. For this one it is not clear to which direction the drift effects.

So clearly, for the last few years the NODC data might not be the most trustworthy. For Argo data, it is best to consult Argo website. There is a section called “>”Advice on Pressure Biases in the Argo Data Set” (UPDATE: direct linking to the page doesn’t seem to work but it can be found through “Argo Information Centre” – additionally, here’s an alternative link from “Argo data management” website giving the same text) that says:

A part of the global Argo data are subject to biases in reported pressures. These biases are usually less than 5db, but occasionally can be larger (> 20db). These bias errors are being steadily removed by the reprocessing of historical Argo data. We expect that by the end of 2010 these errors will be removed from the global Argo data set in both the delayed-mode and real-time data.

So, it seems that we’ll find out more about the ocean temperatures of last few years in next year when they have finished the corrections. NODC will undoubtedly update their data too then. Meanwhile I expect to see lot more claims about oceans cooling after this year or that year, and I doubt it will end even if they would publish corrected Argo dataset showing warming from 2003.

References

Lyman, J. M., J. K. Willis, and G. C. Johnson (2006), Recent cooling of the upper ocean, Geophys. Res. Lett., 33, L18604, doi:10.1029/2006GL027033. [abstract, full text]

von Schuckmann, K., F. Gaillard, and P.-Y. Le Traon (2009), Global hydrographic variability patterns during 2003–2008, J. Geophys. Res., 114, C09007, doi:10.1029/2008JC005237. [abstract, full text]

Additional information

- More information on ocean heat content problems after 2003 (see especially Willis et al., 2008 and Levitus et al., 2009) and ocean temperatures in general can be found from my list of papers on ocean temperature.
Does ocean cooling prove global warming has ended? – John Cook, Skeptical Science
Pielke Sr and scientific equivocation: don’t beat around the bush, Roger – gpwayne, Skeptical Science

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10 Responses to “NODC ocean heat content”

  1. Daniel "The Yooper" Bailey said

    This would make a good post subject on Skeptical Science. John has a quite large number of guest posters there (I even did one).

    Nice job!

    The Yooper

  2. Ari Jokimäki said

    Thanks! I’m already familiar with John’s author scheme. I’ll give it my thumbs up… ;)

    I’ll see what we’ll do with this one there.

  3. Riccardo said

    Ari, the link “Advice on Pressure Biases in the Argo Data Set” doesn’t work and I couldn’t find it in the ARGO website.

  4. Ari Jokimäki said

    They seem to be having some kind of problems there – it first didn’t load for me but then all of a sudden it worked for few seconds and then stopped working again. Here’s alternative link from “Argo Data Management” website.

    Edited to add: Normally it is found under the “Argo Information Centre” in the Argo main page.
    Edited to add 2: Original link seems to be working again now.

  5. Riccardo said

    In the post the link is:

    http://wo.jcommops.org/cgi-bin/WebObjects/Argo.woa/1/wo/FbG6tGihbiS3d9jf2h9LUM/0.0.40.5.3.0

    and it includes the session identification, which expires.

    the alternativee link you give in the above response is ok.

  6. Ari Jokimäki said

    Yes, they seem to have some strange website application there that doesn’t allow direct linking to pages but you have to go through the homepage. I have updated the text above and switched to using the alternative link. Thanks for the help, Riccardo. :)

  7. Sean said

    A lot of folks do follow quite closely the total ocean heat content ever since Dr. Pielke started pushing this metric as a more accurate and less noisy indication of changes in the earth’s heat content as oceans contain 80% of the surface heat. People that follow his site understand that there has been no significant ocean cooling in the last 7 years as measured by the Argo data. Trouble is, there has been no heating either as Jim Hansen had predicted. Josh Willis confirmed the ocean temperature stability as recently as May of this year on Dr. Pielke’s site. Now if there is a revised data set where “they would publish corrected Argo dataset showing warming from 2003″, you should expect the “correction” to be met with great skeptism.

  8. Riccardo said

    Sean,
    in my opinion Pielke is playing with the words. One thing is that the last years have shown no warming trend, another is say that this indicates the halting of global warming. For the latter to be true (accepting his metric) statistical analisys of the trend is required and the change in trend need to be statistically significant. Which is not.

  9. Ari Jokimäki said

    Sean:

    A lot of folks do follow quite closely the total ocean heat content ever since Dr. Pielke started pushing this metric as a more accurate and less noisy indication of changes in the earth’s heat content as oceans contain 80% of the surface heat.

    Well, it seems I might have to do another post on this issue. But I’ll make couple of comments here briefly. There’s an interesting paper (listed in my ocean temperature paperlist mentioned above) by AchutaRao et al. (2007). In their introduction they say that many portions of ocean are poorly sampled by temperature measurements which makes it necessary to infill the data by some methods when the ocean temperature is being determined by ocean heat content. Then they say:

    “Because there is no unique solution to the infilling problem, and in view of concerns that previously applied statistical infilling approaches may alter ocean temperature variability (7, 16), it is preferable to restrict comparisons of modeled and observed variability to the actually observed portions of the ocean and, hence, to volume-averaged ocean temperature rather than OHC.”

    However, there’s not very many studies using the volume-averaged method. I’m aware of couple of studies by the same research team that wrote the AchutaRao et al. paper (but I should check if they have published anything recently). Their most recent analysis of ocean temperature and anthropogenic warming is Pierce et al. (2006). If you’re interested in ocean temperature issues and the role of the mankind in it, you should read this paper. Also, those who wish to argue that mankind is not warming the oceans, this is the paper they should worry about, not the ocean temperature during last few years.

    Ok, back to AchutaRao et al. Note what they say in their abstract:

    “Our work does not support the recent claim that the 0- to 700-m layer of the global ocean experienced a substantial OHC decrease over the 2003 to 2005 time period. We show that the 2003–2005 cooling is largely an artifact of a systematic change in the observing system, with the deployment of Argo floats reducing a warm bias in the original observing system.”

    This paper was published in 2007 and already then they were discussing rather familiar issues on the post-2003 ocean temperatures. I haven’t seen much discussion of this paper relating to the issue, but I wonder if they nailed this issue before Willis? They give five lines of evidence why the apparent cooling is spurious:

    “First, the main contribution to the large global OHC decrease over 2003–2005 is from the Southern Ocean, where Argo coverage increased dramatically after 2003 (Fig. 5F). The massive influx of Argo data reduces preexisting warm biases from XBT measurements. Second, there were no unusually largeOHCdecreases in the Northern Hemisphere oceans over the same period (see SI Fig. 6). Third, global OHC decreases are substantially smaller in No Argo versions of two observational data sets and are consistent with the magnitude of changes typically seen in model simulations (Fig. 3). Fourth, none of the individual instrument types show evidence of global- or hemispheric-scale cooling over the period analyzed by Lyman et al. (12). Finally, analyses of satellite data that are completely independent of in situ observations do not confirm such a decrease (26).”

    People that follow his site understand that there has been no significant ocean cooling in the last 7 years as measured by the Argo data. Trouble is, there has been no heating either as Jim Hansen had predicted.

    Well, actually I would argue that based on Argo data, you can’t currently say what has happened in last few years to ocean temperature. That was the underlying point in my article above. Also, let’s take another quote from AchutaRao et al. (which turns out to be rather useful paper here):

    “Our study does not directly address the accuracy of the Argo measurements. Within the next decade, Argo will vastly improve our knowledge of the oceans and their variability. However, some caution must be exercised in estimating global-scale OHC trends from an observing system that has undergone large and rapid increases in coverage and whose measurement biases have not been adequately quantified.”

    Caution. Caution before declaring that global warming has ended.

    Additionally, I gave a pointer above to the von Schuckmann et al. (2009) which does show warming between 2003 and 2008. In my paperlist you also find recently published Purkey & Johnson (2010) which also is very interesting (I have a post coming up on that) even if it doesn’t address specifically this issue here.

    By the way, where has James Hansen predicted that we should have oceans warming in last few years? I don’t think it is expected that ocean keep showing warming every year. I expect to see some variability there as well. If Hansen has claimed otherwise, then I think I disagree with him on that unless he has convincing arguments about it.

    Josh Willis confirmed the ocean temperature stability as recently as May of this year on Dr. Pielke’s site.

    No link?

    Now if there is a revised data set where “they would publish corrected Argo dataset showing warming from 2003″, you should expect the “correction” to be met with great skeptism.

    Everything in science is already met with skepticism. However, I think it’s rather unfair to call the correction “correction” in any case. If you think there’s something sinister about this correction, then by all means, tell us what they are doing wrong with the correction.

  10. Ari Jokimäki said

    I realised that I have made a mistake here. The problem with SOLO floats is the one Willis found originally and the APEX float problem is more recent development. One problem mentioned Willis as source and other mentioned the year 2003. Both were about pressure problems – so I got them mixed up. I have corrected the article above. For documentation purposes I’ll include the original text here for the relevant parts:

    Let’s see what it says about the problem Willis identified:

    More recently, in early 2009, a problem with the Druck pressure sensor has been found (J. Willis and D. Roemmich, minutes of 10th meeting of International Argo Steering Team). This problem causes pressure sensor drift after deployment. Deployment of new floats was halted temporarily, until the pressure sensor design could be altered. Already deployed APEX floats are being monitored closely for sensor drift. The full extent of this problem is not yet apparent.

    It seems that there are problematic Argo floats included in the NODC data. Another problem is also described there:

    A large number of SOLO floats with FSI CTD packages deployed in the Atlantic Ocean between 2003 and 2006 were found to have a pressure offset problem due to a software error. This error caused pressures to be paired with the temperature measurements from the next lower level, creating the illusion of a cooling ocean. Once the problem was found, a list of such floats was compiled. An effort was made to correct the problem, successful in some floats, not in others. All data from all these problem floats are included in WOD09.

    (Bolding mine.) So, also this problem causes apparent cooling and the data from problem floats is included. So clearly, for the last few years the NODC data might not be the most trustworthy.

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