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.
– 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