Apologies to Josh Willis: Correcting Global Cooling (Part 3)
ON Tuesday, I suggested at this blog that I was not convinced by a story from Josh Willis, a scientist at NASA’s Jet Propulsion Laboratory, explaining why and how he corrected data showing global ocean cooling. The title of my blog post suggested that Dr Willis had changed the data to fit output from computer models. Dr Willis has responded, via Fred Singer, explaining that the correction was made, not on the basis of computer output, but on the basis of high quality temperature and pressure measurement from ocean buoys.
“The XBT data were not changed to fit the models. They were changed to agree [with] other higher quality temperature observations from CTD casts, a select group of Argo floats with high quality temperature and pressure measurements, and to be consistent [with] satellite-based observations of the changing height of the ocean surface. The improved agreement with climate models was as much of a surprise to us as anyone else.
In fact, the motivation to look for such problems in the XBT data did not come from comparisons with models, but rather from a comparison with CTD data by Gouretski and Koltermann in their 2007 GRL paper. Gouretski and Koltermann noted that the bias in the XBT data changed over time. After looking into the bias ourselves, we determined that the cause of the bias was a gradual drift in the fall rate of these instruments. By treating the bias as a problem with the fall rate and comparing the XBT data with CTD, Argo and satellite altimeter observations, we were able to estimate the bias and remove it.
Once this data error was corrected, estimates of ocean warming over the past 40 years were much smoother, and the large “bump” in the 1970s and 80s more or less disappeared from the record. This was something of a relief because the “bump” in the heat content record was not only absent from climate models, there was no evidence for it in any other records and no good explanation could be found for its cause. The reason for that is obvious now: because it wasn’t real.”
Thanks to Dr Willis for the clarification and my apologies for any confusion. I have changed the title of Tuesday’s blog post.