This is a repost of two articles from John Graham-Cumming’s blog. I watched with interest earlier this month where he and a colleague identified what they thought to be a math error related to error calculation when applied to grid cells. It appears now through a journalistic backchannel that the Met Office is taking the issue seriously.
What I found most interesting is that while the error he found may lead to slightly less uncertainty, the magnitude of the the uncertainty (especially in homogenization) is quite large in the context of the AGW signal being sought. John asks in his post: “If you see an error in our working please let us know!” I’m sure WUWT readers can weigh in. – Anthony
I’m told by a BBC journalist that the Met Office has said through their press office that the errors that were pointed out by Ilya Goz and I have been confirmed. The station errors are being incorrectly calculated (almost certainly because of a bug in the software) and that the Met Office is rechecking all the error data.
I haven’t heard directly from the Met Office yet; apparently the Met Office is waiting to write to me when they have rechecked their entire dataset.
The outcome is likely to be a small reduction in the error bars surrounding the temperature trend. The trend itself should stay the same, but the uncertainty about the trend will be slightly less.
Out of the blue I got a comment on my blog about CRUTEM3 station errors. The commenter wanted to know if I’d tried to verify them: I said I hadn’t since not all the underlying data for CRUTEM3 had been released. The commenter (who I now know to be someone called Ilya Goz) correctly pointed out that although a subset had been released, for some years and some locations on the globe that subset was in fact the entire set of data and so the errors could be checked.
Ilya went on to say that he was having a hard time reproducing the Met Office’s numbers. I encouraged him to write a blog post with an example. He did that (and it looks like he had to create a blog to do it). Sitting in the departures lounge at SFO I read through his blog post and Brohan et al.. Ilya’s reasoning seemed sound, his example was clear and I checked his underlying data against that given by the Met Office.
The trouble was Ilya’s numbers didn’t match the Met Office’s. And his numbers weren’t off by a constant factor or constant difference. They followed a similar pattern to the Met Office’s, but they were not correct. At first I assumed Ilya was wrong and so I checked and double checked has calculations. His calculations looked right; the Met Office numbers looked wrong.
Then I wrote out the mathematics from the Brohan et al. paper and looked for where the error could be. And I found the source. I quickly emailed Ilya and boarded the plane to dream of CRUTEM and HadCRUT as I tried to sleep upright.
Read the details at JGC’s blog: Something odd in the CRUTEM3 station errors