Folland has been the leading IPCC authority on bucket adjustments. Folland et al 1993 carries out a comparison from early 1980s measurements of (presumably predominantly insulated) bucket and non-bucket measurements, arguing that the difference was about 0.08 (less than 0.12-0.18 suggested in 2006 by Kent and Kaplan.
They reported a puzzling situation in the Gulf of Alaska where, according to the data base used for the comparison, Canadian data came from “buckets or unknown instrumentation” (Folland allocates “unknown instrumentation” in with buckets for the purpose of his comparison as shown below and states that Japanese data is classified in their data bases as also coming from “buckets or unknown instrumentation”. He goes on to observe that WMO 47 says that over 90% of Japanese data came from engine inlets and accordingly should have been in the opposite pool. One wonders why they wouldn’t have simply written to the Japanese and asked them to clarify the matter. How hard would that have been?
Folland’s allocation of Canadian data to the bucket pool also caught my eye. The discussion of Brooks (1926!) included a comment from a Canadian saying that they were already obtaining accurate SST measurements from engine inlet pipes by 1926. I would be highly surprised if Canadian ships in the 1980s had reverted to the use of buckets. Again, how hard would it have been for Folland to have written to someone in Canada and asked for this information to be confirmed.
I double checked my reading of Folland et al 1993 to be sure that he had really allocated unknown measurements to buckets. If you don’t know how something was measured, what conceivable purpose would there be in including it in one’s comparisons? Here’s the original statement of methodology describing the construction of one group of (a) buckets and unknown instrumentation; and (b) “unflagged” data assumed to be engine inlet and hull sensor (see p 111.)
A reader of this might say that there might be some interpretation of this language under which unknown instrumentation was identified, but not necessarily pooled with buckets. If this were the only statement, then I’d be inclined to seek further clarification from the authors. However, later (p 112), they note that incorrect inclusion of engine inlets classified as “unknown” into the bucket class could lead to an under-estimate of bucket-non bucket differential, a differential that Folland et al 1993 cap at about 25%.
Folland et al 1993 also has a couple of interesting comments on the timing of the introduction of insulated buckets into the UK fleet. On page 97, they stated that:
the U.K. voluntary observing fleet changed from the predominant use of uninsulated canvas buckets to that of insulated (black) rubber buckets in the 1960s and early 1970s.
Thompson et al 2008 stated that:
after the mid-1960s are not expected to require further corrections for changes from uninsulated bucket to engine room intake measurements.
Now I’m not in a position to know the precise schedule of the transition from uninsulated to insulated buckets, but, insofar as the U.K. voluntary observing fleet is concerned, Folland’s statement in 1993 that the transition was taking place in the 1960s and early 1970s hardly justifies the conclusion that the conversion had been completed by the mid-1960s. If the conversion was say only 33% or 50% complete, then some portion of the adjustment would get pushed later into the record. (And this is aside from the point previously made that insulated buckets seem to be intermediate between uninsulated buckets and engine inlets and thus some portion of the total allocation of the adjustment, whatever it is, has to be spread into the 1970s and later when the conversion of insulated buckets to engine inlets was being completed.
And by the way, isn’t it bizarre that engine inlet techniques, already available in 1926, were still not be utilized in the 1960s?
BROOKS, CF. 1926. OBSERVING WATER-SURFACE TEMPERATURES AT SEA. Monthly Weather Review 54, no. 6: 241-253. url
Folland, C. K., R. W. Reynolds, M. Gordon, and D. E. Parker. 1993. A Study of Six Operational Sea Surface Temperature Analyses. Journal of Climate 6, no. 1: 96-113.