Low Head is not a manouevre at a Hollywood party or a physical description of the gnomes of Norwich (the location of CRU), but a lighthouse in Tasmania, which John Daly photographed and brought to the attention of Neil Plummer, who had used it in Jones et al 1990. Plummer wrote back to Daly that the inhomogeneity had been taken into consideration in their revised data in Torok and Nichols. Well, was it?
Actually, yes, or at least a qualified yes and the adjustments are pretty interesting. The version from Jones et al 1990 (recently archived) is shown in red. There is a pronounced increase in maximum temperatures, which John Daly had reported to the Australiean BoM as being attributable to changing landscape at the lighthouse. Plummer replied that this had been allowed for in their High Quality network and, as shown in black, they made substantial adjustments to the series. In some years, the adjustment to the maximum temperature is as high as 1.8 degrees C.
Low Head annual averages from Jones et al 1990 (red) and Torok and Nicholls archive (black, blue). The blue is the calculated annual average. Black is the 13th column which appears to be the adjusted annual average.
Let’s go back to Jones et al 1990. Their argument capping 20th century UHI at 0.05 deg C was based on the supposed small difference between the rather urban-based CRU gridded data and the supposedly “rural” comparandum in China, Russia and Austrlian comparisons – each of which has hair on it. In a spot check of an Australian site in Jones et al 1990 (and this is the only site that I’ve checked), there was a substantial bias in the rural comparandum which was known at least by 1996. Are there similar problems in other series? I don’t know. When Plummer and Coughlan discovered that they needed to re-state the Low Head series so substantially in their High Quality series, they should have published a Corrigendum or some other notice to the community relying on Jones et al 1990 – which continues to be cited, most recently in AR4.