The move accentuates the rise in the global temperature recorded in the 1980s and 1990s that forms the basis of much of the current hysteria about the so-called climate emergency.
The disclosure of the apparent warming and cooling is contained in the latest State of the Climate report from Emeritus Professor Ole Humlum of the University of Oslo, and published by the Global Warming Policy Foundation. Professor Humlum says the post-1975 warming is about +0.1°C and the pre-1975 cooling about -0.1°C. The version-change to the fifth HadCRUT Met Office database “conveys the impression of a somewhat more rapid global temperature increase following the relatively cold period terminating around 1975”. When the Met Office first announced the change in December 2020, it admitted to 0.16°C extra warming, although it didn’t give specifics about cooling and warming either side of the 1975 mark.
Professor Humlum also draws attention to significant retrospective changes in the American GISS surface temperature record. The graph below shows the effect of the changes made since May 2008 on the monthly temperature record, with increases in red and decreases in blue. As with HadCRUT, the changes warm the early part of the record, cool the period from 1900 to 1970, and heat up the later recordings.
