They erased the ”very extraordinary period of warmth” of the 1930s.
We know that polar ice and alpine glaciers melted rapidly between 1910 and 1950. We know that the 1930s were very hot. We know that the 1970s were cold, and ice was expanding.
Yet Hansen and Jones both show the 1970s much too warm, and the 1930s much too cold.
Here is another critical piece of evidence. In 1975, Science News published the graph below of northern hemisphere temperatures, from the National Academy of Sciences.
Since 1940, the temperature of the Northern Hemisphere has been steadily falling: Having risen about 1.1 degrees C. between 1885 and 1940, according to one estimation, the temperature has already fallen back some 0.6 degrees, and shows no signs of reversal
To gain a perspective on these divergent views, SCIENCE NEWS interviewed C. C. Wallen, chief of the Special Environmental Applications Division, World Meteorological Organization, at the wmo headquarters in Geneva. The cooling trend observed since 1940 is real enough, he says, but not enough is known about the underlying causes to justify any sort of extrapolation. Particularly dangerous would be any attempt to generalize from even shorter-term experience, like the bad weather in 1972 and following years, to prognosticate any future weather patterns. On the other hand, the cooling since 1940 has been large enough and consistent enough that it will not soon be reversed, and we are unlikely to quickly regain the “very extraordinary period of warmth” that preceded it. Even this mild diagnosis can have ”fantastic implications” for present-day humanity, Wallen says.
Now look at the composite. Hansen whacked a huge chunk off all temperatures prior to the 1950s. (This graph was corrected from the original published, which had a shift error.)
This is very similar to what Hansen did to the US temperature record. The whole global warming story falls apart without this blatant data tampering.
Hansen continues to tamper with the data set, and Jones is about to do his biggest tampering to date with HadCRUT v4.