It isn’t just the US temperatures which have been corrupted by NASA and NOAA, but they have done the same thing for the entire planet
As of 1975, the Northern Hemisphere’s past was much warmer during the 1940s than it is now. The animation below flashes between the 1975 National Academy of Sciences data in blue, and the current NASA data in red. The baseline periods are not identical, but what is interesting is that the years from 1900 to 1960 got colder, while the post 1960 years got warmer.
The next animation flashes between the 1999 NASA US temperature graph, and the 2014 version.
They publish no disclaimers or explanations with these graphs, and almost every successive year the past gets even colder than it was previously – and the present gets even warmer than it was previously.