I came across an old post of mine from June 2012, which casts some light on how much the US temperature record has been adjusted by NOAA.
The graph plots November temperatures in Alabama. Like all of this old data, this graph is no longer available on NOAA’s website.
As I noted at the time, November temperatures in 1934 were 57.0F, and compared with 55.5F in 2011.
If we fast forward to the current version, we find that November 1934 is shown as 55.8F, and November 2011 as 55.3F. In net terms, relative to 2011, the 1934 temperatures have been reduced by 1.0F.
