Bill Illis found this NCDC graph from 1991. It correctly shows that 1934 and 1921 were the two hottest years in the US.

www1.ncdc.noaa.gov/pub/data/cmb/bams-sotc/climate-assessment-1981-1990.pdf

The graph below is NCDC’s current US graph.

CONTIGUOUS UNITED STATES Climate Summary

I overlaid them on each other, normalized to 1934. The 1991 version is shown in blue below.

Two things become clear

They cooled all pre-1970 temperatures by nearly 0.4C. Note how the 10C line is about 0.4C lower on the old graph than on the current graph. After 1970, all current graph temperatures are increasingly raised. The 1990 temperature in the 2012 graph is 0.2C above its value in the 1990 graph.

This graph doesn’t show any of the damage done after 1990, but you can see that it increases exponentially by comparing versus GHCN HCN temperatures.

Index of /pub/data/ushcn/v2.5/

Conclusion – NOAA/USHCN/GISS/NCDC US temperature trends are a complete fraud.