NCDC published this graph of US temperatures in 1990, showing an average temperature of just under 11.5C.
climate-assessment-1981-1990.pdf
NCDC now shows the average temperature during that same period as just over 11C.
Climate at a Glance | National Centers for Environmental Information (NCEI)
The overlay below shows how NCDC has cooled pre-1990 temperatures by about 0.4C since 1990.
This was needed, because in 1989 they said the US isn’t warming.
U.S. Data Since 1895 Fail To Show Warming Trend
By PHILIP SHABECOFF, Special to the New York Times Published: January 26, 1989
After examining climate data extending back nearly 100 years, a team of Government scientists has concluded that there has been no significant change in average temperatures or rainfall in the United States over that entire period.
The study, made by scientists for the National Oceanic and Atmospheric Administration was published in the current issue of Geophysical Research Letters. It is based on temperature and precipitation readings taken at weather stations around the country from 1895 to 1987.
U.S. Data Since 1895 Fail To Show Warming Trend – New York Times
If the present refuses to get warmer, the past must become cooler.