NOAA Data Tampering : How They Made 1913 Disappear | Real Science

August 1913 was likely the hottest month in Oklahoma history, but NCDC has made the inconvenient month disappear – through massive abuse of the temperature record.

...They did this by warming the present, and massively cooling the past. The graph below shows the difference between their reported maximum temperatures and the actual temperatures measured by the thermometers. All years before  1998 are progressively cooled, and they knocked an impressive 3.6 degrees off of 1913. They also added 0.2 degrees on to 2011.