Yet in the paper he co-authored on the subject with Watts, Christy apparently did not know to take the first and most critical step of
homogenizing the data and removing the climate - unrelated biases introduced by factors like
stations moving and time of
observation changing.
For example, changes in time of
observation, adjustment for a move of a
station that was previously sited next to a heat source to a better location (that now allows the
station to be classed as Class 1 or 2), switch to a different temperature measurement device or system, etcetera, could explain why smaller classes of raw data don't track well with the overall trend calculated from
homogenized station trend data.