by dana1981 and Kevin C , Skeptical Science, August 2, 2012
"An area and distance weighted analysis of the impacts of station exposure on the U.S. Historical Climatology Network temperatures and temperature trends" by A. Watts, E. Jones, S. McIntyre and E. R. Christy
The Underlying Problem
Changing Time of Observations
"There is practically no time of observation bias in urban-based stations which have taken their measurements punctually always at the same time, while in the rural stations the times of observation have changed. The change has usually happened from the afternoon to the morning. This causes a cooling bias in the data of the rural stations. Therefore one must correct for the time of observation bias before one tries to determine the effect of the urban heat island"
Instruments Change, Stations Move
The Amplification Factor
More Apples and Oranges
Adjustments Make Little Difference Globally
Just to be absolutely sure, we can do a further calculation using just rural unadjusted data (using the GHCN station classifications) -- the blue line.