By Dr. Ben Herman on Roger Pielke Sr.’s Climate Science

There is an issue with regards to U.S. surface temperature trends that seems to have been overlooked, although apparently well recognized. I am referring to the HO-83 thermometers that were installed at many USHCN sites as well as first order stations. It has been well documented (Gall et.al. 1992, Jones et.al. 1995, Karl et. al. 1995) and others.that a warm bias existed, primarily in the daily maximum temperature readings reported by these instruments. The error in the Tucson data was about 2-3 deg F, but this error was apparently different with each thermometer. Karl et. al.  (1995) have suggested that the average for this error over the country was on the order of 0.5 deg C on the reported maximum temperatures. Thus, if the maximum temperatures were corrected by this amount, average temperatures in the U.S, would be lowered by about 0.25 deg C, assuming the minimum readings were correct. This would probably pretty much neutralize the reported trend increase during the late 80’s and 90’s in this country. The situation has been covered in some detail in a Climate Audit blog by Steve McIntyre for those wishing more detail on the history of this issue.

See full size image here

These thermometers have subsequently been replaced, but to the best of my knowledge, none of the station data have been corrected for this problem. In view of the probable magnitude of this error, and the time elapsed since the problems with the HO-83 thermometers have been known, why has this issue not only been not corrected, but also, not even mentioned by those that are determining and publishing these trends? It is true that these faulty instruments were probably used primarily in the U.S.  Read more here.

Dr. Benjamin Herman is the former Director of the Institute of Atmospheric Physics and also former head of the Department of Atmospheric Sciences at the University of Arizona. He has been a member of both the Institute for the Study of Planet Earth’s Executive Committee and the Committee on Global Change.