Guest Weblog: Ben Herman Of The University Of Arizona – Maximum Temperature Trends and the HO83

HO83 ASOS Hygrothermometer

(temperature/dewpoint sensor)

Note: This was originally posted on Dr. Roger Pielke Sr’s blog Climate Science at I’m reposting it here since we’ve had a number of posts on the HO83 thermometer inaccuracy and it’s impact on the surface temperature record. Ben Herman raises some very valid points.

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 1992, Jones 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 blog by Steve McIntyre on ICECAP.US ( for those wishing more detail on the history of this issue.

(also see these related posts on Watts Up With That: Inside the HO83, Equipment in the USHCN Network, Reno’s ASOS station)

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.  However, some were apparently sold overseas, but I have no knowledge of where they were sold, or how many were (and may still be) in use. Here in Tucson an all time maximum temperature record was set of 114 deg F. , along with numerous daily records during the time this thermometer was in use, many of these records having been set while no other records were broken within 1000 miles of Tucson (Gall et. al. 1992). Prior to the installation of the HO-83 instrument, the record high for Tucson was 111 deg F, which was reached 6 times. In 1988 and 1989, that record was reached or broken eight times. In 1990 it was equaled or exceeded on 7 days, with 117 deg being recorded during this period. However on 6 of those days records were also set at numerous other locations in Arizona, so they were probably legitimate records (Gall et. al. 1992), although perhaps still too high.Also, it is important to note that these latter records, which seemed more in line with what was occurring at other locations, were set after an apparent sudden  shift downward occurred in the HO-83 readings by about 2 deg in September 1989. (Gall et. al. 1992). No such sudden shift occurred at other stations that I am aware of and the origin of this apparent re-calibration is not known.

These instruments were replaced in the mid to late 90’s and no other comparisons have been made since then that I am aware of. I will close by asking someone in the know to tell me why this apparently very important issue has not been considered in existing station climatic data ( the record high temperatures established during the period when the HO-83 was in place still stand) and it is this uncorrected data that has been used for determining temperature trends in the U.S.


Gall, R, K. Young, R. Schotland, and J. Schmitz , 1992. The Recent Maximum Temperature Anomalies in Tueson: Are They Real or anInstrumental Problem? Journal of Climate Volume 5, Issue 6 (June 1992) pp. 657?665 url

Cyrus G. Jones and Kenneth C. Young , An Investigation of Temperature Discontinuities Introduced by the Installation of the HO-83 Thermometer Journal of Climate Volume 8, Issue 5 (May 1995) pp. 1394?140 url

Karl, T.R., and Coauthors, 1995: Critical issues for long-term climate monitoring. Climate Change, 31, 185?221.

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January 21, 2008 5:23 pm

Amazing, simply amazing. And on this faulty information we are harangued into making sweeping snap policy changes.
As I said before, Eisenhower was right when he warned of the danger of public policy becoming captive of a scientific-technological elite.

January 21, 2008 8:49 pm

And this is the SECOND recorded time that Dr Karl expressed concern about the accuracy of the records. First in ’95, then this:
“In 1999, a U.S. National Research Council panel was commissioned to study the state of the U.S. climate observing systems and issued a report entitled: “Adequacy of Climate Observing Systems. National Academy Press”, online here The panel was chaired by Dr. Tom Karl, director of the National Climatic Center, and Dr. James Hansen, lead climate researcher at NASA GISS. That panel concluded:
“The 1997 Conference on the World Climate Research Programme to the Third Conference of the Parties of the United Nations Framework Convention on Climate Change concluded that the ability to monitor the global climate was inadequate and deteriorating.”

April 19, 2008 12:03 am

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