AMS fellow Joe D’leo writes of a time when Thomas Karl, former director of the National Climatic Data Center (NCDC) actually believed that UHI and station siting was a problem that created a warm bias.

USHCN official weather station at the University of Arizona, Tucson, outside of the Atmospheric Sciences Department. Note that it was measuring the temperature of the parking lot.

He writes:

Tom Karl whose paper in 1988 defined the UHI adjustment for the first version of USHCN (which was removed in version 2) wrote with Kukla and Gavin in a 1986 paper on Urban Warming:

“MeteoSecular trends of surface air temperature computed predominantly from [urban] station data are likely to have a serious warm bias… The average difference between trends [urban siting vs. rural] amounts to an annual warming rate of 0.34°C/decade.  … The reason why the warming rate is considerably higher [may be] that the rate may have increased after the 1950s, commensurate with the large recent growth in and around airports. …

Our results and those of others show that the urban growth inhomogeneity is serious and must be taken into account when assessing the reliability of temperature records.”

Source: https://journals.ametsoc.org/doi/pdf/10.1175/1520-0450(1986)025%3C1265%3AUW%3E2.0.CO%3B2

Local copy: kukla-gavin-karl 1986 (PDF)

Inexplicably, the UHI adjustment Karl argued for was removed in USHCNv2.

Doug Hoyt, once chief scientist at Raytheon wrote:

“It is not out of the realm of possibility that most of the twentieth century warming was urban heat islands.”