AMS fellow Joe D’Aleo 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.
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.”
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.”