Adjustments to account for warming due to the effects of urbanization (purple line) cooled the time series an average of 0.1F throughout the period of record.
The cumulative effect of all adjustments is approximately a one-half degree Fahrenheit warming in the annual time series over a 50-year period from the 1940’s until the last decade of the century.
The mechanism that NOAA used for cheating the Oklahoma temperatures last summer, was upwards adjusting all recent temperatures more than half a degree – without properly adjusting downwards for UHI effects. Their total UHI adjustment is a ludicrous -0.06C.
Compare this to their own research.
the urban locations displayed an apparent upward increase through the time series (1910 through 2000), which was attributed to the urban growth of the region. By the end of the series, there was a +4 to 7 ºC (7 to 13 ºF)difference between the urban minimum temperatures and the rural minimum temperatures. Interestingly, no upward trend was found in the maximum temperatures
Barrow – a small town:
During winter (December 2001–March 2002),
the urban area averaged 2.2 °C warmer than the hinterland. The strength of the UHI increased as the wind velocity
decreased, reaching an average value of 3.2 °C under calm (<2 m s−1) conditions and maximum single-day magnitude of
New York :
Surface air temperature readings from these stations show that the city was several degrees warmer than the suburbs, and up to 8°C warmer than rural areas within 100 km of the city, with conditions that had been sustained throughout the previous night.
By using a completely bogus token UHI adjustment of -0.06C (which is more than an order of magnitude too small) NOAA was able to smear in severely UHI affected nighttime temperatures, and get the average temperatures up for their press release.
Of course they failed to mention that maximum temperatures were much higher in 1913, 1934 and 1936.