It is used now to 'correct' all of the land based thermometers readings that figure prominently in GISS temperature measurement of the Earths surface. They are looking for tenths of a degree change against an average estimate of the urban island effect of around 10 deg. If you think this might be fraught with systematic error, you might be pretty smart.
Roy spencer, who is retired now I believe, was in charge of the U,S, satellite, remote temperature sensing. He says, of the land based thermometer sites, GISS uses only a very few that have not had their environments altered significantly over the last thirty years. He says, rather than assume those sites with no significant alteration were the most reliable, GISS did the opposite, and adjusted the most reliable readings to correspond with the least reliable. I don't know why they would do that. But I have far more faith in the remote sensing, that has its own set of problems. The satellite shows little mean change globally, but It doesn't agree with the land based, thermometer, GISS estimates of change. No good error studies exist. That should be a top priority. The nominal temperature is not important, only the change in mean temperature is important. So a difference in the satellite values from the Earth based values doesn't matter. But there is a difference between the two sets in amount of change detected. That is important!
There has never been any question that a large urban island effect exists. It is typically around ten degrees F.
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