Unfortunately it appears the field has undergone a lot of changes in the past five years. When I last researched the matter, it was considered good evidence -for- AGW (albeit evidence for a “lukewarmist” position), and attention had just been focused to it by the products of a skeptical initiative to document the conditions of temperature stations and a subsequent paper which attempted to de-bias the UHI effect out of the temperature record—given that the de-bias attempt is what -produced- the attention on daily minima (which it found to have increased substantially, with only a statistically insignificant increase in daily maxima), I’m slightly suspicious of any claim that an increase in daily minima has to do with the UHI effect. (Namely, correcting for the UHI -produces- a stronger trend in daily minima compared to daily maxima or averages; if the UHI were -responsible- for this trend, we’d expect the reverse.)
But I have no idea what happened to the original papers, which were substantially better than what I can find today.
The number of data points in that sample, at least, probably don’t support that degree of precision.
As for the minima versus maxima claim, I can only point you in the right direction; Google “declining DTR”.
Unfortunately the science is a lot more all-over-the-place than I had anticipated; the NOAA appears to agree, more or less, with the skeptical claim there (see http://www.nws.noaa.gov/ost/climate/STIP/FY11CTBSeminars/lzhou_052511.htm ), whereas the IPCC appears to disagree (see http://www.ipcc.ch/ipccreports/tar/wg2/index.php?idp=422 ) . Then you have people making claims at odds with both of them (see http://www.co2science.org/articles/V3/N33/C3.php )
Unfortunately it appears the field has undergone a lot of changes in the past five years. When I last researched the matter, it was considered good evidence -for- AGW (albeit evidence for a “lukewarmist” position), and attention had just been focused to it by the products of a skeptical initiative to document the conditions of temperature stations and a subsequent paper which attempted to de-bias the UHI effect out of the temperature record—given that the de-bias attempt is what -produced- the attention on daily minima (which it found to have increased substantially, with only a statistically insignificant increase in daily maxima), I’m slightly suspicious of any claim that an increase in daily minima has to do with the UHI effect. (Namely, correcting for the UHI -produces- a stronger trend in daily minima compared to daily maxima or averages; if the UHI were -responsible- for this trend, we’d expect the reverse.)
But I have no idea what happened to the original papers, which were substantially better than what I can find today.