Interesting, I decided to take a look at this phenomenon with an open mind and selected three remote, rural towns in the mountains mostly surrounded by state and national forest and parkland. And compared them to the records at nearby Pittsburgh. Can't find any evidence of an urban heat island amplifying the warming at Pittsburgh. If anything, as I surmised, the rural locations look to be warming slightly faster. Here is the comparison. All since 1958, except for DuBois [where records exten