The Urban Heat Island
The mechanisms which lead to the creation of an urban heat island (UHI) have been studied for nearly a century and are well understood. Like many other large cities, the PMA has a substantial UHI. As early as 1921, urban effects on the local climate in Phoenix, Arizona were recognized. Analyzing winter-time minimum temperatures in the Salt River Valley, Gordon (1921) found that the weather station in Phoenix, which at the time was roughly two percent of its current population, was warmer than expected for a low-valley location. He noted that the Riverside Nursery is protected on the north by both the diversion of the cold air stream and by the city of Phoenix itself with its warming influence likely making him the first scientist to describe the Phoenix UHI. Since that time, the population has increased nearly 40-fold, resulting in an intensification and expansion of the UHI.
Muller says that UHI isn’t important. With only eight degrees of urban nighttime warming, pin head alarmists are surprised that we don’t have as many record lows as we used to.