Is Urban Warming Causing the Apparent Upward Global Temperature Trend?
Urban areas have many buildings with vertical walls. The walls act like light traps or cavities and they capture and store heat during the day and then re-emit it at night. Cities and towns are enormous col-lections of Trombe walls. Thus, urban areas are warmer than the surrounding country and, in particu-lar, are warmer at night. (This has been known since at least 1850 when people were commenting on the urban heat island around the pioneer town of St. Louis). Thus, the urban heat islands are warmer with smaller diurnal variations. With growing population and growing urban construction, all urban regions can be expected to be getting progressively warmer. These upward temperature trends are probably accelerating because of the exponential growth in population. Airports have similar heat islands. Here, huge paved runways soak up sunshine and act like huge Trombe walls laying on the ground, keeping the locality warmer. The enormous burning of gasoline also helps keep it warmer than the
