A new study by Arizona State researchers, published on May 28 in the Journal of Geophysical Research, concluded that that so much wasted heat is emitted by air conditioning units in Phoenix that it actually raises the city's outdoor temperature at night by between 1 and 2.7 degrees.
Like many cities, Phoenix is an urban heat island, which experiences significantly higher temperatures than its less-developed surroundings. One of the prime causes is the replacement of trees and grass with rooftops and pavement, which make up 60 percent of the surface area of a typical city. Those usually dark surfaces absorb about 80 percent of sunlight, causing them to heat up.
In addition, human activities that generate heat, such as industrial plants and vehicles, also contribute to the effect.