Source: US Department of Energy. Residential Energy Consumption Survey. Table HC7.3 Air conditioning in U.S. homes by year of construction, 2015.
The importance of air conditioning is often not well acknowledged as a factor in the expansion of human settlements in warmer and humid climates, opening new regions and economic opportunities. The first commercial air conditioning devices were available at the beginning of the 20th century and after World War II their use expanded to cover residential, commercial, and industrial facilities. This enabled new areas to be settled, such as Florida, Nevada, and Arizona, which became an important resort and retirement centers. Since the 1970s, the share of housing units in the United States with a form of air conditioning, either central or units, has increased substantially. The highest level is observed in the South, which is characterized by a warm and humid climate. Even in temperate parts of the United States, the share of air-conditioned housing units has increased, such as in the West. This is mainly due to the requirement of more comfortable homes. Climate change may also be a factor having an influence on the growth of air conditioning, particularly in areas that previously had a low prevalence.
In many other parts of the world, air conditioning has enabled drastic changes in the location, planning, and dynamics of cities, particularly in developing economies that are not in temperate climates. A large metropolis like Dubai would not exist without air conditioning. It would exist as a settled location, but it would be enabled to support its existing extensive service function, all of which taking place in air-conditioned structures.