In 1902, Willis Haviland Carrier, a twenty-six-year-old American engineer, designed the first system to control temperature and humidity and installed it in a Brooklyn printing plant. Room air conditioners began to appear in the 1930s and spread rapidly in the 1950s, making possible the industrial and population explosion in the Sun Belt. While this ad promised consumers clean as well as cool air inside the house, it failed to note that air conditioning consumed large amounts of energy and contributed to outdoor air pollution. Hotpoint/General Electric Company.