In 1902 a young engineer named Willis Carrier was working at a printing factory in Brooklyn, New York. The ink kept smudging and the paper kept warping because the summer air was so hot and humid. Carrier designed a machine that blew air over cold pipes, which cooled the air down AND made the moisture in it condense - exactly like dew on cold grass in the morning.
That was the first modern air conditioner. For decades, AC was a business thing - for factories, movie theaters and department stores trying to lure customers in from the heat. Home air conditioners didn’t become common until the 1950s.
Once they did, whole parts of the world became newly livable. Cities like Phoenix, Dubai and Singapore grew huge because people could finally work and sleep through their brutal summers. Air conditioning literally moved millions of people around the planet.
