On this day in 1902, an engineer named Willis Carrier finished his design to control indoor humidity in his printing plant, creating what we know as air conditioning. Air was forced through a filter in a compressor, where it was pumped over coils that were chilled by a coolant. From multi-story buildings to small window units, the technology has not significantly changed from that day to this.

I grew up in a city, where asphalt soaked up the heat all day, and released it back at night. A breeze was all we could hope for; I remember my father telling me that if I sat quietly and very, very still on the screened in-porch I would feel the cool breeze. This may have been a technique to make me be quiet, but it worked. Likely what I felt as a child staring across the street at somebody else’s porch was the motion of the air moving across the sweat dripping down my neck. But at least it felt cool-ish, and a cloth — dipped in a bowl of melting ice — across your forehead and neck was magical comfort for a couple of minutes anyway.

There were always fans, and the whining electric fan swaying back and forth in the living room blew the hot air around the room some. Air conditioning was exotic, something for rich people like color television. In 1955, fewer than 2% of homes had air conditioners; 25 years later, more than half of homes had air conditioners, and over a quarter of those had central air. It was one of the ultimate luxuries turned necessity ever invented.

In its own way, air conditioning was as significant an invention as the printing press.

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Just as the wealthy had scribes and hand-copied books to read, they also had means of cooling their spaces. Cleopatra was rumored (Steve Saylor, "Gordianus") to have a system of fine silk threads hanging from a narrow trough across the top of a door or window. Cold water was poured into the pipes, which drizzled down the threads suspended from them while slaves continually fanned the threads, creating a soft cool breeze in the room.

Just as the printing press made reading more available, so did Carrier’s invention create for the masses climate control. But it also changed the expectations of the public and made a scarce luxury an expected amenity.

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Now, virtually every building, store and house has air conditioning. Our ability to control our climate has become so routine that to have it interrupted is considered an emergency. When there is a power failure, a city opens cooling centers for the victims of once routine humidity and summer heat.

People used to come to places such as Cape Cod, the seashore and the mountains, to escape the heat of cities and the baking inland plains with shimmering, unshaded and unrelenting heat. But now even here in what was once the refuge from the power of the sun, the rooms are cooler than the breezes of the ocean and the stores make you consider bringing along a sweater in case the chill becomes too much.

We have become so conditioned by this cool air that we ignore the energy and resources used to produce it. Electricity, energy, fuel and resource consumption all soar measurably during a heat wave. But we do not even try to bear temperatures that were once routine.

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We produce heat in the winter, and without it, we would die of cold. But while temperatures in the humid 80s are considered unendurable now, humans endured them quite nicely for millennia. Perhaps not nicely, but successfully. To be sure, you can die of heat stroke but not with the same grim efficiency of cold. Heat only makes you wish you were dead. But even now in large swaths of the world, people survive extreme heat and have never heard of Mr. Carrier and his engineering brilliance.

Only 120 years ago today, one man changed how we live and survive in a permanent fashion. So, take the time to raise a glass of iced tea to Louis Carrier and his genius.

Cynthia Stead is a columnist for the Cape Cod Times and can be contacted at cestead@gmail.com.