A couple weeks in the desert will really make you appreciate air conditioning. I came to that conclusion after attending the annual conventions of the Sheet Metal and Air-Conditioning Contractors' National Association and the Heating, Airconditioning & Refrigeration Distributors International.

Both were held during October and by coincidence, at JW Marriott resorts - the hotel company's name for its line of top-end properties. Apart from the natural beauty of the hotels themselves and the surrounding professional landscaping, it struck me that both areas - California and Arizona, respectively - owe much of their success to the ubiquitous place of air conditioning today.

California is a huge, diverse state with many different climates, from the cool temperatures that make the San Francisco Bay area ideal for wine making, to the Los Angeles and San Diego areas, where temperatures are near perfect year-round.

But just a short drive east of Los Angeles, the terrain quickly becomes rocky and the weather, especially in the summer, almost unbearably hot - at least without air conditioning. The landlocked state of Arizona is almost all deserts.

It's the reason

And yet today, these areas are among the fastest growing in the United States. The reason is air conditioning. Take out the often-blistering heat of June through September, and these areas offer abundant sunshine, low humidity and a very temperate climate the other eight months of the year. However, before the invention of air conditioning, mild temperatures for much of the year were not enough to convince many people to live there.

That started to change with the "invention" of air conditioning by Willis Carrier in 1902, although like most life-changing inventions, there are those that quibble over Carrier's role as the "father" of modern air conditioning.

Nevertheless, within a few decades, public buildings that were almost intolerable during the summer, such as movie theaters, started to become very popular ways to escape the oppressive, searing heat. One historic hotel I visited in downtown Phoenix, the San Carlos, claims to have been the first hotel in the city to have air when it opened in 1927.

However, even in the hot, dry desert, air conditioning was slower to move into private homes. Although most public buildings were equipped with air by the end of the 1950s, whole-house air conditioning in Phoenix-area residences did not become standard until the 1970s, according to a current exhibit on home construction at the Arizona Science Center.

Today, thanks to air conditioning, it's much different. An article in one of the Arizona papers delivered to my hotel room noted that October's "moderate" temperatures (in the mid- to upper 80s) meant that residents were finally starting to hang out outside at restaurant patios and in city parks.

Compare that to decades past, when many homeowners would spend their whole evenings - and even sleep - outside, desperate for a little breeze.

Air conditioning has often been cited as one of the greatest inventions in modern history, and with good reason. A 2004 online poll of 2.5 million people by the Henry Ford, a historical park and museum started by the Ford Motor Co. founder, named air conditioning as the top invention of the last 75 years. It beat out personal computers, cell phones, television and even penicillin.

The fact air conditioning topped the list initially surprised me, but after thinking about it, it made sense. Few other inventions have changed our lives so quickly. Computers must be in climate-controlled areas, as must other sensitive equipment or supplies such as medicine. Air conditioning makes all of this possible.

Even today, other "essential" inventions such as cell phones and the Internet (which were both on Ford's list), don't have the same impact. I know several people who still don't have a cell phone and a few who never go online and they seem happy and well adjusted. Spend an hour or two today in a non-air-conditioned building and most people won't be content very long.