Over the past half century, a handful of inventions have reshaped American life. Topping the list are television, passenger jets, computers and — humming in the background — air conditioning.

To step from a sizzling parking lot into a cool, low-humidity shopping mall is to enjoy a degree of instantaneous relief and pleasure available through few other legal means. But this nation’s addiction to air conditioning, like all addictions, is costly.

Air conditioning accounts for 16 percent of the average US household’s electricity consumption, the Energy Department says — the same as all lighting, music systems, televisons, videotape and DVD players, desktop computers and printers combined. Usage peaks in summer, forcing utilities to build generating capacity that sits idle much of the year.

For climate, we’re a middling nation: far from the hottest and not among the coldest. If the planet’s 6.2 billion non-Americans used as much air conditioning per person in their homes as we do, the world’s total electricity requirement for residential AC would be 4 trillion kilowatt hours annually. That exceeds the entire combined electricity supply of China, India, Indonesia, Brazil, Bangladesh, Pakistan, Russia, Nigeria and Mexico, which together are home to more than half of humanity.

An air conditioner makes not only cool, clean, dry air, but also summons its evil twin: global-warming carbon dioxide. Based on Environmental Protection Agency numbers, 3,400 pounds of it are emitted each year to cool the average American home.

About 50 percent of US electricity comes from coal, and 17 percent from other fossil fuels. Coal is the worst carbon culprit, but all means of generating electricity belch carbon dioxide and other greenhouse gases during their construction and operation.

In a vehicle, running the air conditioner means blowing more pollution out the tailpipe. Energy Department figures show that it can reduce city-driving fuel efficiency by 4 miles per gallon. And when an SUV’s engine and air conditioner are left running in a parking lot to keep that new Shih Tzu puppy happy, the percentage reduction in gas mileage is incalculable.

The department says air conditioners in US cars and light trucks use 7 billion gallons of gasoline each year. The oil used to make that gas equals the total consumed annually by Indonesia, a nation of 240 million.

In years to come, we might have to run air conditioners ragged to provide some relief from human-fueled global warming. That will only aggravate the crisis.

And not just because we will be burning more coal, natural gas and oil. We also will be using more refrigerants, air conditioning’s lifeblood. Granted, there have been deep cuts in production of the most voracious ozone-devouring refrigerants, including chlorofluorocarbons. But all commonly used refrigerants are greenhouse gases, and every pound of them on earth is destined someday to escape into the atmosphere during manufacture, use, recharge, leakage during recycling or disposal.

In June a large, bipartisan coalition in the Senate and House endorsed a “bold new goal” of supplying 25 percent of the nation’s energy from renewable sources by 2025. Suppose, after a 20-year crash program, that the typical home gets a fourth of its electricity from renewables. Should it be blowing almost two-thirds of that hard-won “green” power just to maintain October weather indoors when it’s July outdoors?

Air conditioning could also frustrate efforts to reduce dependence on foreign oil. Cooling the interiors of American vehicles for less than five months of 2005 consumed gasoline equivalent to the nation’s entire fuel-ethanol production for the whole year.

Greatly expanded mass transportation, more efficient vehicles, more ecologically sound construction and greater efficiency in existing buildings can go only so far in getting the energy now consumed by “climate control” into line with reality.

“Comfort” will have to be redefined. Better ventilation and more shade can provide some relief from the heat, but they can’t reverse the seasons.

For 99 percent of recorded history, humanity managed to stay cool by finding some shade, getting some air moving, and slowing down when it gets too hot.

Starting this summer, let’s show the world that a mere few decades of air conditioning have not turned Americans into wimps. Turn the thermostat to OFF, throw the windows open, and head for the park instead of the mall.

Stan Cox, a plant breeder and senior scientist at the Land Institute, Salina, Kan., wrote this for the institute’s Prairie Writers Circle. Email to: [email protected]