As anyone who's sweating their way through the current U.S. heat wave can attest, high temperatures are no fun. People become sluggish and irritable. It becomes hard to work, hard to concentrate, hard to do anything. When temperatures scream past 100 degrees, the risk of heat-related death increases dramatically.



Crank up the AC please! (Matt McClain for The Washington Post)

In fact, there are even studies suggesting that extreme heat can strangle a country's livelihood. A 2008 study by three economists, led by Northwestern's Benjamin Jones, found that poorer countries experience a plunge in economic output during hotter-than-average years. It's not just that drought kills off crops. Industrial output declines, and political unrest becomes more unlikely.

What's curious, however, is that this happens mainly in poorer countries — wealthy countries are far more immune to the heat penalty.

One explanation for the difference, of course, is air conditioning. Today, most Americans can minimize their exposure to sweltering weather. We can wake up in our thermostat-tuned homes, hop into our AC-cranked cars, and drive to our cooled offices. Granted, not everyone's so lucky — plenty of people don't have office jobs, and blackouts have left thousands here in D.C. without power — but indoor climate control is a major feature of the industrialized West. And it appears to have large economic benefits.

Stan Cox, in his fascinating book, "Losing Our Cool," offers a long list of ways in which air conditioning has transformed the U.S. economy. Here's a description from the National Building Museum of the state of affairs in the 1920s, before the invention of AC:

Before air-conditioning, American life followed seasonal cycles determined by weather. Workers' productivity declined in direct proportion to the heat and humidity outside — and on the hottest days employees left work early and businesses shut their doors. Stores and theaters also closed down, unable to comfortably accommodate large groups of people in stifling interiors. Cities emptied in summers.... Houses and office buildings were designed to enhance natural cooling, and people spent summer days and evenings on porches or fire escapes.

Everything changed after the discovery in 1928 of chlorofluorocarbons (CFCs), which were used as coolants in air-conditioning (and, we later learned, chewed a hole in the ozone layer). Retail stores could now operate year-round. Americans could flock to otherwise inhospitable regions in the South and Southwest. Cox has even argued that AC was a major factor in the resurgence of the Sunbelt-based Republican Party.

But there's a flip side. All this AC could prove unsustainable. The amount of energy consumed by U.S. homes for air conditioning has doubled in the past 12 years, according to Cox, and now accounts for nearly 20 percent of our electricity use. What's more, developing countries like China and India want in on what's viewed as an utter necessity. The New York Times recently reported that sales of AC units are rising 20 percent per year in those two nations.

If all of these countries keep burning coal to satisfy demand for indoor cooling, the result will be more carbon dioxide in the air. (The newer, ozone-friendly HFCs used in the units are also highly potent greenhouse gases.) That means a hotter planet overall, which will, in turn, require even more air conditioning to survive. As a reminder, here's how frequent 100°F days will become across the United States if carbon emissions keep rising at their current rate:



Source: Global Climate Change Report, 2009

The current "freak heat wave" will become the norm for one-sixth of the year in D.C. (That's in addition to all the other climate consequences — sea-level rise, droughts, agricultural disruption — that could prove far more difficult to adapt to.) In our endless quest to cool ourselves, we've managed to heat the world. So is there a way to break this cycle?

One oft-discussed option is to make air conditioning more energy-efficient. And that might mean more than just tinkering with existing units. In countries like Japan and South Korea, many homeowners find it wasteful to cool a whole vacant house all at once, preferring to focus on individual rooms where people are actually sitting. Better insulation and ventilation can reduce the need for AC, as can plant-covered "green roofs" that cool buildings naturally. There also exist promising alternatives to traditional AC, including ground-source heat pumps, which channel hot air in a house down into the ground during the summer.

In his book, Cox suggests going even further: He argues that people might be better off in some respects if they learn to rely less on artificial temperature control. There's scant evidence that keeping office temperatures at icy levels improves productivity. Indeed, it's possible that the human body is actually healthier when it's not kept enshrouded by air conditioning all the time. Some researchers have even suggested, for instance, that our reliance on indoor cooling has helped spur an obesity epidemic.

Some parts of the developed world are slowly pushing to temper their addiction to air conditioning. In Japan, Cox notes, the government has pressured businesses to keep thermostats at a mild 81°F during the summer. After some initial resistance, businessmen took off their suit jackets and adjusted. Similarly, malls in Hong Kong are now pledging to turn down the AC to save energy.

Still, on a day when temperatures are reaching dangerously high levels in many parts of the United States (the high is approaching 105°F in D.C.), calls for conservation are a tougher sell. Mostly it's worth noting how different heat waves today are from the heat waves of the 1920s — because of how drastically we've adapted.