“Going green” may be an annoying trendy catch phrase, but there’s something to be said for turning down the global thermostat before we all drown in a pool of our own sweat.
Picture yourself on a hot, sticky summer day. Your shirt has cemented your shoulders to the back of your chair; your underarms itch; your pants are way too tight in the crotch; there’s a puddle of condensation ruining the finish on your kitchen table all around your Captain and Coke. You say something unoriginal like, “Christ, I hate this heat,” and some nearby asshole admonishes you with something even less original: “It’s not the heat, it’s the humidity.”
Okay, he’s kind of right, but he’s still pathetic for saying it.
The air-water complex
Here’s how it works. “Humidity” refers to the amount of water that’s vaporized in the air. That water comes from pretty much the same places all our water comes from — the estimated reserve of 326 million cubic miles of the stuff distributed across the planet among oceans, rivers, streams, underground springs, and the polar ice caps. Water combines with the air through the familiar process of evaporation. The warmer the air gets, the more water vapor that air can hold. So hot and humid go together naturally, like cold and dry or jocks and PBR.
When Harvey Leonard or J.C. Monahan or anyone of a broadcast-meteorological bent tells you the humidity is, say, 25 percent, they’re talking about relative humidity, which is to say the amount of water in the air relative to the maximum amount of water air could hold at a given temperature (be it current or predicted).
Got that? There’s a whole lot more to explain and a lot more other factors involved, but that’s the basic concept. (If you’re curious about how confusing it can get, check out the Wikipedia entry on “humidity,” which was apparently written by a full-time nerd and edited by a part-time chimp.)
Hold the thought.
Yeah, but it’s a dry heat
Now imagine yourself in Arizona. The thermometer reads 95 degrees Fahrenheit. (All temperature references in this article will be expressed in Fahrenheit, because, as any real American knows, Celsius is for sissies.) You say something obvious like, “Christ, I hate this heat,” and some nearby asshole waxes sage and retorts: “Yeah, but it’s a dry heat.”
Screw him. As if that’s some kind of compensation for having your lungs recoil with every breath. What’s his point? To shift blame away from the too-oft-maligned concept of temperature? Bottom line, it’s too damn hot.
Now remembering what we discussed above, you know that 95-degree air can accommodate a lot of water. But you’re in Arizona, one of God’s dusty abandoned construction sites. Any useful amount of water you encounter has been drained from snow-capped mountains in faraway states and piped in at great expense to the continental aquifer. So the nearby asshole is right — again: for want of available moisture, the air is hot and dry.
Merely two ways to suffer
All of these technicalities seemingly mean nothing to you as an individual. You’re too hot in Phoenix or you’re too hot in Framingham. It’s two kinds of too hot, but you’re still too hot.
That “dry heat” chestnut tells you only that sweltering at 95 in Back Bay is probably even more uncomfortable than mummifying at 95 in the desert. Like we said, big fucking deal.
Nevertheless, there are real issues involved — vital issues involving health and environmental decay. In recent years, climatologists and health experts have derived a new and meaningful statistic from all this called the “apparent temperature,” a concept best summed up in the phrase, “but it feels like . . . ”
Just how drastic is the difference between infernal dry heat and miserable wet heat? Conspicuously drastic, depending on circumstances.
On a typical mild early-June day, the 91-degree air temperature in Arizona feels like . . . wait for it . . . 91 degrees, because the relative humidity out there is only 10 percent. On the same day in Massachusetts — temperature 85, relative humidity 25 percent — the air feels like — hey! — 85 degrees. It’s called a mild day for a reason.
But at 95 degrees (that’s hot!) and a relative humidity of 75 percent (that’s humid!), the air feels like it’s 130 degrees; though at only 25 percent relative humidity, 95 feels like 94. Really. One less. This is where the not-so-bad dry-desert-heat notion comes from.
Observing the obvious
You don’t have to study one of those color-coded humidity maps too closely to see that on any given day, the air in the American Southwest (painted reds and yellows) is usually dry, compared with the wetter air in the rest of the country (greens and blues).
