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Clouds wash over Mount Katahdin's Tablelands, just a mile or so from the northern terminus of the Appalachian TrailNin the cat on Mount Washington. Illustration by T.B.R. Walsh from Cat in the Clouds







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Is Celsius Better Than Fahrenheit?
(More Cold Facts and Heated Debates about Temperature Scales)

by Eric Pinder

If history had been a little different, we might be debating the merits of the (now obsolete) Réaumur scale today instead of Celsius versus Fahrenheit. In some parts of Europe, the Réaumur scale was once the Fahrenheit scale's main rival. Absolute zero? Not quite. A meteorologist checks the temperature on top of Mount Washington.

In 1730, a French scientist named René Antoine Ferchault de Réaumur designed a scale in which the freezing point of water was set at 0 degrees. The boiling point was 80 degrees. Thermometers with Réaumur degrees were popular in France and most of Europe (though not in Britain) until supplanted by the metric system in the wake of the French Revolution in 1794.

Imagine we're back in 1794 on an alternate Earth. People have suddenly realized, "Hey, metric is great, but we ought to have a temperature scale to go with it. So which shall we choose?" Any scale, including Fahrenheit or Celsius or even Réaumur, can be linked to the metric system with equal ease. The Celsius scale is not really "metric" in the same practical way that, say, centimeters and kilometers are. You can quickly and easily find out how many centimeters are in 1.36 kilometers, unlike inches and miles. (Quick! How many inches in 1.36 miles?) But when it comes to temperature scales, doing the math is just as easy in Fahrenheit as it is in Celsius. Had Gabriel Fahrenheit lived in France and Anders Celsius in Britain, it might have been the Fahrenheit scale which was "attached" to the metric system instead of vice versa.

Lord Kelvin (William Thomson) forever linked the Celsius scale into the metric system by using Celsius-sized degrees. But he could just as easily have made his scale start at absolute zero using Fahrenheit- or Réaumur-sized degrees. (The Rankine scale also starts at absolute zero, a la Kelvin, but uses Fahrenheit-sized degrees. Kelvin and Rankine are equal at absolute zero. The point at which Celsius and Fahrenheit are equal is -40 degrees C or F.)

The scientific community adopted Kelvin instead Rankine, and that pretty much sealed the deal for Celsius. Today’s familiar units such as joules and the calorie (the amount of energy needed to raise the temperature of a gram of water by 1˚C) assume we’re working with Celsius-sized degrees. There’s even a new diet soft drink called Celsius, playing off of the calorie/weight loss connection. We could just as easily have defined the calorie using Fahrenheit-sized degrees (though there’d be more “calories” in your milkshake, and you’d burn more calories on your daily walk). But it’s too late to change now.

You can read more about the history of Fahrenheit vs Celsius and Metric vs English in A Heated Debate. What follows is my personal opinion. After becoming "fluent" in both Celsius and Fahrenheit during my seven years at the Mount Washington Observatory, I've reached three conclusions.

       Both scales have certain advantages.
       All of those advantages are so trivial as to be negligible.
       For talking about everyday weather, I find Fahrenheit slightly superior.

There's no question that the metric system (or rather, the Système International d'Unités) is far superior to the English system in terms of ease of calculation and unit conversion. But I suspect many people let their enthusiasm for metric carry over automatically to Celsius (which is not necessarily superior) just because, hey, Celsius is attached to the metric system and metric is best.

Celsius has one advantage over Fahrenheit. The argument boils down to this: "Zero is freezing, 100 is boiling, and that's nice and easy to remember if you need to bring in your plants off the balcony before they freeze."

I find that somewhat weak. If you can remember half a dozen passwords and phone numbers without any problem, I don't buy the argument that it's a challenging burden to remember a single number like 32˚F. It's not even universally true. Zero and 100˚C are not the melting/boiling points of water on, say, the surface of Mars. Even on Earth, they vary with salinity and pressure/altitude.

When we're talking about temperature, we're usually talking about comfort level, which is what Gabriel Fahrenheit originally based his scale on. 100 degrees F was meant to be human body temperature. Okay, Gabe missed by just a bit. But body temperature varies individually in any case, and slight fevers above 100 are not uncommon, so this doesn't bother me. In general, "Temperature will rise into the triple digits today!" means the outside air will be warmer than your internal body temperature. It's the point at which your body becomes a heat sink instead of a heat source. In terms of comfort, that's very significant and not at all arbitrary. (It's also remains true regardless of salinity or pressure or, for that matter, what planet you're on.) Thar's cold in them thar hills. Photo of Mount Washington's summit by Eric Pinder is available on magnets, mugs and t-shirts.

Base 10

So, we have Celsius, where 0 degrees is the melting point of water and 100 degrees is the boiling point (which is so far off the charts that it's just not a factor when talking about everyday weather.) And we have Fahrenheit, where 0 degrees represents the coldest point Gabriel Fahrenheit could create in his laboratory (pretty arbitrary) and 100 degrees is his rough approximation of human body temperature. Fahrenheit degrees are smaller than Celsius degrees. Or, to put it another way, Celsius degrees have a lower resolution and are less precise.

“Less precise?” you might ask. “Why not just use decimal points?” Many people do. To understand the centigrade scale, remember this little rhyme:

       Zero is freezing, 10 is not.
       20 is pleasant, 30 is hot.

But it's clumsier to communicate using decimal points in ordinary conversation, and especially while broadcasting weather reports. Which is why that clever little rhyme doesn't say, "Zero is freezing, 10.1 is not, 19.8 is pleasant, 30.4 is hot."

Think about a truly decimal "0 = freezing, 10 = boiling" scale. If someone tried to impose that scale on us and started saying things like, "What's the problem? It's easy. Zero is freezing, one is not, two is pleasant, three is hot. If you need more precision, just use decimal points," I doubt they'd be taken very seriously.

Officially, weather stations in the US used to record temperatures to the nearest tenth of a degree Fahrenheit, every one or three hours. These days the official records are in Celsius (though cloud heights are still in feet, oddly). Does that make much of a difference? Probably not. But it is a slight loss in resolution.

The bottom line is that both Fahrenheit and Celsius have units (degrees) in base 10, and are just as easy to calculate with. With meters/kilometers vs miles/inches, the metric system in indisputably superior. ("How many inches in 1.54 miles?" gives me a headache.) But that's just not a factor when it comes to Fahrenheit vs Celsius. In a practical sense, Celsius is no more "metric" than Fahrenheit.

“I don't get it. Celsius has a lower resolution? Huh?”

If you live outside the United States, you're probably not used to thinking in or communicating with Fahrenheit. I used to "talk weather" all day, both on the air and in classroom settings. In casual conversation, I found I could communicate information more quickly and with more nuances in Fahrenheit than in Celsius. It's subtle, and probably has something to do with how humans process language. There are simply a greater number of phrases that can be used to convey subtly different meanings to listeners who are "fluent" in Fahrenheit.

The advantage is trivial, and unless you're a linguist or a meteorologist or a weather nerd, probably all but unnoticeable. But it's there.

I think the U.S. and the rest of the world should come to a compromise. We in the U.S. will finally get rid our clunky miles and gallons and replace them with the more sensible kilometers and liters, if everyone else replaces Celsius with Fahrenheit. But that has about as much chance of happening as the 24-hour day being replaced worldwide by "metric" time. Alas.

More resources:

This useful site will convert temperatures between all five scales, including Kelvin, Rankine, and even Réaumur:

http://www.csgnetwork.com/temp2conv.html

For example, a common, comfortable room temperature is

20 degrees C = 68 degrees F = 16 degrees Réaumur = 293.15 Kelvin = 527.67 degrees Rankine

Going by the rhyme above, “hot” is

30 degrees C = 86 degrees F = 24 degrees Réaumur = 303.15 Kelvin = 545.67 degrees Rankine

You’ll notice I didn't say “degrees Kelvin” or use the degree symbol (˚) the way I did with Fahrenheit and Celsius. The convention is that you don’t say “273 degrees Kelvin,” just “273 Kelvin.”

Follow on TwitterThe history of Celsius, Fahrenheit and the strange English fasincation with the number 12 is explained in A Heated Debate

Enjoy some
ice storm photographs by Eric Pinder.

ice storm photos

Find more weather articles and information at the annotated sitemap.

Looking for a
gift for a meteorologist? Find weather history, weather puns and pictures in Among the Clouds. Read an excerpt here, or buy the book.

 

Read an interview with Boston’s first TV weatherman, Don Kent.

Meet Nin the weather cat in the new children’s book Cat in the Clouds

 

Another common use of temperature scales has nothing to do with the weather. Cooking pizza on Mt. Washington during a mountain rescue can be an adventure, especially if you’re dressed like this:

When the temperature is -40, Celsius and Fahrenheit become equal, and the summit crew on Mount Washington become a little crazy.

 

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Text and photographs © Eric Pinder