The earth may be getting warmer, but we’re getting cooler

The earth may be getting warmer, but we’re getting cooler

Hi everyone, thanks for joining us for episode 231 of Plain English. Like always, the web site includes a full transcript of the program, plus our video lessons, translations, and so much more. That’s all at PlainEnglish.com/231 today, PlainEnglish.com/231.

Coming up today: For 150 years, the conventional wisdom has been that the normal human body temperature is 98.6 degrees. But new research suggests that the new normal is more than a degree cooler. The phrasal verb today is “average out” and we have a song of the week.

The earth is warming, but people are cooling

It’s a number that’s seared into the minds of people everywhere—or at least in the countries that use Fahrenheit. Ninety-eight point six degrees—that’s the “normal” human body temperature. It’s the reference point against which a patient’s fever is measured. It’s almost a ritual for children to cross their fingers with the thermometer under their tongues and hope for a number as high as possible above 98.6 when they don’t want to go to school.

But new research suggests that the normal human body temperature is closer to 97.5 degrees and it’s not exactly clear why. For those of you more accustomed to Celsius—and that would be most of you—98.6 degrees is, of course, 37 degrees Celsius. The “new” normal is 36.4 degrees.

Regardless of which system you use, the new readings are a bit puzzling. There are two possibilities for this variance. Either previous studies were flawed in some way or humans are getting cooler.

Let’s take a look back in time. How did the number 98.6 take hold, anyway? About 150 years ago, a German physician analyzed a million temperature readings from 25,000 people and decided that the normal body temperature was 98.6 degrees. The number was widely publicized and taught and has been accepted as the normal, or correct, body temperature.

Is it possible that this number was never accurate in the first place? When I see numbers like this diverge over time, I always wonder about the way the figures were measured. It’s one thing to say that body temperatures have changed, but if it’s not measured the same way, then the difference could be more about the way it’s measured than the actual target of the measurement.

Over time, of course, our instruments have gotten better. I went to the doctor a few years ago and they took my temperature in no more than 3 seconds with a digital thermometer in my ear. That’s a lot different than when I was a kid, when I had to hold a thermometer under my tongue and—this was the hard part—sit still for a minute or two. The nurse then read it manually from the mercury.

So the instrumentation has changed over the years. There are also multiple techniques for measuring body temperature. You can measure body temperature in four places: in your ear, under your tongue, in your armpit—which I didn’t know until today—and, of course, the other place. They each give slightly different results even for the same person at the same time. Is it possible that the study 150 years ago used primarily one method, whereas today we use a different method?

In addition, there are many factors that influence a person’s body temperature. It’s funny that we say that for the whole human race, there is one normal body temperature. But your age, physical activity, even the time of day can influence body temperature readings. How do we know that the measurements—either the ones today or the ones long ago—aren’t biased toward a measurement that’s typically higher or lower?

These were my questions when I first heard the news that body temperature has gone down, but a new study addresses some of these doubts. The authors of the study looked at large body temperature databases collected over 157 years. If there were a design flaw or bias in the first study, then you would expect that to be averaged out over many different data sets collected by different scientists over a long period of time.

Ideally, we’d have full details on the instruments, methodology, and demographics of the patients over long periods of time; that would allow a statistician to isolate the many factors that influence body temperature. Here in the real world, that’s not available. But still, a trend in the data emerges, which is that body temperature has consistently gone down over the last century and a half.

What could that mean? The body temperature of any animal is roughly correlated with its metabolism. It could mean that our metabolism has slowed down. A higher body temperature is often a response to inflammation somewhere in your system. People today are healthier and have less inflammation, which could also affect body temperature.

This would have been good to know on those borderline days. You know the borderline days. Your fever was 99.5, parents said, you have to go to school, it’s just one degree. I could have used this study, saying that was two degrees above normal and I clearly was in no shape to be in school.

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