Are We Beginning To Hit the Limits of Human Survivability?
We Need To Talk About Wet Bulb Temperature, and What the Latest Research About It Reveals
by umair haque
There’s a term you’ve heard thrown around lately. It’s suddenly started to gain traction, enter public awareness a little — as we go from what UN Secretary General Antonio Guterres has called the era of global warming to “the era of global boiling.”
Wet Bulb Temperature. But what does it mean?
We’re going to discuss it. Because if you don’t know about it yet — you will. In the not so distant future, we won’t check just the temperature before we head outdoors — we’ll check the “heat index,” or the wet bulb temperature, or whatever this comes to known generally as. It’s time, then, to start becoming literate with it now.
See that chart above? That’s the limits of human survivability. It’s effectively wet bulb temperature. Take a second to really look at it. It’s a new way to think about temperature for a lot of us. What does it say? At 50 degrees Celsius, and 8 to 15 percent humidity, we hit the danger zone. That’s 122 degrees Fahrenheit — and places around the world are already beginning to edge towards, if not hit, that limit.
This chart comes from the BBC, where an intrepid journalist went into the lab — to experience extreme heat for himself. We’ll come back to him. The chart itself is based on the most cutting-edge research we have into wet-bulb limits, which is why I used it — you see, our understanding of this new concept called “wet bulb temperature” is advancing, too. So what does this cutting-edge research say? What makes it different? Let me cite it directly.
When the idea of wet bulb temperature was created, it meant this: “Wet-bulb temperature is read by a thermometer with a wet wick over its bulb and is affected by humidity and air movement. It represents a humid temperature at which the air is saturated and holds as much moisture as it can in the form of water vapor; a person’s sweat will not evaporate at that skin temperature.” In other words, at that temperature, the human body can’t cool itself anymore. The brain swells, the organs stop working, and shutdown happens — it’s ugly.
So wet bulb temperature is like an index: it’s like the temperature as we think of it, with humidity factored in. Maybe one way to think about is it how “it feels,” or as “heat stress.” Now we have to think of two temperatures to understand the environment — “the” temperature, and it’s real equivalent on human functioning.
What’s important to understand is that wet-bulb temperature is lower than “the” temperature — for example, if it’s 40 C outside, with 50 percent humidity, the wet-bulb temperature is much lower, because of course the humidity reduces the cooling function of the human body. It’s unfortunate in a way, politically, that this is how we have to express it, because of course, deniers will leap to saying “it’s not that hot!” — when in fact the takeaway message is the precise opposite.
This temperature’s limit for us humans — as the research says — was theorized to be 35 degrees Celsius. But this new research matters because it’s the first time it’s been investigated in a lab — not just theorized. What did the researchers find?
Emphasis mine. That is, the old theory significantly overstated the limit of human survivability. In the lab, they found what the chart above shows — that at temperatures far lower, the limit’s hit. Now, to understand this well, things get a little complex. A temperature of 50C with a humidity of 10–15 percent equals a “wet bulb temperature” of…about 30 degrees or so.
Which is where the research comes in again, with striking conclusion.
See how much lower that is than the old theorized limit? It’s 5 to 10 degrees Celsius lower — 9 to 18 degrees Fahrenheit. That’s a striking difference — a serious reduction of the limits of human survivability.
What’s more, the subjects — and I won’t get into the super details here — were young and healthy, as they often are in these sorts of experiments. Not old and already ill or sick — we can readily assume that the limits for people not in such good shape are even lower.
Now. All that’s complex, abstruse, maybe even difficult to understand. Like I said, becoming literate with this idea takes time — and we’re all still learning. That brings us back to the chart. I’ve thought of long making one myself, but thankfully, the BBC made a very good one, based on all this cutting edge research — it represents the apex of what we know about human survivability in an age of climate change really.
The chart matters, too, because, well, it’s easy to understand. A lot easier than trying to convert “the” temperature into the “wet bulb temperature” in your head, which, let’s face it, is something most people are never going to be able to do. So let’s look at it, because its results are striking.
Places like Arizona have recently had stretches of days running above 110 degrees Fahrenheit. That’s about 43 degrees C. How dangerous is that, really? The chart tells us that temperature, at just 35 percent humidity, human beings begin to enter the danger zone.
Luckily, Arizona’s pretty dry — a desert, basically — you might think. The weather forecast today in Phoenix? LOL — I’m not making this up, I just looked it up, and the results made me…shudder. 111 degrees Fahrenheit — with a humidity of…35 percent.
In other words, it looks like it’s hitting the danger zone…right now.
Now, there’s obviously a lot of caution that you can ascribe to that. As the day goes on, humidity drops, for example. The point isn’t that I’m making a weather prediction, and I’m definitely not saying “there’s going to be a wet bulb event today in Phoenix, Arizona!!” We’re discussing an idea, and its impact on us, and what we can say is this.
The limits of human survivability are lower than we once used to think.
And the planet’s heating up faster than we thought it would.