How Global Warming Will Kill You

Blogging is frustrating, because no matter what the post is about, most of the clicks come from having an exciting title. Last week’s post ("The Destruction of the American Cuisine") had more reads in two days than my last 3 “On Secession” posts combined. This is something I should have learned back when I wrote “Everything Wrong with College”. On Secession will remain on hiatus until I can figure out how to rebrand it. So, this week’s post is another entry in the Cassandra series, inspired by personal experience in the American southwest.

Previous Cassandra posts: A.I. — Global Warming — Antibiotics — Pandemic — Virtual Reality — Monocultures  

This is how it starts

Let’s start with some basic, uncontroversial biology: human beings can exist only at specific temperatures. The reason for this is chemical; each enzyme in the body has a temperature range that it can function in. Some ranges are wider than others, but all have hard-stop temperatures whereby enzymatic activity will cease.

A normal Enzymatic curve

There are a lot of different enzymes, and some of them have surprisingly complex interactions — but detailed knowledge of them isn’t necessary (not even to get through medical school). To put it simply, enzymes are biological catalysts, and almost every biological process relies on them. They are extraordinarily sensitive, and evolution has gone to great lengths to optimize the reaction rates (see: reasons for external genitalia in human males). Without functioning enzymes, life becomes impossible.

This is exactly why the hypothalamus raises body temperature in response to infection (i.e. fever). While the primary purpose is somewhat contested, one of the reasons is that fever inhibits the growth of many infectious agents. Viruses and bacteria suffer for the same reason that we do, they are less able to function when their temperature is outside of their ideal range. Raised temperatures also cause white blood cells to function better, making it easier for your body to fight off infection (that it is almost impossible for people to do anything besides lie down and wish for death is considered a positive side effect, albeit an unpleasant one).

As we can see, the temperature range compatible with life is extremely narrow:

Phyrexia Pyrexia is another word for fever

Less than 2 degrees Celsius (4°F) separates hypothermia from fever. 2 degrees is a very coincidental and auspicious number, and I’ll come back to it later, but first let us consider certain morbid implications: what is the temperature at which people die?

This is a difficult question to answer, not just because we can’t exactly test it, but because animals experience temperature differently. The short answer is that the same temperature feels hotter when it’s humid. But to explain in a little more detail, we have to talk about “wet-bulb temperature”.

As anyone who has spent time on both US coasts will attest, 90 degrees Fahrenheit feels very different when the air is dry, compared to when it is humid. Wet-bulb temperature is the attempt to reconcile the two, defined as the lowest temperature that can be reached by evaporating water into the air (often measured by sticking a thermometer in a wet sock and swinging it around. No, that’s not a joke.)

They look really stupid and you'll feel dumb swinging it around

The wet-bulb temperature is always lower than the “dry bulb” temperature because it’s measuring how much it’s possible to cool down (i.e. the difference between standing outside [dry] and standing outside in front of a fan while being misted with water [wet]). The two temperatures approach the same number as the relative humidity of the air increases. When the humidity of the air is 100%, no additional water can evaporate, and the two temperatures are identical. The reason the wet-bulb temperature is always lower is because evaporating liquids create a cooling effect. Since humans are much more like wet socks than pieces of glass or metal [citation needed?], the wet-bulb temperature provides a good approximation of the subjective temperature experienced. Therefore, we can use it to determine the temperature at which people die.

Don’t act surprised! Obviously, there is such a temperature, we already know that all the necessary enzymes shut off outside of their (narrow) ranges, and we know that the main way that human bodies cool themselves is by sweating profusely, taking advantage of the evaporative cooling effect. At some point, the body is no longer able to prevent itself from heating up, and will rapidly go into hyperthermia and die. This chain of events is why heat stroke is so dangerous; a common, real-life example of the phenomenon. Using the wet-bulb reading, we can isolate important temperatures, including the onset of heat stroke, and the temperature above which is death is certain. That temperature is approximately 95 degrees Fahrenheit (35 degrees Celsius).

This is a counterintuitively low number, but it is important to remember that our bodies are constantly generating heat. Hence it is easy to feel overheated at 80°F (27°C), even though a similar internal temperature would be fatal hypothermia; controlled dissipation of heat is necessary to prevent overheating. There are many online calculators available to convert dry-bulb readings to wet-bulb readings (most depend on atmospheric pressure, which influences the percent humidity), a decent dry-bulb estimate of a 95°F wet-bulb reading is around 110-120°F (43-49°C). (Desert climates have lower humidity, so sometimes the 95°F wet-bulb temperature is not reached until over 120°F.)

For context, let’s look at some maps:

Here we have the Average Summer Temperatures (which are always measured in dry-bulb unless otherwise stated), including the average highs…

and lows…

 Based on NOAA data. Maps from Weather.com

But as we know, this is not the whole picture. Because it’s the hottest days that matter, even if they are statistical outliers. So here is a map of the average highest temperature recorded in a typical summer:

Some places in that white patch are hotter than 118, but they've got to cap it somewhere

As we can see, vast swaths of the United States have day(s) during the summer that are incompatible with human life. Literally “so hot you could die”, and people do so with great regularity. And, of course, anomolous record-high heats can occur almost everywhere:

"Come to Lake Havasu, the hottest place in Arizona! Don't go outside!"

It’s not news that people die during heat waves, but what should be a sobering thought is the degree to which we are dependent on functioning air conditioning in order to literally not die. The excuse of “well we have air conditioning” isn’t especially reassuring, because our power system is not designed to provide continual power to every single person on the grid. Excessive use caused, say, by a massive heat wave, quickly overwhelms ordinary power grids. And while worrying about it now is definitely a little silly, over the long term, you actually do have to deal with extraordinary events. You have to worry about things like earthquakes, hundred-year waves, and other rare but predictable events. The longer you plan on living, the more likely it is that you run into something out of the ordinary.

I would not be harping on this if it was merely an American problem:

Although they are, perhaps, disproportionally represented in comment sections, the number of people who insist the world is not warming (despite all the easily accessible evidence to the contrary) is extremely small. Even those who deny that the warming is caused by human activity rarely go that far. The bigger issue is that as the temperature increases, more and more of the world will become uninhabitable.

That angry dark red splotch that goes through Africa and the Middle East? That’s desert. There are two ways to make a desert and the first is obvious — no rain. The second is less so — heat. Plants have enzymes, same as we do. Get them too hot, and they can’t grow. Heat also reduces the amount of precipitation, but this is fiddly and missing the point — the real problems come much sooner. I cannot be explict enough, our fatal temperature from earlier is assumes people are doing nothing but trying to stay cool. Heat stress, whether due to working outside, walking around, or just standing still in the sunlight, effects humans, plants, and animals alike. Some species are more sensitive than others, and there are small variations due to age and health. But, again, the fatal temperature is a hard stop. It’s not something you can fight, something you can just “power through”. It’s not even fighting biology, it’s fighting chemistry. And I can tell you exactly what happens when you fight chemistry: chemistry wins.

I mentioned our temperature range from earlier: 2°C. This is also the number that the Paris Climate Accord is intended to ensure, though the goal of the accord is to prevent the world from warming more than 2°C. Currently, no one believes that keeping to that number is possible, most estimates put the amount of warming at at least 3°C, though if and when the permafrost melts, it’s anyone’s guess what happens next. Optimistic low-ball estimates come in at around 7°C, meaning a 15°F average worldwide temperature increase (though of course cities will heat up much faster). For a sense of what that might entail, look at our heat maps from earlier, but this time add 10 or 15 degrees onto it. We’re looking at the entire country being as hot as the hottest part of an Arizona summer, and that doesn’t even begin to cover what the rest of the world will look like. Buckle your seatbelts folks, because this is going to get rough.