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I think I’m running out of ways to say it: it’s hot.
Saturday’s heat was crushing in New York, with temperatures topping 90 °F (32 °C) and air that was absolutely sticky with humidity. While I prayed for a breeze, I found myself thinking again about a story I wrote two years ago on how the human body deals with extreme heat. At the time, I wrote about how climate change is pushing the limits of what we can handle.
Since it’s been a while, I decided to revisit the topic and catch up with one of the researchers I spoke to for that story. So for the newsletter this week, let’s talk about just how hot is too hot.
Why is heat a problem?
Our bodies need to maintain a relatively stable core temperature of around 98.6 °F (37 °C). The thing is, we’re constantly making heat as our cells carry out their jobs in our bodies and burn food for energy. “It’s just a function of being a mammal,” says Zachary Schlader, a physiology researcher at Indiana University Bloomington.
So in order to keep a balanced temperature, we constantly lose heat. We get rid of most of it via our skin, which throws heat into the air around us. Sweating can help speed that process up.
But this heat loss, and therefore the whole balancing act, can get derailed when we’re exposed to extreme heat. If your body isn’t able to cool itself down fast enough, a whole cascade of problems can start, from stressing out your heart to throwing your kidneys and liver into chaos.
How hot is too hot?
As with most things related to humans and bodies and health, it’s not quite as straightforward as a single number. “As much as I hate to say this, because everything is complicated … it’s complicated,” Schlader says.
A whole host of factors can alter exactly how our bodies will keep the teeter-totter of our internal temperatures balanced. Age, health status, medications, and how acclimatized we are to heat (more on this later) help determine how much heat your body is able to lose. People who are very old or very young have more trouble regulating their body temperature. And activity level will determine just how much heat your body is making that it needs to get rid of.
In general, though, researchers typically put the theoretical limits of the human body at 95 °F (35 °C) on a scale called wet-bulb temperature.
Wet-bulb temperature is a weird metric, but basically, it’s an effort to incorporate both heat and humidity into one number. In short, it’s the measure of what a thermometer would read with a wet cloth wrapped around it. In a dry environment, water evaporating off that cloth will cool things down, lowering the temperature. But if the air is already saturated with humidity, there will be less evaporation, and therefore less cooling.
Take two examples of conditions that would reach a 35 °C wet bulb temperature. With mostly dry air, temperatures have to top 130 °F (54 °C) to reach that limit. On the other hand, a temperature of 109 °F (43 °C) and a relative humidity of 50% would result in the same wet-bulb temperature.
It’s a useful metric because it can give you an idea of how much your sweat will be able to cool you down. Above a wet-bulb temperature of 35 °C, your body won’t be able to lose enough heat through the evaporation of sweat. But that’s still a theoretical limit—one that hadn’t been tested much in humans until recently.
Early research has found that the limit might turn out to be more varied, but lower, than theory would suggest. One 2021 study found that even in healthy young adults, heat loss couldn’t keep up at lower temperatures than the theoretical limit, especially in humid environments.
Bottom line: researchers are still trying to understand where our limits lie when it comes to heat, though we do know it’ll depend a lot on specific environmental and health factors. There’s also some interesting research showing that our heat tolerance can change over time—as we age, yes, but even with the amount of heat we’re exposed to.
How can we handle the heat better?
One thing that I found fascinating when I started looking into extreme heat a few years ago is the concept of acclimatization: our bodies can adjust to the heat.
If you’re exposed to heat consistently, your body will go through a few changes, Schlader says. You will start making more plasma, basically pushing up your total volume of blood. That means your heart won’t have to work as hard to move blood around (one of the major ways we lose heat is through blood carrying it to our skin). The process of sweating also changes—you’ll be quicker to sweat, your sweat will increase in volume, and it will get more dilute, so you’ll lose fewer electrolytes. The whole thing is somewhat akin to how you can adjust to a higher altitude.
There’s been a lot of fighting online this week over a Washington Post story that talked about this exact concept. People argued not only about whether this effect is real, but also about whether it’s a big distraction from the need to address climate change.
I have two things to say after reading way too many comments and digging into this a bit more since my initial reporting two years ago. First, as Schlader pointed out, this is a real effect, and our bodies’ ability to adapt to all sorts of things is absolutely wild. Second, bodily adaptation won’t be the silver bullet that helps protect humans from heat caused by climate change.
There’s a limit to how much difference these physical effects can make—over the course of a few weeks, your body might be able to adjust to handle a couple of degrees’ worth of additional heat, Schlader says. That’s not enough to keep people safe in extreme conditions, especially if they have to work in the heat. There’s only so much heat people can endure—that might vary by person or place, but the limits still exist.
As temperatures continue to break records around the world, we’ll have to rely a lot more on other ways to stay safe. This includes using cooling devices like air conditioners and fans, seeking shade, or stopping physical activity when possible. That’s why heat is such an equity issue: not everyone has access to reliable cooling technology, or the ability to shelter inside when temperatures rise.
For more on the limits of our bodies, check out my 2021 story on the topic. Stay safe out there.
Keeping up with climate
I spoke with NPR’s All Things Considered about new materials called desiccants being used in air-conditioning. (NPR)
→ Check out my full story if you missed it last week. (MIT Technology Review)
There’s some interesting data in this opinion piece, where the author argues it’s “time to chill out” about AC and climate change. As he points out, today heating accounts for significantly more emissions than cooling does globally. (Bloomberg Opinion)
→ If you ask me, emissions from heat don’t cancel the need to improve the efficiency of air conditioners, given how much demand is expected to grow by 2050. I’d still call AC a climate antihero, as I wrote in the newsletter last week. (MIT Technology Review)
Tesla has a history of overly optimistic range projections for some of its vehicles. The company reportedly put together a special team to cancel service appointments related to range concerns. (Reuters)
Maine is stepping up its heat pump game. The state just blew past its goal of installing 100,000 of the devices by 2025 and re-upped the target to 175,000 by 2027. (Canary Media)
Scientists have previously shown that a major ocean current is weakening, but according to a new study, that collapse could come as soon as 2025. The risk is serious, but there are questions about this research and whether it’s overstating the near-term dangers. (E&E News)
→ I’d highly recommend this deep dive that my colleague James Temple took into this topic in late 2021. (MIT Technology Review)
Companies have sold millions of dollars of credits in programs that promise to capture and store carbon in soil on farmland. But some researchers say that the benefits of new agricultural practices aren’t so clear cut. (Science)
File this under weird climate change impacts: acidifying oceans (the result of more carbon dioxide in the atmosphere) are wiping out crabs’ sense of smell. As ocean chemistry gets more wacky, it could affect how crustaceans and other creatures can sense food and predators. (Hakai)
And activity level will determine just how much heat your body is making that it needs to get rid of. In general, though, researchers typically put the theoretical limits of the human body at 95 °F (35 °C) on a scale called wet-bulb temperature.How much heat can the human body take? ›
They found that this upper-temperature limit lies between 40℃ (104F) and 50℃ (122F) when the human body stops functioning optimally. Further studies are needed to understand how this happens and offer insights as heatwaves and unusually warm temperatures continue to impact regions across the globe.What is the maximum heat your body can handle? ›
According to Zach Schlader, a physiologist at Indiana University Bloomington, a wet-bulb temperature of around 95º F, or 35º C, is pretty much the absolute limit of human tolerance.How much heat can the human body take from the sun? ›
Research indicates that the upper temperature limit for humans is probably between 40°C, or 104°F, and 50°C, or 122°F. Extreme heat makes your body work harder to function and could lead to heat-related illness and even death.At what temp does the human body shut down? ›
If the core temperature continues to rise past 40°C (104°F), organs start shutting down and cells deteriorate. An overtaxed heart can go into cardiac arrest. This is heat stroke.Can humans survive 150 degree heat? ›
If you are asking whether a human can withstand an external temperature of 150 degrees Fahrenheit for a few minutes, the answer is yes. But at that external temperature, you have to realise that the internal temperature of the body would likely be elevated, but still relatively within normal limits.Can humans survive 130 degrees? ›
Death Valley, one of the hottest places on Earth, recorded a temperature of 130 degrees last month. In most cases, once a person's core temperature reaches 107.6 degrees, the heatstroke cannot be reversed and will be fatal. If the humidity is low, humans can endure even hotter temperatures.Can your body build up tolerance to heat? ›
Heat acclimatization is the improvement in heat tolerance that comes from gradually increasing the intensity or duration of work performed in a hot setting. The best way to acclimatize yourself to the heat is to increase the workload performed in a hot setting gradually over a period of 1–2 weeks.Can humans survive 140 degrees? ›
You might be wondering about how much external heat a person can tolerate. Live Science writes that most humans can endure about 10 minutes in 140–degree heat before suffering from hyperthermia, a lethal form of which is the aforementioned heat stroke.Is there a limit to heat? ›
Wikipedia says: Above 1.416785×1032 K, all theories break down. So, that is the theoretical limit. In actuality, 7.2 Trillion°F is the highest known temperature, and that temperature was achieved in Large Hadron Collider (LHC) when they smash gold particles together.
The body's ability to cool itself with sweat can accommodate temperatures up to about 115F with good hydration and ventilation. Slightly higher temps for short exposures. Children and elderly persons can not survive temps of 110F for very long. At 200F one would cook to death in short order.What temperature is best for sleeping? ›
The best room temperature for sleep is approximately 65 degrees Fahrenheit (18.3 degrees Celsius). This may vary by a few degrees from person to person, but most doctors recommend keeping the thermostat set between 60 to 68 degrees Fahrenheit (15.6 to 20 degrees Celsius) for the most comfortable sleep.Why do I absorb so much heat? ›
The normal temperature of the human body is 98.60 F or 370 C. However, due to certain external environmental factors, improper diet, hygiene practices and underlying medical ailments, a state arises where excessive heat is absorbed by a person, leading to a rise in body temperature. This is called heat stress.How hot is too hot indoors? ›
It's advisable to keep your home below 80 degrees throughout the summer. A house that's too warm can be dangerous to people, pets, and the soft surfaces in your home. Set the winter temperature to 68 degrees when you're awake and 62 degrees when you're sleeping.How does heat affect the brain? ›
Extreme heat can slow cognition and increase anxiety, research finds. If you're feeling a bit brain-fogged these days, you might not be wrong to blame it on the heat.What are the limits of human survival? ›
The rule of thumb is that humans can survive three minutes without air, three days without water, and three weeks without food, but there are always extraordinary cases—some have gone up to nine days without water.Can humans survive in 200 degree heat? ›
The body's ability to cool itself with sweat can accommodate temperatures up to about 115F with good hydration and ventilation. Slightly higher temps for short exposures. Children and elderly persons can not survive temps of 110F for very long. At 200F one would cook to death in short order.How much heat can the human body take before melting? ›
Most of what a human consists of doesn't have a melting point. So, a person must first pyrolyze into carbon. At that point it will take about 10,000° F to melt the pile of carbon ash leftover after pyrolysis. So, technically, a person cannot be melted.