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Abstract

ns that the planet would have to warm to an average surface temperature of 122F to be considered generally unsurvivable. At current warming rates of 0.14F per decade, it will take the planet another 4,750 years to reach these temperatures. So we have time.However, these numbers are very basic and do not fully encompass the reality of outdoor air temperatures and how the body functions in different levels of heat and humidity. The complete answer is much more complicated and opaque than simply slapping 122F on the planet and calling it a day.<h1 id="6e51">Wet-Bulb Temperature</h1>The truth of the matter is that far more goes into survivability than simply the number on the mercury. One of the ways that scientists measure temperature is called wet-bulb temperature. Wet-bulb temperature measures the heat by using a special thermometer draped with a wet cloth. The cloth is soaked in water at room temperature, and then air is pushed over the thermometer. This gives scientists a look at the temperature in a way that is more pertinent to human beings.Human beings sweat, and the temperature on the skin is more akin to wet-bulb temperature than it is to the regular temperature. Wet-bulb temperature takes into account humidity and evaporation. The results using this method are surprising.Wet-bulb temperature varies greatly from the air temperature depending on the humidity. For example, in extremely dry environments, the wet-bulb temperature is much lower than the air temperature. It can be 110F outside but in the shade, the wet-bulb temperature might only be 88F if the humidity levels are 30% or lower.Scientists have found that humans start to struggle mightily in wet-bulb temperatures that are 95F or higher. But these numbers are actually very difficult to achieve on a regular basis.<a href="https://www.pnas.org/doi/full/10.1073/pnas.0913352107">A study in 2010</a> found that the “estimated that a wet-bulb temperature of 35 C — equal to 95 F at 100% humidity, or 115 F at 50% humidity — would be the upper limit of safety, beyond which the human body can no longer cool itself by evaporating sweat from the surface of the body to maintain a stable body core temperature.”But even during the hottest heat waves of 2022 in some of the most humid places on Earth, such as Delhi, the wet-bulb temperature was only recorded at 92F at its peak. That is encouraging and shows that we are nowhere near reaching the levels where the planet becomes uninhabitable.This means that humans can actually tolerate much higher levels of heat, given that they can sweat and cool themselves appropriately. Throw in shade and shelter, and you have a much higher limit of survivability than first expected.In dry climates, humans can tolerate much higher levels of heat for much longer than people th

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ink. These margins shrink dramatically when humans are forced to endure high heat in highly humid environments.No doubt, heat waves are incredibly dangerous. In fact, heat waves kill more people than most other natural disasters on an annual basis. But they are by no means ubiquitous killers. If high heat and humidity had the power to wipe out humanity places like Karachi and Austin, Texas would have been depopulated by now. Instead, these places are thriving even in spite of rising temperatures.<h1 id="c829">Mitigation Through Mass Migration</h1>What all of this data means is that humanity as a species will be able to survive for a long time if they migrate to places where the wet-bulb temperatures remain within tolerable limits. Humans might have to leave the humid belt around the equator and move to more northern climates, or they might have to learn to endure drier climates.Mediterranean climates with dry air and relatively high heat will be easier to live in for longer on a warming planet than super humid locations. Similarly, some deserts, like the American Southwest or parts of China, could also be better suited for human survival on a hot planet due to persistent dry air. Humans can move farther north into areas like Siberia and Canada, which have some of the lowest population densities on the planet. In the future, these places might be filled with prime real estate and millions upon millions of people.Migration can help keep humans ahead of the warming curve.<h1 id="f638">Verdict</h1>Given all of this information, humanity will be able to survive for a very, very long time, even in the face of dire global warming. Surviving might not be fun, but it will be possible. People might need to move to different climates than they typically live now, but there are plenty of places on Earth where surviving a hot planet will be more than doable.Some areas, like Miami or Delhi, might become uninhabitable faster than places like Seattle or parts of China, but there will be plenty of places for humans to live where they won’t feel too many effects of extremely high heat.It will take thousands of years for the planet to warm to a point where the entire surface is too hot for humans to survive on a day-to-day basis.So, how hot can it get before humans can no longer survive? Very, very hot. The average ambient air temperature would have to soar above 100F, and it would have to be accompanied by high humidity to become lethal for large numbers of people. Otherwise, people will be able to seek shade, shelter, and new regions to live in. The species will endure for a very long time even with a rapidly warming planet.<figure id="1c0d"><img src="https://cdn-images-1.readmedium.com/v2/resize:fit:800/1*4AnK9mfzD_r39fCr43qJNg.png"><figcaption></figcaption></figure></article></body>

How Hot Can It Get Before Humans Can’t Survive?

Not as simple as it sounds

The planet has been gradually warming since at least 1880. In the past 150 years, global temperatures have risen 0.14° Fahrenheit per decade, resulting in 2023 being the hottest year on record. This warming trend has sparked alarm in the scientific community and has provoked a global backlash against fossil fuels. As the planet continues to warm, it raises an obvious question. How hot can it get before humans can no longer survive?

This is an interesting question and one that has kept people up at night. Is the planet ever going to get so hot that humans can no longer survive? The answer to that question is complicated, but the good news is that such a future is a long way off, if it even exists at all.

A combination of factors influences the answer. First, you have to understand that human resistance to heat is based on wet bulb temperature, an obscure way of measuring heat, and not air temperature or even heat index. Second, the ability to migrate and adapt makes human extinction due to global heat extremely unlikely.

The Easy Answer

According to scientific studies, the human body starts to break down during prolonged exposure to temperatures between 40℃ (104F) and 50℃ (122F). If you are caught in extreme temperatures like this, your body has to work overtime to keep itself cool. Heart rate will go up. Mental functions start to slow down. Blood flow rates increase. People start sweating profusely in these kinds of temperatures.

In the worst case scenario, a person will suffer a heat stroke and could potentially wind up dead if their body is not cooled down fast enough. This range is considered the most dangerous temperature zone for humans.

Any temperatures above 104F could be deadly. Temperatures over 122F are considered to be generally unsurvivable over long periods of time without shelter and proper cooling mechanisms.

Temperatures below 104F can also be dangerous. Humans start sweating uncontrollably at 89F, and temperatures between 90F and 100F can still cause issues, but they are easier to mitigate, and the exposure times are much longer than they are at 104F and up.

That means that the planet would have to warm to an average surface temperature of 122F to be considered generally unsurvivable. At current warming rates of 0.14F per decade, it will take the planet another 4,750 years to reach these temperatures. So we have time.

However, these numbers are very basic and do not fully encompass the reality of outdoor air temperatures and how the body functions in different levels of heat and humidity. The complete answer is much more complicated and opaque than simply slapping 122F on the planet and calling it a day.

Wet-Bulb Temperature

The truth of the matter is that far more goes into survivability than simply the number on the mercury. One of the ways that scientists measure temperature is called wet-bulb temperature. Wet-bulb temperature measures the heat by using a special thermometer draped with a wet cloth. The cloth is soaked in water at room temperature, and then air is pushed over the thermometer. This gives scientists a look at the temperature in a way that is more pertinent to human beings.

Human beings sweat, and the temperature on the skin is more akin to wet-bulb temperature than it is to the regular temperature. Wet-bulb temperature takes into account humidity and evaporation. The results using this method are surprising.

Wet-bulb temperature varies greatly from the air temperature depending on the humidity. For example, in extremely dry environments, the wet-bulb temperature is much lower than the air temperature. It can be 110F outside but in the shade, the wet-bulb temperature might only be 88F if the humidity levels are 30% or lower.

Scientists have found that humans start to struggle mightily in wet-bulb temperatures that are 95F or higher. But these numbers are actually very difficult to achieve on a regular basis.

A study in 2010 found that the “estimated that a wet-bulb temperature of 35 C — equal to 95 F at 100% humidity, or 115 F at 50% humidity — would be the upper limit of safety, beyond which the human body can no longer cool itself by evaporating sweat from the surface of the body to maintain a stable body core temperature.”

But even during the hottest heat waves of 2022 in some of the most humid places on Earth, such as Delhi, the wet-bulb temperature was only recorded at 92F at its peak. That is encouraging and shows that we are nowhere near reaching the levels where the planet becomes uninhabitable.

This means that humans can actually tolerate much higher levels of heat, given that they can sweat and cool themselves appropriately. Throw in shade and shelter, and you have a much higher limit of survivability than first expected.

In dry climates, humans can tolerate much higher levels of heat for much longer than people think. These margins shrink dramatically when humans are forced to endure high heat in highly humid environments.

No doubt, heat waves are incredibly dangerous. In fact, heat waves kill more people than most other natural disasters on an annual basis. But they are by no means ubiquitous killers. If high heat and humidity had the power to wipe out humanity places like Karachi and Austin, Texas would have been depopulated by now. Instead, these places are thriving even in spite of rising temperatures.

Mitigation Through Mass Migration

What all of this data means is that humanity as a species will be able to survive for a long time if they migrate to places where the wet-bulb temperatures remain within tolerable limits. Humans might have to leave the humid belt around the equator and move to more northern climates, or they might have to learn to endure drier climates.

Mediterranean climates with dry air and relatively high heat will be easier to live in for longer on a warming planet than super humid locations. Similarly, some deserts, like the American Southwest or parts of China, could also be better suited for human survival on a hot planet due to persistent dry air. Humans can move farther north into areas like Siberia and Canada, which have some of the lowest population densities on the planet. In the future, these places might be filled with prime real estate and millions upon millions of people.

Migration can help keep humans ahead of the warming curve.

Verdict

Given all of this information, humanity will be able to survive for a very, very long time, even in the face of dire global warming. Surviving might not be fun, but it will be possible. People might need to move to different climates than they typically live now, but there are plenty of places on Earth where surviving a hot planet will be more than doable.

Some areas, like Miami or Delhi, might become uninhabitable faster than places like Seattle or parts of China, but there will be plenty of places for humans to live where they won’t feel too many effects of extremely high heat.

It will take thousands of years for the planet to warm to a point where the entire surface is too hot for humans to survive on a day-to-day basis.

So, how hot can it get before humans can no longer survive? Very, very hot. The average ambient air temperature would have to soar above 100F, and it would have to be accompanied by high humidity to become lethal for large numbers of people. Otherwise, people will be able to seek shade, shelter, and new regions to live in. The species will endure for a very long time even with a rapidly warming planet.