Why Does Humidity Make It Feel Hotter?

Summary

This script delves into the complexities of weather forecasting, emphasizing that temperature isn't the sole indicator of how hot it feels outside. It explains how humidity affects our perception of heat, with sweat not evaporating efficiently in high humidity, leading to a hotter and more uncomfortable feeling. The script clarifies the limitations of relative humidity in predicting comfort levels and introduces the dew point as a more accurate measure. It suggests that a dew point above 18 degrees is when it starts to feel 'sticky and gross,' advising viewers to seek air-conditioned environments on such days.

Takeaways

• 🌡️ Temperature alone isn't the best indicator of how hot or cold it feels outside.
• 💧 Humidity plays a significant role in how our bodies perceive heat because it affects sweat evaporation.
• 🔥 When it's humid, sweat doesn't evaporate as quickly, causing us to retain heat and feel hotter and damp.
• 🌬️ Relative humidity measures how close the air is to being saturated with water vapor, but it's not the best indicator of how hot it feels.
• 🌡️ The saturation point of air increases with temperature, meaning the same relative humidity can feel different on hotter days.
• 🌀 The dew point is a more useful measure of how muggy it feels outside, as it indicates the amount of moisture in the air in absolute terms.
• 🌫️ A higher dew point means more moisture in the air, which can make the environment feel stickier and more uncomfortable.
• ☀️ On a day with 30°C and 50% relative humidity, the dew point would be 18°C, indicating a certain level of mugginess.
• 📈 On a hotter day, like 35°C with the same 50% relative humidity, the dew point would rise to 23°C, making it feel much muggier.
• 🌤️ Meteorologists suggest that a dew point above 18°C starts to feel sticky and uncomfortable, influencing where you might want to spend your day.

Q & A

Why might the temperature not be the best measure of how it feels outside?

Temperature might not be the best measure because it doesn't account for humidity, which significantly affects how hot or cold it feels to the human body.

How does the human body regulate its internal temperature?

The human body maintains a steady internal temperature of 37 degrees Celsius for optimal enzyme function, which is crucial for life-sustaining processes.

What happens to our body when we need to cool down?

When the body needs to cool down, blood vessels dilate to increase blood flow to the limbs for heat loss, and sweat glands produce moisture that evaporates, carrying heat away from the body.

Why does sweat not cool us down effectively in humid conditions?

In humid conditions, the air already contains more moisture, so sweat doesn't evaporate as quickly, which means less heat is carried away, leading to a feeling of being hotter and damp.

What is relative humidity and why isn't it always helpful for determining how hot it feels?

Relative humidity is a measure of how close the air is to being saturated with water vapor. However, it's not always helpful because the saturation point increases with temperature, meaning the same relative humidity can feel different on hotter days.

How does the saturation point of air change with temperature?

The saturation point of air increases with temperature because warmer air can hold more water vapor. As a result, a higher temperature at the same relative humidity means there's more moisture in the air.

What is the dew point and why is it more useful than relative humidity for understanding how it feels outside?

The dew point is the temperature at which air reaches 100% humidity and moisture condenses into dew or fog. It's more useful because it gives an absolute measure of moisture in the air, indicating how muggy it feels.

How does the dew point indicate the actual amount of moisture in the air?

The dew point indicates the actual amount of moisture in the air by showing the temperature at which the air would be saturated with water vapor, regardless of the current temperature.

According to meteorologists, at what dew point does the weather start to feel sticky and uncomfortable?

Meteorologists suggest that if the dew point is above 18 degrees Celsius, it's going to start to feel sticky and uncomfortable.

What is a practical suggestion for dealing with high dew points?

When a high dew point is forecasted, it's suggested to spend the day in places with good air conditioning, such as going to see a movie or hanging out in a bookstore.

Outlines

00:00

🌡️ Understanding Temperature and Humidity

This paragraph discusses the importance of considering humidity when interpreting weather forecasts. It explains that while temperature is a common metric, it doesn't always reflect how hot or cold it feels outside due to humidity's impact. The human body maintains an internal temperature of 37 degrees Celsius, and it cools down by increasing blood flow to the limbs and producing sweat, which evaporates to remove heat. However, in humid conditions, sweat doesn't evaporate as quickly, causing a person to feel hotter and more uncomfortable. The paragraph also clarifies that relative humidity, which indicates how close the air is to being saturated with water vapor, isn't the best indicator of how hot it feels. Instead, the dew point, which is the temperature at which the air would reach 100% humidity and water vapor would condense, is a more accurate measure of how muggy the air feels. A higher dew point correlates with a stickier and more uncomfortable feeling, and meteorologists suggest that a dew point above 18 degrees is when conditions start to feel noticeably uncomfortable.

Keywords

💡Weather Forecast

A weather forecast is a prediction of the expected weather conditions for a specific location and time. In the video, it is mentioned as a common practice people engage in to plan their day or vacations. The script emphasizes that temperature alone, as provided in weather forecasts, might not accurately reflect how hot or cold it feels outside, which is a central theme of the video.

💡Temperature

Temperature refers to the degree of hotness or coldness of the air, typically measured in Celsius or Fahrenheit. The video script points out that while temperature is a standard measure in weather forecasts, it may not be the best indicator of how it actually feels outside, especially when humidity is high.

💡Humidity

Humidity is the amount of water vapor in the air. The script explains that high humidity can make it feel hotter than the actual temperature suggests because it affects the rate at which sweat evaporates from the skin, which is a key process in the body's natural cooling mechanism.

💡Relative Humidity

Relative humidity is a measure of the current amount of moisture in the air relative to the maximum amount the air can hold at a given temperature. The video script discusses how relative humidity can be misleading because it does not account for the varying saturation points at different temperatures.

💡Saturation Point

The saturation point is the maximum amount of water vapor the air can hold at a specific temperature before it condenses into liquid. The script uses this concept to explain why relative humidity alone is not a good indicator of how hot it feels outside, as the saturation point increases with temperature.

💡Dew Point

The dew point is the temperature at which air becomes saturated with water vapor and begins to condense into dew or fog. The video emphasizes the dew point as a more useful measure than relative humidity because it provides an absolute measure of moisture in the air, which directly affects how 'sticky' or 'gross' it feels.

💡Evaporation

Evaporation is the process by which a liquid turns into vapor. In the context of the video, the script explains that when it's humid, sweat does not evaporate as quickly from the skin, which is crucial for the body's cooling process and thus affects how hot or uncomfortable one feels.

💡Blood Vessels

Blood vessels are the body's network of tubes that carry blood throughout the body. The script mentions that when the body needs to cool off, blood vessels dilate, allowing more blood to flow to the extremities to release heat through the skin.

💡Sweat Glands

Sweat glands are the glands in the skin that produce sweat. The video script explains that these glands are part of the body's cooling system, as the evaporation of sweat helps to remove heat from the body. However, in humid conditions, the effectiveness of this cooling mechanism is reduced.

💡Thermometer

A thermometer is an instrument used to measure temperature. While not explicitly mentioned in the script, the concept of a thermometer is implied in the discussion of temperature measurements, which are a fundamental part of weather forecasts and the video's exploration of how temperature relates to perceived heat.

💡Meteorologists

Meteorologists are scientists who study the atmosphere and its physical phenomena, including weather forecasting. The video script references meteorologists as authorities who provide insights into the dew point and its significance in predicting how the weather feels, thus tying the script's discussion to the expertise of professionals in the field.

Highlights

Temperature is not the best measure of how it feels outside.

Humidity is an important factor affecting how hot it feels.

The body maintains an internal temperature of 37 degrees Celsius for enzyme function.

Blood vessels dilate and sweat glands produce moisture to cool the body.

Sweat evaporation is hindered in humid conditions, trapping heat.

Relative humidity measures how close air is to saturation but isn't very helpful for feeling temperature.

Saturation point increases with temperature, affecting relative humidity readings.

Dew point is a more useful measure of how hot it feels, indicating absolute moisture in the air.

A higher dew point correlates with a more uncomfortable, muggy feeling.

Dew point above 18 degrees often signals a sticky and uncomfortable day.

Meteorologists suggest seeking air conditioning when the dew point is high.

The dew point can be used to predict the comfort level outside.

Relative humidity can be misleading due to its dependency on temperature.

The saturation point's increase with temperature affects the perception of humidity.

Dew point provides a clearer picture of the actual moisture content in the air.

A dew point of 18 degrees or higher can make the environment feel muggy and uncomfortable.

The importance of understanding dew point for personal comfort and planning outdoor activities.

Transcripts

Whether you’re planning your next vacation, or you just want to know how many layers you’ll

need to put on in the morning, you probably check the weather forecast pretty often.

But you should know, before you go out with that extra jacket, that the temperature might

not be the best measure of what it actually feels like outside.

Humidity is important, too, which is why you might sometimes think the forecasters must

have been wrong, because it’s definitely about ten degrees hotter right now and you’re

covered in sweaty grossness.

Your body’s built-in thermostat likes to keep your internal temperature at a steady

37 degrees Celsius so that all of your enzymes can do what they’re supposed to do... you

know … keeping you alive.

That's the temperature they like.

When you need to cool off, your blood vessels open up, letting blood flow to your arms and

legs so heat can escape through your skin.

Your sweat glands also start to produce moisture, which takes a bunch of heat with it when it

evaporates.

And it’s this sweat evaporation that runs into a bit of a problem when it’s humid

out.

When there’s more moisture already in the air, your sweat doesn’t evaporate as quickly.

You end up holding onto the extra heat, so you just get hotter … and damp.

Awesome.

You’ll usually see what’s known as relative humidity in the forecast, which tells you

how close the air is to saturation, where there’s as much water vapor in the air as

possible.

But it turns out that the relative humidity forecast also isn’t super helpful for figuring

out how hot it’ll feel, because the saturation point increases with the temperature.

The hotter it gets, the more energy water molecules have, which means more of them can

zoom around in the gas phase.

So you might have two days where the relative humidity is 50%.

But if it’s 30 degrees Celsius the first day and 35 degrees the second day, there’s

way more moisture in the air on the second day, because it’s 50% of a much higher saturation

point.

Which means that the humidity on the second day is going to feel way worse.

So even though people talk about it a lot, the relative humidity forecast isn’t a great

way to tell how hot it feels.

The dew point is a lot more useful.

That’s the temperature where, given the amount of moisture in the air, it would reach

100% humidity and the moisture would condense into dew or fog.

What’s helpful about the dew point is that it tells you how much moisture is in the air

in absolute terms.

So the higher the dew point, the grosser you’ll feel, because there’s more moisture in the

air.

On that first day, for example, where it was 30 degrees out with 50% relative humidity,

the dew point would be 18 degrees.

On the second day, though, the dew point would be 23 degrees, which tells you that it would

feel a lot muggier, even though the relative humidity would still be 50%.

According to meteorologists, a good rule of thumb is that if the dew point is above 18

degrees, it’s going to start to feel sticky and gross.

So if you see a higher dew point in the forecast, you might want to spend the day somewhere

there’s lots of good air conditioing.

Go see a movie, or hang out at Barnes and Noble, reading books.

Thanks to patreon patron Miranda McCarthy for asking this question, I've actually been

curious about it, so thank you.

And thanks to all our patrons, who keep these answers coming.

If you’d like to submit a question to be answered, you can go to patreon.com/scishow.