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What is wet bulb temperature?

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“In Death Valley, California, one of the hottest places on Earth, temperatures often get up to 120°F — but the air is so dry that it actually only registers a wet bulb temperature of 77°F. A humid state like Florida could reach that same wet bulb temperature on a muggy 86° day.”

What is wet bulb temperature and why is this measurement such an important metric to know?

This Grist video explains: Wet bulb temperature is the measure of humid heat—”essentially the temperature we experience after sweat cools us off.” It’s measured by a thermometer covered with a wet cloth. Via

“As water evaporates from the cloth, evaporation cools the thermometer. This mirrors how the human body cools itself with sweat.”

wet bulb
Human bodies are designed to work properly at around 98°F (37°C). When the humidity is higher, it’s harder for sweat to do what it’s supposed to do: Cool bodies down. The science from Grist:

“Sweat works by using a physics hack called evaporative cooling. It takes quite a bit of heat to turn water from a liquid to a gas. As droplets of sweat leave our skin, they pull a lot of heat away from our bodies. When the air is really dry, a little bit of sweat can cool us down a lot.”

evaporative cooling

“Humid air, on the other hand, already contains a lot of water vapor, which makes it harder for sweat to evaporate. As a result, we can’t cool down as well.”

Serious health effects can also occur at lower wet bulb temperatures if someone isn’t sweating enough or taking proper precautions. “Staying well hydrated,” explains Scientific American, “and seeking areas in which to cool down, even for short periods, are important in high heat.”

Via Yale School of the Environment: “Scientists have known for over 150 years how increased carbon dioxide in the atmosphere (from fossil fuel burning and land use change) acts like a heat-trapping blanket, causing global warming.”

And from Sir David Attenborough: “The plan for our planet is remarkably simple: Reduce our impact by making sure that everything we do, we can do forever,” starting with immediately replacing fossil fuels with clean energy.

• Wet Bulb Temperature, a United States Map from the National Weather Service.
• Heat Wave Safety from The Red Cross.
• Prepare for Extreme Heat with
• Evaporative Cooling with Liquids: A vaporizing science project at Scientific American.
• Yale Experts Explain Climate Change
• Renewable Resources, a National Geographic encyclopedic entry

Learn more about solutions for climate change, including:
• How to Save Our Planet with Sir David Attenborough.
• How can nature be used as a tool to restore ecosystems?
• Imagine a world without fossil fuels
Why are peatlands so important?
How can design make climate-resilient buildings?

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