Wet bulb temperature: The crucial weather concept that actually tells us when heat becomes lethal

[Nevilledog]

Link to tweet

https://www.salon.com/2021/07/18/wet-bulb-temperature-climate-change/

The most insidious threat posed by climate change may lie in how it exacerbates existing hazards — making all our problems, conflicts, and vulnerabilities harder to deal with. (Three recent examples, for instance: forest fires intensified by previous heat waves, aggravated immigration pressures, and increased risks from infectious diseases, including future pandemics.) These multiple layers of cause and effect are complex, and make it harder to recognize the damage we are causing.

But sometimes the effects of human-caused global warming is not so subtle and indirect. Indeed, it is quickly becoming dreadfully clear that we can expect more frequent and intense heat waves. Heat waves are already among the deadliest "natural" disasters, and if one could invest in the growth of their destructive power, now would be a good time to do so.

What is less well recognized is that when it comes to heat stress, and where and when things will get bad, not all heat is created equal. Record high temperatures make headlines because we are intimately familiar with these numbers. Yet record temperatures do not tell the full story. When it comes to the brave new climate world we are creating, we need to get familiar with something called "wet bulb temperature" — a much more meaningful concept to ascertaining when hot weather conditions become dangerous. Wet bulb temperature even tells us where and when our cities will become uninhabitable.

What is wet bulb temperature anyway?

The normal temperature of a healthy human is about 98 °F (37 °C). So why don't we feel most comfortable when that's the temperature of the air around us? Because our bodies are engines, burning food to do work, and engines need to lose heat to their surroundings, or they overheat and stop working. As in, die.

*snip*

[Wounded Bear]

1. K & R...for visibility...nt

[Hoyt]

2. Folks who live in the South can tell you about the impact of humidity.

From the linked article:

"Wet bulb temperature also explains why sky-high temperatures in places like Arizona are typically not lethal. Even a warm 100 °F (38 °C) May day in Tucson with relative humidity of 20% is a relatively comfortable wet-bulb temperature of 70 °F (22 °C). But the same dry bulb temperature with the average relative humidity in Jacksonville (75%) leads to a wet bulb temperature of 94 °F (34 °C), close enough to human body temperature to cause severe and potentially fatal heat stress."

"And while extreme temperatures usually get the headlines, globally, humidity dominates wet bulb temperature."

[panader0]

6. This is a good definition. I guess the "bulb" thing threw me.

I live in Az and it was very dry this year, record heat, until two weeks ago. Lots of rain since.

[susanr516]

12. I live on the TX Gulf Coast

With our high humidity, 94 feels like 114. The real killer is that we can expect 60 days when the temperature never drops below 78 with 98% humidity, for a heat index of 81. I love living here, but July and August are brutal.

[NH Ethylene]

3. We need this in weather forecasts instead of the heat index.

We need to be able to look on a chart and know how safe it is outside during heat waves.

This NOAA site gives more info on wet bulb numbers and survival.

https://research.noaa.gov/article/ArtMID/587/ArticleID/2621/Dangerous-humid-heat-extremes-occurring-decades-before-expected

[Kaleva]

4. We may be very near or have passed the tipping point.

"In the study, Raymond and colleagues analyzed data from nearly 8,000 weather stations collected between 1979 and 2017, finding that some coastal subtropical locations have already reported a wet bulb temperature of 35° Celsius.

"Previous studies projected that this would happen several decades from now, but this shows it's happening right now," Raymond said. "The times these events last will increase, and the areas they affect will grow in direct correlation with global warming."

Furthermore, the researchers found that occurrences of dangerous wet bulb temperatures of over 27°C have more than doubled since 1979."

https://www.newsweek.com/hot-humid-weather-human-body-tolerate-here-1502624

[SheltieLover]

5. K&R!

[Nevilledog]

10. ...

[NutmegYankee]

7. I use the dew point temperature as a reference.

https://www.weathergamut.com/2018/07/25/weather-lingo-humidity/

[Lars39]

8. I learned today that hot and humid weather can cause low blood sugar.

This would also surely contribute to physical distress.

[c-rational]

9. K&R - NYC just recorded its highest dew point yesterday.

[LudwigPastorius]

11. Anecdotally, from living in the North Texas area for 50 years, I can tell you...

that the climate is becoming less subtropical and more tropical. (when it's not having record breaking cold snaps)

Humidity and rain have been high all summer this year, and the mosquitoes are way out of control.

[VGNonly]

13. But it's a dry heat...

...most of the year in my area it's a damp cold.