When Will Extreme Heat Become Unlivable?

[Uncle Joe]

Jun 18, 2025

Heat is the deadliest weather hazard in the U.S. and many places around the world, and it's only getting worse.
The most deadly heat waves so far have been dry heat waves. But a new threat is rising: humid heat waves, aka wet-bulb events. Scientists have identified wet-bulb temperatures where sweat can’t evaporate fast enough to cool the human body. And once this threshold is crossed, it doesn’t matter how much shade or water you have: you won’t survive without environmental cooling like air conditioning.
In this episode of Weathered, we break down: What wet-bulb temperature actually means, why it’s so dangerous, what areas will be affected, and why air conditioning, while essential, isn’t enough.

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[BOSSHOG]

1. It is scary right now

I’m 71, mow my lawn at sunrise and am wiped out in an hour. I’m only a few seconds from the garage and a fan and a refrigerator with plenty of liquids. When I’m done, I’m done for the day.

[synni]

4. Mowing in the morning is harder

All the dew from overnight humidity is on it, making the grass tougher to mow.

Try mowing in the evening, after the sun has baked off all that moisture. The grass won't stick and clump, and pushing the mower isn't as hard on you.

Also, spray WD-40 on the bottom deck and blades, to prevent grass from sticking to those surfaces.

Wet grass sticking to the underside of a mower makes it heavier, harder to push, and it mows less efficiently.

The 18-year-old who mows my lawn keeps mowing it in the morning, and I keep telling him to do it in the evening, but he won't listen. He's exhausted after mowing my small lawn, and he's young and strong.

So please, try mowing just before sunset. I think you'll feel less fatigued.

[enid602]

2. 72 degrees

But it will still be 72 degrees year round on the West Coast, near the coast.

[LastDemocratInSC]

3. At anytime and anywhere the danger becomes extreme when a wet bulb thermometer reads the same as a dry bulb thermometer.

At that temperature evaporation of water stops so the cooling effects of sweating also stop which causes one's internal temperature to begin rising. (This sentence is true)

The moment of greatest risk is when an affected subject begins chanting about being "Too hot" and dons sunglasses and a dapper cap and begins clicking his fingers. If left untreated, jets of mist will eventually emerge from the subject's nostrils and a whistling sound, reminiscent of a tea kettle can be heard. (These sentences are not true)

[anciano]

5. Soon.

[hunter]

6. Which major city will be the first to be decimated by a heat crisis?

I'm sure many of us U.S. American baby boomers will be around to witness it.

Some of us may be among the victims.

[NNadir]

7. I don't have the reference handy, but a 2003 heatwave in France reportedly killed...

...tens of thousands of people. I'm sure if one looks, one can find similar reports all over the world in subsequent years.

This is not something that is in the future - and treating it as such is to say the least, unhelpful - it is something already being observed.

The Journal Nature Reviews Earth and Environment (Vol. 6, pp 193-210) offers an account of mortality in some events. Any epidemiological effort will, of course, be subject to inaccuracies but it is illustrative.