"Extreme Heat" seems to be 37-40 degrees Celsius which is bafflingly mundane to me as an Australian who grew up in rural New South Wales. We'd pack 30 kids and a teacher into an un-airconditioned classroom with just a ceiling fan and the windows open in that temperature.

I imagine the buildings there just aren't built to support that heat plus the body height of hundreds or thousands of attendees?

People tend to rely on air temperatures when in reality the lethality of heat is probably more linked to the wet-bulb temperature.

The human body has a natural resting temperature of about 37°C, and metabolism of course generates more heat constantly, so we constantly have to shed that heat. When the temperature is low, we can rely purely on conducting the heat into the atmosphere to shed the heat (which is probably why internal body temperature is higher than the atmosphere!). At higher temperatures, conduction is less efficient, or sometimes even adds heat load into the system (at above 37°C, obviously), so we start relying on evaporative cooling (i.e., sweat) to cool us down.

The wet-bulb temperature is the minimum temperature that can be reached by evaporative cooling. So when the wet-bulb temperature is in the mid-30s °C… people start to become literally unable to regulate their core body temperature, and the heat is lethal. Wet-bulb is largely a combination of the temperature and humidity, but unfortunately, it's not typically reported in most weather reports, so people go off of the air temperature (and the humidity) that is reported.

Which is a long-winded way of saying "the humidity matters a lot for how much a given temperature is bearable." I don't know what environment you come from purely by rural New South Wales, but my first guess is the semi-arid and thus low-humidity bush regions of the state, which means the apparent wet-bulb temperature of 37-40°C would be a lot lower than the equivalent 37-40°C for most of the humid continental climates of Europe.

Looking just at ambient air temperature is an easy mistake to make. I used to be like that, always surprised why people whine so much near the coast in winter with their comfortable numbers and thinking I’m superhuman compared to them. I stopped when I learned first-hand that their negative 17 degrees feel as bad as our negative 30.

If you live in a town in New South Wales where the average humidity is less than 50% in the wettest (or, should I say, least dry) season, you might not understand what it feels like in London where the average doesn’t dip below 65% any time of year.

Today London will feel at least 4 degrees Celsius hotter than Hong Kong. The latter is already an extremely unpleasant place to be in these conditions (and had in fact its own very hot weather warning issued), and unlike London it has a very strong culture of air conditioning.

4 degrees might seem like not a lot, but heat extremes are a tricky beast. Once your body cannot evaporate heat fast enough, you’re literally toast.

Humidity makes a big difference in how stressful the temperature is (wet bulb temperature accounts for this somewhat). The age of the attendees and the tendency of the building to heat would also be factors.

We need a humidity comparison to go with temperature.

I grew up in a humid city and summers were unbearable. Now I live in a dry climate and 30°C is pretty comfortable.

I guess it's different if you are used to it. 40 degrees is absolutely not normal here. Even 35 is very unusual.

Euro buildings are built to keep heat in. Aus buildings are leaky tents.

Yeah we ve reached stupid levels of weather scare. France did have some extreme temperatures over 42, but 40 is a typical Mediterranean heat wave, not Armageddon

And that was after running around a semi-arid playground playing 'tips' or touch footy during recess and lunch!

40C in the Atlantic Spain with the Foehn effect (weather for today and tomorrow) would make 30C in Australia a joke.

The humidity here it's hell. You feel 35C like ~42C in dry climates.

How does the humidity in rural New South Wales compare to London?

I imagine people who lived in the UK for generations have genes that are adapted to a more mild, cooler climate.

https://www.cell.com/trends/genetics/fulltext/S0168-9525(20)...

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the British are notoriously sensitive to heat. They'll call 30 Celsius weather a heat wave.