[Official discussion] Surviving severe heat

Carlotta SusannaStaff - July 30, 2021

[See the full post at: How to survive severe heat]

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> As the climate crisis worsens, official projections show that many areas of the world will become “uninhabitable for humans” for at least part of the year. eg. Phoenix, Arizona is projected to be over 95°F for half of the year.

> That 95°F (35°C) number is important because it’s the “wet bulb” temperature at which the human body can no longer cool itself down.

You’re conflating two different things here – wet bulb temperature and actual temperature, and they are very rarely the same. Wet bulb temperature is basically the temperature of a thermometer if you stick it in a soaking wet sock and then swing it around to let the water evaporate, and so is VERY dependent on humidity. Phoenix is very dry, so the highest wet bulb temperature it hit in all of 2020 was 76.8 degrees. 

There are areas of the world where peak wet bulb temperatures are starting to hit 95, but they’re few and far between. Phoenix isn’t one of them.

 

Thanks for the feedback. We were on the same page conceptually, so we’ve updated some wording to make it clearer. Certainly understand that Phoenix doesn’t hit those wet bulbs today, but we’ve seen projections where it’s included.

See the image near the intro with the ProPublica map, which shows the wet bulb projections in AZ. From their article: 

“While some areas we don’t usually think of as humid, like southwestern Arizona, will see soaring wet bulb temperatures because of factors like sun angle, wind speed and cloud cover reacting to high temperatures,” according to Hannah Hess of the Rhodium Group.

 

I’m pretty sure that propublica map (assuming you mean the one that includes the quote “with some counties in Arizona experiencing temperatures above 95 degrees for half the year.”) is raw, not wet bulb, temperatures. Their map of areas with high wet bulb temperatures isn’t particularly useful either as they don’t define “high” (75 degrees F wet bulb is really damn hot to my northern sensibilities, but perhaps not to someone who grew up on the LA gulf coast), or what the change will be. (A map saying “this area will have 70 days a year of these temperatures” would be more useful if it came with something saying that it only used to have 10 days a year of the same)

> where it’s projected that more than half of the year will be over 95°F and changing weather will turn their traditionally dry heat into a more humid environment at risk of wet-bulb temps.

This still feels like rather poor wording – even Alaska has wet-bulb temperatures in the middle of the winter, as it’s just another scale. Changing it to “dangerous wet-bulb temps” might work.

 

FWIW the ProPublica map is labeled by them as “days with high wet bulb temps.” I generally trust their work / methodology, but am of course open to changing it if something is wrong!

Made the change to “dangerous wet-bulb temps”, thanks for the suggestion.

 

A new study suggests that a dangerous level of wet bulb temperature can be reached at lower temperatures than previously expected. Previously it was thought that a temperature of 35 C (95 F) at 100% humidity, or 115 F (46 C) at 50% humidity – would be the upper limit of safety.

Now, it’s more like a wet-bulb temperature of 31 C (88 F). That would equal 31 C at 100% humidity or 38 C (100 F) at 60% humidity.

Link to the news article, which links to the study: https://theconversation.com/how-hot-is-too-hot-for-the-human-body-our-lab-found-heat-humidity-gets-dangerous-faster-than-many-people-realize-185593