7 ms·

This is the key part: > A sustained wet-bulb temperature exceeding 35 °C (95 °F) is likely to be fatal even to fit and healthy people, unclothed in the shade n

This is the key part: > A sustained wet-bulb temperature exceeding 35 °C (95 °F) is likely to be fatal even to fit and healthy people, unclothed in the shade next to a fan; at this temperature human bodies switch from shedding heat to the environment, to gaining heat from it. The important thing is that passive/evaporative cooling simply stops working. In fact, sitting in front of a fan would actually speed up your death. You'll also die shockingly quickly (20 or so minutes, even for healthy, fit adults). The only thing that can save you is: - air conditioning - getting in a cold tub - going somewhere cooler (obviously) like a basement or parking structure There are two thing that make this frightening: 1. We have already, for the first time in history, started seeing spikes of wet-bulb temperatures that exceed these values. Fortunately so far they have been in uninhabited areas. 2. If we ever see these temperatures in a city, odds are that the electrical grid would fail on account of the strain by A/C units. So picture this: a heat wave of this magnitude hits a large city. Bangkok, Phoenix, Melbourne. It lasts for 48+ hours. The grid fails on account of the strain. We're looking at a mass casualty event with millions of dead in a matter of hours/days.

causi 5y ago
That prompts a lot of questions I'd never thought about before. Assuming a failed grid, are there enough off-grid cooling units to keep the population alive? If such a thing happened in my city people would pile into vehicles and use that AC, but my city has an average car ownership of two per household. The next century will definitely create a market for refrigerated trucks full of bunkbeds. I wonder how long a fridge-sized freezer filled with water and then frozen could keep you alive in such a heatwave.
- jazzyjackson 5y ago
  I don't think you need active phase-change cooling to survive a heat wave, there are architectural solutions found in deserts the world over (India and Iran have great examples). Namely, thick stone walls as heat mass so interior stays cool where nights are cool, and encouraging airflow through great public halls (wind will form where-ever there's a temperature gradient, breezeblocks or jaali can aid in increasing airflow while blocking sunlight) Courtyards with a pool of water will have noticeably cooler ambient temps, these are found all over the middle east. At the extreme, you get underground cities like Nūshābād.
  - roughly 5y ago
    One of the things I’m going to be interested to see over the next couple decades is what happens to building design - especially for houses, we’ve switched entirely over to a mode of building that’s effectively optimized for cost and consistency, as opposed to localized to the environment. You’ve got houses built the same in Arizona and Montana, which is insane on the face of it and assumes sufficient energy availability that we can ignore local climates. It would be great to see a move back towards those older building techniques that are tailored better towards their environments.
    - germinalphrase 5y ago
      If we have any architecture buffs here, I’d love a starting point for learning more about climate specific architectural design (that doesn’t center around active climate technologies like HVAC). Keywords?
      - jazzyjackson 5y ago
        Check out the wind catchers or wind-towers (burj al hawwa) of Iran [0], as well as Qatar [1] <- some helpful diagrams Jaali is the latticework that at first glance is merely decorative but is in fact functional, see this paper [2]: "Different names- Takhrima in Yemen, Shanashil or Roshan in Iraq and Saudi Arabia, with differences in design, materials, etc., calls them but the function remained the same as a climate control tool in the harsh deserts." [0] https://www.bbc.com/travel/article/20180926-an-ancient-engineering-feat-that-harnessed-the-wind https://www.bbc.com/travel/article/20180926-an-ancient-engin... [1] https://www.iloveqatar.net/guide/places/traditional-air-conditioning-cooling-in-doha-qatar https://www.iloveqatar.net/guide/places/traditional-air-cond... [2] https://ijseas.com/volume2/v2i2/ijseas20160211.pdf https://ijseas.com/volume2/v2i2/ijseas20160211.pdf
  - sidewndr46 5y ago
    The pool of water would only be able to keep the temperature down due to the constant evaporation of water taking heat out of the environment. This won't work once the wet bulb temperature crosses a threshold.
cleancoder0 5y ago
This got me wondering, how do humans handle a hot bath? Wet-bulb temp is much higher than 35 °C, right? I mean, it's probably going to hit moist areas first. So India should be one of the first countries to experience lethal wet-bulb temperatures.
- mattmaroon 5y ago
  A hot tub is a little above it. But it’s very important to remember your head is above the water. So the wet bulb temperature for your most vital organs is much lower. Also you really aren’t supposed to stay in for a long time and it definitely can hurt/kill you to do so. It’s not very common because you can leave at any time and you’ll feel growing discomfort long before the danger zone but people do die that way.
- deleted 5y ago
  [deleted]
mattmaroon 5y ago
Well, indoor temperatures would still probably not get that hot thankfully in many places so most people would be able to survive. Millions dead from it in a two day period likely wouldn’t happen. Also peak temps usually only last a few hours with significant drops outside. The hottest day ever in Phoenix hit 122F but the day started at 90 and ended around 100. Also in places likes this everyone’s AC runs non-stop every day for 6 months a year at peak times and the power grid doesn’t fail. Power grids fail in places that aren’t used to it, like what happened when Dallas froze. People will die from it, sure, but millions of deaths in a few days from a heatwave isn’t going to happen.
- sidewndr46 5y ago
  When you say "ended" do you mean sundown or midnight?
- klyrs 5y ago
  The amount of power an a/c unit requires to maintain a fixed inside temperature grows with the outside temperature. If folks are already running their a/c nonstop, are they actually prepared for significantly higher temperatures? And if they aren't actually running 24/7 at full blast, is the grid prepared for that?
  - mattmaroon 5y ago
    Significantly higher temperatures aren’t what we’re talking about. We’re talking about a 10-15F spike. Because heat flows at a rate proportional to the delta, it’s useful to think in terms of the delta between outdoor temperatures and desired indoor (let’s say 70 to make the math easy). So Phoenix has a few 120Fcdays a year, so delta of 50, and we’re talking 135F (so delta 65) for a 30% increase. Most peoples AC is not sized to handle that, so it already runs basically full stop on the hottest days and can’t quite keep up. Maybe your home is 75 instead of 70. Making the exterior hotter has no effect of your power consumption once your AC is running full blast, it just makes the interior warm, so some people are going to have 80+ degree houses. They’ll be annoyed but won’t die and the power might spike let’s say 25%. The power grids in these places are equipped for that because it’s life or death. You never hear about Vegas or Phoenix having a blackout on a particularly hot day because it’s not unexpected. Same with cold days in Minnesota. (You hear about it in California but that’s due to mismanagement and often unrelated to weather anyway.) Now in Dallas when they froze you were looking 0F temps or thereabouts in a place where average winter temps are 56 and peak lows around 40. Further complicating it was that supplies of fossil fuels for heating ran out because it went on for so long. So you went from let’s say a 30 degree delta to 70, and electrical demand even higher than you’d expect when they ran out of natural gas and started plugging in space heaters. So you’re looking at like 2-3x previous peak demand, rather than 1.3. Nobody’s grid is prepared for that. So again I’m fairly confident that if Phoenix hits a peak of 135 it is going to suck and a few hundred people will die for sure. It won’t be millions. Global warming thankfully grows on 1 degree per decade kind of time scales which sucks ecologically but isn’t faster than we can grow the grid.
jazzyjackson 5y ago
> (20 or so minutes, even for healthy, fit adults). As someone who enjoys sitting in a sauna I wonder what physics are at play here. Heat stroke trying to work in >100* heat I get, but death even at rest?
- klyrs 5y ago
  I wonder about that myself. I know my limits and can't stay in a sauna for too long, but I've heard that folks in Finland take it really far. But... reading up on the World Sauna Championships, it seems that even the most heat-adapted Finns tapped out after 16 minutes or so. That was in a ludicrous 110C with a steep humidity ramp, and they stopped running the competition after a contestant died and another one nearly died after about 6 minutes. I've tried to look for better statistics about how much folks in Finland can actually tolerate, but all I found was this spectacular batshit: https://www.reddit.com/r/finlandConspiracy/comments/op97qm/the_great_sauna_conspiracy/ https://www.reddit.com/r/finlandConspiracy/comments/op97qm/t...
- alvarlagerlof 5y ago
  The important thing is the moisture level. You need to be able to sweat, which you usually do in a sauna.
- el_nahual 5y ago
  The humidity is the issue. Wet-bulb temperatures exceeding body temperature means sweating no longer cools you off. That's why steam rooms peak at ~110 and saunas at ~150. A steam room at 110 is almost unbearably hot, it's hard to last more than 5 or 10 minutes in one. Think about a human having a fever of 108—that's the temperature at which you'd start to have convulsions.
- deleted 5y ago
  [deleted]
roughly 5y ago
Among other things, this is why it’s worrying to see electric grids fail in Texas, hospitals getting overwhelmed during COVID, and the supply chains falling apart for basic supplies - we’re not even scratching the surface of what the world’s got in store for us over the next century.
elil17 5y ago
There are a few technologies that could help us mitigate this disaster scenario (although laws to address GHG emissions are needed to truly avoid it): - Smart thermostats which let utility companies cap peoples AC use - you can stop people from cooling down to room temp, keep everyone at 85 wbt instead. You can pre-cool peoples houses before the hottest point in the day (e.g. turn the temperature down to 60 in the morning and then turn the AC off and let it ride back up to 85 wbt during the heat wave). In the worst case scenario, you can shut off peoples AC and make them go to cooling shelters. - Thermal storage - traditional ice thermal storage uses glycol to freeze ice at night when the condenser temperature is really low, and then stores this ice to cool buildings during the day. The problem is that glycol systems are expensive and impractical on a small scale, so all ice thermal storage systems are huge (take a look at Chicago’s district cooling as an example). New thermal storage materials (e.g. polymer phase change materials) can be frozen/unfrozen at the evaporator temperature of existing AC systems, so they would require less retrofitting to install and could be used for smaller buildings. - More efficient dehumidifiers - ARPA-E is finding a bunch of projects around this right now. Some, like isothermal membrane-based air dehumidification, could be 4x more efficient than existing vapor compression dehumidifiers. Many other technologies, like energy recover ventilators, hybrid and adiabatic cooling towers, and inverter chillers, to name a few, are making HVAC more efficient!
DesiLurker 5y ago
I am thinking about animals in these superhot regions. yes humans can turn the AC on but such temperatures are effectively death sentences for everyone except human. Now I do not know the exact WB temperature for each animals but 1) their body temperature equilibrium must be around current conditions. 2) for smaller (than humans) surface area/mass equation would tip towards for being worse for them in terms of survivability (think kids needing more layers). I do not have a good feeling about this!
Hitton 5y ago
Interesting. Could you explain why would sitting in front of fan speed up your death though?
- mattmaroon 5y ago
  The answer everyone missed: boundary layer. Air has friction. When you sit there, a boundary layer of much slower moving (relative to the motion of unobstructed air as connection occurs) air creates an insulating effect around you. The fan removes the boundary layer by blowing it away. This effect is why food that is boiled cooks so much faster than food at 99C. You’d otherwise expect it to cook only a little over 1% faster but the actual effect is far greater. The boiling churns the water and disrupts the boundary layer. Similar principle in a forced convection oven.
- joak 5y ago
  Yes, exactly. If you pour water on you and sit in front of a fan, why the windchill effect wouldn't work anymore?! I think this stuff only happens in absence of wind...
  - function_seven 5y ago
    Because the temperature we're talking about is the wet bulb variety. That means it accounts for evaporation. What is normally a windchill is now a "windwarm" effect. (Yes, I know that windchill effect isn't solely due to evaporation-cooling. It's also stripping the layer of warm air away from you.) The environment is hotter than you. Blowing hotter air (laden with moisture, so it won't evaporate your sweat) won't do anything to cool you down.
- el_nahual 5y ago
  A fan works by speeding up the rate of evaporation from your skin, which cools you off. At these wet bulb temperatures the ratio of heat/humidity is so high that blowing hot air over your skin just heats you up faster. Kind of like turning on the convection feature in an oven.

causi 5y ago

That prompts a lot of questions I'd never thought about before. Assuming a failed grid, are there enough off-grid cooling units to keep the population alive? If such a thing happened in my city people would pile into vehicles and use that AC, but my city has an average car ownership of two per household. The next century will definitely create a market for refrigerated trucks full of bunkbeds. I wonder how long a fridge-sized freezer filled with water and then frozen could keep you alive in such a heatwave.

jazzyjackson 5y ago
I don't think you need active phase-change cooling to survive a heat wave, there are architectural solutions found in deserts the world over (India and Iran have great examples). Namely, thick stone walls as heat mass so interior stays cool where nights are cool, and encouraging airflow through great public halls (wind will form where-ever there's a temperature gradient, breezeblocks or jaali can aid in increasing airflow while blocking sunlight) Courtyards with a pool of water will have noticeably cooler ambient temps, these are found all over the middle east. At the extreme, you get underground cities like Nūshābād.
- roughly 5y ago
  One of the things I’m going to be interested to see over the next couple decades is what happens to building design - especially for houses, we’ve switched entirely over to a mode of building that’s effectively optimized for cost and consistency, as opposed to localized to the environment. You’ve got houses built the same in Arizona and Montana, which is insane on the face of it and assumes sufficient energy availability that we can ignore local climates. It would be great to see a move back towards those older building techniques that are tailored better towards their environments.
  - germinalphrase 5y ago
    If we have any architecture buffs here, I’d love a starting point for learning more about climate specific architectural design (that doesn’t center around active climate technologies like HVAC). Keywords?
    - jazzyjackson 5y ago
      Check out the wind catchers or wind-towers (burj al hawwa) of Iran [0], as well as Qatar [1] <- some helpful diagrams Jaali is the latticework that at first glance is merely decorative but is in fact functional, see this paper [2]: "Different names- Takhrima in Yemen, Shanashil or Roshan in Iraq and Saudi Arabia, with differences in design, materials, etc., calls them but the function remained the same as a climate control tool in the harsh deserts." [0] https://www.bbc.com/travel/article/20180926-an-ancient-engineering-feat-that-harnessed-the-wind https://www.bbc.com/travel/article/20180926-an-ancient-engin... [1] https://www.iloveqatar.net/guide/places/traditional-air-conditioning-cooling-in-doha-qatar https://www.iloveqatar.net/guide/places/traditional-air-cond... [2] https://ijseas.com/volume2/v2i2/ijseas20160211.pdf https://ijseas.com/volume2/v2i2/ijseas20160211.pdf
- sidewndr46 5y ago
  The pool of water would only be able to keep the temperature down due to the constant evaporation of water taking heat out of the environment. This won't work once the wet bulb temperature crosses a threshold.

cleancoder0 5y ago

This got me wondering, how do humans handle a hot bath? Wet-bulb temp is much higher than 35 °C, right? I mean, it's probably going to hit moist areas first. So India should be one of the first countries to experience lethal wet-bulb temperatures.

mattmaroon 5y ago
A hot tub is a little above it. But it’s very important to remember your head is above the water. So the wet bulb temperature for your most vital organs is much lower. Also you really aren’t supposed to stay in for a long time and it definitely can hurt/kill you to do so. It’s not very common because you can leave at any time and you’ll feel growing discomfort long before the danger zone but people do die that way.
deleted 5y ago
[deleted]

mattmaroon 5y ago

Well, indoor temperatures would still probably not get that hot thankfully in many places so most people would be able to survive. Millions dead from it in a two day period likely wouldn’t happen. Also peak temps usually only last a few hours with significant drops outside. The hottest day ever in Phoenix hit 122F but the day started at 90 and ended around 100. Also in places likes this everyone’s AC runs non-stop every day for 6 months a year at peak times and the power grid doesn’t fail. Power grids fail in places that aren’t used to it, like what happened when Dallas froze. People will die from it, sure, but millions of deaths in a few days from a heatwave isn’t going to happen.

sidewndr46 5y ago
When you say "ended" do you mean sundown or midnight?
klyrs 5y ago
The amount of power an a/c unit requires to maintain a fixed inside temperature grows with the outside temperature. If folks are already running their a/c nonstop, are they actually prepared for significantly higher temperatures? And if they aren't actually running 24/7 at full blast, is the grid prepared for that?
- mattmaroon 5y ago
  Significantly higher temperatures aren’t what we’re talking about. We’re talking about a 10-15F spike. Because heat flows at a rate proportional to the delta, it’s useful to think in terms of the delta between outdoor temperatures and desired indoor (let’s say 70 to make the math easy). So Phoenix has a few 120Fcdays a year, so delta of 50, and we’re talking 135F (so delta 65) for a 30% increase. Most peoples AC is not sized to handle that, so it already runs basically full stop on the hottest days and can’t quite keep up. Maybe your home is 75 instead of 70. Making the exterior hotter has no effect of your power consumption once your AC is running full blast, it just makes the interior warm, so some people are going to have 80+ degree houses. They’ll be annoyed but won’t die and the power might spike let’s say 25%. The power grids in these places are equipped for that because it’s life or death. You never hear about Vegas or Phoenix having a blackout on a particularly hot day because it’s not unexpected. Same with cold days in Minnesota. (You hear about it in California but that’s due to mismanagement and often unrelated to weather anyway.) Now in Dallas when they froze you were looking 0F temps or thereabouts in a place where average winter temps are 56 and peak lows around 40. Further complicating it was that supplies of fossil fuels for heating ran out because it went on for so long. So you went from let’s say a 30 degree delta to 70, and electrical demand even higher than you’d expect when they ran out of natural gas and started plugging in space heaters. So you’re looking at like 2-3x previous peak demand, rather than 1.3. Nobody’s grid is prepared for that. So again I’m fairly confident that if Phoenix hits a peak of 135 it is going to suck and a few hundred people will die for sure. It won’t be millions. Global warming thankfully grows on 1 degree per decade kind of time scales which sucks ecologically but isn’t faster than we can grow the grid.

jazzyjackson 5y ago

> (20 or so minutes, even for healthy, fit adults). As someone who enjoys sitting in a sauna I wonder what physics are at play here. Heat stroke trying to work in >100* heat I get, but death even at rest?

klyrs 5y ago
I wonder about that myself. I know my limits and can't stay in a sauna for too long, but I've heard that folks in Finland take it really far. But... reading up on the World Sauna Championships, it seems that even the most heat-adapted Finns tapped out after 16 minutes or so. That was in a ludicrous 110C with a steep humidity ramp, and they stopped running the competition after a contestant died and another one nearly died after about 6 minutes. I've tried to look for better statistics about how much folks in Finland can actually tolerate, but all I found was this spectacular batshit: https://www.reddit.com/r/finlandConspiracy/comments/op97qm/the_great_sauna_conspiracy/ https://www.reddit.com/r/finlandConspiracy/comments/op97qm/t...
alvarlagerlof 5y ago
The important thing is the moisture level. You need to be able to sweat, which you usually do in a sauna.
el_nahual 5y ago
The humidity is the issue. Wet-bulb temperatures exceeding body temperature means sweating no longer cools you off. That's why steam rooms peak at ~110 and saunas at ~150. A steam room at 110 is almost unbearably hot, it's hard to last more than 5 or 10 minutes in one. Think about a human having a fever of 108—that's the temperature at which you'd start to have convulsions.
deleted 5y ago
[deleted]

roughly 5y ago

Among other things, this is why it’s worrying to see electric grids fail in Texas, hospitals getting overwhelmed during COVID, and the supply chains falling apart for basic supplies - we’re not even scratching the surface of what the world’s got in store for us over the next century.

elil17 5y ago

There are a few technologies that could help us mitigate this disaster scenario (although laws to address GHG emissions are needed to truly avoid it): - Smart thermostats which let utility companies cap peoples AC use - you can stop people from cooling down to room temp, keep everyone at 85 wbt instead. You can pre-cool peoples houses before the hottest point in the day (e.g. turn the temperature down to 60 in the morning and then turn the AC off and let it ride back up to 85 wbt during the heat wave). In the worst case scenario, you can shut off peoples AC and make them go to cooling shelters. - Thermal storage - traditional ice thermal storage uses glycol to freeze ice at night when the condenser temperature is really low, and then stores this ice to cool buildings during the day. The problem is that glycol systems are expensive and impractical on a small scale, so all ice thermal storage systems are huge (take a look at Chicago’s district cooling as an example). New thermal storage materials (e.g. polymer phase change materials) can be frozen/unfrozen at the evaporator temperature of existing AC systems, so they would require less retrofitting to install and could be used for smaller buildings. - More efficient dehumidifiers - ARPA-E is finding a bunch of projects around this right now. Some, like isothermal membrane-based air dehumidification, could be 4x more efficient than existing vapor compression dehumidifiers. Many other technologies, like energy recover ventilators, hybrid and adiabatic cooling towers, and inverter chillers, to name a few, are making HVAC more efficient!

DesiLurker 5y ago

I am thinking about animals in these superhot regions. yes humans can turn the AC on but such temperatures are effectively death sentences for everyone except human. Now I do not know the exact WB temperature for each animals but 1) their body temperature equilibrium must be around current conditions. 2) for smaller (than humans) surface area/mass equation would tip towards for being worse for them in terms of survivability (think kids needing more layers). I do not have a good feeling about this!

Hitton 5y ago

Interesting. Could you explain why would sitting in front of fan speed up your death though?

mattmaroon 5y ago
The answer everyone missed: boundary layer. Air has friction. When you sit there, a boundary layer of much slower moving (relative to the motion of unobstructed air as connection occurs) air creates an insulating effect around you. The fan removes the boundary layer by blowing it away. This effect is why food that is boiled cooks so much faster than food at 99C. You’d otherwise expect it to cook only a little over 1% faster but the actual effect is far greater. The boiling churns the water and disrupts the boundary layer. Similar principle in a forced convection oven.
joak 5y ago
Yes, exactly. If you pour water on you and sit in front of a fan, why the windchill effect wouldn't work anymore?! I think this stuff only happens in absence of wind...
- function_seven 5y ago
  Because the temperature we're talking about is the wet bulb variety. That means it accounts for evaporation. What is normally a windchill is now a "windwarm" effect. (Yes, I know that windchill effect isn't solely due to evaporation-cooling. It's also stripping the layer of warm air away from you.) The environment is hotter than you. Blowing hotter air (laden with moisture, so it won't evaporate your sweat) won't do anything to cool you down.
el_nahual 5y ago
A fan works by speeding up the rate of evaporation from your skin, which cools you off. At these wet bulb temperatures the ratio of heat/humidity is so high that blowing hot air over your skin just heats you up faster. Kind of like turning on the convection feature in an oven.