Wet Bulb Temperature Soon to Become Leading Cause of Death


As our Abrupt Climate Change Catastrophe becomes more extreme the leading cause of death on the planet will be humans hitting their   Wet Bulb Temperature.

“It has been widely believed that a 35°C wet-bulb temperature (equal to 95°F at 100% humidity or 115°F at 50% humidity) was the maximum a human could endure before they could no longer adequately regulate their body temperature, which would potentially cause heat stroke or death over a prolonged exposure.”

“Wet-bulb temperature is read by a thermometer with a wet wick over its bulb and is affected by humidity and air movement. It represents a humid temperature at which the air is saturated and holds as much moisture as it can in the form of water vapor; a person’s sweat will not evaporate at that skin temperature.”

“But in their new study, the researchers found that the actual maximum wet-bulb temperature is lower — about 31°C wet-bulb or 87°F at 100% humidity — even for young, healthy subjects. The temperature for older populations, who are more vulnerable to heat, is likely even lower.”
Humans can’t endure temperatures and humiditie’s as high and previously thought”

Short cut to calculating Wet Bulb Temperature

“In a recent study with Matt Huber, we showed that it doesn’t take that many degrees of global warming to permit peak heat summertime heat stress to (occasionally) become unsurvivable, in many parts of the world that are currently highly populated.”

“We came to this conclusion by considering a meteorological quantity called the wet-bulb temperature. You measure this quantity with a normal thermometer that has a damp cloth covering the bulb. It is always lower than the usual or “dry-bulb” temperature; how much lower depends on the humidity. At 100% humidity (in a cloud or fog) they match. In Sydney and Melbourne, even during the hottest weather, the wet-bulb usually peaks in the low 20’s C. The highest values in the world are about 30-31C, during the worst heat/humidity events in India, the Amazon, and a few other very humid places.
Climate Change Research Centre (CCRC) – The University of New South Wales Sydney NSW  Australia, paper shared here:  ‘What is Wet Bulb temperature?

Orange – Heat stroke probable, Red – Heat stroke imminent

Heat Index

I'm an anti-imperialist, environmental activist and blue ocean sailor, who is passionate about the earth and all it's inhabitants without favour. Brace for imminent impact as we bare witness to the non-linear unraveling of the biosphere and habitability disappearing for most if not all complex life on the only habitable planet we know of. To quote President Niinistö in North Russia: ‘If We Lose the Arctic, We Lose the World’. Folks we have lost the Arctic.

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Posted in Habitat, Rapid Climate Change, Warnings
165 comments on “Wet Bulb Temperature Soon to Become Leading Cause of Death
  1. Reblogged this on Move for Change and the Brooklyn Culture Jam and commented:
    ‘Wet bulb Temperature’ is probably a new phrase for many of you. It won’t be for much longer. We’re drifting into a superheated world where humans will die from being out of doors at the wrong time of day. And temperatures in wet bulb range are not friendly to human agriculture, either. Read and weep.

    Liked by 2 people

  2. bill says:

    My understanding of maximum survival wet bulb temperature is: Water vapour in the air cools the air, once that saturation of water vapour is 100% a certain temperature in despite of the water vapour cooling is not survivable. The wet bulb temp mentioned is 35c. Plse correct me if I’m mistaken!?

    Liked by 1 person

    • bill says:

      The main means of cooling is sweating which maintains survivable core temp and skin temp at 35c.Sweating enables temps of up to 45c+ to be survived. But high humidity makes sweating increasingly ineffective in its cooling function: the higher the humidity gets the more it imposes a heat load on the body like it blocks the shedding of heat from the body through sweating. Water vapour in the air therefore does not cool the temperatures?

      Liked by 1 person

  3. bill says:

    Found this tells how wet bulb temps and humidity can kill:
    What is clear is that to prevent our core temperature rising too high, our skin temperature must not exceed 35 °C for more than a few hours. In dry climates sweating will cool the skin sufficiently even in temperatures of 45 °C or more. But in humid climates where the air is nearly saturated with moisture, sweating makes little difference.

    So temperature alone is a very poor guide to what people can survive. A better indicator is the “wet-bulb temperature”. This is the temperature that a mercury thermometer wrapped in a wet cloth would record. It is a measure of both heat and humidity, and reflects the temperature you could lower your skin to by sweating.

    Even fit and healthy people couldn’t survive sustained wet-bulb temperatures above 35 °C, say Sherwood and Huber. This heat-stress limit applies even to people sitting naked in the shade next to a fan. Without air conditioning or access to cooler or less humid places, they will die.

    The claim that people cannot survive a wet-bulb temperature of 35 °C or more for long is reasonable, says Chris Byrne, an exercise physiologist who specialises in human thermoregulation at the University of Exeter, UK. “At any temperature above that, we switch from a state where we’re losing heat from the skin to the environment to one where the environment imposes a heat load through the skin,” he says. “There’s no doubt that if those conditions arise, you’re probably looking at a lethal situation for the vast majority of the population.”


    Basically the more humid the climate the less able sweating is to cool our skins down to 35c

    Liked by 2 people

  4. rabiddoomsayer says:

    Wet bulb of 35 °C is barely survivable if you are doing absolutely nothing. Try doing laps in a pool heated to 28 °C, it is just too damn hot.


  5. Kevin Hester says:

    We were sold the lie that 2C would be safe but for the thousands of people dying now from hitting their Wet Bulb temperature it patently isn’t safe at 1.6 C above baseline.

    Liked by 3 people

  6. Kevin Hester says:

    The best strategies to keep cool in a heatwave according to the Guardian.


  7. Kevin Hester says:

    Another great article from Andrew Freedman discussing the threat of heatwaves .
    Bare in mind that these are happening at 1.5C above baseline as we track to and beyond the IPCC worst case scenario of 6C.


  8. Kevin Hester says:

    “On Thursday, July 22nd, the temperature in Mitribah, Kuwait, set an all-time record for a temperature recorded outside of Death Valley, California, with a reading of 129.2 degrees, Fahrenheit (54 degrees, Celsius). The top temperature, 134 degrees Fahrenheit, was recorded in Death Valley in 1913. As Jeff Masters, Director of Meteorology at Weather Underground, notes in this article, “If verified, this would be Earth’s hottest temperature ever reliably measured outside of Death Valley…” Verification of temperature is performed by the official weather service in the country in which the temperature has occurred and can take anywhere from a few days to a few months.”


  9. Kevin Hester says:

    Excellent presentation on Wet Bulb Temperature from Paul Beckwith. Beware the clear skies on high wet bulb days folks, we will see more of them every day.

    Liked by 2 people

  10. Kevin Hester says:

    “Levermann of the Potsdam Institute said that as a climate scientist it’s interesting to see some of the projections about global warming impacts playing out in 2015.

    “There had been projections of the dying of coral reefs worldwide. They are becoming true now. You know the science, you trust the science, but to see this actually happening, it’s an interesting experience. If you look at the graphs, it shows that, at 1 degree of global warming, the death curve for corals is taking off. At 1.5 degrees, they’re practically all gone, and we’re right at that point,” he said.”

    Liked by 1 person

  11. Kevin Hester says:

    “In the Summer months, 84 inmates at the Price Daniel Unit, a medium-security prison four hours west of Dallas, share a 10-gallon cooler of water that’s kept locked in a common area. An inmate there can expect to receive one 8 oz. cup every four hours, according to Benny Hernandez, a man serving a 10-year sentence at the prison. The National Academy of Medicine recommends that adults drink about twice that amount under normal conditions and even more in hot climates. According to Hernandez, in the summer the temperature in his prison’s housing areas can reach an astonishing 140 degrees.
    “It routinely feels as if one’s sitting in a convection oven being slowly cooked alive.”


  12. Kevin Hester says:

    “When the mercury surges, people die. A heat wave in 2015 melted asphalt in New Delhi, India, and caused the deaths of at least 2,500 people.”

    Liked by 1 person

  13. Pat O'Dea says:

    It is not commonly known, but heatwaves even in developed countries are the most deadly of all natural disasters.


    Liked by 1 person

  14. Kevin Hester says:

    “Deadly heatwave continues in India as 21 people die this week with temperatures hitting 45C 120F”


  15. Kevin Hester says:

    What is Wet Bulb temperature?
    “In a recent study with Matt Huber, we showed that it doesn’t take that many degrees of global warming to permit peak heat summertime heat stress to (occasionally) become unsurvivable, in many parts of the world that are currently highly populated.”

    “We came to this conclusion by considering a meteorological quantity called the wet-bulb temperature. You measure this quantity with a normal thermometer that has a damp cloth covering the bulb. It is always lower than the usual or “dry-bulb” temperature; how much lower depends on the humidity. At 100% humidity (in a cloud or fog) they match. In Sydney and Melbourne, even during the hottest weather, the wet-bulb usually peaks in the low 20’s C. The highest values in the world are about 30-31C, during the worst heat/humidity events in India, the Amazon, and a few other very humid places. This map shows peak annual afternoon wet-bulb temperature attained in the present climate (this is a better-quality version of the figure in our PNAS paper).”

    Liked by 1 person

  16. Kevin Hester says:

    The biosphere is unraveling now, not long off in the future. prepare as best you can for the worst, it’s knocking at the door now.
    Hitting our Wet Bulb Temperatures soon to be the leading cause of death on the planet.


  17. Kevin Hester says:

    “This very severe high temperature came just one day after the thermometer struck 52.9 C (127.2 F) on Wednesday and is the strongest temperature spike of a broader Middle Eastern heatwave that has been baking the near-Persian-Gulf-region for many days. Such severe heat did not, however, tip wet bulb readings above the 35 C human self-cooling threshold despite an extremely hazardous heat index near 142 F. A combined dew point of 72 F, a 129 F temperature, and 995 hPa pressure resulted in wet bulb readings of around 30.2 C for the city — quite dangerous, but not beyond the human limit for temperature self-regulation.”


  18. Kevin Hester says:

    David Pate “The wet-bulb temperature is the temperature a parcel of air would have if it were cooled to saturation by the evaporation of water into it, with the latent heat being supplied by the parcel. A wet-bulb thermometer will indicate a temperature close to the true wet-bulb temperature. A quick technique that many forecasters use to determine the wet-bulb temperature is called the “1/3 rule”. The technique is to first find the dewpoint depression (temperature minus dewpoint). Then take this number and divide by 3. Subtract this number from the temperature. You now have an approximation for the wet-bulb temperature.”

    From the National Weather Service in the USA. Just plug in the numbers 👍


    Liked by 1 person

    • Meteorologist Nick Humphrey says:

      It’s interesting, Wet Bulb is one of the first things I learned about in lab class as a undergraduate meteorology student. As wet-bulb is the temperature the dry-bulb temp (temp in unsaturated air) cools too as a result of latent heat of evaporation, it’s typically important in winter weather forecasting (rain falls through dry cold air and cools it bringing down snow level) and in determining accurate summertime temps in humid environments (evapotranspiration from soils/vegetation can keep air temps from getting quite as hot…why you see the Southeast US typically cooler on hot days than the desert Southwest). Mets usually use heat index to approximate how the temp “feels” to the human body and threatening levels of heat. But when you start getting very high heat and humidity…it’s clear the research on human health and climate change is pointing toward the 35 C threshold as being truly life-threatening for all situations. With wet-bulb, the value is always between the air temperature and the dewpoint temperature (temp air must decrease too given its current moisture content to reach saturation). If the dew point is at or above 35 C, your wet bulb will be at least that high, regardless of the air temperature, unless there is a mechanism to dry the air. However, if you have a still high dew point (above 30 C) and air temp below 40 C, the wet bulb will be nearing 35 C as well. The thing with saturation temperatures exceeding 30 C is that the actual moisture content of the air (the mixing ratio in grams of water/kg of dry air) is becoming quite large. Air at sea level has 19 g water/kg of air at a dew point of 24 C…but nearly 35 g/kg at a dew point of 34 C. I can see physically why there would come a point where a human simply cannot evaporate enough sweat fast enough in such a moist environment to regulate their own body temperatures even without physical exertion. The highest wet bulb I’ve probably experienced is around 30 C on the Central Plains.

      Liked by 1 person

  19. Kevin Hester says:

    The Paris Agreement calls for global warming to be limited to 1.5–2 °C. For the first time, this study investigates how different regional heatwave characteristics (intensity, frequency and duration) are projected to change relative to increasing global warming thresholds. Increases in heatwave days between 4–34 extra days per season are projected per °C of global warming. Some tropical regions could experience up to 120 extra heatwave days/season if 5 °C is reached. Increases in heatwave intensity are generally 0.5–1.5 °C above a given global warming threshold, however are higher over the Mediterranean and Central Asian regions. Between warming thresholds of 1.5 °C and 2.5 °C, the return intervals of intense heatwaves reduce by 2–3 fold. Heatwave duration is projected to increase by 2–10 days/°C, with larger changes over lower latitudes. Analysis of two climate model ensembles indicate that variation in the rate of heatwave changes is dependent on physical differences between different climate models, however internal climate variability bears considerable influence on the expected range of regional heatwave changes per warming threshold. The results of this study reiterate the potential for disastrous consequences associated with regional heatwaves if global mean warming is not limited to 2 degrees.

    Heatwaves, defined as prolonged periods of excessive heat1 are a distinctive type of extreme temperature that inflict disastrous impacts on human health2,3,4 infrastructure5,6, and biophysical systems7,8. Since as early as the 1950’s, increases in the in the duration, intensity and especially the frequency of heatwaves have been detected over many regions9. As anthropogenic influence on the global climate intensifies, future increases in heatwaves are unavoidable10,11,12,13,14,15. Some regions where intense heat is already common may become inhabitable .


  20. Kevin Hester says:

    Wet Bulb temperatures will be reached far sooner than predicted in this article and when they occur all the sapiens will need access to cold water and electricity for air-conditioning. When the aircon goes off the sapiens will drop like flies, naturally all the other species who are completely innocent of causing the 6th great extinction will be what the US military calls “Collateral Damage”.



  21. Allan says:

    The birds will drop out of the skies first before we die

    Liked by 1 person

  22. Steve Axford says:

    I worked in a Sth African gold mine for a while in 1971. On one occasion I went into a stope (working place) underground that was 96 deg F (35.6 deg C) wet bulb. This was above the limits that were set by the chamber of mines, which was 94 deg F (33.4 deg C), after which the black workers got a short shift of only 4 hours. I remember it well because I had been shown a safety film the day before which said that you have 15 minutes to cool down once you get heat stroke, or you die. That wasn’t a very reassuring as getting into that working place took about 30mins of scramble through a stope that was twisted and cracked due to movement of the ground and varied from 60cm to about 120cm in height. I sat collapsed on the ground for quite a while, occasionally shining my light up a crack in the roof that extended out into blackness and clearly wasn’t a good omen. I was literally bathed in rivers of my sweat. We eventually got out by a quicker route, which was fortunate as I’m not sure I could have taken much more. One of the curious things that happens when you do get heat stroke like that is that it makes you more susceptible on subsequent occasions. I find that even 30 deg wet bulb is too much for me now, though age may also have something to do with that. I think that now I would die quite quickly if I was exposed to 35 deg wet bulb or more. It is probably the most frightening experience of my life.

    Liked by 1 person

  23. Kevin Hester says:

    “With repeated exposure to high temperatures, the body can become more efficient at shedding excess heat. That’s why a person can move from cold Minneapolis to steamy Miami and get used to the higher heat and humidity. But there is a limit to how much a person can adjust, which depends on the person’s underlying health and the ambient temperature and humidity. If the outside is hotter than the body, blood at the skin surface won’t release heat. If humidity is high, sweating won’t cool the skin. Two scientists proposed in 2008 that humans cannot effectively dissipate heat with extended exposure to a wet-bulb temperature, which combines heat and humidity, that is greater than 35° C.”


  24. Kevin Hester says:

    “Two scientists proposed in 2008 that humans cannot effectively dissipate heat with extended exposure to a wet-bulb temperature, which combines heat and humidity, that is greater than 35° C.”


  25. Kevin Hester says:

    If the electricity fails and people lose access to aircon and fans people will start dropping like the proverbial………………………..


  26. Kevin Hester says:

    Let’s talk about sex baby, lets talk about you and me, let’s talk about all the good times and the bad times that maybe, Let’s talk about sex!


  27. Alex Smith says:

    This thread just becomes more valuable as it builds in time. Thank you Kevin. I’ve book marked this, in part as I’m collecting material for a show on the heat crisis of summer 2018 (in the Northern Hemisphere). I think we’ve reached a turning point here.

    One thing to consider is that a paper in 2014 showed that while climate impacts in general have a lag of anywhere from 30 years to hundreds of years (like glacier melt and sea level rise) – after the initial emissions – but heat itself only lags 10 years from emissions. So this 2018 burst comes from emissions and possibly other factors in 2008 or so. I’m wondering if that driver was actually the 2007 disappearance of Arctic sea ice? It’s even possible the sea ice loss was itself an echo of the amazing El Nino heat year of 1997-98, when the Indonesian peat burned. Are there waves and echoes in heat? I’m looking into that.

    Anyway, it seems that heating of the planet is more of a staircase than a ramp.

    Liked by 1 person

  28. Alex Smith says:

    Also note that over 60 people died of heat in the Canadian province of Quebec in early July.

    When I was young living in Canada, I never saw an air-conditioner, did not know they existed until I visited Florida in my late teens. Now you can’t sell a house in southern Canada without an air conditioner.

    Folks I know in Montreal who resisted air-conditioning, just went out and bought one. They could not live in their homes without it.

    When Canada needs air-conditioning to survive, you know the world is in big climate trouble.

    Liked by 1 person

  29. Kevin Hester says:

    “Heat exhaustion is a condition whose symptoms may include heavy sweating and a rapid pulse, a result of your body overheating. It’s one of three heat-related syndromes, with heat cramps being the mildest and heatstroke being the most severe.”


  30. Kevin Hester says:

    “We’re Going to Die in Record Numbers as Heatwaves Bake The World, First Global Study Shows”
    “Be alarmed.”



  31. Kevin Hester says:

    “At 50C – halfway to water’s boiling point and more than 10C above a healthy body temperature – heat becomes toxic. Human cells start to cook, blood thickens, muscles lock around the lungs and the brain is choked of oxygen. In dry conditions, sweat – the body’s in-built cooling system – can lessen the impact. But this protection weakens if there is already moisture in the air.”

    “A so-called “wet-bulb temperature” (which factors in humidity) of just 35C can be fatal after a few hours to even the fittest person, and scientists warn climate change will make such conditions increasingly common in India, Pakistan, south-east Asia and parts of China”


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Kevin Hester

Kevin Hester is currently living on Rakino Island, a small island in the Hauraki Gulf near Auckland, New Zealand, monitoring the unravelling of the biosphere and volunteering at the Rakino Island Nursery is currently developing a proposal to create a marine reserve near by. The Island has no grid tied electricity or reticulated water.  I catch my own water from the roof and generate my electricity from the ample solar radiation on the island.

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