> Study results indicate that limiting global warming to 1.5 °C would prevent most of the tropics from reaching the wet-bulb temperature of the human physiological limit of 35 °C.
> why haven't we seen mass death from repeated 35℃ breaches?
Because we haven't seen very many 35℃ wet bulb temperature breaches yet. The nominal air temperature is much higher than that all the time around the world, but it's only when there is very high humidity at that temp that humans start to overheat.
IIRC there have only been a few instances so far where the web bulb temp limit has been breached, e.g. some instances around the Persian Gulf, and maybe also in Mexico near the Gulf of California (not sure about the latter if it's even been breached yet, but I know it's at risk).
The breach is in wet-bulb temperature, not dry-bulb temperature. When you hear weather reports cover the temperature, then it's going to be the dry-bulb temperature--the actual temperature of the air.
Wet-bulb temperature is the minimum temperature you can reach by evaporative cooling (i.e., sweating). When wet-bulb temperature gets too close to core body temperature, you are physically incapable of shedding heat if you are not in air-conditioning, and how close it needs to be depends on how good health you are in.
But we actually have seen deaths in previous heat waves, which largely didn't even breach 30C wet-bulb. The 2003 European heat wave caused about 70,000 people to die, for example.
Do you have data on the demographic breakdown? The papers i have seen have the overwhelmong majority of those deaths in the 80 plus demographic, which is not anywhere near equivalent to an 18 to 50 year old death when doing the cost benefit analysis on any of the mitigation or avoidance policies we could enact
Please don't confuse the heat in Death Valley with humid heat. Don't get me wrong, that Death Valley heat will kill you, but as long as you have water and shade you will survive.
dear fact-impaired readers - global temperature records are carefully kept by a multitude of authoritative sources, and increasingly so..
the Year 2023 was the Hottest Year on Record to date globally.. each month of 2023 (edit maybe not jan-feb?) was also the hottest recorded globally. The hottest day cumulatively across the world was in 2023. The nine hottest years on record globally were the last nine years.
Please use librarianship and science skills for factual information. multiple references available for the search-impaired
I assume that you're alluding to the air conditioner, which was invented in 1901? The first home installation was in 1914, but that wasn't the date of the invention.
> limiting global warming to 1.5 °C would prevent most of the tropics from reaching the wet-bulb temperature of the human physiological limit of 35 °C.
We've had one year at the level of warming that is not yet expected to yield mass death from wet bulb events.
Give it time. There's no reason to think that the current warming trend will slow, stop, or reverse itself in the near term.
Why is there “no reason?” This has happened repeatedly throughout history. Climate has always changed. The only difference now is that “preventing” climate change is a huge industry.
Of course climate has changed in the past, but over geological time scales. We're witnessing change in real time, over a period of decades. It's the rate of change in climate that is accelerating.
"Maybe it'll just -waves hands- magically happen" is "no reason". Saying "climate has changed in the past and therefore there is reason to believe that it will change in this particular way, in the future" does not logically follow.
Climate has changed repeatedly throughout history. Every time a temperature increase has changed to a temperature decrease, this must be preceded by the rate of temperature increase decreasing.
We observe the rate of temperature increase, continuing to increase.
Thus there is reason to believe that it will get hotter for some time, before it again gets colder.
Seriously the people who say "there is money to be made by lying about climate change" and then pointing to the few millions of dollars available in public research into climate and NOT the trillions of dollars from multiple countries in selling energy in the form of carbon bonds are just goofy.
These are the kind of people that had to cheat off you to pass biology yet insist that "the immune system works like this"
The 1.5 degrees are the average heatup over the globe, it varies across the regions - in Europe we have a higher raise, but we are not near the unliveable conditions, though we have plenty of heat deaths already. And of course, there is air condition. So even if temperatures reach dangerous levels, few people will experience it in full force.
Comments here on the temperature fail to add WBT is related to a high humidity.
'The wet-bulb temperature (WBT) is the temperature read by a thermometer covered in water-soaked (water at ambient temperature) cloth (a wet-bulb thermometer) over which air is passed.'
Edit: because a high humidity means the body cannot cool anymore by sweating. A higher temperature combined with dry air is generally not a life threatening situation (if you stay in de shade and drink a lot of water).
Wish all articles like this would start including wet bulb temperature, so reader wouldn't have to keep finding temp and humidity and find it on a chart.
A wet-bulb temperature of 95°F (35°C) is the theoretical limit for human survivability for up to six hours of exposure. This is equivalent to a heat index of 160°F (71°C). However, more recent research indicates that a wet-bulb temperature of 88°F can be hazardous even for young
Aug 17, 2023
Understanding Wet-Bulb Temperature: The Risks of High Wet ...
> A wet-bulb temperature of 95°F (35°C) is the theoretical limit for human survivability for up to six hours of unshaded outdoor exposure
Both the sources you linked say that 35 degrees is the limit in the shade as well.
> It has been thought that a sustained wet-bulb temperature exceeding 35 °C (95 °F)—given the body's requirement to maintain a core temperature of about 37°C—is likely to be fatal even to fit and healthy people, unclothed in the shade next to a fan
Guess technically, since shade is cooler, then if the temperature was X and shade is (X-shade), then if wet bulb was at 95, then you could go into some shade to get cooler. Or, since wet bulb is at 95 is same in sun and shade, then if it is at 95 deg in shade you are in danger, and if you walked into the sun, you'd be in even more danger.
or to try and say another way. Temperature is Temperature, and if in Sun you are probably hotter. But wet bulb 'limit' would be same, and you'd hit the limit faster in the sun.
The heat dome in BC in 2021 was brutal. My car showed 47*C (not exactly scientific but it gives you an idea) and the LCD display on the dash started to malfunction. It was like the contrast was off. I'd only seen that before in extreme cold.
With the high humidity in the area, it was quite dangerous. An estimated 600 deaths due to the heat.
I'm sorry the people of the Philippines are going through this.
> The air conditioning is set at 14-18 C during the hottest part of the day
I wonder what actual temperature that gives them. I'd expect that whatever temperature they set below 25C would have the AC go full power either way, and never reach that target until at night perhaps.
I live in a very hot and dry area, and noticed that at 15% humidity the heat index matches temperature, below 15% results in a heat index below the temperature, and above 15% gives a heat index above the temperature.
That's my understanding too. In fact, the hottest surface temperature recorded on Earth is much higher than the official temperature record because a surface gathers heat not only from air convection/conduction but direct radiation as well.
> Temperatures measured directly on the ground may exceed air temperatures by 30 to 50 °C (54 to 90 °F).[6] The highest natural ground surface temperature ever recorded may have been an alleged reading of 93.9 °C (201.0 °F) at Furnace Creek, California, United States, on 15 July 1972.[7] In 2011, a ground temperature of 84 °C (183.2 °F) was recorded in Port Sudan, Sudan. [1]
Because the effect of the sun induces massive, extremely localized variations in apparent temperature. Are you wearing a black shirt or a white shirt? That changes apparent sun temperature. What is the color of the ground you're standing on? What is the material, for that matter?
Note that all of these effects will only increase the temperature (during daytime, at least). The shade temperature is thus a good indicator of what the coolest possible outdoor environment will be.
Chapter 1 of Ministry for the Future tells the fictional story of a massive heatwave with power failure (nice AC you got there...) across a region of India.
And as a fictional story, it's just the author's completely arbitrary rendering of something that hasn't yet happened anywhere in the world. It's tiresome to see people citing that piece of text as if it were in any way a scientific source or prediction of anything.
A bit like citing Paul Ehlrich's hypothetical predictions of massive famines in the world of his future.. Oh but wait, they all turned out to be completely false.
Global albedo modification happens today its just not very directed (eg. pitch black tarmac next to concrete sidewalk there is significant difference in temperature on sunny days, AC bills would be probably bit cheaper we didn't have tarmac).
Yeah I'm sure it'll be great and we will think about every single potential side effects, just like with asbestos, DDT, lead in gas, freon in fridges, &c.
We're most likely utterly fucked whatever we do unless we go back to live like pre industrial revolution humans
Imagine if all that wealth spent on battling climate effects have been spent in the past to prevent them instead. What a world we could have. Dreamer I am, I know. Hope it is not too late and we still have some chances.
Can someone help me understand the thermodynamics behind this?
My naive understanding would be that if the temperature > human body temperature, we can only gain heat from the environment, leading to death. Obviously sweating is involved. But how?
Evaporative cooling is one of physics's great magic tricks.
Basically, when we talk about a substance's temperature, that temperature is the average temperature of the system.
Temperature is just "how quickly are the atoms/molecules here jiggling?" When the atoms/molecules collide, some of them speed up, some slow down. That means that some atoms are "hotter" than the average temperature, and some are cooler.
Liquids have a certain energy above which a molecule is ejected from the puddle. This is evaporation.
Even if the average temperature (read: energy) is below that threshold energy, some molecules are moving faster, because they have collided with other molecules in just the right way. Those fast molecules get ejected. Evaporation!
But now that the puddle lost the fast (read: hot, read: high energy) molecules, the average energy of the system is lower. The whole thing cools down!
In dry environments, it's possible for sweat to evaporte (cool) at a rate that is faster than the rate at which your body heats up from hot colliding air.
In humid environments two things happen: evaporation slows down, and you heat up faster.
So there is a combination of temperature & humidity at which, if either of those parameters is exceeded, you gain heat faster than you lose it.
The goal of human metabolism is to maintain a consistent body temperature. Metabolism creates heat (as a byproduct of doing useful work) that needs to be shed, this is in addition to the natural heat flux.
Heat flux is proportional to temperature difference, and is solely in the direction of hot to cold.
Let us suppose that at 27 C, the natural heat generation is shed, and let us also suppose that the core body temperature is 37 C. (The actual values don't matter, but this feels approximately correct and gives nice round numbers). In this case, if the temperature is below 27 C, then we are losing too much heat and our body temperature will decrease. If it is above 27 C but below 37 C, we're not shedding our body heat fast enough, so body temperature will increase. If it is above 37 C, then the environment is actually adding excess heat into our body instead of cooling it--and we still have natural metabolic heat to shed.
So we have three main mechanisms we use to regulate body temperature.
The first mechanism is to change the heat flux: by changing our clothing, we can control heat loss. This is obviously more effective for cold temperatures than warm temperatures.
The second mechanism is to change our internal heat generation. For example, staying more active in cold conditions or being less active in hot conditions. The response of shivering is in fact an attempt to generate extra heat to mitigate heat loss.
The final mechanism is to use evaporative cooling. Converting liquid water to gas requires energy. So if you coat yourself in water that gets evaporated, it actively sucks heat away from you in the process. The wet-bulb temperature is a measurement of the coolest you can make something in this method... and that's why wet-bulb temperatures near body temperature are lethal: it's the point at which you just cannot shed any heat whatsoever.
4) Increase/decrease the blood flow towards our skin and arms/legs.
This is why in hot conditions, blood vessels may widen, the heart pumps harder to increase core <-> skin heat exchange, and you see people blushing.
In turn, this "heart pumps harder" (or failing to do so) may worsen other conditions (especially in older people), and eg. contribute to kidney failure (and that in turn, to blood poisoning).
Evaporation (specifically phase change of liquid water to water vapor) draws away a LOT of heat.
Without sweating, we’d be dead even if the air temp was near body temp because of the delta in temperatures required to transfer excess heat from our bodies.
thermokinetic energy is required for water to transition from liquid to vapor.
when heat [thermokinetic motion] spreads from the body to the liquid water, this is a net loss loss of heat from the body as water transitions to vapor phase and diffuses away from the body. if surrounding air is already saturated with vapor [relative humidity 100%] no evaporation can occur at a temperature, that humans will survive
also let's not forget that there are animals too who suffer. And thy don't have AC, water bottle, or fridge to live.