Study: Global Warming is Raising the Tropical Wet Bulb Maximum Temperature

Guest essay by Eric Worrall

According to a study, for every degree of warming, peak wet bulb temperature in the tropics also rises by a degree, so even a small amount of warming is a grave threat to human health. But there are these things called thunderstorms which create a non-linear cutoff to maximum temperatures.

Global heating pushes tropical regions towards limits of human livability

Rising heat and humidity threatening to plunge much of the world’s population into potentially lethal conditions, study finds

Oliver Milman
@olliemilman
Tue 9 Mar 2021 03.00 AEDT

The climate crisis is pushing the planet’s tropical regions towards the limits of human livability, with rising heat and humidity threatening to plunge much of the world’s population into potentially lethal conditions, new research has found.

Should governments fail to curb global heating to 1.5C above the pre-industrial era, areas in the tropical band that stretches either side of the equator risk changing into a new environment that will hit “the limit of human adaptation”, the study warns.

The research team looked at various historical data and simulations to determine how wet-bulb temperature extremes will change as the planet continues to heat up, discovering that these extremes in the tropics increase at around the same rate as the tropical mean temperature.

This means that the world’s temperature increase will need to be limited to 1.5C to avoid risking areas of the tropics exceeding 35C in wet-bulb temperature, which is so-called because it is measured by a thermometer that has its bulb wrapped in a wet cloth, helping mimic the ability of humans to cool their skin by evaporating sweat.

Read more: https://www.theguardian.com/science/2021/mar/08/global-heating-tropical-regions-human-livability

The abstract of the study;

Projections of tropical heat stress constrained by atmospheric dynamics

Yi ZhangIsaac Held & Stephan Fueglistaler 

Extreme heat under global warming is a concerning issue for the growing tropical population. However, model projections of extreme temperatures, a widely used metric for extreme heat, are uncertain on regional scales. In addition, humidity needs to be taken into account to estimate the health impact of extreme heat. Here we show that an integrated temperature–humidity metric for the health impact of heat, namely, the extreme wet-bulb temperature (TW), is controlled by established atmospheric dynamics and thus can be robustly projected on regional scales. For each 1 °C of tropical mean warming, global climate models project extreme TW (the annual maximum of daily mean or 3-hourly values) to increase roughly uniformly between 20° S and 20° N latitude by about 1 °C. This projection is consistent with theoretical expectation based on tropical atmospheric dynamics, and observations over the past 40 years, which gives confidence to the model projection. For a 1.5 °C warmer world, the probable (66% confidence interval) increase of regional extreme TW is projected to be 1.33–1.49 °C, whereas the uncertainty of projected extreme temperatures is 3.7 times as large. These results suggest that limiting global warming to 1.5 °C will prevent most of the tropics from reaching a TW of 35 °C, the limit of human adaptation.

Read more (paywalled): https://www.nature.com/articles/s41561-021-00695-3

The claim that maximum wet bulb temperature will rise linearly with global temperature in my opinion is dubious. Unfortunately we can’t see their full study, but in the real world sea surface temperatures exhibit a sharp cutoff. From Willis’ post “Argo and the Ocean Temperature Maximum”.

Since the sea is 70% of the world’s surface, this sharp cutoff has a major impact on global temperatures.

Why is there such a sharp cutoff on sea surface temperature? The reason is if temperatures rise much above 30C, thunderstorms spontaneously form and cool the surface.

This is why the tropical belt wet season is so wet – all those storms are busy pumping excess heat from the surface, punching a hole through the bulk of the greenhouse blanket, and dumping excess heat at the cold edge of space. Anyone who has seen a thunderhead soaring into the sky has personally witnessed water vapour punching a hole through the bottom of the troposphere.

What if you live too far from the ocean or a large body of water to receive much benefit from this ocean cooling effect? In that case, you are not going to experience extreme humidity – so wet bulb temperature will remain at survivable levels. High humidity requires a source of water vapour.

But what if I’m wrong? Thankfully here in Australia we have pioneered a novel solution to surviving extreme heat.

In the tropical far North of Australia, people install solar heating systems for their swimming pools, not to warm the pools, but to run them at night time. These solar “heaters” at night time function as radiators, dumping excess pool water heat into the cooler night air. That way when wet bulb temperatures soar to uncomfortable heights, we have comfortably cool swimming pools available to help maintain a survivable body temperature.

We have also discovered drinking beer for medicinal purposes helps our bodies dump heat by expanding our surface capillary blood vessels, so to get the full benefit of our radiator cooled swimming pools you have to keep a sixpack of beer on ice in a floating cooler box, and drink bottles of beer at regularly intervals.

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H.R.
March 9, 2021 6:08 pm

Eric Worrall: …so to get the full benefit of our radiator cooled swimming pools you have to keep a sixpack of beer on ice in a floating cooler box, and drink bottles of beer at regularly intervals.

Looks to me like maybe you were consuming some beer at regular intervals. I like a man who practices what he preaches.
😜

fred250
Reply to  Eric Worrall
March 9, 2021 10:38 pm

“I don’t need the medicinal beer!.”

Depends how you define “need” I guess 😉

Last edited 7 months ago by fred250
AndyHce
Reply to  Eric Worrall
March 9, 2021 11:02 pm

It is not only the very wealthy that can afford swimming pools and solar heaters but such are definitely way above the possibilities for most people.

RickWill
March 9, 2021 6:49 pm

But what if I’m wrong? 

I can give you a 100% guarantee you are not wrong. Open ocean surface temperature is regulated to 30C. It cannot exceed 32C because the sky literally goes perpetually dark. The rainfall you notice is the consequence of convergence from cooler zones to the warm pools that knocks the top of the possible peak such that the surface regulates at 30C.

All there oceans do the same thing. How would that be possible for some delicate balance. And the same regulation occurs in the Pacific and Indian Oceans even in the depths of glaciation. Tropical Atlantic goes cold though.

The tropical ocean surface temperature has not changed in 4 decades according to moored buoys and NOAA/NCEP..

Nino34_NCEP.png
RickWill
Reply to  RickWill
March 9, 2021 6:50 pm

Pacific regulating at 30C.

Slide1.PNG
RickWill
Reply to  RickWill
March 9, 2021 6:51 pm

Atlantic regulating at 30C.

Slide2.PNG
RickWill
Reply to  RickWill
March 9, 2021 6:52 pm

Indian regulating at 30C.

Slide3.PNG
Kevin kilty
Reply to  RickWill
March 9, 2021 9:02 pm

Interesting graphs, but it looks like the axis labels have a typo. Showt?

RickWill
Reply to  Kevin kilty
March 10, 2021 2:33 pm

Thank you for the keen observation. I will correct that.

Terry
March 9, 2021 7:08 pm

I live in Canada which is actually the limit of habitability due to cold.and I’m doing find. The folks near the equator will too.

Crispin Pemberton-Pigott
Reply to  Terry
March 10, 2021 3:16 am

Terry you point out the obvious. According to the WHO chronic underheating leading to serious medical consequences starts below 18 C. So according to the author’s theory, no one can survive outside the 18-35 range.

All of Canada will be uninhabitable according to that mental state, I guess I can call it. It you seriously believe that being above 35 will kill you, it means Africa is largely uninhabitable as is India, east Asia, central, South and North America + Russia (etc) because of the cold.

Perhaps technology will save us. Clothes, for example.

Rick W Kargaard
Reply to  Crispin Pemberton-Pigott
March 10, 2021 8:24 am

Apparently there is no one alive in Phoenix

markl
March 9, 2021 7:24 pm

🙂

Alexy Scherbakoff
March 9, 2021 7:38 pm

Could someone tell those turkeys to lookup hygrometers on Wikipedia. They are so wrong that I couldn’t be bothered rolling my eyes.

Crispin Pemberton-Pigott
Reply to  Alexy Scherbakoff
March 10, 2021 3:18 am

They do seem to be sitting the basics of how the atmosphere works, and more.

Alexy Scherbakoff
Reply to  Crispin Pemberton-Pigott
March 10, 2021 8:16 pm

Laboratory scale of humidity determination is performed on small air samples. Anything over a few litres doesn’t fit. Again a Wikipedia comment. If you need a definite number about how things work outside a laboratory you need to go to airconditioning websites. The most obvious screwy nonsense that they came up with was about wet-bulb temperatures. Wet-bulb is always lower than dry-bulb.

commieBob
March 9, 2021 7:48 pm

They seem to treat everything between 20S and 20N the same, but as far as I can tell, it isn’t.

The equator is cooler than tropical areas off the equator. link It’s not exactly a secret. The mechanism is well known.

If the planet got a bit warmer, wouldn’t the equatorial region broaden? Given the evaporation mechanism that keeps the equator cooler than it otherwise might be, wouldn’t the warm areas just move toward the poles?

Abolition Man
March 9, 2021 7:57 pm

Hey, Eric!
Just like most practitioners of scientism, these jamokes seem oblivious to the real world. How they missed the temperature regulating feature of T-storms is a mystery to climate realists!

Speaking of reality, here in the high desert Southwest I have found that medicinal margaritas are much more efficacious for treating severe thirst and heat problems! The Vitamin C in the lime juice is quite helpful and adding juice from pomegranates or açaí berries gives extra nutritional value to the blend! At one ranch I worked at we added lime Emergen-C to them for extra energy on hot afternoons! Cheers!

Redge
Reply to  Abolition Man
March 9, 2021 11:47 pm

Don’t forget medicinals G&T’s with ice and lime.

If you drink enough of them you won’t get COVID 😉

March 9, 2021 8:02 pm

Thanks again to Eric Worrall for more useful and practical advice on how to avoid bad effects from the non-existent Global warming.

March 9, 2021 8:13 pm

I have large pool in my backyard here in Arizona-Sonoran Desert for exactly that same reason. I can get out of my 86 ºF (30 ºC) water temp pool on a July night air and quickly find myself shivering in 90 ºF air due to the rapid evaporation of the water from the skin and no sunlight to warm it. A quick towel-off and a then a chilled malted beverage makes everything good again.

ATheoK
Reply to  Joel O'Bryan
March 10, 2021 10:21 am

And pick fresh oranges, lemons or other ripe tropical fruits in your backyard.

RickWill
March 9, 2021 8:28 pm

On the same topic – does any atmospheric physicist in the house know how to calculate the level of free convection for given surface temperature for a saturated lower zone?

Also are you taught any insight into the minimum level of water vapour needed to produce a level of free convection?

Reply to  RickWill
March 10, 2021 3:34 am

Is there any connection between wet bulb temperature and dewpoint ?

Reply to  Krishna Gans
March 10, 2021 1:08 pm

Wet bulb temperature is just a way of measuring dewpoint.

RickWill
Reply to  Krishna Gans
March 10, 2021 2:39 pm

No – the level of free convection is the consequence of moist air buoyancy in dry air. Most air has a lower density than dry air but there is a point in the atmosphere, once the water column reaches a certain level, that a moist parcel will happily sit below a dry parcel until the situation becomes unstable and cloudburst occurs.

rah
March 9, 2021 8:31 pm

And yet people flock to Florida and the Tropics for retirement. And yet there is not one bit of evidence that people are migrating from the tropics towards the poles. And yet there is no evidence that Antarctica is becoming more habitable, But still the warmanistas dump this kind of bilge on us daily.

I think there is going to be a saturation point eventually just as we are now seeing begin to happen with the COVID scare.

I did a run down to Smithville, TN. Took a 10 hour break in a little truck stop in TN. Though the state is still under a mask mandate not a single person in that truck stop was wearing a mask. Not even the girls behind the counter.

The left has a real problem. They have used every way they can to increase the COVID morbidity and mortality numbers and they have no new way to increase them to show a spike. At the same time, the flu season is coming to an end and so the many cases of influenza that have been reported as COVID 19 is on the decline.  Many of the people most likely to die from COVID-19 are already gone and many others have had it and recovered. And now there are an ever growing number of people being vaccinated. And then there is the fact that we can’t go a week without a story of some Governor or Mayor blatantly violating the very restrictions they have ordered enforced upon their citizens. And finally, spring is coming on, and so is spring fever, and people are just done with this whole thing.  

Kevin kilty
Reply to  rah
March 9, 2021 9:07 pm

Wish I could give you a “+” for each sentence in your post.

Reply to  rah
March 9, 2021 9:52 pm

And Dementia Joe won’t make to the summer. Like the attack on Julius Ceasar, Kamala is coming for Joe’s job once the cabinet appointment confirmations are complete.

rah
Reply to  Joel O'Bryan
March 10, 2021 2:31 am

Well I did make a mistake. There is a group of people migrating towards the poles. They are the illegal immigrants trying to get into the US. And those illegal immigrants that are COVID positive are being released into the general US populace and could spike the morbidity and mortality numbers.

If I were the governor of Texas I would have my NG and State Police right down there. Every bus full would be tested and the COVID positive detained. Then I would have a dedicated airliner and put those that are COVID positive on it and take them to Washington, DC and let them go.

Chaswarnertoo
Reply to  rah
March 10, 2021 8:33 am

Record wheat harvests, too.

ray g
March 9, 2021 8:56 pm

Didn’t I read somewhere that most warming was in the winter and at night time?

Rick C
March 9, 2021 9:34 pm

So a wet-bulb temp of 35 C is unsurvivable? The annual Finish sauna death toll must be huge,

Abolition Man
Reply to  Rick C
March 9, 2021 9:50 pm

Sauna should be a dry heat like a Phoenix summer afternoon. Now a Turkish steam bath or a Native American temescali (sp) would be the place to look for the bodies!

Rory Forbes
Reply to  Rick C
March 9, 2021 11:08 pm

Saunas are very, very low humidity … usually between 5 – 10%. Steam baths are high humidity (100%) and much lower heat.

March 9, 2021 10:19 pm

Here at ~19°S 146E we used to hear this sort of nonsense on a regular basis. Gets tiresome having to explain why 29°C and 90% RH is more uncomfortable compared to 35°C and 20% RH. BoM are still displaying sea surface temperatures up to 34°C on a scale that goes to 36 +

fred250
March 9, 2021 10:37 pm

In case people haven’t already got it

This pdf is a fun read.

https://www.thegwpf.com/content/uploads/2021/03/A-Short-History-Of-Climate-Alarm.pdf

Keith Woollard
March 9, 2021 10:52 pm

but a non-Australian beer in the photo????????

Rod Evans
Reply to  Keith Woollard
March 9, 2021 11:15 pm

Relax Keith, I have experience of Australians drinking beers from wherever. They have a full on willingness, to accept beer from any source…. 🙂

KAT
Reply to  Eric Worrall
March 10, 2021 4:58 am

Reminds me of the second officer (deck officer acting as medical officer) that reported to the captain of a merchant ship that there is a case of gonorrhea that in spite of all his efforts – he cannot get rid of.
The captain’s advice was to give it to the engineers. “They will drink anything!”

Rory Forbes
March 9, 2021 11:12 pm

The climate crisis is pushing the planet’s tropical regions towards the limits of human livability, with rising heat and humidity threatening to plunge much of the world’s population into potentially lethal conditions, new research has found.

Naw … the authors need to quit smokin’ that funny tobacco. There’s been no “new” research. Typically they pull that nonsense out of their rectums by the yard for the BBC the Guardian and such. Like all the rest of the Lefties … everything they do is by “projection”.

Last edited 7 months ago by Rory Forbes
Matthew Sykes
March 9, 2021 11:22 pm

Yep, thats the way to survive the heat! I prefer Rose, but thats a minor detail!

To bed B
March 9, 2021 11:56 pm

Singapore’s highest maximum was 37°C back in 1983. It lasted for only a short time before dropping to the low 30s, presumably due to cloud cover.

Garissa, Kenya, have an average high of about 38°C for February and March (highest on record only 41.0 for those months). The low humidity allows more solar radiation through. One would expect that higher humidity would also lead to lower maximums.

When did the original postulate that most of the warming would be of minimum temperatures at high latitudes and altitudes get ditched?

The highest wet bulb temperatures seem to be on the Arabian peninsula where heat builds up in the dry weather and then the humidity rolls in. It’s not something that they put up with every day.

Stephen Richards
March 10, 2021 12:55 am

But there are these things called thunderstorms which create a non-linear cutoff to maximum temperatures.

Willis did a great blog on this subject here on WUWT. Well worth a recap.

Climate believer
March 10, 2021 1:48 am

Couldn’t give a monkeys about their “new research” twaddle, but having looked at the twitter feed of the Guardian twerp Milman, I did discover that the Huffington Post (recently brought by Buzzfeed) is having a mass layoff of staff.

Oh happy days, it’s as if nobody is interested in their divisive lefty claptrap.

ATheoK
Reply to  Climate believer
March 10, 2021 10:37 am

It’s going to be hard finding anybody above the bottom of the barrel at huffpo. Not that buzzfeed has been any better this past year.

Gary Ashe
March 10, 2021 2:04 am

Oh dear i wake up another morning and boom smacked between the eyes with another climate disaster, and its far worse than we thought, haven’t even had a cup of tea yet and have to deal with this, my own fault for reading here before i had wiped the sleep from my eyes.
Well it will have to solve itself i’m having a up of tea and a shyte first.

Alasdair Fairbairn
March 10, 2021 2:59 am

The reason for the magic 30C cut off point shown by the Argos buoy data is because the vapour pressure of water with temperature rises very rapidly, starting at around 25C and at 30C the rate of rise is more or less vertical to go up off graph at the top. This controls the rate of evaporation which matches any heat input such as solar or GHE and converts the energy into latent heat at CONSTANT temperature. This temperature being that of the oceans. Due to the buoyancy of the vapor/gas produced this latent heat is driven UP through the atmosphere and clouds for dissipation with a proportion going into space. Hence the thunderstorms and those high cirrus clouds radiating energy into space.

The same principle applies in the atmosphere; so the authors of this paper have manifestly got it wrong and need to go go back to basic principles if they are to reach the right conclusions.
.

March 10, 2021 3:31 am

We have also discovered drinking beer for medicinal purposes helps our bodies dump heat by expanding our surface capillary blood vessels, so to get the full benefit of our radiator cooled swimming pools you have to keep a sixpack of beer on ice in a floating cooler box, and drink bottles of beer at regularly intervals.

Cold drinks are not as good as thought. The body produces more heat to equalise the cold shock.
Warm drinks cause the blood vessels to dilate and the fluid to be better absorbed by the blood. One can compensate more efficiently for the loss of fluids due to summer temperatures.
Warm drinks are therefore actually more sensible to help your body cool down, as the additional heat signal ensures that we sweat constantly – but only slightly. By the way, it’s better to avoid alcoholic beverages, as they dehydrate the body even more. Warm drinks are particularly recommended, which at best supply the body with additional electrolytes, which are also lost during sweating.

JeffC
Reply to  Krishna Gans
March 10, 2021 4:14 am

That must be why beer in the south of England is always served warm!

eyesonu
Reply to  Krishna Gans
March 10, 2021 8:10 am

I guess I will remain an ‘abuser’ for all times. I like my beer ice cold and my whiskey on ice and my women on fire!

ATheoK
Reply to  Krishna Gans
March 10, 2021 10:50 am

“Asterix and Obelix” in Britain; “Warm Beer!”

Including where Dipsomanix can get the pub barman to “Take the chill off” of the beer.

David Dibbell
March 10, 2021 4:07 am

I live in upstate NY. Population has been declining, and the tax base is shaky. But surely any day now, climate refugees from the tropics will arrive to “build back better.” Or not.

Sara
March 10, 2021 4:25 am

Just a question: we’re really a tropical species that somehow managed to learn to survive in really, really bad cold weather (along with a lot of other mammals), so how come warmth is now a threat?

I have seldom run across anything as silly as “:warmth is a threat to Hoomans” in a long time.

If it’s a threat, then why do we run a furnace or set a fire in the fireplace in the winter?

Just askin’, because without even grazing across the sordid details, it comes off as just plain dumb to say that heat is a threat to Hoomans. Or maybe I’m on the wrong planet… again.

sky king
Reply to  Sara
March 10, 2021 5:34 am

Here in Subic Bay today was 77F-92F with 75% humidity. People are multiplying faster than Wuhu or Duterte can kill them. Heat and humidity just make us more randy.

PCman999
Reply to  Sara
March 11, 2021 3:53 pm

Environmentalists don’t care about humans, they fantasize about getting the population down below a billion and even suggested a form of ebola as the means. Misanthropes can’t be trusted – they work for the enemy.

Lurker Pete
March 10, 2021 4:58 am

and the winner of the 2021 WUWT Bad Science award is…

OweninGA
Reply to  Lurker Pete
March 10, 2021 8:31 am

In hot competition with a large number of competitors. It is only March, they are just getting warmed up!

John Kelly
March 10, 2021 6:42 am

That’s what I love about your commentary Eric; all sorts of practical solutions for everyday life that boring climate scientists would never understand because it pops their theories.

Mohatdebos
March 10, 2021 6:53 am

As Judith Curry asked rhetorically, “how does a paper like this get published?” You would think they would map population density by latitudes. They will found density is highest in humid tropical and equatorial latitudes. I was at a seminar recently where the presenter showed charts (attributed to Brookings Institution) about how people will be moving to upper Michigan and Canada to avoid heat. As a property owner in Michigan, I was pleased. However, the presenter went ballistic when I pointed out that most of my neighbors moved south when they retired.

eyesonu
Reply to  Mohatdebos
March 10, 2021 8:15 am

“how does a paper like this get published?” —— Keep it behind a paywall and hope no one reads it.

Editor
March 10, 2021 7:50 am

Eric ==> Bruce Van Sant developed a method for comparing economies and their costs of living based on the cost of a bottle of beer: loaf of bread == 1 bottle of beer country X, 1.3 bottles country Z. I believe he called it “beer-onomy”.

ATheoK
March 10, 2021 10:10 am

Here we show that an integrated temperature–humidity metric for the health impact of heat, namely, the extreme wet-bulb temperature (TW), is controlled by established atmospheric dynamics and thus can be robustly projected on regional scales.

For each 1 °C of tropical mean warming, global climate models project extreme TW (the annual maximum of daily mean or 3-hourly values) to increase roughly uniformly between 20° S and 20° N latitude by about 1 °C.

This projection is consistent with theoretical expectation based on tropical atmospheric dynamics, and observations over the past 40 years, which gives confidence to the model projection.”

More self aggrandizing model nonsense

Dale S
March 10, 2021 11:13 am

“For a 1.5 °C warmer world, the probable (66% confidence interval) increase of regional extreme TW is projected to be 1.33–1.49 °C, whereas the uncertainty of projected extreme temperatures is 3.7 times as large. These results suggest that limiting global warming to 1.5 °C will prevent most of the tropics from reaching a TW of 35 °C, the limit of human adaptation.”

We already have a ~1 C warmer world from abritrary-19th-centry-levels already, 2/3rds of the way there. It would be useful to show what the observations from the warming so far actually show for “tropical land”, but without access to the paywall their figure 3 (seems to have observations) is unreadable. Figure 4 is readable, and shows a +1.5C impact of about +1.3C for tropical land, more than I would have expected. But the TMax for tropical land is about +2.0C and in a wide range between +1.0C and +3.5. Given that *most* of the warming has already occurred, this seems like an awfully large “projected” range, and contrary to what would be expected from a constant forcing.

PCman999
Reply to  Dale S
March 11, 2021 4:27 pm

But it’s exactly what would be expected from scientists just making crap up.

S.K.
March 10, 2021 1:40 pm

Mother Nature knows how to deal with imbalances and she totally ignores uneducated opinions and advice.

March 10, 2021 4:29 pm

I’ve just been writing about the problems caused by decreasing tropical temperatures over the last 1000 years. I only read this because I thought it might have some actual data… but no! Yet again another silly speculative article with no scientific basis.

Loydo
Reply to  Mike Haseler (aka Scottish Sceptic)
March 10, 2021 10:22 pm

“decreasing tropical temperatures over the last 1000 years”

Really? Got a link?

observa
March 11, 2021 5:55 am

Seems children aren’t going to know what dust looks like in Britain-
Extreme rainfall in Britain to be 10 times more likely this century: Met Office (msn.com)

old construction worker
March 11, 2021 2:16 pm

Wet Bulb? I didn’t know Co2 had a “wet bulb” temperature? So, tell me again why we should regulate Co2? (sarc)

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