Short takes on science, business, health, agriculture and possibly the kitchen sink

Robert Wise   email  
Living with Heat II: Clothing and Accessories
Just common sense? Not necessarily.
(Second in a series on living and working in hot weather, in non-air conditioned spaces.)

"Face into the sun", they told the young man; "Stand still". There he stood for half an hour, at midday in the Negev desert at 100 degrees Fahrenheit. He sweated heavily into his black, double layered Bedouin robes and hood. The air was only 100F, but the surface of his robe was 117F.

Enhanced interrogation? No- he had fallen in with a gang of zoologists, researching a subject so mundane it rarely gets scientific attention: the color of clothing.

These professors from Harvard and Tel Aviv U. wondered why Bedouin tribesmen wore black robes in the desert heat, when black absorbed more of the sun's energy than any other color. An identical set of white robes, worn by the same long-suffering man, registered only 106F after a 30 minute exposure. The black robes absorbed nearly three times as much solar heat as the white robes.

Paradoxically, the man was just as comfortable - or not - in either color robe. His skin temperature registered the normal 91F, the air circulating next to his skin remained 100F, and he sweated at the same rate in either color. He sweated slightly more in a tan army uniform, and even more when wearing only a pair of shorts.

The results of this 1980 experiment were never explained. The researchers speculated that there was a "bellows" effect enhancing the airflow under the robes, or a "chimney effect" with hot air rising rapidly through the robe and flowing out at the neck. Recent articles have credited better convection under the black robes, or the thickness of the double layered garment.

All agree it had something to do with air circulation within the man's clothing. Which suggests that convective and evaporative cooling are more complex, and maybe more effective, than the simple estimates I presented in the post before last.

Choosing Hot Weather Clothing
Scientific advice on clothing for hot weather is hard to find, but at least the two authoritative sources I found were in agreement:

Indoors, or in full shade, wear as little clothing as you are comfortable with. Choose lightweight fabrics and loose-fitting garments.

For outdoors, you still want light weight and loose fit, but must also protect yourself from the sun's beam, to stay cool and avoid sunburn. Dark fabrics may be OK for a well ventilated garment. But if you need tight fitting clothing for some reason, look for lighter colors; bright white would be best.

A loose fit provides better ventilation, enhancing the body's principal cooling mechanism: perspiration. At air temperatures above 91F or so, it's the only way your body can keep cool (see this post). You can sweat a good deal without feeling sweaty, in well ventilated clothing, or in bare skin in the shade. In dry air, you may not feel it at all.

The "light and loose" guidelines leave a wide range of choice in men's clothing, and much wider in women's. The experts in my references gave no specific advice on garment choice except for Professor Ross Di Corleto's remark, "Bring on the kilts!"

Reasoning from their guidelines, a garment should have as many non-elasticized openings as possible, for good ventilation and a possible bellows effect. Shirts and blouses shouldn't be tucked in. The long skirts and sleeves sometimes worn by ladies in warm weather may work well, if they ventilate well.

The standard baseball cap, T-shirt and shorts, almost a uniform for men in my community, is not an optimum choice. A T-shirt feels light and airy when you put it on in an air conditioned room, but it clings to the shoulders, back and chest. When you walk out into the sun and begin to sweat, it clings worse.

A button-front shirt provides more airspace, and the front opening gives some extra ventilation even when buttoned. Short sleeves ventilate best. If you want the protection of long sleeves, keep the cuffs as wide open as possible.

Baseball caps don't shade the face very well, and don't shade the ears or neck at all. A wide-brimmed hat is best- the wider, the better, though you run into tradeoffs with weight and clumsiness. At the maximum, you could go with a wide coolie-style straw hat, or a sombrero. I've never seen the cartoon type sombrero, wide enough to take a nap under, but someone probably makes them.

Shorts are a good choice, provided they are loose fitting. However, if you can prove Celtic ancestry, you might consider a kilt.

Protecting against ultraviolet and the risk of skin cancer
UV protective clothing can be well ventilated. Some UV shirts have mesh panels under flaps to enhance air flow. But quality is critical; some discount store brands have heavier, less breathable fabric that enhances the feeling of warmth.

I wish there were more data available on the UV protectiveness of ordinary fabrics. Obviously, thick, tightly woven cloth such as denim is opaque to UV as well as visible light. You can hold fabric up to a light and see how much shines through. As a first guess, if it stops visible light it probably stops near-visible UV, but I have no data to back that theory.

There's also the beachy approach to UV protection: minimal clothing and a generous coat of sunscreen. But the lotion may interfere with the body's cooling. According to Professor George Havenith,

"..sunscreen sometimes affects sweating. So the sunscreen then might reduce the amount of sweat evaporation or the amount of sweat production."

I've discussed scientific advice on hot weather clothing, but it's also available from men's and women's magazines. The suggestions reflect personal taste and experience as well as science; I've given some references below.

One fashionisto made an excellent point; "Never wear a hat Unless it's straw," going on to describe some lightweight straw hats. But the point is: hats interfere with ventilation around the head, where you need it most. No matter how perforated the crown may be, it slows the air flow around the head, while the band presses directly against the flesh. So when you're in shade, take it off and let your head cool a bit more. For an old-fashioned alternative, see below.

Accessories: bringing your own shade; wearing air conditioning
"Parasol" sounds like a throwback to the 19th century, yet it's highly effective. Stepping off the bus one day when our heat index was 103F, I noticed a young Hispanic lady ahead of me putting up a black umbrella. Strange, I thought. But I had a long walk home, and after the first mile I was wishing I had followed her example.

An ordinary double-fold umbrella held at the proper angle will shade your entire upper body and also alleviate the need for a hat. A dark fabric stops most of the sunlight and probably the UV as well. For more protection, you can buy UV-protective parasols, some with a silvered finish for ultimate reflectivity.

Several manufacturers offer cooling neckbands, which are either soaked in water or cooled in the freezer to provide a local cooling effect. Two studies of these devices disagreed as to whether they actually cooled the body or just made the wearer feel cooler. For an athlete striving for peak performance, just the feeling of being cooler may help, to a point. Similar technology has been applied to cooling hats, bandannas and vests. They probably don't work longer than an hour or two, helpful for an athletic event but not a long hike or bicycle trip.

Other sources of information, and a caution
For more information on dressing for heat, you may want to subscribe to The Thermal Environment, where Dr. Ross Di Corleto discusses heat stress from an occupational health point of view. He also offers a cell phone app to predict heat strain by the ISO 7933 standard.

I'm not the only one thinking about future heat stress as a result of global warming. The European Union is sponsoring a research initiative called HEAT-SHIELD, looking at ways to mitigate increasing workplace temperatures in Europe. Twenty institutions are joining in the effort, including the University of Loughborough's Environmental Ergonomics Research Center, led by Dr. Havenith, quoted above.

And by the way, if you're walking on the beach some day and see a man coming toward you in black robes and a hood, don't assume he's a Jihadi. It could be me, trying out the Bedouin approach.

Some recommended togs and tools: My favorite hat, some UV-protectant shirts, a double-fold umbrella and a golf umbrella.


Post a comment...
All comments are moderated. I may answer flame mail directly, but will not post it unless it makes a good point.

"Why do Bedouins wear black robes in hot deserts?", Nature 283, 373-375 (24 January 1980). The full text of this article is behind a paywall. Non-subscribers can rent temporary access for $3.99.

"Summer Science: Clothes Keep You Cool, More or Less", July 25, 2012. An interview with Dr. George Havenith, lead researcher of the Environmental Ergonomics Research Center, Loughborough University, UK.

"How Important is the Colour of Clothing When it comes to Heat Stress?", Dr. Ross Di Corleto. One of many articles on heat stress on Corleto's website The Thermal Environment. Other topics include long sleeves, hydration, over-hydration, heat stress and alcohol, personal cooling devices and the free heat stress prediction app.

5 Principles for Hot Weather Clothing | How to Dress Cool in Warm Weather | Dressing For The Heat, article on Real Men Real Style website.

"What to Wear When It's Too Hot To Wear Anything", Rachel Besser, July 15, 2016, Refinery29 website.

"The Best Hot Weather Clothing That’ll Help You Survive Summer" , Michelle Persad, Huffington Post, July 15, 2016.

Revisions to this post:

The Grass Really is Greener, Especially Between the Rails
Some thoughts on Europe's resilience and how we could emulate it

My wife and I just returned from a cruise up the Rhine from Amsterdam to Basel, followed by a few days in Switzerland. The contrasts with home were remarkable. In many ways, Europeans are better positioned for energy transition and global warming - mainly because of decades of public policy and investment, but also because of certain habits and attitudes.

A freighter passes our ship, heading into a bend, in the Rhine Gorges area. Notice the vineyards on the slopes.

All the way up the Rhine, the water was amazingly clean, despite heavy commercial traffic, factories and power plants. People were swimming in it, fishing in it, camping beside it. At every stop, swans and ducks swam up to our ship to beg for bread.

The Rhine has been thoroughly cleaned up since the 1970s, when it was described as "the sewer of Europe." In the worst incident, a single toxic discharge killed all aquatic life from Basel down to the Rhine gorges.

Today, strict regulations on discharges keep the water quality high. It must have been very expensive to clean up, and costs to industry and shipping continue, but the result is beautiful: a major transportation corridor also provides a fishery and a source of clean water.

Passing a campground beside the Rhine.

The nearest American analog is the Ohio River - similar in length and volume of commercial traffic, and also the subject of a long cleanup campaign. The eight-state commission in charge of the cleanup has made great progress, but has more to do if the Ohio's water quality is ever to equal the Rhine's. Unfortunately, the commission voted in 2015 to relax some water quality standards.

Today there's an annual Ohio River Swim. But is the stream really safe for swimming? The commission answers unequivocally,

"'Yes and no.' Most every activity that humans engage in carries with it some level of health risk.."

Fecal coliform and E. Coli levels are monitored weekly from April through October. Fox affiliate WXIX in Cincinnati offers a cell phone app to check the latest readings.

The lakes in Lucerne and Zurich appeared even cleaner than the Rhine. Everywhere along the lake shores you could see bottom, with luxurious growths of lake weed for the swans and ducks to graze on. These lakes have the advantage of a strong current moving through them. Even so, I was amazed at their cleanliness, with towns and villages lining the shores.

Perhaps there was less turf grass and lawn fertilizer than at home. A few odd statistics suggest that total fertilizer use is less than in the states, possibly 33 per cent less. But this includes farms and grazing land, and the comparison may not be apples-to-apples.

Left: A swan feeds on lake weed in Lake Lucerne, paddling constantly to stay in place in the strong current. / Right: The paddle steamer City of Zurich backs away from the dock at Rapperswil. Launched in 1909, she carries passengers daily on Lake Zurich.

Air conditioning is unusual though not rare in northern Europe. It's not really needed, except in the "unseasonable" summer heat waves which are becoming more common. One of the worst killed thousands in 2003. Still, there's a cultural bias against using air conditioning. German visitors to the US return with tales of over-cooled rooms, feeling chilly and even catching cold from the ubiquitous AC.

We had an air conditioned cabin on our river ship, but often turned the AC off and opened the window. Near Zurich, we stayed in a very comfortable, modern hotel which was not air conditioned. The windows were big and openable, like every European hotel I can remember. There were two-layer drapes to keep out the sun when necessary. The walls were the usual thick masonry, probably built around a core of hollow "silo tile" like I've seen in construction elsewhere in Europe. Always assuming cool weather, the staff made up our bed with a sheet-enclosed quilt and no top sheet.

There's a personal side to this paucity of air conditioning: most people are walking and bicycling on their errands. Shopping involves walking city streets, rather than the air conditioned corridors of an enclosed mall. People are used to being outdoors, and probably well acclimated to the normal outdoor weather of their region. It helps in warm weather, as I've discussed elsewhere.

Every European city we visited was alive with bicyclists, riding on dedicated bikeways segregated from pedestrians. In Amsterdam, the bike lanes were painted red- "to hide the bloodstains," critics said. There were massive bike parks at railway stations and ferry landings, as well as bike-share programs.

Bicycle traffic on the main street of a small town. The street is closed to autos from about 9AM to 5PM.

Amsterdam led the trend with an average of two bicycles per resident. The city literally could not exist without the bicycle. To organize the same population, industries and commerce along the lines of Atlanta or Orlando would take at least ten times as much land area, all paved.

I thought there were more bicycles than I'd seen on previous visits, but statistics show that bike usage is rising very gradually. Usage varies between countries, but biking and walking are much more popular than in North America. Not just for recreation, but for everyday commuting, shopping and errands.

A table compiled in 1998 shows the contrasts:

From an article on the website.

Maybe automobile culture is an Anglo thing. Anywhere in the U.S., Canada or Great Britain, 60 per cent or more of all trips were made by car, reaching 84 per cent in the U.S. Anywhere in continental Europe, only about 40 per cent- the rest were made by foot, bicycle or public transit.

Attitudes toward the bicycle in Great Britain resemble those in the states. A study by sociologists at Lancaster University concluded that "Many people barely recognize the bicycle as a legitimate mode of transport; it is either a toy for children or a vehicle fit only for the poor and/or strange.."

Denmark and the Netherlands are ahead of the rest of Europe in bicycle usage, partly because they are so flat. A Danish joke about continental Denmark claims "If you stand on a box, you can see the whole country." Other continentals prefer walking over bicycling, but all use public transport heavily.

Most riders are dressed for work, shopping or going out- not exercise. You see women riding in high heels, but not many riders with helmets. According to our Dutch tourguide, "We consider bicycling as more or less like walking; you wouldn't put on a helmet."

Left: Riverside bike park in central Lucerne. / Right: The bicycle my younger daughter needs.

Public transit is much better developed in Europe. Trains go virtually everywhere, and nearly every major city has a subway. In the small Zurich suburb of Kloten where we stayed, there were more tram lines around the city than we have bus routes in my home county.

We bought 24-hour transit passes for 13 francs at our hotel, which took us back and forth on commuter rail to Zurich, back and forth across the city on trams, and even onto the lake steamers going to nearby towns. The 24 hour period spanned enough of two days to cover nearly all our local travel.

Thick grass turf grew on either side of the rail line, as well as between the tracks, to minimize rattling. Nearly all the trains and trams we saw were electric - no engine noise or smoke.

We saw an exception one morning when boarding the commuter train. A beautiful old steam locomotive softly chugged into the next platform, pushing a caboose, with a blue-uniformed railway officer keeping watch in front. It must have been their mascot.

Think what would happen here in a liquid fuels crisis- an oil price spike, or a general shortage. A great deal of Europe's rail/tram/subway net is electrified, and a lot of power is generated by hydroelectric, nuclear, wind and solar power plants. Sustainable or not, they would keep running in the near term, allowing a good proportion of the trains to keep operating. Service would be rationed, of course; a lot of local lines would be shut down, and the trains in service would be crowded.

But here you have a population that routinely walks or bikes, at least to the tram stop. People would have to travel further under their own power, maybe wait for a second train on the commuter line, but many could still keep their normal work schedules. Wealthier folks, now relying on automobiles, could join the masses on foot or commuter rail.

Contrast the U.S., where only 16 per cent of trips are made without an automobile. A liquid fuel crisis would put commuters and shoppers in deep trouble.

We can't undo our decades of investment in streets, roads and highways to suddenly switch over to rail. But in most of the country, the rudiments of a public transit system already exist. My county, for instance, has a network of bus lines. Each bus has a rack for up to three bicycles, so you can carry your bike along. Most of us couldn't commute to work via this system; the schedules and stops are too sparse. But if your schedule is flexible, you can get almost anywhere.

Think of Atlanta, with its spiffy commuter rail lines running North-South and East-West, linked across each quadrant by a bus network that goes everywhere. The legions of auto commuters ignore the bus network, but it's there and could be utilized.

Americans aren't condemned to long-distance driving for intercity transport, either. There are long-established regional bus lines that provide good service at a decent price. I think of the Van Galder and Badger lines in the upper Midwest; there must be similar carriers in other regions.

And a new outfit, Megabus, provides intercity service from Miami north into Maine and Canada, and as far west as San Antonio and Council Bluffs - not to mention some key cities in California and Nevada. They charge as little as $5 for a 300 mile ride, depending on how early you book.

I've ridden Megabus to and from Atlanta a few times. It reminds me of the old-time second class rail cars in Europe. Everyone climbs aboard with blankets, books and bags of snacks to amuse themselves along the way. The buses are comfortable, strongly air conditioned, and have low-voltage hookups for battery/computer/cell phone charging.

A Megabus at the curb in California. From the media photo gallery at

We who are aware of peak oil and global warming could help grow these existing systems by slightly changing our habits. Ridership is the bottom line, and it's lack of ridership that discourages municipalities and private companies from investing in public transit.

If you can use your local bus service without too much inconvenience- if not for commuting, maybe for some errands or taking a bike to some new area to ride- you'll provide a little support for public transit in your community. (As well as saving a bit of fuel and reducing greenhouse gas emissions.)

If this works for you, you can vote for public transit with your feet and your dollars. You don't have to wait for a referendum, and you can vote as often as you like.

One factor that discourages people from riding the bus is class consciousness. Of course we don't recognize class in America, except for middle class. So let me be even more crass for a moment, and call it race consciousness. You'll be sitting on benches with people of various races - side by side with the working class, the looking-for-work class, the homeless and the carless.

Will you be safe? Most likely, if you stick to daylight hours and major streets, and don't ride through a gang-war zone. And from time to time, you'll meet some friendly and interesting people.

You can promote bicycling and walking the same way, by doing them. When everyone sees pedestrians and bicyclists on the streets, or is one, it's easier to persuade local government to invest in bike paths and walkable neighborhoods.

Even auto and air conditioning usage can be reduced by a deliberate change in habits. If you're old enough to remember the 1970s, you know all about this. Turn the thermostat up to 80 during the day, then cool the house down at night. Batch your errands so you don't make individual car trips for each one. Consider car pooling. Remember the question displayed on the dashboard of every government vehicle in those days: "Is this trip necessary?"

These measures won't bring the millennium, even if we all do them. But they can save a bit of gasoline, keep a bit of carbon dioxide out of the air, and help shape habits and consciousness in the direction our whole society needs to be going. Just a nudge in the right direction. And if a friend or neighbor likes what you're doing and decides to follow suit, your influence doubles.

There are several versions of this bumper sticker. This one is available from Zazzle in Australia for AU $8.25 plus shipping - totaling about US $10 for my address.

The next post will return to the "Living with Heat" theme, discussing clothing and accessories for hot weather.

Sept 27
I love the latest article. Of course, it mirrors a lot of what we've all been reading (with most of us ignoring it) for some time. The huge stumbling block is this: motivating people to behave in a climate-cooperative way instead of an I'll-do-what-I-please way. I wish I knew the answer to forcing that shift. Perhaps the real answer is to ban auto advertising to anyone under 21.
- George Meyer
Tampa, Florida

Glad you approve. I don't think there's any way to force a shift in attitude; it has to come from the grass roots. Particularly so in a country where political leaders and would-be leaders are so distrusted. Most of my posts are pitched to an audience who are aware of peak oil and global warming. There are a good many of us- enough to support a number of blogs and websites, not to mention a new literary genre. If we could deliberately change our habits as I've suggested above- and as many others have suggested- we could start a trend.
- Bob

Post a comment...
All comments are moderated. I may answer flame mail directly, but will not post it unless it makes a good point.

Anne Schulte-Wülwer-Leidig, Deputy Secretary, International Commission for the Protection of the Rhine, "From an Open Sewer to a Living Rhine River". Available from a symposium archive here.

USA Today, " Ohio River again tops for industrial pollution", March 2015.

Radio station WXIX: app to check Ohio River water quality. table of bicycle usage for trips by country Europe and North America, 1998.

Malcolm J. Wardlaw, " History, risk, infrastructure: perspectives on bicycling in the Netherlands and the UK ", Journal of Transport and Health, Vol 1(4) December 2014.

Elizabeth Rosenthal, " On Biking, Why Can’t the U.S. Learn Lessons from Europe?", Yale Environment 360, July 14, 2011.

Elizabeth Rosenthal, " What makes Europe greener than the US?"/ Yale Environment 360, Sept 28, 2009.

Matthew Schofield, " In sweaty Europe, air conditioning is no way to cope with the heat",, August 10, 2015.

Revisions to this post:
Oct 1: Replaced a picture I couldn't get permission to use, fixed a typo, some minor rewording.

Living with Heat: The Challenge and the Body's Response
How the human body copes with heat stress and learns to do it better

Photo from "Riding and Training in the Heat",, permission requested.

To feel comfortable, even to survive, your body must continually shed heat. It generates heat by metabolizing food and working its muscles. In sunlight, it gains heat constantly from the sun's beam. Walking in full sun in moderate temperatures, it must continually lose the heat equivalent to six 100-watt light bulbs, or a small space heater. It's easier if you are acclimated to your outdoor environment.

The body sheds heat by convection*, radiation and perspiration. But as temperatures rise toward the normal skin temperature of 91 Degrees Fahrenheit, radiation and convection become less and less cooling. Above 91F, they begin to warm the body. As I described in my last post, you feel warm even in shade, and a breeze feels hot. In these temperatures, only perspiration keeps you from heat stroke.

"Sweat- ewwh!" you might be thinking. Folks raised in cool climates may see it as an extreme condition, to be avoided- "Don't sweat yourself." Growing up with bright sunlight and heat, you learn to tolerate it and even appreciate it to a degree. If you're exercising in this heat and not sweating, then you have something to worry about.

I constructed the chart below to show how the body cools in various temperatures, from a comfortable 70F to the 105F often used in hot-room (Bikram) yoga. It assumes you are walking, bareheaded, in full sun with a light breeze. The dashed lines show the body's heat load under the above assumptions, also walking in full shade, or resting in full shade. (In full sun, even a broad-brimmed hat will reduce your heat load significantly.)

Chart of the cooling and heat load on an average human body in a 5 mph breeze, mostly following the calculations in the UBC Physics Department reference given below. In the lower 70's, cooling exceeds the heat load on the body; a light windbreaker might be needed.

Cooling by convection and radiant heat is almost proportional to air temperature in these conditions- proportional, that is, to the difference in temperature between your skin and the surrounding air. Above skin temperature, these processes begin to warm the body, adding to its heat load.

Convection works much better in moving air. With no wind, it cools only half as much as radiation. In the light wind shown on the graph, it cools about four times as much.

Increasing wind speed brings diminishing returns; the first few miles per hour are the most significant. Ceiling fans need only stir the air, at their lowest setting, to cool people in the room.

Radiative cooling is harder to estimate. It's the balance between the heat radiated by your body and the heat radiated to it by the surfaces around you. The graph assumes that the surfaces around you are about the same temperature as the air- an assumption often used in studies of indoor climate. But it won't be true if you are walking on a hot asphalt pavement or riding in an air-conditioned car.

Perspiration and humidity
The graph assumes that your body will start sweating as soon as it needs to, and will sweat enough to take care of any heat load not dissipated by convection or radiation. This will happen if you are acclimated to your outdoor environment (discussed below), if you're drinking plenty of water and if the air is dry enough for sweat to evaporate easily. The wind helps; evaporation goes slower in calm air.

Perspiration works better in dry climates- sweat evaporates so quickly you hardly notice it. Down home, in heat and high humidity, you are easily drenched in sweat. I didn't find a good way to represent this on the diagram, but the Heat Index provides an idea of the additional heat load caused by high humidity (table in notes below).

Near 105F, you need to sweat enough to dissipate 1000 watts or more- about 1-1/2 quarts of sweat per hour. This is about the maximum sweat output considered "normal." But with acclimation to extreme heat, some people can sweat as much as 2-4 quarts per hour.

Acclimation: learning to live in your climate
I'm sometimes tempted to ask certain neighbors, "Do you really live in Florida, or just a set of air conditioned boxes with the thermostat set to Upper Michigan?"

Not a fair question, because I spend most of my day in air conditioning too. But I like to know I can tolerate the climate I live in. I get out in it regularly, whether bicycling in Florida summer or walking in the snow in Wisconsin winter.

However you feel about it, acclimation will improve your health, especially if you work or exercise outdoors. As the climate warms, it's going to be more important for more people, more often.

The best way to acclimate to a warm climate is to work or exercise in the heat, preferably two hours a day for 2-3 weeks. About 75% of the benefits are gained in the first five days. An hour every other day will do, but the process takes longer.

Working out in an air-conditioned gym won't do it, though acclimation goes quicker if you're already in good shape. Hot-room yoga won't accomplish it, either: there's plenty of heat stress, but little exercise.

How does the body change with acclimation? It sweats faster and starts sweating at lower temperatures. Blood volume increases, and heart function, blood pressure regulation and blood distribution improve. Less salt is lost in sweat and urine. Your overall ability to perform work or exercise improves.

It works differently for hot-dry climates than hot-humid, where the body must learn to sweat even more. Humans seem better adapted to the hot-dry environment.

Acclimation isn't permanent: we lose it within a few weeks if not regularly exposed to heat. So we probably all need to get re-acclimated each spring. But if you're able to keep up regular program of outdoor exercise or work year-round, you'll re-acclimate as a matter of course.

So one way to build resilience in the face of global warming is to make sure you stay acclimated to your local climate- provided your health permits it. For most of us, our climate is already hotter than the climatic normal, and will probably get a little hotter each year.

And it may help to keep in mind the basic heating and cooling processes acting on your body. At least you won't make the mistake of seeking your "place in the sun."

I'll add some footnotes to this post in a day or two, with the full derivation of the numbers in the diagram, and some background on thermal radiation. The next post will discuss clothing and accessories that help in hot weather.

* Convection has two scientific definitions. Here I'm using the more general one: any transfer of heat through a liquid or gas. Convection also denotes the motion generated by such heat transfer, such as the growth of cumulus clouds or the bubbling in a lava lamp.

National Weather Service Heat Index Chart

From NOAA web page

Computation of chart data
Numbers for the chart were computed using equations presented in the article "Heat Balance in the Human Body", a web page on the University of British Columbia's website. Assuming that the human body is in thermal balance with its surroundings, the cooling processes must balance the heat gains:
M + S = C + R + P
Where M is the metabolic rate needed to support minimal body processes plus muscle movement,
S is the heat energy absorbed from sunlight,
C is the body's cooling by convection,
R is cooling by radiant heat, and
P is cooling by perspiration.
As I've described, C and R can turn negative, heating the body rather than cooling it. My chart doesn't show "negative cooling", just the additional perspiration needed to balance it. There are some much smaller heat gains or losses by conduction through the soles of the feet, which are ignored here.

Metabolic rate: The heat generated by basic metabolic processes for an average human body, awake and at rest, is about 100 watts; sleeping, about 70. When walking, about 325 watts is generated;; when running or bicycling fast, between 450 and 800 watts.

Sunlight: The full power of the sun's beam is about 1000 watts per square meter. Assuming that only half a square meter of the body's total 1.8 square meter area is exposed to direct sun, and that half of that is covered with clothing, the power of the heat and light received from the sun's beam is about 250 watts.
S = (0.5)(1000 W/m**2)(0.5 m**2) = 250 W
We assume no heat gain from sunlight falling on clothing, which may not be correct. I'll revisit this point in a later post.

Convection: Cooling or heating by convection is proportional to the temperature difference between the skin and the surrounding air, and to the total area of skin. An empirical factor relates their product to the wind speed.
C = (K)(Area)(skin T - air T)
where T is in degrees Kelvin. Normal skin temperature is about 33 deg C (91.4 deg F) = 306 deg K.
K is 3 W/m**2/deg K in calm air, or 26 W/m**2/deg K with a 2 m/sec wind (4.47 mph)
Surface area of an average human body is about 1.8 square meters.

Radiation: Cooling or heating by thermal radiation is proportional to the difference in the fourth power of temperature, in deg K, between the skin and the surface(s) radiating heat towards it. This implies an average temperature for the surfaces surrounding the body, called the Mean Radiant Temperature. For indoor measurements, this is often assumed to be the same as air temperature, and this assumption is used in the chart.(Some more notes on radiant hear below.) We also assume that the clothed and unclothed regions of the body have same skin temperature.
R = (Area)(e)(S)((skin T)**4 - (air T)**4)
e is the emissivity of human skin, about 0.98
S is the Stefan-Boltzmann constant, 5.67 x 10**-8 W/m**2/deg K**4
(Although the temperature differences work out to huge numbers, the resulting curve of R is almost a straight line in the range of temperatures shown on the chart; you can see a very slight curvature.)

Perspiration: The heat lost by perspiration can be calculated, as shown in the UBC article. But rather than calculate it, for the chart I assume that any excess of heat load over cooling by convection and thermal radiation is made up for by perspiration.

Note on Light vs Radiant Heat:
It's all radiation, of course, but the wavelengths are very different. Imagine an electric stove burner which you have just switched on. At first it's not too warm to touch, then a little too warm, and holding your hand a few inches above you can feel the radiant heat. It's in long wavelengths, the ones typically given off by objects and creatures on earth. As the burner warms, you feel the heat become more intense. Just before it begins to glow, you feel intense heat, from shorter wavelengths like the ones in the sun's beam. About half the energy of the beam is in these wavelengths. When the burner begins to glow, it is starting to radiate in visible wavelengths, emitting light rather than heat. About forty per cent of the sun's energy comes in these wavelengths, most of them much shorter than the stove burner emits, sensed as very bright light. A small percentage comes as still shorter wavelenghts, not visible as light: ultraviolet, the wavelengths that cause sunburn.


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University of British Columbia, Physics Department, "Heat Balance in the Human Body,"
..estimates heat load and cooling effects on the human body, with full calculations and an example..

Cornell University, student downloads, "DEA 3500 Notes: Thermal Regulation"

Korey Stringer Institute, U. of Connecticut,"Heat Acclimatization",

Human Performance Resource Center, "How can heat acclimatization prevent heat illness?",

Tan, C.L, Wong, N.H. and Jusuf, S.K., "Outdoor mean radiant temperature estimation in the tropical urban environment", Building and Environment · June 2013

..diagrams in this paper show Mean Radiant Temperature approximating air temperature at night and in shade..

Shashua-Bar, L, Perlmutter, D. and Erell, E., "The influence of trees and grass on outdoor thermal comfort in a hot-arid environment" INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 31: 1498–1506 (2011)
..infrared photography of test site shows radiant temperature of various surfaces..

ACE Study Examines Effects of Bikram Yoga on Core Body Temps April 21, 2015

..mentions "standard" of 105 deg F, 40% humidity, limited water breaks..,"New Study Finds Bikram Yoga Poses Potential Threat of Causing Heat Related Illness,"

Revisions to this post:
Aug 16: Revised cooling chart, minor rewording.
Aug 21: Added notes on chart calculations. Recomputed chart, corrected 100 watt error in heat load used on earlier version.
Sept 9: Corrected seven to six in first paragraph, minor changes to others.

Heat: the Feeling and the Science
I've been griping about this unusually hot Florida summer, but after three days in Las Vegas I will complain no more. Temperatures were above normal there, too, in this unusually hot summer of an unusually hot decade.

It's a dry heat, they say, and the Heat Index confirms it. When the air temperature reached 113 Thursday afternoon, it only felt like 106. Whoopee.

Shade gave no relief from the heat. Our hotel entry yard, permanently shaded by a roof, felt oppressively hot. Twenty feet underground, on the lowest level of the parking garage where the sun never shines, it was hot.

The hotel's pools were crowded with guests trying to cool off. Everyone wore shoes to the edge of the pool to avoid putting bare feet on the scalding pavement. Attendants offered everyone two towels- one to dry off with, the other to spread on your lounger, which was too hot to touch. The water felt just a shade cooler than a heated pool.

The misters around the roof of the poolside bar were highly effective, unlike those at Florida theme parks. Droplets never reached table level, evaporating instantly into a jet of cool air.

Even the wind felt hot. At dinner on the pool patio- 108 degrees two hours after sunset- the occasional gust from dry thunderstorms nearby felt like a hot blast from a space heater.

Walking around the strip at night- about 100 degrees at 11 PM- I was surprised to see beggars sitting along the walkway with their signs and cups. How could homeless people survive in this heat?

Some of them live underground. Las Vegas has a network of storm drains, many big enough to walk in, where it can be 20 degrees cooler than the surface. Some homeless live in the drains; some duck in during the day when the heat in their tents and shanties is too much. They enjoy a cooler environment than the tourists, though even moderate rain can make a storm drain into a death trap.

Storm drain entrances, Las Vegas. From, permission requested.

What I actually sensed as "heat" was not the temperature, but the my body's interaction with the air and nearby surfaces. The body needs to lose heat constantly to maintain its 98.6 degree temperature. At moderate air temperatures, it cools by conduction to the surrounding air and even by convection- as if little cumulus clouds floated up from the skin. But when the air temperature exceeds body temperature, convection stops, and conduction begins to warm the body.

Another part of the sensation is radiant heat. The body radiates heat, and if it's warmer than most of its surroundings, it loses more radiant heat than it gains. But walk on a hot asphalt pavement, and you feel the difference: you're gaining more radiant heat than you lose.

The sun's beam is a strong source of radiant heat as well as light, and at moderate temperatures you feel cooler in the shade. It can be quite comfortable at 90 degrees in shade with a light breeze, if you haven't trained your body to expect air conditioning.

But in full sun you feel the radiant heat, as well as heat from the sunlight- absorbed by your skin and clothing and transformed into heat.

With all earth's climates growing hotter, and air conditioning becoming more expensive as energy costs rise, we'll all need to deal with more heat in the future. It's something worth thinking about. My next post will review some techniques for living in hot weather without air conditioning.

August 7, 2016
Mr. Wise:
Several years ago, I came close to moving to Las Vegas. A close friend was an editor at the Las Vegas Sun and there was a window for me to become a local columnist, with my friend's support. It turned out the office politics didn't unfold our way.

During the time I was considering it, though, I spent some time in Vegas, and I discovered the heat was dramatically different from what I experienced in Florida. The lack of humidity made human sensitivity to heat quite tricky. I could never quite tell how to stay properly hydrated outdoors.Also, the aridity of the area made for shocking differences from Florida. It was very clear that without constant engineering intervention in the water supply nothing would flourish for a large population. Returning to the area about 10 years later, I was a little frightened -- more people and cars; less available water; rising heat levels.

Since I've stayed in Florida, I'm becoming alarmed about the sure and certain rising sea levels. In about 50 years, we're going to have serious flooding from I-4 south. Miami Beach is already having serious flood control difficulties. My home city of Tampa is making some plans -- changing regulations for new housing; reinforcing some coastal areas -- but we're still building roads that will certainly go underwater in heavy storms within a few years.

Given the huge changes that are sure to come, we'll need to invest heavily in how to deal with a new landscape. I know that will create investment opportunities. I wish I could see investors getting organized in ways that will make the changes solvable and profitable, especially since the public appetite for taxation for public improvements is at a low point.

I can't help but feel that many of the solutions will be applicable to both Nevada and Florida, despite their differences. Some young entrepreneur will do well if he or she steps up with a strong voice and a plausible plan.

George Meyer
Tampa, Florida

Thanks for your thoughts. I don't see how Las Vegas can cope, in the long term, with rising energy costs and a prolonged drought in the southwest. The water level in Lake Meade is already near its minimum. If blackouts or brownouts start to happen, those folks in the storm drains may have a lot of company.

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Revisions to this post:

A Whiff of Sulphur
A correction, with some background on the biggest corporate tax break of all

Many of the shopping centers, office parks and industrial parks around us were built during a multi-decade surge in commercial construction starting in 1954, when Congress revised the tax code to permit “accelerated depreciation”. In effect, any new commercial building became a tax shelter. Owners and investors could take huge tax deductions in the first few years of a building’s life, making income from the building tax-free and often sheltering income from other sources. Accelerated depreciation fed a boom in shopping center construction, to the detriment of retailers in urban business districts. It was one of the main drivers of the century-long decline of independent retail.

A non-expert observer might think that accelerated depreciation was still fueling this boom. I did. Developers continue to build suburban shopping centers. Uptown business districts decay unless deliberately redeveloped or “gentrified”. Stores sit vacant in older shopping centers while new centers go up nearby. Accelerated depreciation still provides the biggest corporate tax break, in terms of total dollars saved. And in my personal experience, entering tax data for my rental property always leads me to the Modified Accelerated Depreciation System (MACRS). “Accelerated” is its middle name.

Yet MACRS is so strongly Modified it negates its Accelerated tag, at least for real estate. It depreciates commercial real estate on a straight-line basis over 39 years, a hairs-breadth faster than the 40-year straight-line depreciation used prior to 1954. Enacted in 1986, MACRS removed the strong tax incentive that biased developers and investors toward new construction.

In Standing Alone: The Independent Retailer in America , I wrote that the tax code ought to be revised “ put renovations and major repairs on an equal footing with new construction.” I stand by that opinion, but I must thank the very prescient members of the 99th U.S. Congress for addressing my concern long before I was aware of it. Which is a little embarrassing for me, but encouraging for the future of independent retail.

Still more encouraging is an evolving set of tax rules introduced in 2010 with incentives for improvements to existing stores and restaurants. These expenses can be claimed as depreciation on a 15-year schedule, yielding deductions even more generous than those allowed on new construction during the 1960s-70s.

The same rules apply to new restaurant construction and to improvements in leased property (such as the build-out required to open a store in a shopping mall.) An unrelated rule allows theme parks to be depreciated over 12.5 years.

When improving an existing store or restaurant, part or all of the expense can be claimed in the first year, like an ordinary repair, under section 179. The line between repair and improvement blurs; IRS advises that if a repair is “a betterment to the property” or “to restore the property”, it can be depreciated as an “improvement”. The property owner can tune these options depending on how fast his business income will repay the expenses.

So today we have strong tax incentives to repair and improve existing buildings. The bias toward new construction has been reversed, except for new restaurant buildings and theme parks.

(WARNING: Please don’t take any part of the this discussion as tax advice—talk to your tax advisor instead. If “the devil is in the details,” U.S. tax law is an earthly hell teeming with multifarious detail. This post can convey no more than a mild whiff of sulphur.)

And a Note: Minor changes were made to the book text on June 21, 2016 to reflect the above information. Any copies printed after that date will be correct on these points. Since this was not a full revision, the ISBN remains the same.

June 20
The rules on depreciation are complex and confusing - so much so that Senator Ron Wyden (D-OR), top Democrat on the Senate Finance Committee, has vowed to simplify and reform this issue.
- Rose Page, Tax Preparer
Merritt Island, FL

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“U.S. Tax Policy and the Shopping-Center Boom of the 1950s and 1960s”, Thomas W. Hanchett, The American Historical Review, Vol. 101, No. 4 (Oct., 1996), pp. 1082-1110 (partial paywall)
Abbreviated versions of Hanchett's analysis can be found here and here, but only the journal article details the tax code revisions of 1986.

“Tax Breakdown: Accelerated Depreciation,” Committee for a Responsible Federal Budget, 2013

IRS Publication 946: How to Depreciate Property

Turbotax 2015 (I used the program to check various depreciation situations in a what-if tax return.)

Revisions to this post:
June 16: minor rewording
Aug 16: added note on manuscript changes

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