Originally Posted by
East Hill
And, would it not be possible to direct some of that energy into cooking food?
East Hill
Oh please! Don't encourage him!
The body's perception of heat involves several factors -- direct sunshine, ambient temperature (which in turn can be influenced by reflection and radiation from earthly sources), wind, humidity and the body's core temperature plus its reaction to ultraviolet radiation exposure (sunburn).
If some or all of these is controlled, you are able to mitigate the effects. Shade alone won't do it all.
The only way to exclude the sun's direct rays is with a solid object... such as a tree trunk, and even a dense, intertwined hedge of leaves. Or else get under a roof. They all create a shadow, and there is 100% sun exclusion behind any one of them -- what is reflected from other sources is another matter.
As we all know, just sitting under a 100% SPF object won't mitigate the effect of heat if the humidity is high and the air is still, and the ambient temperature is high, too. And if the body is overheated from exercise... well, the effects can compound.
People work all day in intense sun. In fact, the penetration of UV and IR radiation is probably the same if the sky is clear but on one day a cold wind is blowing, and on another a hot wind is blowing.
This is all putting aside sunburn and cancer risk.
A couple of other things that I have picked up along the way. If you want to stay cool in very hot weather, use water and air movement to create evaporation. In the tropics this can be difficult because the air already is overloaded with moisture.
The experts in desert living, the Arabians, have used canvas tents for eons, and use the evaporative effects of water to provide cooling. It's the one really good asset of cotton garments.
The opal mining town of Coober Pedy has dwellings mined into the ground. Sure, it excludes sunlight, the 100% exclusion factor, but it's also known that getting down under the ground is a great insulator.
People who visit Australia ignore at their peril advice to use lots of sunscreen and blocker and especially the further south they go, to Tasmania, for instance. The "thinning" of the atmosphere towards the poles makes penetration of UV radiation more severe (apparently) than at the atmospherically thicker equator (ie, you less likely to suffer such severe sunburn in the tropics).
And, when apples are prone to sunburn, orchardists spray on a mix of water and kaolin clay to coat the fruit. A simple and very effective protective factor.