Antarctica, 1940
On the Little America III base, Paul Siple and Charles Passel noticed something.
In a place as cold and deserted as the Antarctic,
the cold was completely bearable as long as there was no wind.
As soon as the wind would blow, frostbites and actual life-threatening conditions would arise.
They started developing experiments to devise a new 'perceived temperature' scale
which would take into account our sensitivity to the wind
and let us know what to expect when going out into the cold.
This new scale was used between 1945 and 2001
then amended to make it more accurate.
In the winter, any Canadian weather forecast gives you both the temperature
and the perceived temperature as it was created in Antarctica in 1945.
This is its story.
In order to create an equation for a perceived temperature,
they filled a bucket with melted ice water
with a kind of thermometer.
They hung the bucket high up and let the water freeze.
They measured the amount of time it took for the water to turn into ice
as well as the wind velocity and current temperature.
They repeated this experiment over 80 times.
In the Antarctic, calculations were made simpler;
in the winter the sun doesn't rise for 4 months
and the air is extremely dry.
This means the experimental conditions were kept constant for all measurements.
This is the equation for the perceived temperature that was created in 1945.
Although we call it 'perceived temperature', that isn't the right term.
Terms like 'wind chill' or 'wind factor' are much more appropriate
and you'll understand why by looking at the equation.
It mixes wind speed (m/s) with temperature (C).
We all learned we can't compute carrots+apples
and we have the same issue here.
If we do compute them, we can't give the result a unit.
So a perceived temperature of -20 is just that.
It isn't a perceived temperature of -20°C.
A perceived temperature is not a temperature,
it's an index that was adjusted so that it would look like a temperature.
Since 1945, several flaws in the equation have been pointed out
and a new one was devised.
The original researchers had assumed that our skin temperature was at 33°C
but in the cold, it is much lower than that.
Wind speed was measured at a height of 10m
while we live between 1.5 to 2m from the ground.
And the list goes on but one major issue is this:
How can a bucket of water represent what we feel as humans?
In 2001 the equation was changed to this one.
This time it took into account that humans wear so many layers in the winter
that only our heads are relevant for the index.
Yep, it's still just an index, not a temperature.
They used a hollow tube to represent a human head, and they covered both ends.
They placed it in a blower to experiment with it.
After many measurements and theoretical considerations, they came up with this new equation.
But it doesn't solve all our problems and even creates some new ones.
What about humidity?
0°C in France, where the air is humid,
is much harder to bear than 0°C in Québec
where the air is very dry.
The wind is measured here and there in the city
but certainly not in the sheltered or windy street you specifically walk.
The problem isn't really the equation, which can always be perfected,
but the idea behind it.
How do you represent the way a temperature is perceived when you can't control all the parameters?
Not to mention that everyone perceives a given temperature differently.
Depending on how you dress, on your tolerance to the cold,
on your cardiac rhythm, on your fatigue level,
on how much fat your body holds, etc...
you will perceive the cold differently from the next person.
If the actual temperature measurement isn't suitable for us because of all the factors that affect us,
and that the perceived temperature measurement isn't perfect either,
how do we communicate the degree of cold and all the dangers it entails?
Is perceived temperature a good index after all?