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Comment by mr_mitm | Hacker News Reader

You don't need an absolute scale, you just need a sensible origin. I suggest taking human perception into account.

When talking about the weather or everyday objects, one could argue that the border between "hot" and "cold" is somewhere at room temperature, so around 21°C. At that temperature, it's neither hot or cold. If it's 30°C, it's 9°C of "hotness", so 39°C would be twice as hot. I don't know if it feels twice as hot, as that's quite subjective, but if you want more precision we should switch to another vocabulary entirely.

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Water-freezing temperature is an absolutely sensible zero. The difference between e.g. 2 °C and -2 °C is really quite obvious for the exposed skin: while it's merely "yeah, it's cold" feeling when it's above zero, it almost feel like the frost is biting, almost literally, when it's below zero.

This is not true, and it's why we developed separate scales for wind chill (which factors in wind) and heat index (which factors humidity).

Looking at the wind chill chart[0] for frostbite times, there is nothing particularly special around the freezing point temperature, even at absurd wind speeds. Ironically, actually, the 0 point for Fahrenheit is far more relevant threshold for frostbite.

[0] https://www.weather.gov/safety/cold-wind-chill-chart

Neither of those are as important as “when water freezes” (ice snow weather effects), boils, and having a nice 100d in between

The freezing point of water is indeed one reasonable origin point but the temperature at which water boil (at sea level) isn't very relevant to most people's day to day experiences much less having a nice interval between the two points. You have to use Kelvin as an absolute scale for a lot of scientific and engineering calculations anyway although it would be pretty silly for day-to-day use.

I'd argue that boiling water (or water-based liquids) is something we encounter pretty often in day to day life (eg. while cooking, brewing tea, ), making it a reasonable reference

But then this is also valid if the zero is at 21°C. There is also nothing special at 0°F, it’s just the colour scale that makes it look like that. And if we based the scale on human perception we’d have to define many other parameters besides wind and humidity, like body shape and metabolism rate. It’s more of an argument against basing a temperature scale on human perception (and then I agree completely, which is why I find the centigrade scale much better, except for serious business that demands kelvins).

Yeah, it's not like Fahrenheit or any temperature scale is literally calibrated to human perception (they're all now defined as transformations from kelvin anyways), that's just a (minor) ancillary impact that can be discussed.

Wind chill is a mostly stupid number that weather reports like to trot out so they have a amped up "wow it's really cold" factor. Yes, a number of factors p[lay into our subjective perceptions of temperature but you're probably not walking around in a bathing suit when it's below freezing with a howling wind.

Sure, same with heat index. They are tools for communicating the impact of additional axes (wind speed for cold and humidity for heat) on subjective perception. I won't wander out without a scarf, or neck covering, if it's freezing and 40mph winds, but I don't mind to if it's freezing and no wind.

I don't think they are aiming for the wow factor. Most people arguably watch the weather report to find out how cold or warm it feels outside, which heat index and wind chill are far better at reporting.

How given temperature feels depends on humidity, airflow, local culture, individual human and specific condition of that human (sitting/moving/sleeping, caffeinated, just ate a meal, bored, enthusiastic).

- I know someone who wears a puffy jacket indoors if it's 24 degrees.

- You will find sitting in 20 degrees with 88% humidity much more miserable than 20 degrees and 33% humidity.

- 42deg with 20% humidity and slight breeze is fine, 38deg with 90% humidity can make you pass out in minutes if you need to walk anywhere in the sun.

To take ratios you need an absolute zero because otherwise ratios aren‘t even defined.

See also my other comment here: https://news.ycombinator.com/item?id=37928268

36.6C?

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