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Comment by iknownothow | Hacker News Reader

  for anyone who thinks 49C in Delhi is some extreme temperature it's not really that far from usual maximum (2019 and 2020 both May max. 46C).

That's a 3C increase!

Sure that's only a 6.5% increase in temperature w.r.t. to 46C but that's an incorrect way of looking at it. If you were to set your air-conditioning to 32C, then the energy required to cool from 49C to 32C is 21% more than the energy required to cool from 46C to 32C.

32C is also the wet-bulb temperature, so when thinking about tolerability, at least use 32C as the baseline (and not 0C) when comparing temperatures.

P.S. Humidity is a major factor. I'm assuming humidity is the same this year as it was the previous years.

Edit: To clarify, my comment was about not giving into your insticts and underestimating the effects of 3C rise w.r.t. 46C. Thinking of 3C rise in terms of energy increase or comparing it to a baseline of wet-bulb temperature give you better intuitions.

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Pretty sure that's well within the bounds of normal variation we'd expect between different locations within a major city. There's all kinds of weird microclimates in most cities, you really do have to compare like with like here - it's entirely likely that there were actually higher temperatures in Delhi in the past and there just weren't automated weather stations in those locations at the time.

> it's entirely likely that there were actually higher temperatures in Delhi in the past and there just weren't automated weather stations in those locations at the time

Ok, great, so maybe at some point in the past there was a hotter temp. It’s amazing how rather than focusing on the miserable experience nearly 50° weather is for those there, we get into a weird measuring fetish over who’s number is biggest.

Except the 49C here is not a weird microclimate of some small part of New Delhi, but rather is the average temp across the city.

Which means that places with weird microclimates that were 49C when the overall temp was 46C are now 52C and above.

Which stations reported 52C? I’d think that would be the headline of true.

except the real temperature was around 46C and only two new weird stations reported 49C, I wonder how is their accuracy even regardless microclimates

> That's a 3C increase!

Not if you don't compare apples and oranges, these high temperature data come ONLY from 2 NEW automated stations with no previous data to compare, other stations used for years didn't report such crazy temperaturs, so you should take these new data with grain of salt. You should be comparing stations in same location with comparable data from previous years.

I agree with the important sentiment in your comment, i.e. that a 3 °C increase is a lot… but:

> Sure that's only a 6.5% increase in temperature w.r.t. to 46C

That's not how this works at all. The Celsius (and Fahrenheit) scale sets an arbitrary zero point. To compute the increase in temperature, you need to use an absolute scale, such as Kelvin: 49 °C is 322 K, and 46 °C is 319 K. The increase from 319 K is about 1%.

Think about it this way: Distances are typically measured in absolute units – m, km, feet, miles, whatever. Suppose I introduce a new unit with an arbitrary zero-point, say "1 Blarf is 2 m, but 0 Blarfs is defined as 5 m". That means that 3 m is -1 Blarf, 7 m is 1 Blarf, etc. That still doesn't mean that 2 Blarfs (9 m) is twice as long as 1 Blarf (7 m), even though it would seem that way from naively considering the numeric values of the two lengths in Blarfs.

TLDR: Arbitrary zero points are stupid.

You haven't corrected the posters mistake, you've repeated it.

Intervals can only be converted into percentages across another interval, you've decided that the whole interval is the interesting part but it isn't, 0K is as abitrary as 0C for this purpose. Is a day 1/7th of a week or 1/365th of a year? Yes. It's also some tiny fraction of all time since the Big Bang, but who cares about that? That's your absolute interval.

There isn't a proper way to do it and it's nearly always a mistake to try.

No, 0 K isn't arbitrary. That's exactly the point; it's the lowest temperature for which the definition of temperature makes sense.

Your analogy about days relating to weeks or years is wrong. This is a matter of scaling. In this sense, Kelvin is of course arbitrary, but said scaling does not matter for the computations in question.

If the poster had written "49 C is 6% further than 46 C from the point at which water freezes", then we'd be in agreement that their choice of interval is no worse or better than others. But absent such a clear labelling, the only notion that makes sense is the absolute one.

No. You are comprehensively wrong about the relationship between intervals and other intervals with regard to percentages, and you have refused to learn from what I just said.

> Kelvin is of course arbitrary

Listen to yourself if you won't listen to me.

Edit: read up on the difference between temperature and heat. I suspect that your mental model of that relationship is wrong, and that's why you're making this mistake.

> > Kelvin is of course arbitrary

> Listen to yourself if you won't listen to me.

Like I said: Kelvin is arbitrarily scaled. Scaling doesn't matter when it comes to ratios. Celsius on the other hand is also arbitrarily offset. That matters.

> Edit: read up on the difference between temperature and heat. I suspect that your mental model of that relationship is wrong, and that's why you're making this mistake.

I'm quite aware, thank you very much. This whole subthread is about temperature. To be clear: I'm not criticising OP's writings about energy requirements. I'm merely talking about:

> Sure that's only a 6.5% increase in temperature w.r.t. to 46C

Yes, that is indeed followed by

> but that's an incorrect way of looking at it.

but that refers to a discussion of energy that follows. My whole point is that it's *NOT a 6.5% increase in temperature". OP's point seems to be that we shouldn't be considering the increase in temperature, but rather the increase in energy needed. That's fine. No objections. I'm just saying that the statement about the increase in temperature is also wrong.

> Kelvin is arbitrarily scaled.

Percentages are unitless, you're making a trivial observation that didn't need to be said.

I conclude that you lack the appropriate education to discuss this subject.

> Percentages are unitless, you're making a trivial observation that didn't need to be said.

My original observation was that Celsius and Fahrenheit are arbitrarily shifted, and that matters. Then you countered that Kelvin is arbitrary too, to which I write that it is only arbitrarily scaled, and that is fine (of course, for the exact trivial reason that you point out).

If your best argument is that I made a correct but trivial statement in addition to my main point, then I don't think there's much more to be had from this discussion.

I bid you farewell.

I disagree.

Their way of doing the conversion is far more principled than the original commenter's.

It's absolutely appropriate to do a percentage conversion based in Kelvin, the percentage has a fundamental meaning in terms of the actual increase in kinetic energy. You would get the same percentage if you did the calculation in Rankine because they're both 0-based temperature scales.

For some reason you seem to have ignored the second half of the sentence I wrote.

> Sure that's only a 6.5% increase in temperature w.r.t. to 46C ... but that's an incorrect way of looking at it.

I've added an edit to clarify what I was aiming at.

> For some reason you seem to have ignored the second half of the sentence I wrote.

I can't see that the second half rectifies it though. The rest, the part about the energy needed being what mattered, I wholeheartedly agree with. It's still incorrect to say that the temperature is 6% higher.

Sure, I agree that it's incorrect. I should have used 0K as base.

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