Global flattening

[MikeW]

PM substitute for "the elephant"

You have PM's blocked so I can't send you this privately -- sorry

The over-sized picture you posted above sends my browser into coniptions. It may be causing inconvenience for other users too.

A little editing may be beneficial ?

The only way I could get back into this thread was to foe you, and I would much prefer that to be as temporary as possible
(oily flattery removed - even I was too embarassed to do that in public)
thank you

[MikeW]

Assuming this is not a deliberate troll:

18+ years as a pipe organ builder.

You mentioned the continuing upward drift in tuning notes, which usually seems to get a rise, so naturally I wondered if you were trolling. Apologies if that was not your intention.

Period wind instruments were typically built to the pitch center of their major city in the area. That pitch center was typically determined by the as built/voiced pitch of the pipe organ.

...

So even as we have historic data showing pitch centers for different regions, and even as A-440 was established by committee (at 65 degrees F), they still postulate that organs were built at A-438?

That does seem to be the implication of the article. I think the crux of the proposition/hoax lies in the question of whether organs of the period were tuned at the time of construction against a standard known to be at 415 Hz, or whether the frequency was determined in modern times by measurement (of the frequency, or of the pipe lengths). I certainly don't know enough to answer that question, and I haven't found anything on that topic on the Internet. I was hoping someone with expertise in your field could settle it, one way or the other.

[MikeW]

Caculating the effect of CO2 on pitch is a chore, but most of the work is already done in the “Handbook for the Speed of Sound in Real Gases, Vol III”.

Atmospheric CO2 before the industrial revolution was fairly steady around 160 to 180 ppm.

Current level is at or about 400 ppm, so the increase is about 220 to 240 ppm (definitely less than 300).

According to the Handbook, increasing the level of CO2 by 100 ppm reduces the speed of sound, and thus the pitch of an organ pipe, by 31 ppm. We are thus fairly safe in saying that pitch has fallen by less than 93 ppm, or 0.0093%.

Comparing this with the 5.5% suggested in the original article, there seems to have been a shift in the decimal place: I guess it must originally have been an April Fool article, but the reference to it was mentioned in a March issue of the New Scientist (which gave fair warning that the references had not been checked).

So ok, I got clowned.

[Art Hovey]

Maybe I have too much spare time on my hands, but....

We know that air density is proportional to the average molecular mass of the air.
We also know that the speed of sound (and hence the resonant frequency of a standing wave) is inversely proportional
to the square root of the air density. That means a one-percent increase in density will cause a 0.5% decrease in frequency.

Going down one semitone means decreasing the frequency of a note by about 5.61%, so the 0.5% decrease mentioned above
corresponds to 0.5/5.61 = 0.089 semitone, or about 9 “cents” on your tuner. Consequently, if the density increases by X%,
the pitch goes down by about 9X cents.

Without the carbon dioxide, dry air is 78% nitrogen, 21% oxygen, and 1% argon, along with insignificant amounts of other gases.
The molecular mass of nitrogen is 28, oxygen is 32, and argon is 40. The average molecular mass of that mixture comes out to 28.96.
(Please check my arithmetic and let me know if I am wrong.)

The molecular mass of carbon dioxide is 44. Before the industrial revolution (around 1760) the carbon dioxide concentration was
about 0.028%. Adding that much CO2 to the pure air described above increases its average molecular mass to:

(28.96 + 0.00028 x 44)/(1.00028) = 28.964.

Today’s CO2 concentration is about 0.0395%, so the average molecular mass is now

(28.96 + 0.000395 x 44)/(1.000395) = 28.966.

Comparing those two values, 28.964/28.966 = 1.000067. That means the air density has increased by about 0.0067% due to the
increase in CO2, which implies a pitch decrease of 9 x 0.0067 = 0.06 cents.

As explained elsewhere, a one-degree (Celsius) change in temperature causes a pitch change of about 3 cents.
So the CO2 effect is roughly equivalent to an air temperature decrease of about 0.02 degrees,
which seems pretty insignificant.

Another factor to consider is humidity. Air can contain up to 5% water vapor, and the molecular mass of water is 18.
So the average molecular mass of humid air is actually less than that of dry air: (28.96 + 0.05 x 18)/(1.05) = 28.44.

Comparing the density of humid air with dry air, 28.44/28.96 = 0.982. That means addition of water vapor can decrease the
air density by about 1.8%, corresponding to a pitch rise of about 16 cents. When you play a cold wind instrument a lot of the
moisture in your breath condenses quickly. When you play a warm instrument less moisture condenses, so more of it remains
as vapor, causing even more rise in pitch than the temperature effect alone would predict. The breath that you exhale may
contain slightly more CO2 than the surroundings, but that effect is insignificant.

These calculations do not in any way imply that the growth of atmospheric CO2 is not a serious issue for global climate.
I am still convinced that this planet is more sensitive than a tuba.

[pgym]

Atmospheric CO2 before the industrial revolution was fairly steady around 160 to 180 ppm.

Source?

Every reputable source I've seen cites the pre-IR atmospheric CO2 level at ~280-300 ppmv. See, e.g., Historical CO2 record derived from a spline fit (20 year cutoff) of the Law Dome DE08 and DE08-2 ice cores; Global Atmospheric Concentration of CO2; Climate Change - European Environmental Agency.

That's a good 50-75% ppmv higher than the figures you're claiming.

[MikeW]

Atmospheric CO2 before the industrial revolution was fairly steady around 160 to 180 ppm.

Source?

Every reputable source I've seen cites the pre-IR atmospheric CO2 level at ~280-300 ppmv. See, e.g., Historical CO2 record derived from a spline fit (20 year cutoff) of the Law Dome DE08 and DE08-2 ice cores; Global Atmospheric Concentration of CO2; Climate Change - European Environmental Agency.

That's a good 50-75% ppmv higher than the figures you're claiming.

I picked up those numbers somewhere on the web: I can't find them again, or anything like them, so let's just assume that Wikipedia's opinion is close enough for Government work; Wikipedia gives the pre-IR level as 280 ppm, which is higher than the numbers I used, making the change in CO2 concentration (and hence the change in the speed of sound) even smaller. This has no effect on the major conclusion - I still fell for a dead hoax that has been hanging around the web since 1998.