Pressure Change and Real Standard Pressure

The standard mean sea level pressure is defined as 101.325 kPa. This is the standard used in US and International Standard Atmosphere. This value is all over the place. In reality this value was agreed upon by committee and at no time represented the true mean sea level pressure. Most certainly it does not represent the true value today. Today I will try to calculate what the real value should be. I will be using data from NOAA’s ESR Lab.

You will need gnuplot:

sudo apt install gnuplot

# bash
# Zoe Phin, 2020/02/05

wget -qO- '' | awk '$1>1947&&$1<2020{print $1" "$2/10}' | sed 1d > surpres.txt

wget -qO- '' |  awk '$1>1947&&$1<2020{print $1" "$2/10}' | sed 1d > seapres.txt

echo 'set term png size 740,740; set key below
set title "Pressure (kPa)"; set xrange [1947 to 2020]
set yrange [98.58 to 98.46]; set format y "%5.2f"
set y2range [101.24 to 101.12]; set format y2 "%6.2f"
set grid xtics mxtics ytics y2tics mytics my2tics
set xtics 10; set mxtics 2; set ytics 0.02; set y2tics 0.02; set mytics 2; set my2tics 2
plot "surpres.txt" u 1:2 axes x1y1 t "Surface (Left)" w lines lt 1 lw 2 lc rgb "red",\
     "seapres.txt" u 1:2 axes x1y2 t "Sealevel (Right)" w lines lt 1 lw 2 lc rgb "blue"' | gnuplot > pres.png

Run it:

> bash

Result is three files: surpres.txt, seapres.txt, and pres.png

Mean Surface & Sealevel Pressure (kPa)

I have trouble believing global data before the 1979 full global satellite era. In any case we see that both surface and sea-level pressure have been decreasing. This is odd considering that temperatures have been going up, but I will not go into that today.

To figure out the real mean sea-level pressure I will simply average the data between 1979 and 2019 (inclusive):

>  awk '$1>=1979 && $1<=2019 { SUM+=$2; NUM+=1 } END {print SUM/NUM}' seapres.txt


The mean sea-level pressure in the post-satellite era is: 101.159 kPa and NOT 101.325 kPa.

All those using the committee-established value of 101.325 kPa will not be reflecting reality.

The average surface pressure between 1979 & 2019 is 98.4976 kPA.

Enjoy 🙂 -Zoe

Published by Zoe Phin

40 thoughts on “Pressure Change and Real Standard Pressure

  1. Zoe:

    It’s been claimed that AGW is responsible for atmospheric pressure changes – as near as I can tell, dropping at the poles and rising more or less in the tropics:


    “They find that polar regions – both north and south – have experienced decreases in sea-level pressure over the last 50 years and the North Atlantic Ocean, Europe North Africa, India, and other tropical to mid-latitude regions have had increases in sea-level pressure.”

    Are you able to examine pressure changes zonally? (They then go play with their models to claim the changes are evidence of AGW.)

    Articles: (2003: Gillett et. al.)

    Abstract excerpt:

    “We find increases in sea-level pressure over the subtropical North Atlantic Ocean, southern Europe and North Africa, and decreases in the polar regions and the North Pacific Ocean, in response to human influence. Our analysis also indicates that the climate models substantially underestimate the magnitude of the sea-level pressure response. This discrepancy suggests that the upward trend in the North Atlantic Oscillation index 7 (corresponding to strengthened westerlies in the North Atlantic region), as simulated in a number of global warming scenarios 8,9,10, may be too small, leading to an underestimation of the impacts of anthropogenic climate change on European climate.”

    Also: (2005: Gillett, Allan & Ansell) (2009: Gillett & Stott)



    Liked by 1 person

  2. Excellent as usual Zoe. More people need to be looking beneath or feet and at ground level, rather than, essentially, exclusively into the heavens to understand our tiny warm l marble in a cold and hostile universe.

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  3. Well,well,well. It seems to me that the ideal gas laws come into play here. The molar form can be solved for T. You can sub into the equation molecular densities, molar weights and pressures to solve for T. Something that has bothered me for some time is that estimates of temperature change from a doubling of CO2 that are large (say anything over 2 degrees) require big changes in pressure. I have never found someone that advocates for high ECS level that can explain how those belief square with the ideal gas laws. You need really big changes in pressures from a .04% increase in CO2 molecules (a doubling). off the top of my head I seem to remember that you need a 2% pressure change from a .04% increase in CO2 molecules. That’s way to big to make sense in my view.

    I’m glad that you are posting at Watts up with that!

    Keep up the good work.

    If I wasn’t so lazy I would download all of the CRN data, the CO2 data, solar data, ENSO and AMO data and set up a cross sectional/time series model that tests for the significance of CO2 changes on Temperature. Alas, too busy.

    Liked by 1 person

  4. Ok, I’m puzzled. Why do you expect a pressure change from a temperature change? Pressure will increase if a gas is confined,but the atmosphere isn’t. It will expand, but the total mass in the air column doesn’t change.

    Liked by 1 person

    1. Surface pressure is determined by the mass of the atmosphere divided by the surface area. Hence temperature has no effect on pressure until the temperature falls low enough to cause a reduction in the mass of the atmosphere via condensation.


      1. Temperature = Translational Kinetic Energy = M/2*(Vavg)^2.

        Mass can stay fixed, but velocity will increase.

        Seriously this was worked out 150 years ago. The mass in the gas box remained fixed. Temperature was raised and so was the piston. Don’t neglect the velocity component.


        1. I am a professional physicist (retired) and an amateur “Climate Scientist”. Some years ago I used FEAs to model airless bodies:

          I am working on a paper for publication that might benefit from greater programming skills than I possess. This involves a model for bodies with atmospheres.

          If you are interested I would prefer to communicate “Off Line”. My email address is peter(at)


        2. If we’re going by how venerable the laws being applied are (rather than whether they are being applied correctly), I’m afraid Camel wins hands down — he’s just using Newton’s laws of motion and gravitation, which are well over twice the age of the gas laws.

          I can’t see any problems with Camel’s use of those laws. I don’t think relativistic effects or the fact that the Earth is a rotating rather than an inertial frame of reference are going to be significant, and those are the only places I can see where you could try to undermine his argument. The gas law, PV = nRT, on the other hand, does not imply, as you seem to suppose, that increasing T implies increasing P. It is perfectly consistent with Camel’s position. If you apply it to a fixed volume V adjacent to the ground, the increased T can be balanced by a decreased n — the expansion of the atmosphere means that some molecules leave the volume, ending up above its upper surface. If you apply it to a fixed amount n of atmosphere, the expansion increases the V. In either case, the gas law stays satisfied.

          What you can say, however, is that at any level above the surface of the Earth (but not at it), increasing temperature will, ceteris paribus, cause increased pressure. That is because the thermal expansion of the atmosphere will mean more of the atmosphere will be above that level, and will therefore have to be supported by the pressure at that level.


        3. Ken, atmospheric pressure and gravitational pressure run in opposite directions. Look at a hydrostatic equilibrium diagram.

          We’re talking about the bottom cubic meter expanding due to kinetic energy, and having to lift the mass above it. This does cause the atmosphere to expand, due to kinetic energy, i.e. temperature.

          Expansion is not free. You need to subvert gravity to expand.


        4. It looks like we are agreed that a general increase in the temperature of the atmosphere will cause thermal expansion. (So the V and the T in PV = nRT will increase, for a parcel of the atmosphere of fixed mass.) But I am just not getting your argument that the P will also increase. Could you go through the argument again making the assumption that I am not very bright and need every step explained?

          Also, could you explain what is wrong with Camel’s argument that the pressure would remain constant? (Or rather, reduce very slightly, as the thermal expansion would reduce the weight of the atmosphere very marginally, by moving some of it to positions where the local acceleration due to gravity, g, is smaller than before.) It really seems water-tight to me.

          You argue that the increase in temperature increases the average velocity, and therefore momentum, of gas particles hitting the surface of the Earth. Correct, ceteris paribus this would indeed increase the pressure, as force equals rate of change of momentum. The frequency of each molecule hitting the surface would also increase in proportion to the velocity, again increasing the pressure. So, other things being equal, the pressure should increase in proportion with the square of velocity, i.e. in proportion to temperature. But we are agreed that other things will not be equal — there will be thermal expansion, which reduces the density of the gas and therefore the number of molecules hitting each unit area of the Earth’s surface in unit time, which reduces the pressure. Camel and I think the effects increasing and reducing the pressure must (almost) exactly cancel out, because we have a way of calculating atmospheric pressure that is independent of temperature. (The pressure equals the weight of the atmosphere above a unit area of the surface.) You think the pressure-increasing effect of the higher molecular velocities will predominate over the pressure-decreasing effect of the lower density. I have not yet understood why you think that that is the case.


        5. Expansion is atmo pressure. To lift atmo higher you need molecules moving faster. Faster moving molecules exert more pressure on the surface. Expansion works two way.


        6. Mass doesn’t stay fixed. Upward expansion causes gases that were at the surface boundary or beneath it to get sucked into the vacuum created.


        7. Warmer air causes air pressure to rise. When air molecules collide, they exert a force on each other. When gas molecules are heated, the molecules move more quickly, and the increased velocity causes more collisions. As a result, more force is exerted on each molecule and air pressure increases.


        8. My apologies for triggering a “failure to agree”.

          My interest in Zoe is her apparent expertise in massaging data. For example I fancy that she could process the “Level 3” Diviner data that crashed my lunar spreadsheet.

          I am a physicist and engineer who can handle assembler level programming but not much else when it comes to programming. I learned Pascal but never managed to get comfortable with “C”. Now I need expertise in Python.

          If Zoe can’t help is there anyone here who can?

          My project involves replicating Figures 7(a) & 7(b) in this paper:


        9. Yes, the piston went up because the cylinder confined the gas. I get that.

          But an atmosphere confined only by gravity will expand, mirabile dictu, precisely so that the number of those zippier little molecules hitting our square inch will decrease until the force on that square inch of surface is exactly what it was before — the weight of the air column above it. The units are pounds per square inch, after all. That should be a clue. Unless you want to be all metric about it.


        10. The reason more gases don’t escape from the surface and oceans RIGHT NOW is because there’s a mass of gas sitting on their face. More heat (higher surface T) will indeed raise that mass of gas, and the vacuum left underneath will be filled by those subsurface gases that couldn’t rise before, but now can.

          Now there’s more atmo P due to higher T.


        11. “……until the force on that square inch of surface is exactly what it was before — the weight of the air column above it……..” Sounds kind of right. I’d be a bit shy about being too ideological about it all. Since to my mind there is some sort of moratorium on rational gravity research. The way you make it sound, the extra heat could lead to LESS air pressure. Since it may be that if the air molecules are further away they might exert less downward force on the situation. Or it could be an in-between situation where the extra force between molecules leads to extra downward force and therefore pressure. Or it could be more towards the spectrum of where Zoe is talking about particularly as great heat might lead to a great many more molecules in gaseous form.

          I would just caution against people being to ideological about it, because while all these gas laws work well in the lab, the study of gravity has been put in the deep freeze. We have all this cult of personality and ancient heritage formulae and not a great deal of free enquiry. I would say gravity is a wild card here.

          The other thing with Venus is that; while I don’t know how good Velikovsky’s source material was, he does appear to have had great predictive power. There was a comet that came near to Jupiter. I presume that a sun-Jupiter-comet electrical connection was made and the luminosity of the comment increased one million times. Velikovsky says that the ancients saw Venus come clean out of Jupiter. Which to my mind is preposterous. But if the comet that became Venus made that same electrical connection, and then became luminous, that would explain the source data, supposing that Velikovsky is interpreting correctly.

          Now the thing is the comet that became Venus could have gone through the outer atmosphere of Jupiter and picked up far more than its fair share of gas. While Hydrogen is easily lost, and methane would be split up and the hydrogen lost, the carbon retained ….. the net effect could be that when Venus normalised as a planet it had much more than its fair share of atmosphere.

          We know so little about gravity but it turns out that its easy for even a small planet to hold onto CO2 and very hard to hold onto hydrogen. People just apply gas laws and get one result. But if you send the satellite out there to detect what is being lost, both earth and Venus are basically only losing hydrogen. And in the case of Venus this hydrogen has to be assumed pristine.

          Liked by 1 person

        12. “Or it could be more towards the spectrum of where Zoe is talking about particularly as great heat might lead to a great many more molecules in gaseous form.”

          Indeed. Very observant.

          The reason more gases don’t escape from the surface and oceans is because there’s a mass of gas sitting on their face. More heat will indeed raise that mass of gas, and the vacuum left undeneath will be filled by those subsurface gases.

          Many people don’t understand this very important second part (not you, you do).


  5. “This effort failed as my spreadsheet could not handle even the “Level 3” data. The Diviner team did much better and showed that the Moon’s average temperature is 197.3 Kelvin.”

    Camel are you completely happy with that? Because I followed the links through, and they sound like they are using measurements along the equator and just extrapolating. Am I reading them wrong? How much of this study do you think was empirical and how much were they working the rest out on their own? Don’t want to go out of my way to seem too dimwitted, but how confident are you in their study, being as you had attempted a similar undertaking?


    1. The foundation of my model is the replication of the published data for the lunar equator.

      However you will note that I included averages for the entire body. This required slicing the Moon up by latitude (10 degree slices) and then integrating the results. Running Finite Element Analysis programs on a laptop is time consuming. Each slice takes days to complete.

      Given that I had tried to build a spreadsheet lunar model and failed I was impressed when Roy Spencer published this:

      The beauty of this approach is that it is about 500 times faster than my FEA model. The downside is that it does not replicate the Diviner data with good accuracy.

      I was able to fix the problems with Dr. Roy’s spreadsheet by making a few simple changes that had no noticeable effect on its speed:
      1. Replaced the lumped thermal capacitance with a 10 layer model.
      2. Replaced the constant Albedo with Vasavada’s 8th order polynomial dependent on the angle of incidence of solar radiation. The Moon is “Non-Lambertian” for short wave radiation.
      3. Improved the time resolution around dawn and dusk.


      1. But am I right to think we don’t have an empirical temperature for the moon? If they say the average temperature is 197K that is an estimate based only on data from the equator? Is that right?


        1. The Diviner Lunar Radiometer Experiment thermally mapped the Moon over an entire year which accounts for the huge amounts of data. Even the level 3 data is beyond the capability of my old laptop. You can find the data here:

          Here is a plot of the temperature over 12 lunar days (about one year Earth time). Notice how the temperature varies at high latitudes showing the Moon’s axis has a slight tilt (5 degrees relative to the ecliptic):


  6. Zoe:

    Thank you for the post and the code.

    There is something interesting here.

    Overall, the total weight of the atmosphere and its pressure should be determined by the mass and the gravitational constant, not by temperature or velocity.

    Locally there are substantial fluctuations arising from tidal forces and the Bernoulli effect in addition to all the weather stuff.

    If the temperature of the lower troposphere is increasing, given the Clausius-Clapeyron equation, I would expect some increase in total humidity, total mass, and thus pressure. I think this increase should be observable. The magnitude is in question because what we observe is the result of convective/advective mixing with the possibly cooler upper atmosphere.


    1. Andy,

      “Overall, the total weight of the atmosphere and its pressure should be determined by the mass and the gravitational constant, not by temperature or velocity.”

      A planet at 0K would have its gases laying as solids on its surface. They still have mass and gravity, and therefore a pressure, but there is 0 atmosphere.

      Atmospheric pressure and gravitational pressure run in opposite direction in hydrostatic equilibrium.

      You need translational kinetic energy (temperature) to “defeat” the gravitational force that wants to compact molecules to the surface.


      1. The only way temperature can affect the surface pressure of a body is by condensing gases.

        Zoe clearly understands this given this statement:
        “A planet at 0K would have its gases laying as solids on its surface. They still have mass and gravity, and therefore a pressure, but there is 0 atmosphere.”


  7. Howdy Zoe,

    This is an interesting discussion but a few things seem a bit off. A global MSLP describes a world without winds. Without winds driven by pressure gradients between areas of relatively higher and lower pressures gives us a world without regions of convergence between these localized systems of contrarily spinning highs and lows, and so, a world without precipitation much. An average pressure over land being less than that of one over water leads to a world without offshore winds.

    To invoke and rely on concepts of Ideal Gas to predict behaviours of Real Gas can lead only to incorrect predictions. To assert that atmospheric pressure is, somehow, the weight of a column of air above a point on the earth is certainly one over-simplification driving many misconceptions. If true then it would become somewhat more easily predictable. Except that gravity itself varies quite measureably but often unpredictably on, above, and below different locations on earth. And except for variations in the composition, density, temperature and depth of the various layers of atmosphere. And then there’s the complication of water and it transitioning between it’s various states within the column. We speak of it as gas but treat the atmosphere as a semi-compressible liquid for engineering purposes. None of these things really get figured into the MSLP puzzles much, and yet, each and all would need to be figured into a dependable weight calculation for this hypothetical (stationary) vertical column of air.

    The point being that all the expectations given by so-called ‘Laws’ can be dead wrong when taken out of context or presumed to function where they clearly do not apply. Any use of average, mean, ideal, or otherwise hypothetical concepts or derived numbers as somehow meaningful can never approach describing the reality of weather. It’s non-linear and dynamical, so treating this multiplicity of ever-changing and perpetually moving sub-systems in any way as static – decidedly fails to describe reality, let alone lead to a fuller comprehension.

    A well established property of matter in the state of gas is that it expands to fill the container. This is true of a gas, whatever the temperature, volume, or shape pf the container. When is a gas not a gas? = when it is a solid, liquid or plasma … so your atmosphere at 0K argument is not even wrong. How is there gas pressure after you take away the gas? Without something to press against, gas pressure is difficult to even conceive of – being a scalar quantity and conditional on boundary. On a global scale, land and sea can be said to form one boundary, akin to the bottom of a box. There can be no sidewall, as such, to this global box, obviously, except maybe to suggest that the aforementioned regions of convergence act as partition walls within. Now the questions emerge: what is and how functions the top of this box?

    One other aspect of atmospheric functioning worth mentioning but currently being studiously overlooked in the mainstream, (or accidently on purpose left out), is that of electro-magnetic influence. That EMFs can and do push, pull, heat, sort, and many ways otherwise affect atomic, molecular, and ionic behaviour is fairly well known. They appear as conjugate, orthogonal. Could it be that highs and lows are paired on earth as like sunspots are on the sun, and following the same mechanism? Lows would be as the cathode and highs as the anode in this scenario, with electrical flow heading upward out of the lows and downward into the highs, thereby creating these so-called pressure systems that we see and love. Rotation of air around the systems follows the right-hand rule govening magnetic force. Water naturally moves by this mechanism acording to it’s polar configuration. Once the basic structure is created, then all of the other (lesser) possible influences can have their way, as nature tends to elegantly simple by most efficient means.

    “The majority believes that everything hard to comprehend must be very profound. This is incorrect. What is hard to understand is what is immature, unclear and often false. The highest wisdom is simple and passes through the brain directly to the heart.” – Viktor Schauberger.

    Liked by 1 person

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