Robert Brown: Beer, Boiling and Bypassing the Greenhouse

Posted: January 3, 2012 by Rog Tallbloke in atmosphere, climate, Ocean dynamics, weather

Another guest post from Dr Robert Brown, Physicist at Duke University.

 I make beer. On part of making beer is boiling the wort for some hours to reduce the fluid volume of the barley-sugar-water to the right specific gravity to ferment to the desired target alcohol level (and do things to proteins and sugars and at the right point to bitter and flavor it with the hops). Big pot, lots of fluid, hot on the bottom, cool on the top (even before the boil). The otherwise reasonably clear liquid is full of little chunkies of coagulated proteins as well, so the liquid has a clearly visible “texture” that lets you see the movement of the fluid.

As any good fluid physicist should understand, the heating on the bottom relative to the top creates instability. Warm water is much less dense than cold water, from 4C right up to 100+ C (beer/syrup boils a bit over 100C). Conduction is slow. Radiation is very slow. Rather than heating the water in a stratified way, bottom to top, as the bottom water heats, it expands and experiences a buoyancy force from the denser cooler water above and around it. It is pushed up. Of course at the top there is nowhere to go (it’s in a pot, bound by gravity) so it just displaces the cooler water there, which sinks, is heated at the bottom, rises to the top, gives off its heat via evaporation and conduction and radiation, cools a bit, sinks, picks up more heat, iterate indefinitely.

But the rising and falling are not uniform. The wort creates convection rolls of warmer lower pressure lower density rising liquid and cooler higher pressure higher density falling liquid, heating at the bottom, transporting the heat to the top, giving it off there, and going back to the bottom for another load all while the liquid itself gradually warms. When the convection is obstructed, one can quickly build up a much higher temperature differential, and it actually takes MUCH longer to reach equilibrium — you can actually boil off all of the liquid on the bottom in local patches and scorch things in contact there because the bottom of the pan isn’t COOLED by the convection rolls.

In a pot, the convection rolls are clearly manifest — usually it goes up on one half of my pot and down on the other, unless I stir it or have it really perfectly aligned on the heat. On the earth, the same process occurs in a very irregularly shaped, heated, and cooled “pot”. Heat is dumped in from the sun, but in a constantly varying pattern as clouds move around reflecting a large fraction of incident energy from some areas and not others. It is differentially absorbed by the ground and the water. Some of that heat is differentially released immediately into the air (which is itself also directly warmed by the light that passes through it). Some causes evaporation of water, cooling the surface of land or water but carrying away absorbed heat into the air. Air, too, rises when warm and falls as it cools and this creates huge masses of air that are just as trapped as the beer in my pot, rising over here, falling over there, and running along the ground or upper troposphere in between in both vertical rolls and in horizontal cycles as well. This air all moves in a rotating frame that causes it to deflect as it moves, creating large scale patterns of circulation around low and high pressure systems. All of this is driven by thermal differentials that move energy around, carrying it from where there is a lot to where there is less as an approximate rule, carrying it from where it is relatively hot (down low) up to where it is relatively cool (above) as an approximate rule.

Radiation is what ultimately removes the energy picked up from the sun, but it is not all radiation from the solid ground that does it, nor is it all, or even mostly, CO_2 in dry air responsible for obstructing that heat transport. This is why, in the desert where the humidity is very low, on a quiet night it can freeze by morning where the temperature rises to close to 100F during the day. Not much of a “greenhouse” effect there, I’d say (and the best possible measure of true greenhouse effect cooling, one that is unfortunately not generally directly studied).

When the heat is transported up by convection, it goes through the greenhouse reflector. The stronger the greenhouse trapping, the greater the thermal pressure differential, the comparatively stronger the convective transport process becomes and the more efficient the cooling becomes. The “stratified” reflective blanket is penetrated by the cooling holes of convective rolls, by the active transport of heat from where it is trapped to where it is not. All of this favors smaller sensitivities.

If there is a real lesson in this, this is it. It is a simple principle of very elementary thermodynamics that all perturbations away from the simple radiative model of cooling obstructed by greenhouse gases will increase the cooling rate compared to the purely radiative baseline. It will do this because the greater temperature differentials are a source of free energy that is begging to do work. The system will nearly invariably self-organize to do work, and in the process reduce the temperature differential between the lower and upper troposphere. This, in turn, will increase the efficiency of the radiative cooling by lifting the heat to be lost up above the greenhouse blanket. I don’t know why this simple argument is ignored so often in climate studies when it is the source of the very instability that produces the convective rolls in my heating beer, the wind in my hair, the rain on my garden, and the seasons. Heat trapping is never improved by a heat-differential instability — that would just make the system even more unstable!

Hence the full expectation that the climate sensitivity and feedback should be expected to be negative and cool the earth compared to what one might expect from “pure” CO_2 greenhouse trapping even before one looks at its details. This is just the “fluctuation/dissipation theorem”, and the climate models that postulate egregiously high climate sensitivity are egregious because they violate it. Given the existence of multiple modes (e.g. radiation and convection) for non-equilibrium energy transport, blocking one will increase the rate of others, not vice versa. Sometimes so well that it is difficult to see any effect of the blockage.

This argument doesn’t really depend much upon water, but the evaporative cycle in general is a perfect example. It cools down low and warms up high, with a very, very few exceptions brought about by peculiar geography (e.g. Santa Ana winds) because in general the warmer moist air rises, gives off its heat, condenses as (cooler) water, and falls. Yes, the clouds and water vapor modulate albedo and greenhouse trapping, but most of this modulation is random compared to improved transport as the temperature differential increases. Again one expects the overall effect of water to be negative to neutral, not positive feedback, because it will in general consume free energy to move water around relative to static stratified models, energy seeking equilibrium with outer space at 3K far overhead, energy that wants to move vertically (on average) from the warm surface to the cold overhead and horizontally from hot places to cooler places.


  1. George says:

    One thing that seems to be a recurring theme when discussions of greenhouses come up is that the Earth has no barrier to convection like a greenhouse does. But it does have such a barrier at the tropopause. This acts, effectively, as a lid on the greenhouse. Now the trouble is, the “greenhouse” is then only as effective as the layer above it is to blocking LWIR radiation. So just as the only part in the greenhouse that really matters is the extent to which the covering blocks LWIR (and re-radiates a portion of that heat back into the greenhouse), the only part of the atmosphere that should really matter would be the stratosphere which would be the portion that has the ability to absorb the radiation from the tropopause and re-radiate a portion of that back down.

    Everything that goes on from surface to the tropopause as far as CO2 is concerned shouldn’t matter, I don’t think. Increasing CO2 in that portion of the atmosphere won’t have really any impact due to convection which will cause heat to simply bypass that portion of the GHGs. It is only that portion of the atmosphere above the tropopause that is going to impact temperatures because surface air will not be able to convect above it.

    I’m not seeing any indication of increased radiation from the tropopause warming the stratosphere.

  2. Scute says:

    I would guess that greater turbulence in the upper atmosphere means a greater surface area radiating out to space (think of a roiling pot of boiling water versus a smooth water surface at lower temperatures). My physics teacher always emphasised the matt/rough surface characteristics of good black body radiators.

  3. George says:

    Actually, now that I think more about it, what I would expect to be the result of greenhouse warming is a increase in temperature of the very tropopause itself. The stratosphere might be thought of as the air above the greenhouse glass. The tropopause itself would be the very glass. Has the temperature at the tropopause increased? I don’t know where I would find such data to find out for myself.

  4. Scute says:

    George, do you mean that the lack of warming of the stratosphere from LWIR means that LWIR is passing straight through without warming it. In other words, the extent to which the stratosphere blocks and reradiates is negligible? I presume that’s what you mean. Please correct me if that’s wrong.

    Incidentally, my last comment wasn’t in reply to yours- I happened to post it one minute after you, but it is a related theme.

  5. Brian H says:

    “Sometimes so well that it is difficult to see any effect of the blockage.” Yes, the harder one looks for the specifics of the GE, the less one finds. There’s very little there there.

  6. Roger Andrews says:


    “Has the temperature at the tropopause increased? I don’t know where I would find such data to find out for myself.”

    I don’t know of any site that lists temperatures at the troposphere, but gives you temps at different elevations. 100mb might not be too far off.

  7. Clark says:

    Rog, I looked through your reasoning above, and I’ll have another go tomorrow; the physics should be within my grasp, but I’d be much happier if you’d add some sketch diagrams, graphs, rough equations or whatever; I get lost with just words.

  8. Clark says:

    Oops, I see I should have addressed my comment to Dr Brown.

  9. George says:

    George, do you mean that the lack of warming of the stratosphere from LWIR means that LWIR is passing straight through without warming it.

    Well, I haven’t put that fine a point on it yet. I’m just saying that it would be obvious that convection is going to move heat to the top of the troposphere. For there to be greenhouse warming, I would expect that interface at the top of the troposphere to warm. That would be expected to warm the troposphere but maybe not enough for us to see, but what we SHOULD be able to see is a warming of the actual interface itself.

    The system is so complex, though, that I can’t work out how we can tell the difference between warming from greenhouse causes and warming from other causes such as a change in albedo. Either case will result in a warming of the troposphere. So how do I tell in a greenhouse how much warming is due to the greenhouse and how much is due to it just being a warm day outside?

    I would take the difference between the air temperature inside and the air temperature outside (at an hour before dawn) and that should give me the greenhouse effect. I can’t do that with Earth’s atmosphere. I suppose the temperature difference between the upper troposphere and the lower stratosphere at an hour before dawn might give me what I need to know but I’m not sure. I am assuming that the troposphere itself acts almost as a radiating membrane of sorts.

    It’s confusing to me but there’s something there, I just don’t have a feel for what it is yet. The tropopause is the lid on the greenhouse. If there is greenhouse warming, I should be able to tell but telling the difference between greenhouse warming and natural sources of warming becomes troublesome.

  10. George says:

    100mb might not be too far off.

    Trouble is the tropopause varies in altitude by a considerable amount.

    Also, the stratosphere contains nearly no water vapor at all, it is nearly completely dry. It should, however, contain about the same amount of CO2 as the rest of the atmosphere. CO2 caused warming should be most evident in the stratosphere.

    Now maybe these models that don’t take convection into account are incorrect in that any mid-troposphere “hot spot” would immediately convect upward to the tropopause. But any increase in CO2 greenhouse should then manifest as stratospheric warming.

    In other words, without convection maybe you get mid-tropospheric warming and stratospheric cooling. With convection, maybe you get no mid-tropospheric warming and stratospheric warming. Problem is that it can be completely swamped by natural variation. So today we see no mid-troposphere warming and a cold stratosphere.

  11. tallbloke says:

    George: Co2 is heavier than air, so it is not evenly mixed thoughout the atmosphere. In the troposphere it gets carried up by convection, but not in the stratosphere. Ozone takes over as the main GHG higher up. To complicate things, ozone is destroyed created by solar UV (which was stronger in the late C20th by quite a lot – UV varies far more than other solar wavelengths), and also by galactic cosmic rays – (which get lower into the atmosphere near the poles – hence aurorae and ozone holes).

    As usual with climate science, there is lots of poorly measured and theorised stuff to learn about. Try Erl Happ’s blog, linked left.

  12. p.g.sharrow says:

    Robert Brown makes his own beer! This man is a real scientist and not one of those armchair want to be posers. Studying the behavior of a simmering pot is a good proxy for convection of nonideal fluids on the earth or the sun. Even better, after you are done with the experiment, there is beer to consume as you ponder the significance of your observations. 8-) pg

  13. Richard111 says:

    Thank you Dr Brown. Nice way to get us laymen thinking. Mind you I also think of the beer. You wouldn’t have a pdf recipe handy? :-)

    Your comment about the lack of study for cooling in deserts cheers me no end. I’ve been harping on that point for some time now.

    I have no training in physics so this may be a silly question. CO2 in the atmosphere is already excited above its 15 micron emission temperature which is about -79.8C so just how much 15 micron radiation from the surface can the CO2 absorb?

  14. Vuk says:

    Don’t know anything about beer brewing…. but growing grapes, making wine and distilling brandy is sort of thing my family did for generations, so I have acquired certain expertise from the very early age, but alas not practised for some years now.

  15. George says:

    George: Co2 is heavier than air, so it is not evenly mixed thoughout the atmosphere.

    The CO2 content of the stratosphere sits year-round at roughly the seasonal average for the troposphere. By this I mean that the amount of CO2 in the troposphere will vary with season. The amount of CO2 in the stratosphere tends to not vary seasonally but sits roughly at the seasonal average. For example, in a study done in 1963, the tropospheric CO2 measured from air samples by the International Meteorological Institute was about 320ppm in the spring and about 311ppm in the fall. Stratospheric CO2 was measured at about 316ppm at all times during that year with some gradual uptrend over the course of the year of less than 1ppm. ( Space and time variations of the CO2, content of the troposphere and lower stratosphere By WALTER BISCHOF and BERT BOLIN, International Meteorological Institute, Stockholm 1965) I’ll assume for the sake of this posting that the atmosphere still works today the same as it did in 1965, it was simply a reference I had handy.

    ozone is destroyed by solar UV

    Uhm, sure you don’t have that reversed? Ozone is created by UVB and UVC reacting with O2. Ozone goes away once UV exposure goes away such as in polar winter.

  16. George says:

    In other words, pretty much the entire “ozone layer” sits within the stratosphere and the concentration of O3 in the lower stratosphere is generally higher than in the troposphere. During polar winter the O3 levels are depleted due to lack of UV and sequestering of the polar air by the circumpolar jet.

    Maybe you were talking about the mesosphere which is the next layer where convection picks up again and temperatures again begin to fall with altitude. But even the mesosphere shows about the same ration of CO2 as the troposphere in the lower mesosphere but this does deplete somewhat and is attributed to UV breaking down CO2 into CO and O in the upper mesosphere.

  17. tallbloke says:

    OK, sorry guys, very early in the morning and I got myself mixed up in a few places there. Thanks for the corrections, and thanks for the pdf George.

  18. tallbloke says:

    Vuk, you’ll have to join me sometime to sample some of my home brewed Belgian style beers.

  19. colliemum says:

    Beer – wine & brandy – well, I made marmalade, and what Dr Brown describes is what I have observed in my marmalade kettle, without the attached physics!

    What strikes me about this post is that it is an excellent way of describing what is happening to lay people, who haven’t been taught any maths, physics, chemistry in school.
    The various TV ‘scientists’ who populate our screens are generally AGW proponents. It would be great if someone could make a few youtube videos along the lines described by Dr Brown, so people could actually see why the AGW ‘consensus’ fails.

  20. Tenuc says:

    George says:
    January 3, 2012 at 2:05 am
    “One thing that seems to be a recurring theme when discussions of greenhouses come up is that the Earth has no barrier to convection like a greenhouse does. But it does have such a barrier at the tropopause. This acts, effectively, as a lid on the greenhouse…”

    If only it were that simple!

    Lets look at what the tropopause really looks like, rather than those tidy pictures shown in the textbooks. First some basics. The height of the troposphere is indeterminate and varies between 4 miles and 12 miles thickness, dependant of latitude, weather, season, time of day etc

    It contains around 80% of the total mass of our atmosphere and temperature here is driven mainly by convection, evaporation and collisions of by photons from the sun with air molecules. These collisions cause photons change direction (impact scattering) and gives each of those air molecules hit a kinetic energy boost of indeterminate quantity. As all matter continuously emits photons, air molecules are also impacted by out-bound planetary photons, which tend to be less energetic al la Boltzmann.

    The temperature of the troposphere decreases with decreasing atmospheric pressure as you increase altitude until it meets the boundary with the stratosphere, when the temperature stabilises for 6 miles or so, before starting to increase again in the stratosphere. Nice chart of this effect here…

    (Ignore the neat boundaries shown on the chart. In the real world they are messy and changeable)

    The tropopause is a wide band of air exhibiting great turbulence. It contains ‘structures’ which are the result of spatio-temporal chaos and the number and position of these ‘structures’ varies over short and long time periods. It is an area of great mixing of gases and exhibits pressure changes due to air density changes over different time scales.

    Doesn’t sound like any greenhouse I know, more like a maelstrom to me!

  21. Vuk says:

    Hi tb,
    Thanks for the invite, I’m not much of a beer man, but if my way takes me to the lands of the roast beef and Y pudding, I shall drop you a note.

    While we are at the cooking business and kitchenelia rather than repeat myself here is my comment on the WUWT addressed to two lovely ladies Gail Combs and Pamela Grey :

  22. Tenuc says:

    @Vuk – Thanks for reminding me of that thread, from which comes a link to this paper from Ian Wilson…

    In the paper he predicts an Oort-like minimum (1010 to 1050 A.D.) that will last from roughly 2005 to 2045, not a Maunder-like minimum. Well worth a read… 8-)

  23. gallopingcamel says:

    You brew beer too! Why didn’t we discover that when we worked in the physics department before my retirement? Back then I used to brew 10 gallons in a glass “Carboy”. When fermentation was complete the beer was transferred through a yeast filter into two 5 gallon stainless kegs pressurised with CO2 @ 20 psi. I gave all that equipment away when I left North Carolina. You might have appreciated it

    The models claiming (falsely) that minute traces of CO2 have a significant effect on global climate have a huge failing. They don’t take water into account. First there is the gigantic (at least compared to CO2) concentration of water vapour in the lower atmosphere and then there are clouds that prevent the direct transfer of IR radiation from the surface.

    Please accept my apologies if you already saw this link in one of my earlier posts:

  24. cdquarles says:

    With all due respect, tallbloke, gravitational fractionation of air does not happen until you get to the very top of the atmosphere, where the rms velocity of the lighter gases allow them to escape diffentially to the heavier ones. One of the first things I learned in chemistry is that all gases are miscible. Carbon dioxide and water are variable gases/vapors in the atmosphere because they have differential sources and sinks, particularly in the boundary layer.