Cooling of Atmosphere Due to CO2 Emission: A Critical Analysis

[Andre]

http://www.informaworld.com/smpp/content~content=a788582859~db=all



G. V. CHILINGAR, L. F. KHILYUK, and O. G. SOROKHTIN, 2008, Cooling of Atmosphere Due to CO2 Emission, Energy Sources, Part A, 30:1–9, 2008 ISSN: 1556-7036 print/1556-7230 online DOI: 10.1080/15567030701568727

Heads and tails of the study:

Introduction

Traditional anthropogenic theory of currently observed global warming states that release of carbon dioxide into atmosphere (partially as a result of utilization of fossil fuels) leads to an increase in atmospheric temperature because the molecules of CO2 (and other greenhouse gases) absorb the infrared radiation from the Earth’s surface. This statement is based on the Arrhenius hypothesis, which was never verified (Arrhenius, 1896).
The proponents of this theory take into consideration only one component of heat transfer in atmosphere, i.e., radiation. Yet, in the dense Earth’s troposphere with the pressure pa > 0:2 atm, the heat from the Earth’s surface is mostly transferred by convection (Sorokhtin, 2001a). According to our estimates, convection accounts for 67%, water vapor condensation in troposphere accounts for 25%, and radiation accounts for about 8% of the total heat transfer from the Earth’s surface to troposphere.

Thus, convection is the dominant process of heat transfer in troposphere, and all the theories of Earth’s atmospheric heating (or cooling) first of all must consider this process of heat (energy)– mass redistribution in atmosphere (Sorokhtin, 2001a, 2001b; Khilyuk and Chilingar, 2003, 2004). …

...

Conclusions

…Accumulation of large amounts of carbon dioxide in the atmosphere leads to the cooling, and not to warming of climate, as the proponents of traditional anthropogenic global warming theory believe (Aeschbach-Hertig, 2006). This conclusion has a simple physical explanation: when the infrared radiation is absorbed by the molecules of greenhouse gases, its energy is transformed into thermal expansion of air, which causes convective fluxes of air masses restoring the adiabatic distribution of temperature in the troposphere. Our estimates show that release of small amounts of carbon dioxide (several hundreds ppm), which are typical for the scope of anthropogenic emission, does not influence the global temperature of Earth’s atmosphere.

I can follow that logic. Discussion?

 

[Count Iblis]

I don't follow the logic at all. You need warming due to absorption of infrared radiation leading to expansion and more convection and then you get a net cooling? But if you get a net cooling you don't have the warming you need to explain the expansion and the extra convection you need. It is self contradictory.

 

[ray b]

are not the upper levels of the atmosphere near the tropopause cooler then expected
where you get the .2 atm
while the lower air near surface air is warmer

so hot or cooler may depend on how high up you are

 

[Andre]

I don't follow the logic at all. You need warming due to absorption of infrared radiation leading to expansion and more convection and then you get a net cooling? But if you get a net cooling you don't have the warming you need to explain the expansion and the extra convection you need. It is self contradictory.

Okay, Indeed, it's not happening on the same levels. Let me elaborate.

First some understanding about convection:

http://www.ace.mmu.ac.uk/eae/Weather/Older/Convection.html

One way that heat is transferred through air is by convection. Convection of heat energy in the atmosphere involves the movement of air. Air is a poor conductor of energy, so convection is a major process of energy movement in the Earth’s atmosphere. In the atmosphere, convection occurs when a shallow layer of air in contact with a hot surface warms by conduction, acquires buoyancy (warmer air is less dense than colder air), and rises, taking with it the energy that it stores. As the Earth is heated by the Sun, bubbles of hot air called thermals rise upward from the warm surface...con'td

Note that convection is visible most of the time as it produces cumulus clouds, thunderstorms, tornadoes, hurricanes.

Hence, convection is a means of transporting and distributing heat-energy within the atmosphere, causing the higher levels to be warmer than the natural http://www.bbc.co.uk/weather/features/understanding/lapse_rates.shtml . Why? because convection due to solar heat only works at day time, not at night, when the Earth cools due to radiation. This only makes the air in contact with the surface cooler and hence more dense, which prevents convection backwards.

However, the warmer air that has convected to higher atmospheric layers also radiates out heat, basically 50% to the Earth and 50% to the universe, also cooling in the process, not only at daytime but also at night!

Now the article argues that more greenhouse gas enhances the transfer of heat energy from the surface to the lower layers of the atmosphere, which obviously gets warmer faster but this amplifies the rate of convection and also the rate of cooler air from aloft replacing the convecting air, neutralizing the warming effect at the surface.

At the higher altitudes however, the increase of concentration of greenhouse gasses makes the energy radiation out of the atmosphere more effective, which increases the cooling rate, which is supposed to balance the increase of energy at the surface.

What they don't even consider, is that the overal effect of the 24/7 day night operation of enhanced radiative cooling in the upper atmosphere should compensate more than for the daytime only increase of thermal energy convection. Hence increase of greenhouse gasses seems to cause a net stronger radiative cooling.

Does that help?

Notice again that the greenhouse effect hypotheses attributes the difference between blackbody temperature and actual temperature attributes to radiation, whereas in reality this difference is mainly caused due to the one way convection of energy, only up, not down, just like a vertical conveyor belt..

 

[blimkie.k]

I could see inscreased CO2 in the atmosphere eventually having a cooling effect. According to global warming increased CO2 in the atmosphere inscreases the greenhouse effect and increases temperature. If it is true that temperature is increasing will that not increase evaporation resulting in heavier cloud cover and rain. Also melting of ice caps should cool the ocean or slow down the currents which carry heat away from the equator. I suppose this could also have a negative impace on regions near the equator.

Anyways I live in south east ontario and this summer was not very summerish at all. It was not as hot as it should have been and it rained a hell of alot. We broke 100 year old rainfall records in some areas. There was hardly any days with clear blue skys. Even the nicest days were still filled with cumulus clouds. Shady or even rainy periods. I have been wondering if its just a freak summer or if it could have something to do with climate change.
Also the farmers almanac calls for a colder then normal winter. Just awesome.

 

[vanesch]

I think qualitative dynamics like this doesn't mean much, especially when different dynamics work in opposite directions: one should put them in a computational model and see how all this behaves. In fact, as long as one doesn't have a computational model that is 1) based upon sound physical basis (and not on empirical parameter fitting black box dynamics) and 2) corresponds to genuine experimental data, I think speculation is running loose.

 

[Andre]

But it's a start, since classic greenhouse effect ideas might underestimate the energy transport by convection, it's unlikely that the current models do justice to the effect of convection.

 

[wolram]

This may be totally naive, but why can not scientists fill a chamber with gasses in some proportions and measure it properties to reflect, absorb whatever light/heat.

 

[Gokul43201]

This may be totally naive, but why can not scientists fill a chamber with gasses in some proportions and measure it properties to reflect, absorb whatever light/heat.

Because the physics is not scale invariant. Nor is there any kind of easy scaling theory for any of this.

 

[Andre]

Indeed, there isn't, moreover the processes are not linear. You could compare the double effect of heating and cooling with a tap opening a bit more (heating) to fill a bucket with a hole in the bottom, which we make a bit bigger (cooling). there is no way to tell what the water level is going to do, without quantification.

Although you could quantify both warming and cooling rates logaritmically proportional to the density of the greenhouse gas, but quantifying the increase in convection rate would be rather complicated especially when the role of water evaporation and condensation is taken into consideration.

It may be noted that problems in the basic mechanisms of the greenhouse idea have been signalled by Miskolsci here as well as Douglass et al here.

Bottom line however from the study remains that it makes a case that the atmosphere is primarily heated by convection instead of radiative effects. It appears that this would reduce the effect of radiative forcing heating or greenhouse effect considerably.

 

[Andre]

It may be recalled that also our cbacba had some issues with his model here.

That brings to question, what does cause the Earth to be warmer if ghgs don't have much of anything to do with it.

It seems that Chilingar et al 2008 pretty much have answered that question, convection. Curiously enough I learned that already some four decades ago, going for my glider flying permit. However, there is very little mentioning of convection in the IPCC 4AR WG1 climate issues. Why?

 

[billiards]

But surely if CO2 becomes more important to heating at higher altitudes, then this would make the atmosphere more buoyantly stable. In other words, wouldn't increasing CO2 have the opposite effect to that proposed, ie, it would tend to inhibit convection??

 

[Andre]

The idea is, that it becomes more important at cooling the higher altitudes by radiating out the convected energy.

Alternately consider the null hypothesis, suppose that there was no greenhouse gas in the atmosphere. It would still be heated by conduction at the lowermost levels, which would still generate convection.

But since the convection is one way traffic only, without the possibility to loose that heat energy by radiation, the atmosphere would continue to heat up by convection until the lapse rate was to become stable, preventing further convection, then the atmosphere would be a lot warmer than without the radiative cooling at higher levels.

hence, in this simplified setting, it appears to be the greenhouse effect, the capability to radiate out the heat in the higher atmosphere, that keeps convection going.

 

[billiards]

Why is cooling by radiation more important at higher altitudes? I can see how the inverse would be true: that heating by absorption would be more important as a mechanism of heat transfer at higher altitudes, simply because there is no surface to conduct heat to the air at high altitudes. I guess what we really need to know is the net effect, in terms of relative importance, as to the effect of greenhouse gases to heat transfer as a function of altitude. If it turns out that air at high altitude emits radiation at a higher rate than it absorbs then this is unstable and convection may ensue.

Of course, we have convection, and we can explain it without the need to resort to this effect. Then we may reasonably ask, how important is this effect? What is the relative order of magnitude of this effect in relation to the standard model of atmospheric convection: hot air rises, expands and cools, advects, and sinks. Afterall, the concept of the Hadley cell, which fits global observations of convection patterns neatly, does not rely on this effect. This might suggest that this effect, if it exists at all, is negligible.

 

[Andre]

See the OP. Jack:

According to our estimates, convection accounts for 67%, water vapor condensation in troposphere accounts for 25%, and radiation accounts for about 8% of the total heat transfer from the Earth’s surface to troposphere.

 

[Andre]

Another way of looking at it is measuring the temperature/altitude of the outgoing radiation emitted by CO2 and H2O

http://www.bom.gov.au/weather/satellite/about_satpix.shtml#wV

In normally moist atmosphere , most of the WV radiation received by the satellite originates in the 300-600 hPa layer, but when the air is dry some radiation may come from layers as low as 800hPa.

So if these are the normal atmospheric levels that radiate IR energy out, as a consequence, these levels should logically be cooling.

 

[billiards]

See the OP. Jack:

Andre, the quote is meaningless in terms of my objections. I'm not objecting to the assertion that convection is important, and that if there were more convection we would lose heat quicker and thus cool, I agree with that point. I was objecting to whether the presence of CO2 actually had a sensible impact on atmospheric convection.

Another way of looking at it is measuring the temperature/altitude of the outgoing radiation emitted by CO2 and H2O

http://www.bom.gov.au/weather/satellite/about_satpix.shtml#wV



So if these are the normal atmospheric levels that radiate IR energy out, as a consequence, these levels should logically be cooling.

I'm sorry, you're going to have to spell this one out to me. I really don't follow your point.

 

[Gokul43201]

Also, in this context, perhaps someone might like to comment on the following paper.

Lunt et al, Nature 454, 1102-1105 (2008)

Late Pliocene Greenland glaciation controlled by a decline in atmospheric CO2 levels

Abstract: It is thought that the Northern Hemisphere experienced only ephemeral glaciations from the Late Eocene to the Early Pliocene epochs (about 38 to 4 million years ago), and that the onset of extensive glaciations did not occur until about 3 million years ago. Several hypotheses have been proposed to explain this increase in Northern Hemisphere glaciation during the Late Pliocene. Here we use a fully coupled atmosphere–ocean general circulation model and an ice-sheet model to assess the impact of the proposed driving mechanisms for glaciation and the influence of orbital variations on the development of the Greenland ice sheet in particular. We find that Greenland glaciation is mainly controlled by a decrease in atmospheric carbon dioxide during the Late Pliocene. By contrast, our model results suggest that climatic shifts associated with the tectonically driven closure of the Panama seaway, with the termination of a permanent El Niño state or with tectonic uplift are not large enough to contribute significantly to the growth of the Greenland ice sheet; moreover, we find that none of these processes acted as a priming mechanism for glacial inception triggered by variations in the Earth's orbit.

http://www.nature.com/nature/journal/v454/n7208/abs/nature07223.html

 

[Andre]

Also, in this context, perhaps someone might like to comment on the following paper.

Lunt et al, Nature 454, 1102-1105 (2008)


http://www.nature.com/nature/journal/v454/n7208/abs/nature07223.html

That would well be worth its own thread, Gokul, as one post would not do justice to tons of publications about this kind of material.

Furthermore, from the abstract only, there is little chance to comment on the scientific merit. But we see 'model' and then they "find", etc. Now, recall the scientific method, what is the role of a model? Merely to work out a hypothesis. A hypothesis can be considered only substantiated (not proven), if the forthcoming predictions (i.e. from models) are confirmed with solid evidence and we can't really see any of that in the abstract.

Secondly, working out a single hypothesis to explain correlation is inferior to comparing two hypotheses, exchanging cause and effect. Such a competing hypothesis could be: variation in temperatures may cause variations in atmospheric CO2 due to the variation in oceanic capacity with temperature to store CO2. So what is cause and what is effect?

If we agree that cause comes before the effect, then the ice cores produce no support for the idea that CO2 changes lead to temperature changes. As apparently temperature changes lead CO2 with some 600 years in this case of the last glacial termination:

http://gallery.myff.org/gallery/145232/EPICA2.GIF

data:

ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/antarctica/epica_domec/domec_co2.txt
ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/antarctica/epica_domec/edc96-iso-45kyr.txt

Yes there is something about positive feedback but before using that argument it may be an idea to find the publication first that demonstrates the physical feasibility of such a mechanism using these ice core data. I'm not aware of its existence.

Furthermore there are examples of higher temperatures coupled with moderate CO2 concentration, in the Paleocene for instance: http://www.sciencemag.org/cgi/content/abstract/sci;292/5525/2310

Abstract

.. Our reconstruction indicates that CO2 remained between 300 and 450 parts per million by volume for these intervals with the exception of a single high estimate near the Paleocene/Eocene boundary. These results suggest that factors in addition to CO2 are required to explain these past intervals of global warmth.

Incidentily, a "needle" was found under the ice sheet of Greenland when drilling the NGRIP ice core.

http://www.gfy.ku.dk/~www-glac/ngrip/billeder_eng.htm

Later it proved to be willow bark (not published, communication with the authors) What would that say about the age of the Greenland ice sheet?

 

[Andre]

Andre, the quote is meaningless in terms of my objections. I'm not objecting to the assertion that convection is important, and that if there were more convection we would lose heat quicker and thus cool, I agree with that point. I was objecting to whether the presence of CO2 actually had a sensible impact on atmospheric convection.

it appears that we have a misunderstanding here, Jack I'm sorry. What is sensible? Chilingar et al attribute 8% to radiation (greenhouse effect). Estimates of the CO2 contribution to radiation, run from 5 to 25%, the rest mainly being water vapour. This would seem to get you at a maximum of 2%, disregarding feedbacks.

I'm sorry, you're going to have to spell this one out to me. I really don't follow your point.

trying again. As the satellites measure the IR frequency finger print of the outgoing radiation it is clear that it is radiated from these middle trophospheric levels and mostly by water vapor. So, if this is the out radiating source, then it is also place where the atmosphere cools effectively, since net out radiation means losing energy. Obviously this cooling is in some dynamic equilibrium with heat sources from below, in which convection seems to dominate. Hope it helps

 

[Andre]

Query for "convection" in the IPCC report,

http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_Ch02.pdf

Ozonesonde measurements over the southwest Pacific indicate an increased frequency of nearzero ozone in the upper troposphere, suggesting a link to an increased frequency of deep convection there since the 1980s (Solomon et al., 2005).
...
While GCMs have other well-known limitations, such as coarse spatial resolution, inaccurate representation of convection and hence updraft velocities leading to aerosol activation and cloud formation processes, and microphysical parametrizations, they nevertheless remain an essential tool for quantifying the global cloud albedo effect.
...
Models also have weaknesses in representing convection processes and aerosol distributions, and simulating updraft velocities and convection-cloud interactions
...
Modelling the cloud albedo effect from fi rst principles has proven diffi cult because the representation of aerosol-cloud and convection-cloud interactions in climate models are still crude (Lohmann and Feichter, 2005).
...
Using these data some studies (Sekiguchi et al., 2003; Quaas et al., 2004) indicate that the magnitude of the RF is resolution dependent, since the representation of convection and clouds in the GCMs and the simulation of updraft velocity that affects activation themselves are resolution dependent.

See also fig 2 FAQ 2.1. pp 136, no convection mentioned.

http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_Ch03.pdf

The upward motion comes from air rising over mountains, warm air riding over cooler air (warm front), colder air pushing under warmer air (cold front), convection from local heating of the surface, and other weather and cloud systems. Hence, changes in any of these aspects alter precipitation.
...
In contrast, the NAO index is only weakly correlated with the North Atlantic SST during the AMO positive phase. Chelliah and Bell (2004) defined a tropical multi-decadal pattern related to the AMO, the PDO and winter NAO with coherent variations in tropical convection and surface temperatures in the West African monsoon region, the central tropical Pacific, the Amazon Basin and the tropical Indian Ocean.
...
Tropical SSTs determine where the upward branch of the Hadley Circulation is located over the oceans, and the dominant variations in the energy transports by the Hadley cell, reflecting its strength, relate to ENSO (Trenberth et al., 2002a; Trenberth and Stepaniak, 2003a). During El Niño, elevated SST causes an increase in convection and relocation of the ITCZ and SPCZ to near the equator over the central and eastern tropical Pacific, with a tendency for drought conditions over Indonesia.
...
As the climate changes and SSTs continue to increase (see Section 3.2.2.3), the environment in which tropical storms form is changed. Higher SSTs are generally accompanied by increased water vapour in the lower troposphere (see Section 3.4.2.1 and Figure 3.20), thus the moist static energy that fuels convection and thunderstorms is also increased.
...
The potential intensity, defined as the maximum wind speed achievable in a given thermodynamic environment (e.g., Emanuel, 2003), similarly depends critically on SSTs and atmospheric structure. The tropospheric lapse rate is maintained mostly by convective transports of heat upwards, in thunderstorms and thunderstorm complexes, including mesoscale disturbances, various waves and tropical storms, while radiative processes serve to cool the troposphere. Increases in greenhouse gases decrease radiative cooling aloft, thus potentially stabilising the atmosphere. In models, the parametrization of sub-grid scale convection plays a critical role in determining whether this stabilisation is realized and whether CAPE is released or not. All of these factors, in addition to SSTs, determine whether convective complexes become organised as rotating storms and form a vortex.
...
Consequently, the oceans have not warmed uniformly, especially at depth. SSTs in the tropics have warmed at different rates and help drive, through coupling with tropical convection and winds, teleconnections around the world.

So chap 3 acknowledges convection as a predominant process of something, even energy mentioned, however chap2 does not seem to take convection into account as a heating mechanism of the atmosphere like Chilingar et al 2008. One would at least expect it to be a "forcing" factor in chap2.

http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_Ch03.pdf Convection not mentioned

 

[chjoaygame]

The paper by Chilingar, Khilyuk, and Sorokhtin 2008 entitled "Cooling of atmosphere due to CO₂ emission" needs to be read carefully in order to see its logic, which has several steps. If the logic of the paper is not followed carefully, then its message is not conveyed.

Step 1 is to say that convection is most important, and should be the backbone of a heuristic argument.

Step 2 is to say that CO₂ has an immediate effect on convection by virtue of its molecular weight. This immediate direct effect makes the atmosphere more dense. Taking into account the concurrent immediate radiative effect through the coefficient C_r in a model based on convection leading to near adiabatic gas law conditions, this leads to a warming of less than 0.01 K for a doubling of the present CO₂ level.

Step 3 is to note that the mere immediate effect of addition of CO₂ is not the whole story. There are feedbacks to CO₂ addition: in particular, added CO₂ is partly absorbed by the ocean and deposited as insoluble carbonates; the particular carbonates involved have the effect of taking oxygen from the atmosphere because of the reductive capacity of FeO. It is also partly replaced by oxygen when plants use it as food. Unlike the "feedback on radiative forcing by CO₂" doctrine of the Arrhenius devotees, these are true feedbacks. These feedback effects have the side-effect of longterm reduction of atmospheric density.

Step 4 is the consequent longterm climate cooling, by a little less than 0.1 K.

Though the long term side-feedback effects are greater than the immediate direct effects, both immediate direct and side-feedback effects are miniscule and not practically important from a physical or geographical viewpoint. Mistaken impressions on this subject have, however, a mighty emotional and political impact.

 

[chjoaygame]

I don't follow the logic at all. You need warming due to absorption of infrared radiation leading to expansion and more convection and then you get a net cooling? But if you get a net cooling you don't have the warming you need to explain the expansion and the extra convection you need. It is self contradictory.

Count Iblis:

In terms of the Arrhenius-IPCC doctrine of "feedback to radiative forcing by CO2", your concern is logical.

But the doctrine is unphysical, and so its logical consequences are in general also unphysical.

The error of the doctrine is that it assumes that the only direct effect of CO2 is to enhance the radiative processes. It ignores the physical fact that CO2 also directly and immediately affects convection, which is the main mechanism of heat transport from the surface to the upper atmosphere. The Arrhenius-IPCC doctrine demotes the convective effect to a "feedback" status; this is not even correct logic: even, for the sake of argument temporarily granting the doctrine's putting the radiative mechanism as the only direct effect, the convective effect should properly be called a compensatory effect not a "feedback" effect. A doctrine that ignores or demotes the main physical effect cannot be relied upon; that is the reason for the Chilingar Khilyuk and Sorokhtin paper.

The physics of the Chilingar Khilyuk and Sorokhtin paper "Cooling of atmosphere due to CO2 emission" is that the main immediate direct effect of CO2 is not the "radiative forcing" that is the only admitted immediate direct effect of the Arrhenius-IPCC doctrine. Physically, the main direct effect is to change the threshold for convection. The result is that at the same temperature, the convection is affected, without need for any radiative effect, putative or actual. The threshold for convection is changed because of the molecular weight of CO2. The most sensitive threshold for convection is deep tropical convection that goes right to the tropopause, prevalent in the intertropic convergence zone. The effect is to weaken convection slightly, and, taking into account also the radiative properties of CO2, this slightly warms the system, by less than 0.01K indeed for a doubling of CO2.

But there are delayed feedback effects which have side effects. These side effects are the main long-term influence. They continue the long-term cooling of the earth. They are chemical in nature, removing some oxygen from the atmosphere, and eventually they make the atmosphere less dense, and this leads to long-term cooling, a bit less than 0.1K. This happens because the lesser density enhances convection at the same temperature, without need for any radiative effect, putative or actual.

 

[Andre]

So I toyed a bit with MS Excel today, I was wondering what the chance is for a single photon (IR), emitted from the Earth surface, to escape into space. This would largely be dependent on two factors.
First: the maximum length of the path (optical depth?) it follows until it is absorbed and assuming that it is re-emitted in a random direction and assumingly for 100%
Second: the vertical thickness of the atmosphere in that same unit, the number of vertical path lengths/optical depths between Earth surface and the 'top' of the atmosphere.

So in the gross little model I defined that maximum path length as one unit and made one dimensional random walk simulating a photon emitted from the surface each time making a random step between -1 and +1 under various optical depths of the atmosphere. I used 20,000 cells for the random walk and would reset for the next photon each time, it hit the extreme values either <0 for re-absorption on the Earth surface or when bigger than the preset number of optical depths. For each optical depth values I averaged the result of 10 runs and got these results:

Optical depth: 1 unit; escaped percentage of photons 24.7%
Optical depth: 2 units; escaped percentage of photons 15.8%
Optical depth: 4 units; escaped percentage of photons 8.6%
Optical depth: 20 units; escaped percentage of photons 2.0%
Optical depth: 40 units; escaped percentage of photons 1.0%
Optical depth: 100 units; escaped percentage of photons 0.1%

Now, I have no idea what the optical depth is for a IR photon under various atmospheric conditions, maybe millimeters or hundreds of meters and the number of optical depths of the Earths atmosphere probably orders of magnitudes more. So it seems I don’t get the photons out of the Earth Surface, they drop back in almost all the time. Am I doing something wrong?

Next, I wondered about a photon starting at a certain altitude, with X optical depths below and Y optical depths above the starting point. But when I modified the program I began to realize what the outcome would be: the chance of escape of a photon versus absorption on the Earth surface would be X/(X+Y) and that was indeed supported by the simulation runs.

So this means that the only way to get photons/ IR radiation out of the atmosphere and balance the incoming solar radiation is by emission from a higher altitude, and the most effective way to get the required energy at higher altitudes is convection.

Note that the role of the concentration of greenhouse gasses is undefined here, if the concentration increases it affects both the number of optical depths below and above the initial emission altitude, and if that ratio doesn’t change, so would the number of emitted photons not change.

If there is no convection in a thick atmosphere, then it seems that the energy can not be emitted out. Would that help explaining the difference between Earth and Venus where there is no convection in the lower levels of the atmosphere?

 

[vanesch]

The problem with your approach is that you have an almost identical physical setting as the diffusion of particles in a material - like neutrons in a moderator. That's well-described by the diffusion equation, but I think you miss the essence of the physics then. The essence is that photons can be absorbed, that this heats the material locally, or excites molecules, and that photons of different wavelengths can be emitted (through specific de-excitations, or through general black body radiation, which is a kind of statistical average of many low-energy emission processes which are too complicated to follow up individually).

 

[Andre]

I agree that it's all very simplified and I'm aware of the complications when I said "and assumingly for 100%" but I wonder what would change to the general idea. Replace photon with "certain fixed amount of energy in whatever form", and what would be the difference?

 

[vanesch]

I agree that it's all very simplified and I'm aware of the complications when I said "and assumingly for 100%" but I wonder what would change to the general idea. Replace photon with "certain fixed amount of energy in whatever form", and what would be the difference?

The difficulty is that the optical depth, and the scattering, is a function of the photon wavelength. So it matters a lot if your "amount of energy" is in the form of a single, blue photon, or in the form of 5 infrared photons, or of 10 infrared photons with bigger wavelengths. And the essence of the all the greenhouse, and irradiance, and absorption and so on things lies exactly in those transformations. If the properties of the photons were more or less independent of it, and we would just have scattering, then we would have a perfect diffuser. The solutions for that are known, they are simply the diffusion equation. It is for instance what you can use for neutron populations in a moderator. But the same equation is also valid for heat transport.

 

[vanesch]

BTW, there are computer codes which do exactly that:
http://en.wikipedia.org/wiki/List_of_atmospheric_radiative_transfer_codes

or http://www.geocities.jp/null2unity/mcarats/

Look under "monte carlo" codes. I never used them.

 

[Andre]

Still it would be very useful to calculate the chance from photon/ bits of energy generated at certain altitudes, after convection of that energy from the Earth surface, to hit either the Earth surface or escape into space as function of greenhouse gas concentration.

For instance the vertical latent heat transport (evaporation) sort of "hides" higher temperatures until condensation, when the heat is released again and the consequent radiation can start.

Would those models do that? I don't see any mentioning of that mechanism.

 

[vanesch]

Still it would be very useful to calculate the chance from photon/ bits of energy generated at certain altitudes, after convection of that energy from the Earth surface, to hit either the Earth surface or escape into space as function of greenhouse gas concentration.

For instance the vertical latent heat transport (evaporation) sort of "hides" higher temperatures until condensation, when the heat is released again and the consequent radiation can start.

Would those models do that? I don't see any mentioning of that mechanism.

I don't know. As I said, I never used these codes. It takes time and effort to plunge into a scientific computing program like that. I know similar codes (not in the public domain at all) for nuclear radiation transport (in my opinion, the two categories of problems are very similar, that's why I think I can have the pretension to open my mouth in this kind of discussion). Now, nuclear radiation transport codes are very accurate because real working stuff is based upon them, like power reactors, radiation protection and criticality avoidance in radiochemical plants ; we can't permit ourselves to have ununderstood fudge factors and group think or we all blow ourselves in the air ! So these codes are tested against a lot of known test cases.

But probably optical radiation transport is harder than nuclear radiation transport because there are molecular interactions and things like that. Nuclear radiation transport codes usually do not include hydrodynamical effects in themselves: you have to couple different codes in order to achieve that. Convection by itself, as a hydrodynamical problem, is already extremely difficult. Add to that things like condensation and so on, and you have something very hard to do ab initio. So I guess - although I don't know - that these codes are doing just the radiation transport, with all matter "fixed".

To really find out, you should look into the user manuals. I could very well be totally wrong.

 

[DEMcMillan]

Convection has been linked to CO₂ and heat transfer from Earth’s surface. The abstract mechanism is “absorption” and has heating leading to convection. The reply strings, especially chjoaygame’s, generated a model without the original heat transfer problem in a cloudless and dust-free troposphere.

chjoaygame pointed out that CO₂ raises the density of air. This property fascinated me several years ago because water vapor has the opposite effect. Water vapor addition makes air more buoyant, carrying the water vapor upward, usually until the water vapor condenses into haze, fog or clouds. While buoyant water vapor-containing air is rising heavier dry air elsewhere is descending to replace it as pressure gradients develop. Water vapor entry is a major mediator of vertical motion in the troposphere. The easily mixing adiabatic troposphere is disrupted as water vapor adds energy by changing in state. Rising CO₂ accelerates this process but doesn’t change the rate of heat transfer to and within the troposphere. My numerical calculations failed to portray any substantial change in tropospheric heat distribution. More rapid mixing actually stabilized its convective heat distribution. Liquid and solid water-mediated temperature inversion is the major inhibitor of tropospheric mixing, giving us smog and other urban and regional problems. But in general inversion has only a limited effect on radiation balance.

The major role of Earth’s convection is the movement of heat from the tropics toward the poles. The atmosphere’s role is to drive the oceans great streams to transfer heat. The trade wind Easterlies are generated by high air descending and returning to the tropics. The resulting Western flow is due to conservation of angular momentum. Ocean water transmits far more heat than the atmosphere itself. The sea surface temperature in the Temperate and Frigid zones is raised and the Tropics lowered by the steady ocean water anti-cyclonic movement. Periodically, characteristically in November and December, this process breaks down and the Earth’s weather changes. In a year, the trade winds return and the briefly heated Earth cools in proportion to its previous heating, but now over two years. One can wager that the jet streams benefit from the Easterlies loss. The stratospheric velocity increase brings on storms that would not otherwise ascend the continental mountains. How such behaviors affect radiation into space is not clear. The marked tropical rise is incorporated into a general planetary rise. The descent path from the jet streams has not been identified but must sweep more directly back to the tropics. The overall system’s effect is to raise surface temperatures. The effect of stratospheric temperatures is less clear. I used 1997-8 as a test year for convection breakdown. http://www.cpc.noaa.gov/products/stratosphere/temperature/ The upper and lower stratosphere don’t show any clear change in temperature during this period. Where does carbon dioxide’s molecular weight fit in? How does it make the Earth’s energy balance negative in general? The ultimate balance must be radiative and thermal.

I would like to point out to vanesch that none of the cited models allow treatment of the IR emissive nature of the atmosphere itself that markedly reduces the greenhouse gas line by line radiative return to the Earth’s surface. Gray body and optical depth maneuvers act only to hide the modeling deficiency. https://www.physicsforums.com/showthread.php?t=261966

 

[Andre]

I don't know. As I said, I never used these codes. It takes time and effort to plunge into a scientific computing program like that. I know similar codes (not in the public domain at all) for nuclear radiation transport (in my opinion, the two categories of problems are very similar, that's why I think I can have the pretension to open my mouth in this kind of discussion). Now, nuclear radiation transport codes are very accurate because real working stuff is based upon them, like power reactors, radiation protection and criticality avoidance in radiochemical plants ; we can't permit ourselves to have ununderstood fudge factors and group think or we all blow ourselves in the air ! So these codes are tested against a lot of known test cases.

But probably optical radiation transport is harder than nuclear radiation transport because there are molecular interactions and things like that. Nuclear radiation transport codes usually do not include hydrodynamical effects in themselves: you have to couple different codes in order to achieve that. Convection by itself, as a hydrodynamical problem, is already extremely difficult. Add to that things like condensation and so on, and you have something very hard to do ab initio. So I guess - although I don't know - that these codes are doing just the radiation transport, with all matter "fixed".

To really find out, you should look into the user manuals. I could very well be totally wrong.

Let's do a bit of back side of the envellope educated guessing first:

As the absolute/relative humidity is course directly affecting water vapor feedback, let's see what is required to get those increased values. For ballpark figures, from http://www.usclivar.org/Organization/Salinity_WG/workshoppresentations/Evp-salinityLisanYu.pdf here let's assume average annual evaporation of a meter per year. That's 2.74 liters (2740 g) per m2 per day or 114 g per hour is 0.032 gram per second. It takes 2500 joule to evaporate one gram of water, so for 0.032 gram that's 79 joule per second per square meter or 79 W/m2

Now to keep relative humidity constant when increasing the ambient temperature of 15 C to 16 C, suppose a dewpoint of about 9 degrees we see http://www.humirel.com/All_about_humidity-calculation2.htm a decrease of 67% to 63%. Obviously we also have to raise the dewpoint one degree to get back to 67% Now the absolute humidity calculated http://www.humirel.com/All_about_humidity-calculation2.htm goes from 9 gram/m3 at a dewpoint of 9 degrees to 9.6 gram/m3 at a dewpoint of 10 degrees, an increase of 7%. To sustain an increase of 7% more water vapor in the atmospere it seems logical that the rate of evaporation also has to increase by 7% as well, which in turn requires 7% more energy. Hence I'd need 7% of 79 W/m2 or 5.5 W/m2 extra to maintain constant relative humidity. So how much excess energy is there to get that positive water feedback in? Weren't we talking about 3-4 W/m2. So is anything wrong here?

 

[vanesch]

To sustain an increase of 7% more water vapor in the atmospere it seems logical that the rate of evaporation also has to increase by 7% as well, which in turn requires 7% more energy. Hence I'd need 7% of 79 W/m2 or 5.5 W/m2 extra to maintain constant relative humidity. So how much excess energy is there to get that positive water feedback in? Weren't we talking about 3-4 W/m2. So is anything wrong here?

The point is that there will be increased condensation too somewhere and that will then act as a heat source of equal importance (5.5 W/m2 in your example: somewhere, these 5.5 W/m2 will be returned). Of course, everything will depend on *where* this condensation will take place and hence *where* the latent heat which has been subtracted from the ground by increased evaporation, will be rendered to the atmosphere (and act as a source of heating). If this is low in the atmosphere, then the heat which was extracted by evaporation, will be rendered on the spot, and in this case, the evaporation heat loss (as well as the condensation heating) will not have to be included in the balance. If it is higher up, then of course, this will act as a heat vector.

What's also a matter, is that water vapor is a lighter gas (18 amu) than air (28 or 32 amu), and hence water vapor (even not hot) is a drive for convection. As I said somewhere else, it is the main drive for the convection in cooling towers (where the heat source is in fact on top: one makes hot water (in the form of drops) fall from the top of the cooling tower down into the cooler air).

 

[chjoaygame]

Andre and vanesch PF Mentor, the chance of a "single photon" (IR), emitted from the Earth surface, to escape to space.

The chance of escape depends very much on the wave number within the IR band. There is an "atmospheric window" of wave numbers, rather arbitrarily but reasonably defined in detail as from 720 cm^-1 to 1260 cm^-1 by Miskolczi, in which the chance of escape of a single photon is quite good, better than 1/2, variably dependent on the water vapour content and CO₂ content, as well of course as on cloud fraction. Outside the window, the chance of escape of a "single photon" is extremely small, practically zero. This is why is it is not overly useful to think of the atmosphere as "grey".

There are thus two regimes for IR in the atmosphere, the window and the non-window. In the window, the optical depth is less than 1. Outside the window, the optical depth is perhaps 30.

The window is translucent, partly transparent. It is, as it were, variably "muslin curtained" by water vapour and CO₂. The water vapour content varies from place to place, usually being largest near the equator and least at the poles, and quite rapidly from time to time. The CO₂ content is less rapidly variable. There is a small spatial variation with latitude, and a seasonal cycle, and in the time it has been measured over the past decades a slow drift of increase. Also the window is variably "venetian blinded" by clouds, which are practically opaque in the window, but of course are patchily or fractionally distributed in space, as well as variable in time.

Outside the window, where the cloudless atmosphere is opaque to IR, the propagation of heat from the land-sea surface to the lower skin of the atmosphere, and through the atmosphere except in its upper reaches, is described by the diffusion limit of the radiation transfer equation (Mihalas and Mihalas 1984). Fourier's law of heat diffusion reigns here. Though very widely customary, it is not good physics to try to speak or think here of "radiative transfer" as distinct from conductive-convective-evaporative transfer. The radiative part of the heat transfer is much better thought of as part of the diffusion-conduction. Both ponderable matter and radiation share inseparably in the conduction of heat. The mean free path of the IR "single photons" is some tens of meters, a distance over which the temperature of the air changes only a little, because of convection. It is thus futile to think separately of "radiative transfer" from the land-sea surface outside the window. In other words, the commonly touted story of "back-radiation", from the bulk of the atmosphere to land-sea surface, is futile, poor physics, confusing or misleading, practically meaningless outside the window. Outside the window, the rate of transfer of heat from land-sea surface to lower atmospheric skin is directly proportional to the local temperature gradient, as expressed by the Fourier heat diffusion law, and one can forget a separate radiative transfer here.

Inside the window, one is interested in separate radiative transfer of heat from the land-sea surface. The mean free path of "single photons", when the air is relatively dry and the CO2 relatively little, can be hundreds of kilometers. The very importantly and greatly variable IR radiative flux through the window, direct from the land-sea surface to space, is on the order of magnitude of 60 W m^-2. In a cloudless sky, the notion of "back-radiation" does not arise here.

Consequently, the overwhelming varying, and nearly the only, flow, of back radiation from atmosphere to land-sea surface is from the lower surfaces of clouds. Because it arises from clouds which are cooler than the land-sea surface, it is fractionally less in magnitude than the radiation from land-sea surface through the window which is blocked by the clouds. The clouds are good radiators in the IR because they are practically opqaque to IR. From the upper surface of clouds there is also radiation through the window direct to space. Overall the clouds are cooled by the window radiation because they have window radiation reaching them only from below, while they radiate nearly equally both upwards and downwards.

The land-sea surface is partly warmed by the back radiation downwards through the window from the clouds. On the other hand, the net cooling of the clouds by the window radiation leads eventually to convection of cooler air from altitude down to the land-sea surface and thus eventually to a greater temperature gradient driving diffusion from land-sea surface to atmosphere; this partly cools the land-sea surface to partly offset the partial warming by the clouds' window back radiation.

The 24-hour partial result of this mechanism is slight warming of the land-sea surface and slight cooling of the clouds. This tends to increase the vertical temperature gradient, the lapse rate, and tends to increase convection, both horizontal and vertical.

Apart from the window back radiation outside the window wave numbers, and its consequences, the clouds hardly affect intra-atmospheric radiative heat transport, because outside the window the atmosphere is practically opaque anyway. Of course latent heat and convective transport are important in clouds.

But during the day the clouds exert another kind of radiative effect, in another, non-IR wave number regime. They reflect, from their upper surfaces directly back to space, a big fraction of the visible sunlight that hits them. This is described as albedo. This is a strong cooling effect of clouds during the day, affecting the whole atmosphere and land-sea surface. On the other hand, at night, the clouds exert a slight warming effect on the lower atmosphere and the land-sea surface because of their window back radiation and its consequences.

I have not seen the above account written elsewhere, so far as I can recall, but then I have an appalling weakness of memory.