Global warming is not caused by CO2

[Andrew Mason]

C02 is only a problem for respiration when it displaces the required oxygen, it is not otherwise toxic.

I don't think that is correct. CO₂ is absolutely toxic at concentrations over 5%. This is not due to displacement of O₂ (humans can breathe if the oxygen level is 16%). It is due to acidification of the blood and tissues (acidosis) which becomes a problem at CO₂ levels of about 1.5% according to this article.

AM

 

[Andre]

So far, no one has been able to establish one fact that is inconsistent with increased CO₂ concentrations causing the average temperature of the surface of the Earth to increase,

You mean like this?

 

[vivesdn]

explanation needed for newbie:

Conclusion is clear but I would like to learn about Hadley and MSU temperatures.

 

[Andre]

...Conclusion is clear but I would like to learn about Hadley and MSU temperatures.

Hadley is the British Met Office producing monthly temperature series here. http://www.cru.uea.ac.uk/cru/data/temperature/hadcrut3vgl.txt is the global set.

The first row in the year is monthly temperatures, the second is percentage of the globe covered.

http://www.ssmi.com/msu/msu_data_description.html produces monthly temperature data through the atmosphere as processed by satellites, the http://www.ssmi.com/msu/msu_data_description.html#msu_weighting_functions obviously, being relevant:

 

[Andre]

So far, no one has been able to establish one fact that is inconsistent with increased CO₂ concentrations causing the average temperature of the surface of the Earth to increase, nor with the increased CO₂ concentrations being generated directly or indirectly by human activity.

I hope it's not too much of a trouble but could you give an example anywhere in the past what supports that statement:

increased CO₂ concentrations causing the average temperature of the surface of the Earth to increase.

It may look like a redundant question, since not a day will go by or you'd catch phrases like this somewhere. But which data sets exactly would support that?

So what are those other reasonable alternative explanations? So far as I can tell, they are:

...

Are there any others?

Albedo variation mainly due to cloud cover, see this post

Not too bad, it seems, for two decades:

Note that in the top graph the Y-axis both depicts the variation in albedo in percentage and the temperature variation in tenth of degrees Kelvin.

 

[mheslep]

I don't think that is correct. CO₂ is absolutely toxic at concentrations over 5%. This is not due to displacement of O₂ (humans can breathe if the oxygen level is 16%). It is due to acidification of the blood and tissues (acidosis) which becomes a problem at CO₂ levels of about 1.5% according to this article.

AM

Yes I expected that at some absurdly high level CO2 would be toxic; even water is toxic at some point. But I (incorrectly) believed that lack of O2 from displacement would always be the more immediate problem. At least for enclosed space where the CO2 slowly replaces O2 consumed by respiration or combustion, apparently the CO2 will grow toxic before the onset of suffocation. Of course if you are suddenly immersed in a CO2 cloud (e.g. volcanic release) the lack of O2 will cause suffocation first.
http://vulcan.wr.usgs.gov/Glossary/Lakes/description_volcanic_lakes_gas_release.html

 

[Andrew Mason]

I hope it's not too much of a trouble but could you give an example anywhere in the past what supports that statement.

Perhaps I should have said that there is no fact that is generally accepted as proven fact, that is inconsistent with the observed average increase in global temperature being due to human activity.

It may look like a redundant question, since not a day will go by or you'd catch phrases like this somewhere. But which data sets exactly would support that?

It is a matter of the absence of proven facts contradicting the stated hypothesis ie. that global temperature increase is being caused by human activity.

Note that in the top graph the Y-axis both depicts the variation in albedo in percentage and the temperature variation in tenth of degrees Kelvin.

Yes. I could add the albedo effect as a separate explanation for global warming. The only problem is that a signficant change in albedo effect can be a mechanism that affects global temperature but it is merely a symptom of an underlying cause. A significant change in albedo effect begs the question: what is causing it? If it is the loss of polar ice, which is in itself caused by global increase in temperature due to increase in CO2 concentration, albedo effect is not the primary cause.

BTW, I am not so sure that your graphs are correct. As you point out, the greatest albedo effect appears to be cloud cover. This article suggests that the cloud albedo effect is INCREASING despite general global temperature increase.

AM

 

[Andre]

Perhaps I should have said that there is no fact that is generally accepted as proven fact, that is inconsistent with the observed average increase in global temperature being due to human activity.

It is a matter of the absence of proven facts contradicting the stated hypothesis ie. that global temperature increase is being caused by human activity.

You have a curious view about the onus of proof. The (necesary) elements of the hypothesis in question are:

1. CO2 and CH4 are greenhouse gasses,
2. greenhouse gasses are the main cause for the atmosphere to be warmer than grey body temperature.
3. increases concentration of greenhouse gasses increase the temperature of the atmosphere significantly, (global warming).
4. humans increase the concentration of greenhouse gasses.
hence humans cause global warming

There is little reason to challenge elements #1 and #4, but how about #2 and #3? If those were to be true then variations in greenhouse gasses in the past would necesarely lead to corresponding changes in global temperatures. So whether or not that evidence is there, should be decisive for the confirmation or falsification of those elements #2 and #3.

So how about that proof?

albedo effect is not the primary cause.

Albedo variation is only a link in the chain of causes and effects. Variation in cloud cover may have many causes, not necesarily warming.

BTW, I am not so sure that your graphs are correct. As you point out, the greatest albedo effect appears to be cloud cover. This article suggests that the cloud albedo effect is INCREASING despite general global temperature increase.

AM

Now, isn't that a coincidence? We're talking about the same source! However, what Pallé et al (2006) failed to verify, is the correlation between their results and the global temperatures. They just erroneously assumed that the temperatures continued to rise, perhaps because that's what you hear all the time.

See also this thread

 

[Andrew Mason]

You have a curious view about the onus of proof. The (necesary) elements of the hypothesis in question are:

1. CO2 and CH4 are greenhouse gasses,
2. greenhouse gasses are the main cause for the atmosphere to be warmer than grey body temperature.
3. increases concentration of greenhouse gasses increase the temperature of the atmosphere significantly, (global warming).
4. humans increase the concentration of greenhouse gasses.
hence humans cause global warming

All that is needed for a successful hypothesis is an explanation that is rational, plausible and that is not inconsistent with any facts.

In this case, it can be shown that CO2 absorbs infrared radiation and is, therefore, capable of causing the surface of the Earth to become warmer(1). It can also be shown that humans directly add about 30 GT of CO2 to the atmosphere annually (4). The total mass of CO2 in the atmosphere at present is about 3,000 GT which results in a CO2 concentration of 383 ppm by volume. So the addition of 30 GT could add as much as an additional 1% or almost 4 ppm to the CO2 concentration of the atmosphere. So the explanation is rational and plausible.One merely has to show that there are no proven facts that conflict with the hypothesis.

So my question is: what facts is this hypothesis inconsistent with?

As I said, however, this does not make it the correct explanation. One would need to look at all other alternate explanation and see if there are facts which conflict with them. Only by eliminating all other hypotheses with proven facts can one reach a reasonable conclusion that a hypothesis is correct.

There is little reason to challenge elements #1 and #4, but how about #2 and #3? If those were to be true then variations in greenhouse gasses in the past would necesarely lead to corresponding changes in global temperatures. So whether or not that evidence is there, should be decisive for the confirmation or falsification of those elements #2 and #3.

Having established a rational and plausible explanation, one does not have to directly prove your points 2 and 3. Your question really is" do variations in greenhouse gas concentrations in the past (assuming there is a consensus that these variations are proven) conflict with points 2 and 3?". I don't think there is a consensus that they do.

Albedo variation is only a link in the chain of causes and effects. Variation in cloud cover may have many causes, not necesarily warming.

Agreed.

Now, isn't that a coincidence? We're talking about the same source! However, what Pallé et al (2006) failed to verify, is the correlation between their results and the global temperatures. They just erroneously assumed that the temperatures continued to rise, perhaps because that's what you hear all the time.

See also this thread

Are you saying that average global temperature is not increasing?

AM

 

[vanesch]

All that is needed for a successful hypothesis is an explanation that is rational, plausible and that is not inconsistent with any facts.

In this case, it can be shown that CO2 absorbs infrared radiation and is, therefore, capable of causing the surface of the Earth to become warmer(1). It can also be shown that humans directly add about 30 GT of CO2 to the atmosphere annually (4). The total mass of CO2 in the atmosphere at present is about 3,000 GT which results in a CO2 concentration of 383 ppm by volume. So the addition of 30 GT could add as much as an additional 1% or almost 4 ppm to the CO2 concentration of the atmosphere. So the explanation is rational and plausible.One merely has to show that there are no proven facts that conflict with the hypothesis.

So my question is: what facts is this hypothesis inconsistent with?

As I said, however, this does not make it the correct explanation. One would need to look at all other alternate explanation and see if there are facts which conflict with them. Only by eliminating all other hypotheses with proven facts can one reach a reasonable conclusion that a hypothesis is correct.

Indeed. What you write is the difference between what I like to call suggestive evidence (sure there is !) and conclusive proof, and what annoys me is that the first is presented as the second. There's a big difference between both on the scientific side. In the second case, it becomes almost ridiculous to contest the statement, while in the first case, a critical analysis is due, and by flipping too fast from the first to the second, one could make a big mistake and "lock it in".

I would say that the biggest problem facing "CO2 is the sole drive for AGW and this will lead to dramatic increases in temperature" as a definitive statement is that there is no ab initio model, purely based upon physically known facts (with no fitting parameters) that numerically predicts correctly all the main quantities involved.

Indeed, there's no discussion that CO2, in a static atmosphere, acts as a greenhouse gas, but that effect, by itself, is about 0.8K per CO2 doubling. Even adding the important water vapor feedback fully, one arrives at 1.5K per CO2 doubling. That is, for a static atmosphere, in which there is no convection (which cools), and without doing anything to the Earth surface except keeping the water vapor pressure as given by the surface temperature. But AGW proponents say that this must be between 1.5 and 6 K, with a preferred value around 3 K.
So the purely physical effect we know about CO2 is simply not strong enough to explain the larger effect needed for a dramatic AGW.

That doesn't mean that there cannot be positive feedback mechanisms, but these mechanisms are hence the essential point of the AGW thesis, and they have not been modeled ab initio, but at most they are *fitted* to some data in which one took *already* the hypothesis that the drive was CO2. These are much more difficult issues and the system is much more complicated than just "CO2 is a greenhouse gas, and if we put more in the atmosphere, it will get hotter". The essence of the AGW theory is based upon ununderstood feedbacks which have not been modeled.
That doesn't mean they don't exist of course, and that doesn't mean that AGW is wrong. But it means that it is not "a rational plausible explanation that is not in contradiction with the facts". It is a totally hypothetical phenomenon that needs to be introduced *in order* for CO2 to be the sole culpritt.

 

[Andre]

Are you saying that average global temperature is not increasing?

I merely showed the results of the computations of the Hadley weather office and the RSS satellite observation for global temperatures:

which would make it a bit difficult to maintain that the global temperatures continued to rise in the last decade, despite the continuous rise of the CO2. Moreover the trend change corresponds to the trend change of the Albedo of Pallé et al 2006. But they missed that, since they omitted testing their results to global temperature series, which leads to that very curious but wrong assumption that albedo and temperature rose together.

Furthermore, in addition to the explanation of Vanesch:

2. greenhouse gasses are the main cause for the atmosphere to be warmer than grey body temperature.

Chilingar et al 2008 deal with the role of convection and latent heat mentioned by Vanesch and substantiate why these are the main vectors for heating the atmosphere to be warmer than grey body temperature. It's the OP subject in this thread

Apart from that from that 33 degrees difference, the more that must be attributed to convection/latent heat, the less is available for pure greenhouse effect, which would also mean lesser effects of changes in greenhouse gas concentrations.

3. increases concentration of greenhouse gasses increase the temperature of the atmosphere significantly,

Appears to be very obvious, the increase of radiative gasses would interact more with IR radiation in the absorption and emission of energy, which would lead to more energy in transit in the atmosphere molecules, ie higher atmospheric temperatures and more energy redirected to the Earth surface. But that's not what Miskolsky 2007 finds (thread here) who argues, based on observations, that the optical depth for IR radiation does not change notably with changes in greenhouse gas concentration.

So, having feasible conflicting hypotheses, it seems appropriate to revert to all available observations to see which notion is supported and which is not.

So, where is the evidence for global warming being caused by human activity / increase of greenhouse gas concentration?

 

[Andrew Mason]

Furthermore, in addition to the explanation of Vanesch:


Chilingar et al 2008 deal with the role of convection and latent heat mentioned by Vanesch and substantiate why these are the main vectors for heating the atmosphere to be warmer than grey body temperature. It's the OP subject in this thread
Apart from that from that 33 degrees difference, the more that must be attributed to convection/latent heat, the less is available for pure greenhouse effect, which would also mean lesser effects of changes in greenhouse gas concentrations.

Given Chillingar's earlier work I have serious doubts about the reliability of his conclusions. In any event, all you have shown is that there is another theory that is inconsistent with the hypothesis (that increased CO2 concentrations in the atmosphere will lead to global warming). You need facts.
Chillingar's model may be too simple. One cannot divorce the atmosphere from the earth. One has to take into account and the physical and biological effects that these increases of atmospheric CO2 may have on the further release of greenhouse gases.

Appears to be very obvious, the increase of radiative gasses would interact more with IR radiation in the absorption and emission of energy, which would lead to more energy in transit in the atmosphere molecules, ie higher atmospheric temperatures and more energy redirected to the Earth surface. But that's not what Miskolsky 2007 finds (thread here) who argues, based on observations, that the optical depth for IR radiation does not change notably with changes in greenhouse gas concentration.

So, having feasible conflicting hypotheses, it seems appropriate to revert to all available observations to see which notion is supported and which is not.

So, where is the evidence for global warming being caused by human activity / increase of greenhouse gas concentration?

Again, this is merely another theory which conflicts with the hypothesis. You need facts. Moreover, it is a theory that has not yet been subected to rigourous testing or peer review.

AM

 

[Andrew Mason]

Indeed. What you write is the difference between what I like to call suggestive evidence (sure there is !) and conclusive proof, and what annoys me is that the first is presented as the second. There's a big difference between both on the scientific side. In the second case, it becomes almost ridiculous to contest the statement, while in the first case, a critical analysis is due, and by flipping too fast from the first to the second, one could make a big mistake and "lock it in".

I would agree with you that the anthropogenic global warming model has not been proven scientifically. The "consensus" of climate scientists does not mean it is proven. It may be generally correct but in need of refinement. Or it may be completely wrong and some other theory that has not yet been developed may provide the correct explanation. All I am saying is that to disprove it one needs proven facts that are inconsistent with the theory. If it is not disproven AND there is no plausible, rational alternative explanation that is consistent with all known facts, then it is the only explanation that scientists and governments can support.

So far, I do not see any other explanation that is consistent with the known facts.

For example:

1. the increase in CO2 is not caused by volcanos. Volcanos contribute only a few hundred megatonnes of CO2 a year - less than one percent of total global CO2 emissions. See this article.

2. The warming trend is not consistent with the solar cycles. See also:
http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000099000004048501000001&idtype=cvips&gifs=yes.

I would say that the biggest problem facing "CO2 is the sole drive for AGW and this will lead to dramatic increases in temperature" as a definitive statement is that there is no ab initio model, purely based upon physically known facts (with no fitting parameters) that numerically predicts correctly all the main quantities involved.

I don't think the IPCC is saying that CO2 is the sole driving force for AGW. Scientists are merely saying that human emissions of CO2 contribute to global warming. There may be other significant factors and it may be even more complex that it appears.

But even if there were other significant factors and even if CO2 should turn out not to be the main cause of GW, the fact is that 30 GT of CO2 is being dumped into the atmosphere each year. How long do we continue mindlessly and wastefully burning fossil fuels and unnecessarily adding new CO2 to the biosphere? For example, we know that a lot of this is taken up by the oceans. How long can this go on before the acidification of the oceans becomes a problem?

AM

 

[Andre]

Given Chillingar's earlier work I have serious doubts about the reliability of his conclusions.

This is an ad homimen. I have shown in that thread that a similar study came to the same conclusion and all are peer reviewed including this one. Hence one should look at the work directly, instead of shooting the messengers and find flaws in the logic or find compelling evidence against it.

You need facts.

Exactly, where is the evidence that changes in greenhouse gasses have been a decisive factor in changes in global temperature in the geologic past?

In favor of Chilingar et al is this thread which essentially shows that no activity could be attributed to the variation of CO2.

 

[Andrew Mason]

This is an ad homimen. I have shown in that thread that a similar study came to the same conclusion and all are peer reviewed including this one. Hence one should look at the work directly, instead of shooting the messengers and find flaws in the logic or find compelling evidence against it.

It is not up to me to find flaws in the logic or compelling evidence against it. It is up to scientists who work in that field to do it. Until his theory is vetted and tested by scientific peers, one is left with the scientist's reputation. It is not a matter of attacking the person. You are asking us to accept Chillingar's word that he has done a correct analysis based on correct experimental work. His reputation is not one that inspires confidence in me that I can put any weight in his conclusions before his work is fully vetted and tested.

AM

 

[Andrew Mason]

Exactly, where is the evidence that changes in greenhouse gasses have been a decisive factor in changes in global temperature in the geologic past?

That is not really the issue. A scientific theory is not proven by the abundance of evidence in favour of it. Such evidence just tests it. A theory is "proven" by the lack of evidence establishing facts that contradict it and the existence of evidence proving facts which conflict with all alternative theories.

The observations of the precession of mercury and the bending of light by the sun did not prove the Theory of General Relativity. Since 1915 scientists have not established any fact that conflicts with the Theory of General Relativity. That doesn't mean it is correct. But since no one has come up with another plausible theory that explains all the observed phenomena, it is the one we go with. AGW is kind of like that.

AM

 

[Andre]

Again, the mere existence of alternate hypotheses warrants a closer look of the evidence supporting or falsifying any hypothesis. The basic idea of Chilingar et al is indeed extremely basic. I learned that principle of convection some 40 years ago (wow really, am I that old?), when applying for a glider flying permit.

Estimates of quantifying that effect, is sophisticated modelling for highly skilled profesionals, granted, but testing the effect of large CO2 changes in the Pleistocene past, can be done more easily and again, the results of that do support a significant role for CO2 to regulate temperatures.

But feel free to demonstrate where changes in CO2 were likely to have caused changes in temperatures, that warrants the idea of the strong warming effects.

Let's make this very easy. Check this:

http://arxiv.org/ftp/arxiv/papers/0804/0804.1126.pdf

Due to other activities it may be some days to react to that.

 

[Andrew Mason]

Chilingar et al 2008 deal with the role of convection and latent heat mentioned by Vanesch and substantiate why these are the main vectors for heating the atmosphere to be warmer than grey body temperature. It's the OP subject in this thread

Not having access to this article, can someone explain the mechanism by which convection and latent heat are supposed to cause cooling?

The latent heat must be the latent heat of water because CO2 does not change state in the atmosphere on on the Earth's surface. While evaporation of water does have a cooling effect on the Earth's surface, water vapour in the atmosphere is a GHG that traps heat. In any event, for net cooling, you have to have an INCREASE in the amount of water vapour in the air. This will only occur if the vapour pressure increases, which requires an INCREASE in temperature. So the argument seems to be there will be a cooling effect only if the temperature increases.

I am not sure how convection causes net cooling either. Convection is the result of an air mass that is not in thermal equilibrium. The heat flow within the air mass does work (on parts of itself). So, by the first law of thermodynamics, the internal energy (temperature) of the moving air will not increase as much as it would if the air remained stationary. But it will still increase because but the overall flow of heat into the air must still be positive in order for convection to occur (2nd law of thermodynamics). (And this also results in a more volatile air mass, which is hardly a benefit).

AM

 

[Andre]

Not having access to this article,

PM me an email address.

The latent heat must be the latent heat of water because CO2 does not change state in the atmosphere on on the Earth's surface.

2500 J/g water is not something neglglible.

water vapour in the atmosphere is a GHG that traps heat.

Why would that be? water has excellent radiative properties in a big frequency range throughout the IR and would increase the radiative activity (absorption/emission) in ALL directions. But the clouds are emitting closer to the top of the atmosphere, increasing the chance that an emitted energy parcel escapes into space rather than returns to the Earth surface. Moreover, the amount of water vapor at higher levels is declining fast, providing less obstruction to emitted IR photons. So the higher the effective radiation altitude, the bigger that chance of emitted energy leaving the atmosphere rather than returning to the Earth surface.

can someone explain the mechanism by which convection and latent heat are supposed to cause cooling?

Convection removes warmer air from the surface, to be replaced by cooler air from above (disregarding adiabatic expansion/compression effects). The ascending water vapor, having taken up the evaporation energy (2500 J/g) is relatively 'cold' and because of that, it does not emit a lot of photons (Stefan Boltzman). As the convecting air gets higher, condensation is taking place, releasing the latent heat, which can now emit IR photons from a higher altitude, increasing that chance of escape into space.

So if you'd increase the GHG in the atmosphere, the greenhouse effect at the surface layers increase, heating it faster, increasing the instability and causing more convection, which means more latent heat goimg up, producing more clouds, with two effects: more radiation into space and increasing the albedo which decreases insolation.

 

[vivesdn]

If this evaluation of water vapour effect is accurate, a high albedo surface as forests would be a cooling system: it provides energy and water (trees are continuously evaporating water) to convection.

Among several theories to explain Little Ice Age, one states that Black Death was the cause of a human population decrease, and this decrease was the cause of a significative amount of fields reclaimed by forests. So the effect would be through cloud formation more that CO2 reduction.

Not a proof of anything, but just some hypotheses that match together and with facts...

 

[Andrew Mason]

PM me an email address.

Done

Why would that be? water has excellent radiative properties in a big frequency range throughout the IR and would increase the radiative activity (absorption/emission) in ALL directions.

Well, its really not a matter of dispute that water vapor is a greenhouse gas, which mean that it traps heat. The fact that the water molecule radiates energy has little to do with it. If matter is in thermodynamic equilibrium, it will radiate as much as it absorbs. The Earth has to radiate as much energy as it absorbs. The composition of the atmosphere does not change this fact. It just affects the temperature at which equilibrium occurs. The question is: what is the surface temperature at Earth's thermodynamic equilibrium?

But the clouds are emitting closer to the top of the atmosphere, increasing the chance that an emitted energy parcel escapes into space rather than returns to the Earth surface. Moreover, the amount of water vapor at higher levels is declining fast, providing less obstruction to emitted IR photons. So the higher the effective radiation altitude, the bigger that chance of emitted energy leaving the atmosphere rather than returning to the Earth surface.

This may have some logical appeal. But it is more complicated than that.The clouds are in thermodynamic equilibrium with the surrounding air. So the water molecules in clouds or at all levels in the atmosphere must be absorbing as much energy as they are radiating.

In order to have a cool surface, the surface has to radiate energy into space directly without being absorbed by the atmosphere. If it is absorbed by the atmosphere it will necessarily be radiated from the atmosphere at the same rate. This means the temperature of the atmosphere (and therefore the surface) will increase. That is the essence of the greenhouse effect.

AM

 

[vanesch]

This may have some logical appeal. But it is more complicated than that.The clouds are in thermodynamic equilibrium with the surrounding air. So the water molecules in clouds or at all levels in the atmosphere must be absorbing as much energy as they are radiating.

If the atmosphere were in thermodynamic equilibrium, there would be no convection.
As you say yourself, it is pretty complicated, but I'm pretty sure that convection leads to cooling, as heat is transported from a hotter place to a colder place, where it can radiate away easier than if it were confined to its hotter place.

In order to have a cool surface, the surface has to radiate energy into space directly without being absorbed by the atmosphere. If it is absorbed by the atmosphere it will necessarily be radiated from the atmosphere at the same rate. This means the temperature of the atmosphere (and therefore the surface) will increase. That is the essence of the greenhouse effect.

Yes, that's true, as long as things are static. But if you consider the cycle: hot surface heats (through radiation or even through conduction) lower air layer, by convection this layer moves up to high altitudes, and there it cools through radiation, before coming down again as cold air, you get a net heat transport which is not considered by radiation only.
Now, there are 2 things which promote convection: 1) temperature gradient 2) evaporation (water vapor is lighter than air)
(ok, there's also specific density, and some argue that the increase of heavy CO2 in the atmosphere promotes convection - I'm not clear about that).

So it seems at first sight that convection is going to act as a negative feedback (a regulatory mechanism) on radiative forcing, no ?

 

[Andre]

There can never be a equilibrium because of the daily cycle. Mind that the solar flux varies between 0 and 1367 * Cos (inclination) Wm2. At night the atmosphere cools a few degrees due to outradiation allowing for convection during the day again.

Even in theoretical equilibrium (Earth hypothetical in tidal lock with the sun) the IR radiative cooling of the upper atmospere would keep the convection going.

 

[Andrew Mason]

If the atmosphere were in thermodynamic equilibrium, there would be no convection.
As you say yourself, it is pretty complicated, but I'm pretty sure that convection leads to cooling, as heat is transported from a hotter place to a colder place, where it can radiate away easier than if it were confined to its hotter place.

There is no doubt that for a given amount of heat flow into an air mass the temperature will be greater if the air remains static than if convection occurs. But this is just basic thermodynamics. The air does not cool by radiation. The rising warmer air will cool much more quickly due to conduction of heat to the cooler surrounding air than to radiation. The atmosphere will radiate exactly the amount of radiation that it absorbs - it cannot cool by radiation. Besides, the radiation from the atmosphere is in all directions. Just as much radiation is directed from the atmosphere toward the earth. It is this radiation from the atmosphere back toward the Earth that increases the surface temperature.

Without any radiation being absorbed by the atmosphere, the surface temperature of the Earth would be 255K (-18 C), based on a .3 albedo factor (ie. Earth emissivity .7). This is just simple blackbody physics - Stefan Boltzmann law. We know that the Earth surface is warmer than this - about 279 K. So the "theory" that the presence of infrared absorbing atmosphere increases the surface temperature has a pretty solid factual foundation. We are living proof of that.

Yes, that's true, as long as things are static. But if you consider the cycle: hot surface heats (through radiation or even through conduction) lower air layer, by convection this layer moves up to high altitudes, and there it cools through radiation, before coming down again as cold air, you get a net heat transport which is not considered by radiation only.
Now, there are 2 things which promote convection: 1) temperature gradient 2) evaporation (water vapor is lighter than air)
(ok, there's also specific density, and some argue that the increase of heavy CO2 in the atmosphere promotes convection - I'm not clear about that).

So it seems at first sight that convection is going to act as a negative feedback (a regulatory mechanism) on radiative forcing, no ?

The only way convection can increase is if the atmosphere's temperature increases. While is true that for a given heat flow into an air mass the static air mass will have a higher temperature than the convecting air mass (because work must be done on the air mass to get it moving) the temperature still increases.

AM

 

[Andre]

There is no doubt that for a given amount of heat flow into an air mass the temperature will be greater if the air remains static than if convection occurs. But this is just basic thermodynamics. The air does not cool by radiation. The rising warmer air will cool much more quickly due to conduction of heat to the cooler surrounding air than to radiation.

Better check out the textbooks on this. Cooling during convection is adiabatic and is caused by expansion

The atmosphere will radiate exactly the amount of radiation that it absorbs -

Plus the amount of energy that went into the evaporation after it is released again during condensation.

 

[vanesch]

There is no doubt that for a given amount of heat flow into an air mass the temperature will be greater if the air remains static than if convection occurs. But this is just basic thermodynamics. The air does not cool by radiation. The rising warmer air will cool much more quickly due to conduction of heat to the cooler surrounding air than to radiation. The atmosphere will radiate exactly the amount of radiation that it absorbs - it cannot cool by radiation. Besides, the radiation from the atmosphere is in all directions. Just as much radiation is directed from the atmosphere toward the earth. It is this radiation from the atmosphere back toward the Earth that increases the surface temperature.

Without any radiation being absorbed by the atmosphere, the surface temperature of the Earth would be 255K (-18 C), based on a .3 albedo factor (ie. Earth emissivity .7). This is just simple blackbody physics - Stefan Boltzmann law. We know that the Earth surface is warmer than this - about 279 K. So the "theory" that the presence of infrared absorbing atmosphere increases the surface temperature has a pretty solid factual foundation. We are living proof of that.
The only way convection can increase is if the atmosphere's temperature increases. While is true that for a given heat flow into an air mass the static air mass will have a higher temperature than the convecting air mass (because work must be done on the air mass to get it moving) the temperature still increases.

I'm not contesting the greenhouse effect of course. (btw, I'm not even contesting AGW ; I'm contesting the scientific certainty of AGW at the level promoted by the IPCC, because IMO there are difficulties in this explanation - difficulties which might be overcome, but which will need more scrunity than actually displayed by their authors).

However, concerning convection, I must disagree. Of course, the amount of heat radiated by the atmosphere is equal to what it absorbs, but what counts, is how much of this is UP and how much of this is DOWN. In fact, what counts, is the "thermal resistance" of the atmosphere, that is, what is the temperature gradient necessary to bring a certain heat flux from the surface to the outer space. Of course, this "resistance" is composed not only of conduction, but also of radiation (the usual transport mechanism) but also of convection, and is as such a non-linear resistance.
It should be obvious that if hot air can move higher up, without having to transport its heat via radiation into the overlying layers, but flow directly to a higher place, that the effect of this on the overall resistance is to lower it. It is an extra transport mechanism of heat outward.

 

[Andrew Mason]

Cooling during convection is adiabatic and is caused by expansion.

The only way adiabatic expansion of air can reduce the temperature of the air is if it does work. (if it expands but does no work, ie. a free expansion - the temperature does not change). If it does work on surrounding air by adiabatically compressing it, the temperature of the surrounding compressed air will increase. This is because, by the first law, if dQ = 0 (adiabatic), dT = W/nCv where W is the work done on the gas (ie. if work is done by the gas, W<0 and dT is negative; if work is done on the gas, dT is positive).

Chillingar's paper appears to ignore the simple fact that by absorbing infrared radiation emitted by the Earth's surface, the atmosphere reradiates some of that energy back to the earth. It doesn't just radiate outward (ie into space or the stratosphere). If the atmosphere does not absorb any (very little) of the inward radiation from the sun but absorbs and reradiates back to the Earth much of the outward IR radiation from the surface, the radiation energy flux incident upon the Earth's surface is greater than it would be with a non-IR absorbing atmosphere. Since the inward energy flux has to equal the outward energy flux if there is thermal equilibrium, the presence of IR absorbing gases in the atmosphere has to increase the energy flow away from the surface - meaning it has to increase surface temperature. The only question is how much of this energy flow is carried away by radiation and how much by other energy transfer mechanisms. Chillingar et al suggests that more than ALL of the additional energy is carried away by convection. I don't understand how that can be and I have no faith in his ability to analyse it correctly, so I will await confirmation of his "theory" by real data and by the reviews of his scientific peers.

AM

 

[vanesch]

The only way adiabatic expansion of air can reduce the temperature of the air is if it does work. (if it expands but does no work, ie. a free expansion - the temperature does not change). If it does work on surrounding air by adiabatically compressing it, the temperature of the surrounding compressed air will increase. This is because, by the first law, if dQ = 0 (adiabatic), dT = W/nCv where W is the work done on the gas (ie. if work is done by the gas, W<0 and dT is negative; if work is done on the gas, dT is positive).

The adiabatic cooling comes about because the pressure is lower at higher altitude, and as such it does work (yes, "free" expansion does work).

Chillingar's paper appears to ignore the simple fact that by absorbing infrared radiation emitted by the Earth's surface, the atmosphere reradiates some of that energy back to the earth. It doesn't just radiate outward (ie into space or the stratosphere). If the atmosphere does not absorb any (very little) of the inward radiation from the sun but absorbs and reradiates back to the Earth much of the outward IR radiation from the surface, the radiation energy flux incident upon the Earth's surface is greater than it would be with a non-IR absorbing atmosphere. Since the inward energy flux has to equal the outward energy flux if there is thermal equilibrium, the presence of IR absorbing gases in the atmosphere has to increase the energy flow away from the surface - meaning it has to increase surface temperature.

I didn't read that paper. And your explanation is of course correct. But what actually happens is that you can consider a gas column as different layers, and each layer radiates upward and downward, and absorbs from the layers on top and below it. And as such, you can consider that the net effect is radiation that has to "work its way outward" from the ground to the upper layers, into the "outward radiation" part. Now, depending on how easy it is to get absorbed and re-emitted and so on, the higher must be the temperature gradient between "outer space" (essentially 0) and the emitting Earth surface (essentially the absolute temperature of the Earth surface) for a given energy flux, which has to equal of course the total incoming solar flux (minus albedo). As such, an absorbing and re-emitting set of layers acts as a kind of " distributed thermal resistance", each layer adding a bit of resistance to the whole path of the thermal flux from ground level to outer space.

This resistance is nothing else but the "greenhouse effect". However, they are not linear resistors like in Fick's law in heat conduction.

Now, if you can have a "transport mechanism" which takes heat from a lower layer, and put it *directly* into a higher layer, then you will improve the overall heat flux, simply because you've shunted a set of layers (resistors). This will then lower the overall effective heat resistance of the entire atmosphere. That's what convection does, and that's also (apart from changing albedo) what evaporation and condensation in higher layers does. So this diminishes the thermal resistance, and hence the overall greenhouse effect.

The only question is how much of this energy flow is carried away by radiation and how much by other energy transfer mechanisms. Chillingar et al suggests that more than ALL of the additional energy is carried away by convection. I don't understand how that can be and I have no faith in his ability to analyse it correctly, so I will await confirmation of his "theory" by real data and by the reviews of his scientific peers.

As I said, I didn't read the paper, and I would also be surprised to see that it carries away *everything*, but for sure, it must carry away *something*.

And that's BTW the main difficulty I have with the current claims of certainty of AGW: there seems to be a discrepancy between the "purely physical numbers" for CO2 doubling (between 0.8K and 1.5K for a static atmosphere), and the IPCC "best fit" of 3K (between 1.5K and 6K) without any "first principles", but just a fit to the data *assuming* that the only drive is the CO2 radiative forcing ; in other words, the famous positive feedbacks which are not modeled, but which are *postulated*. That doesn't mean that they are not there, but I would have liked to see somewhat more "hard physics" in there before being certain about the claim.

 

[Andrew Mason]

The adiabatic cooling comes about because the pressure is lower at higher altitude, and as such it does work (yes, "free" expansion does work).

If an expanding gas does work then it is not a free expansion. If it does work it cools but the gas that it does work on warms. There can be no net cooling. It is prohibited by the second law of thermodynamics.

All convection does is lower the temperature gradient by mixing the air. It does not alter the average temperature of the air. We are talking about convection in the troposphere which extends up to about 60,000 feet (11 miles or 17 km) and an existing thermal gradient of 6.5 Kelvin/ km. Chilingar is suggesting that additional CO2 will increase the average temperature of the atmosphere but cause more convection so that smaller thermal gradient results in an actual decrease of temperature at the surface.

Chilingar has problems explaining how his model fits Venus. Does the 95% CO2 atmosphere of Venus cool the surface of Venus? Venus has a very high albedo factor of .75 (compared to Earth's .3). Although its solar irradiation is about double Earth's (2614 watts/m^2 versus 1367 for earth), the albedo results in a lower blackbody temperature (231 K or - 42 C versus 255K for earth). But, in fact the surface temperature of Venus is much higher (750 K!). At an altitude of 100 km the temperature goes down to 180K. This means it has an average temperature gradient of 5.7 degrees K per km. compared to Earth's 6.5. But this slightly lower gradient certainly does not result in a lower surface temperature.

Chilingar explains Venus by suggesting that chemical reaction in the upper troposphere on Venus - suggesting that this is creating a continuous heat source that heats the surface from something less than its blackbody temperature to 750 K! He just throws this out as if it was a proven fact! This appears to be news to NASA.

AM

 

[vanesch]

If an expanding gas does work then it is not a free expansion. If it does work it cools but the gas that it does work on warms. There can be no net cooling. It is prohibited by the second law of thermodynamics.

Think of the individual parts as locked up in balloons. One balloon goes up, containing hot, wet air, and another one, containing dry, cool air, goes down. The air in the rising balloon will expand, and cool adiabatically, and the balloon going down will be compressed and will adiabatically heat. If both movements compensate, all the other air will not be compressed or expanded, will at most be horizontally displaced, and will not undergo any effect.

All convection does is lower the temperature gradient by mixing the air. It does not alter the average temperature of the air. We are talking about convection in the troposphere which extends up to about 60,000 feet (11 miles or 17 km) and an existing thermal gradient of 6.5 Kelvin/ km. Chilingar is suggesting that additional CO2 will increase the average temperature of the atmosphere but cause more convection so that smaller thermal gradient results in an actual decrease of temperature at the surface.

I don't think that there will be an actual *cooling* but as I said, I haven't studied that paper. I'm just talking in general about convection. If convection MIXES air, then there is no convection! It would then be diffusion. Convection is the flow within flux tubes of air in the vertical direction, driven by a density gradient (itself induced by composition - water vapor - or temperature). Of course, there will be *some* mixing due to microturbulence, and there will be *some* conduction. But I take it that you can consider convection essentially as a loopy flow with "air bubbles" going up, and other "air bubbles" going down as if they were adiabatically insulated, like in balloons.

So IMO, convection cannot do anything else but *reduce* the greenhouse effect as compared to a static atmosphere. If Chilingar claims that it *overcompensates* and actually leads to a cooling, then I should study his argument, but it is not my point. My point is simply that convection IS a more efficient way to cool the surface than *just* radiation transport through a static grey atmosphere, and as such, when taken into account, will lead to some diminishing of the greenhouse effect as compared with a non-moving atmosphere.

Chilingar has problems explaining how his model fits Venus. Does the 95% CO2 atmosphere of Venus cool the surface of Venus? Venus has a very high albedo factor of .75 (compared to Earth's .3). Although its solar irradiation is about double Earth's (2614 watts/m^2 versus 1367 for earth), the albedo results in a lower blackbody temperature (231 K or - 42 C versus 255K for earth). But, in fact the surface temperature of Venus is much higher (750 K!). At an altitude of 100 km the temperature goes down to 180K. This means it has an average temperature gradient of 5.7 degrees K per km. compared to Earth's 6.5. But this slightly lower gradient certainly does not result in a lower surface temperature.

Chilingar explains Venus by suggesting that chemical reaction in the lower troposphere on Venus are creating a continuous heat source that heats the surface from something less than its blackbody temperature to 750 K! He just throws this out as if it was a proven fact!
This appears to be news to NASA.

As I said, I'm not arguing Chilingar's paper, and if that claim is there, it would be very dubious indeed.

Just a single remark concerning Venus, which just occurs to me right now, and not with much thought behind it: it is funny that the vertical gradient on venus and Earth are similar, given the totally different situations. That could mean that there is a kind of maximum gradient in the atmosphere above which strong feedback mechanisms such as convection lock up the maximum gradient. As such, there is a maximum greenhouse effect for a given atmospheric thickness (pressure).