If you look at any explanation of the “Greenhouse effect” you will undoubtedly find it explained in simple terms as CO2 acting to “trap heat” in the atmosphere like a blanket. That is provably false and this article explains why.
The “heat trapping” or “blanket” model invariably goes along with the following type of diagram. This diagram is not “wrong” in the sense it largely correctly accounts for the various heat “flows”, but it is wrong as a physical model of the greenhouse effect because it doesn’t even mention the critical factor which is the temperature of the atmosphere. And without knowing that the model is nothing but a set of meaningless numbers and any explanation using it is complete twaddle.
Do Academics believe the heat trapping model?
The heat trapping model is clearly baloney and as such I have assumed that the academics didn’t really believe it themselves, but recent conversations have caused me to question this. So now I have to say, that I’ve very little evidence to indicate that most, or indeed any, climate academics know it is wrong. This is incredible – and it may just be that I had an unfortunate discussion and that somewhere those with more understanding are keeping quiet.
From the beginning I knew the heat trapping model was unphysical because all IR interactive models both absorb & transmit IR. And therefore to only talk about absorption was a physical impossibility.
It took me a while to work out what was really going on, but when I did, I simply assumed that the standard “heat trapping” model was a short hand given to the public to explain the much more complex processes that occur in the atmosphere. That is to say, the climate academics knew it wasn’t right, but it was presented to the public and student because the atmosphere is so complex, it would not be possible to explain it in detail. But I assumed none of them actually believed the model was physically valid, and certainly that none of them would use the “heat trapping” model themselves except in the most general sense of an overall summary of “heat flows”. At one point I did come across something suggesting that they were aware of the “average radiant height”. Which led me to believe that some understood the “blanket” model was far from perfect.
However, whether or not academics actually believe it (which I still don’t seriously believe), the blanket analogy is baloney.
Greenhouse gases don’t absorb IR, it’s colder molecules that absorb
The first problem with the heat trapping model is relatively simple. It’s the old paradox of whether painting shiny surface black will make it cooler or hotter. The answer is that if the surface is in surroundings where the environmental IR is warmer, then the black will increase the take-up of heat. If however, the surface is in an environment where the IR temperature is lower than the surface, then it will cool.
Likewise, a Greenhouse gas like CO2 or H2O (or to be more accurate an IR interactive gas) has the same response to the atmosphere as painting a surface black. The part of the atmosphere where the IR interactive gas is located tends to pick up more heat BUT ONLY IF THE RADIANT TEMPERATURE OF THE IR FROM ITS ENVIRONMENT IS HIGHER and it tend to emit heat IF THE RADIANT TEMPERATURE OF THE IR ENVIRONMENT IS LOWER.
The effect of a greenhouse gas molecule is to cause that part of the atmosphere to become closer to the IR temperature of the average radiant temperature of the surfaces from which IR is reaching it. And therefore it is meaningless to talk about “Greenhouse gases” without referring to the temperature of its surroundings. Indeed, the only reason the heat trapping model works, even as a vague general indicative principle,is because most of the effect occurs in the troposphere where there the temperature decreases with height. Indeed, if the atmospheric temperature increased with height, adding CO2 would cause global cooling! Like painting a surface black the effect of CO2 is entirely dependant on the relative temperature of the atmosphere to its surroundings.
Changes to “greenhouse” gases have negligent effect at low levels in the tropopause.
The biggest problem with the “heat trapping” model, is that there is very little explanation of what happens to the heat that is trapped. And … because by the laws of conservation of energy it has to go somewhere.
But … it’s like a blanket I might hear you say. To which I reply: a blanket stops the flow of heat. That is, it reduces the amount of energy flowing from hot to cold. Whereas, you can’t stop the flow of heat in the atmosphere. Because according to the heat trapping model, the same amount of heat reaches the world irrespective of the amount of “greenhouse gas”, so if you reduce the outflow of heat (by even a tiny amount) you will always get “runaway warming”. To put this the other way around, if the incoming radiation changed by even a small amount, and there is a fixed “blanket” causing a set outflow of heat, then the earth would either be an icy ball (if the sun’s energy dropped) or a fiery flaming furnace (if the sun’s energy marginally increased). Of course, that is total nonsense and I suspect this false interpretation of this model is the sole reason we get this ridiculous idea of “runaway” or “tipping points” in the climate.
The Lapse rate regulates the atmospheric temperature
not Greenhouse gases
Now, please think about the actual effects in the tropopause. Anyone that has climbed a mountain knows it gets colder as we climb. This effect is called the “lapse rate” and it is defined by scientific laws that when convection occurs, the temperature will get cooler as we rise. Or to turn it around, convection is the process that stabilises the lapse rate gradient through the atmosphere. If the surface temperature is too high (such as on a sunny day), the amount of convection increases to stabilise the temperature gradient. Likewise, if too much heat is lost at “top” of the atmosphere, then again, convection will increase so as to bring heat from the surface up to the “top” and regain much the same gradient**.
So, convection acts to maintain the lapse rate irrespective of greenhouse gases.
So, what is the effect of increasing or decreasing CO2 or any other IR inactive gas on the temperature gradient. The answer is next to nothing. That is because any change in the heat being absorbed (or emitted) will be compensated by changes in the rate of convection which acts to nullify any changes in IR absorption or emission.
In other words, changes in CO2 have little or no effect on the temperature gradient in the convective atmosphere. And so the heat trapping model is largely baloney. Also greenhouse gases have little or no effect on the temperature at “the top” of the atmosphere, which by energy conservation rules, must be the same as an equivalent black body (255C)++
What then is the effect of CO2?
CO2, has negligible effect on the temperature gradient in the atmosphere. And as such the “heat trapping” or “blanket” model is completely false.
CO2 has no effect on the necessary temperature at the “top” of the atmosphere which is set by radiative balance to be (255C)++ (strictly speaking by “top” I refer to the average radiative temperature (average of T4) of the topmost surface or molecules).
Thus the only significant effect of changes to CO2 are where the “top” or to be more accurate “top most” molecules and surfaces are located:
- An increase in CO2 causes a small increase in the average height (and therefore reduced temperature of the molecules) from which IR leaves the atmosphere. Thus reducing IR emissions slightly.
- A small increase in CO2 means a small change in the % of IR that leaves from the (colder) atmosphere rather than the (warmer) ground. This also marginally reduces the IR emissions.
So is the “heat trapping” or “blanket” model wrong? The answer is that like all models it is a simplification of the actual processes which works in some part but fails in other parts. It works by correctly indicating that increases in CO2 will have an effect on the greenhouse temperature. But in almost every other aspect it is a completely wrong. But it is particularly “fake news” when people start combining the “Mickey-mouse” “heat trapping” model with the idea of constant IR input as we have seen by many quack “science” activists.
Now we have the concept that there’s a constant inflow of energy, but that less energy is escaping. It therefore follows that the quacks believe (or even worse, they knowingly spread the false belief) that there is a net radiative imbalance and that the world must become hotter than the sun. This is clearly what is being shown in the following type of fake-science drawing that has become ever so familiar.
Whether this is because the quack academics understand it or not, this is the combination of two incompatible ideas: 1. Heat trapping (meaning less heat escapes) and 2. Constant heat input.
The reality is that changes in greenhouse gas concentration are unequivocally stable.
“Contradiction” of Heat Laws
Finally, just a comment on those who regularly cite that the heat trapping model contradicts “laws of heat”. Their argument is daft because a colder surface can make a hotter surface warmer when it acts to change the flow out from a warmer surface – like a coat on a person. Indeed, I have even wondered how many of them are paid agitators with a remit to make us sceptics look like scientific illiterates.
However, whilst their argument is wrong, so too is the idea that CO2 causes the atmosphere to heat up causing “back heating”. This is easily squashed because the lapse rate controls the temperature gradient of the atmosphere, so the temperature of the atmosphere will not change (unless something happens to totally interrupt convection which CO2 is not going to do).
Instead the actual physically correct changes of CO2 when Looking from the ground up are:
- Just as a thicker atmosphere means the average height of molecules emitting the IR as “seen” from space will be higher (so colder), so the average height of molecules emitting the IR as “seen” from the ground will be lower (and so colder). However, because the distance IR travels is so small in the dense atmosphere near the ground (10s or 100s of meters), this effect is relatively small.
- A small change in the average radiant temperature (T4) as seen from the ground because there will be an extremely small change at some frequencies so that more of the average radiant temperature (T4) of the sky will originate from CO2 molecules in the atmosphere rather than the much colder background temperature of space.
And for completeness, it is best to think of a rise in CO2 having a marginal effect on the rate of convection rather than CO2. That is to say, for the world to warm marginally to regain equilibrium at the marginally higher temperatures, convection processes will drop in magnitude so that less heat is lost through convection until equilibrium is restored and they regain their previous intensity.
** The gradient also depends on water content, but for the argument here it is ignored as it doesn’t change the drift of the argument only the scale of the lapse rate.
++For simplicity I ignore changes to emissivity which would change the surface temperature. Because again, it changes the specific temperature, but the general argument remains the same.
T4 (T^4) – when averaging “radiant temperatures”, we average the following: the effective surface area of each (A) and temperature (T) and get average of (A0 T04, A1 T14, … An Tn4, ). This is because we average the energy flows and the energy flow is proportional to T4
The blanket illustration never made any sense to me.
It’s what’s under the blanket that makes the difference. A body generating 98.6F is going to get hotter if more blankets are piled on.
A covered bed, however (with no body to generate heat), remains the same temp as its surroundings, no matter how many blankets are piled on. There’s no heat to “back-radiate”.
If you consider the atmosphere to be the “blanket”. The analogy would be that the blanket is more insulating. That would imply there is a greater C/km of “thermal resistance” for escaping heat going through the atmosphere. But since the lapse rate maintains this at 6.5C/km, there is no added thermal resistance due to CO2. Thus irrespective of the amount of CO2, the thermal resistance will remain 6.5C/km.
Increased absorption means LESS thermal resistance, because increased absorption means increased rate of transfer from the surface. Thermal resistance increases from less absorption in surroundings, like the non-gh-gases that heat up by conduction at the surface. If any gases are insulating, it would be those gases. But free convection takes care of that, by mass transfer of the heated gases, which transport more heat away than radiation alone could do without the cold, average -18°C air.
Your argument would hold weight if it wasn’t that most IR is absorbed within a short distance from the surface. Yes at the margins of the “IR windows” there is a small effect as you describe, but in the overall scheme of things it is small.
The heat lost is solely dependent on the average radiant temperature of the earth. That in turn is determined by the temperature of the last surface or molecule from which the IR escapes. That in turn is determined by the lapse rate.
What is key is the temperature and what determines that is the lapse rate of about 6.5K/km.
You only have to look at the numbers to see they are completely wrong. They show that two-thirds of the energy absorbed at the surface comes from the atmosphere and only one-third comes from the sun. In fact it all comes from the sun. Recycling energy is fake physics. A cold atmosphere cannot add energy to a hotter surface.
And a coat that is colder than a person (as they all are) cannot make a person warmer. That argument is completely bogus – and you need only go out on a cold starry night as it turns to cloud to realise the colder clouds have the same effect as a cold coat in making us warm.
However, the point I’m making is that because the atmosphere has convection, the thermal resistance through the atmosphere will be about 6.5C/km IRRESPECTIVE of the amount of CO2.
It is the energy of the body that keeps us warm. The coat just reduces the rate of heat transfer from our body surface. The coat does not return energy to us.
Clouds at night do not make us warm. They just reduce the rate at which we cool compared to if there are no clouds.
I have also been sceptical of the standard ‘blanket’ explanation but for a different reason. The traditional greenhouse effect rests on a proportion of the IR reflected from the Earth’s surface being absorbed by CO2 and re-emitted back to the surface. But it does not seem to include the effect on the incoming IR from the Sun. Incoming IR is presumably also absorbed by greenhouse gasses and part of that will be re-emitted out to space. If you do the sums, the more CO2 you add to the atmosphere the less IR will reach the surface. So greenhouse gasses cause cooling.
This must be wrong. Can anyone enlighten me?
You are right that CO2 absorbs heat from the sun. However, the main mechanism operating in the troposphere is convection. If the temperature gradient is too high, there is an increase in convection that tends reduce the gradient and visa versa. The result is IRRESPECTIVE of CO2 levels, the temperature gradient in the troposphere remains fairly constant at about 6.5C/km. Solar heating from IR does have an effect, but because the lapse rate mechanism is self-stabilising, the effect is not to change the temperature gradient but the scale (or height) of convection. The same is also true of IR from the ground – again the IR from the ground and CO2 levels have very little effect on the gradient through the troposphere.
Thanks very much for your reply. I am gradually learning that this apparently simple and ‘settled’ mechanism has a good many wrinkles attached.
SS, you are not correct when you say that there is no affect from GHGs, there is an easily observable affect from H2O.
Dry Deserts have the closest high & low temperatures to the airless moon.
What H2O does is provide a buffer to the large swings of temperature that would otherwise occur. But it is a balancing act of reducing Solar in and slowing LWIR out.
Whereas increased CO2 has increased the outgoing LWIR in the messosphere.
The only (or almost only) factor effecting the temperature gradient from the surface to the point convection stops is convection and the lapse rate process which stabilises the temperature gradient irrespective of the greenhouse gas concentration.
That is not the same as saying H2O and other greenhouse gases do not have an effect. And yes, the RH concentration does effect lapse rate – but I do add the note”The gradient also depends on water content”. I don’t cover it in the article because it doesn’t greatly alter the point I’m making so I gloss over it to avoid going into unnecessary complexity.
The key point is that the overwhelming bulk of the atmosphere is unaffected by greenhouse gases – which is not at all what you would expect from the idea of CO2 being a “blanket”.
And yes with the messosphere I specifically state: “An increase in CO2 causes a small increase in the average height” of emissions. In other words more radiation from higher up in the atmosphere.
So I can’t see a substantial difference between us.
The blanket-people imply that the atmosphere acts as a blanket as thermal insulation. I found that this argument is easily torn apart by the thermodynamics in one single wiki-article:
“Heat flow is an inevitable consequence of contact between objects of different temperature. Thermal insulation provides a region of insulation in which thermal conduction is reduced or thermal radiation is reflected rather than absorbed by the lower-temperature body.”
As you can see, thermal insulation does the opposite of what the gh-effect does. Which means that gh-gases are coolants, since they increase absorption of heat in colder surroundings.
Which of course is logical, adding dry ice (co2) to already cool air, will of course cool the air even more. With constant heat flow which is limited, adding heat absorbers to the flow reduces the available heat per molecule. And the average kinetic energy per molecule is the definition of temperature.
The concept of thermal insulation is the only one needs to make the gh-theory burn to the ground.
Mike, excellent post, thank you.
The following link demonstrates that the sun, not CO2, is the primary cause of climate change …
… or google Roger Higgs Researchgate sea level.