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