With apologies to my many readers who understand the basics of heat transfer in the atmosphere and really want to hear more about feedback, uncertainty, real science..
Clearing up basic misconceptions is also necessary. It turns out that many people read this blog and comment on it elsewhere and a common claim about climate science generally (and about this site) is that climate science (and this site) doesn’t understand/ignores convection.
The Anti-World Where Convection Is Misunderstood
Suppose – for a minute – that convection was a totally misunderstood subject. Suppose basic results from convective heat transfer were ridiculed and many dodgy papers were written that claimed that convection moved 1/10 of the heat from the surface or 100x the heat from the surface. Suppose as well that everyone was pretty much “on the money” on radiation because it was taught from kindergarten up.
It would be a strange world – although no stranger than the one we live in where many champions of convection decry the sad state of climate science because it ignores convection, and anyway doesn’t understand radiation..
In this strange world, people like myself would open up shop writing about convection, picking up on misconceptions from readers and other blogs, and generally trying to explain what convection was all about.
No doubt, in that strange world, commenters and bloggers would decry the resulting over-emphasis on convection..
First Misconception – Radiation Results are All Wrong Because Convection Dominates
There are three mechanisms of heat transfer:
Often in climate science, people add:
- latent heat
In more general heat transfer this last one is often included within convection, which is the movement of heat by mass transfer. Although sometimes in general heat transfer, heat transfer via “phase change” of a substance is separately treated – it’s not important where “the lines are drawn”.
Update note from Dec 9th – I leave my poorly worded introduction above so that readers comments make sense. But I should have written
In fact in atmospheric physics we almost always see the breakdown like this:
Latent heat being the movement of heat via evaporation – convection – condensation. Sensible heat being the movement of heat via convection with no phase change. Conduction is actually also included in sensible heat, but is negligible in atmospheric physics.
Therefore when convection is written about it is both sensible and latent heat. That is, heat transfer in the atmosphere is via either convection or via radiation.
End of update note
Let’s look at conduction, safe from criticism because it is largely irrelevant as a form of heat transfer within the atmosphere. Conduction is also the easiest to understand and closest to people’s everyday knowledge.
The basic equation of heat conduction is:
q =- kA . ΔT/Δx
where ΔT is the temperature difference, Δx is the thickness of the material, A is the area, k is the conductivity (the property of the material) and q is the heat flow. (See Heat Transfer Basics – Part Zero for more on this subject).
Notice the terms in this equation:
- the material property (k)
- the thickness of the material (Δx)
- the temperature difference (ΔT)
- the area (A)
Where are the convective and the radiative terms?
Interestingly, conduction is independent of convection and radiation. This is a very important point to understand – but it is also easy to misunderstand if you aren’t used to this concept.
It doesn’t mean that we can calculate a change in equilibrium condition – or a dynamic result – only using one mechanism of heat transfer.
Let’s suppose we have a problem where we know the temperature at time = 0 for two surfaces. We know the heating conditions at both surfaces (for example, zero heat input). We want to know how the temperature changes with time, and we want to know the final equilibrium condition.
The way this problem is solved is usually numerical. This means that we have to work out the heat flow from each mechanism (conduction, convection, radiation) for a small time step, calculate the resulting change in temperature, and then go through the next time step using the new temperatures.
For many people, this is probably a fuzzy concept and, unfortunately, I can’t think of an easy analogy that will crystallize it.
But what it means in simple terms is that each heat transfer mechanism works independently, but each affects the other mechanisms via the temperature change (if I come up with a useful analogy or example, I will post it as a comment).
So if, for example, convection has changed the temperature profile of the atmosphere to something that would not happen without convection – the calculation of conduction through the atmosphere is still:
q = -kA . ΔT/Δx
And likewise the more complex equation of radiative transfer (see Theory and Experiment – Atmospheric Radiation) will also rely on the temperature profile established from convection.
So – an ocean surface with an emissivity of 0.99 and a surface temperature of 15°C will still radiate 386 W/m², regardless of whether the convection + latent heat term = zero or 10 W/m² or 100 W/m² or 500 W/m².
Second Misconception – Atmospheric Physics Ignores Convection
This is a common claim. It’s simple to demonstrate that the claim is not true.
Let’s take a look at a few atmospheric physics text books.
From Elementary Climate Physics, Prof F.W. Taylor, Oxford University Press (2005):
From Handbook of Atmospheric Science, Hewitt & Jackson (2003):
From An introduction to atmospheric physics, David Andrews, Cambridge University Press (2000):
In fact, you will find some kind of derivation like this in almost every atmospheric physics textbook.
Also note that it is nothing new – from Atmospheres, by R.M. Goody & J.C.G. Walker (1972):
Both convection and radiation are important in heat transfer in the troposphere.
Lindzen (1990) said:
The surface of the earth does not cool primarily by infrared radiation. It cools mainly through evaporation. Most of the evaporated moisture ends up in convective clouds.. where the moisture condenses into rain..
..It is worth noting that, in the absence of convection, pure greenhouse warming would lead to a globally averaged surface temperature of 72°C given current conditions
Note the important point that convection acts to reduce the surface temperature. If radiation was the dominant mechanism for heat transfer the surface temperature would be much higher.
Convection lowers the surface temperature. However, it only acts to reduce the effect of the inappropriately-named “greenhouse” gases. And convection can’t move heat into space, only radiation can do that, which is why radiation is extremely important.
The idea that climate science ignores or misunderstands convection is a myth. This is something you can easily demonstrate for yourself by checking the articles that claim it.
Where is their proof?
Do they cite atmospheric physics textbooks? Do they cite formative papers that explained the temperature profile in the lower atmosphere?
No. Ignorance is bliss..
Third Misconception – Convection is the Explanation for the “33°C Greenhouse Effect”
Perhaps in a later article I might explain this in more detail. It is already covered to some extent in On Missing the Point by Chilingar et al (2008).
As a sample of the basic misunderstanding involved in this claim, take a look at Politics and the Greenhouse Effect by Hans Jelbring, which includes a section Atmospheric Temperature Distribution in a Gravitational Field by William C. Gilbert.
If you read the first section by Jelbring (ignoring the snipes) it is nothing different from what you find in an atmospheric physics textbook. No one in atmospheric physics disputes the adiabatic lapse rate, or its derivation, or its total lack of dependence on radiation.
Clearly, however, Jelbring hasn’t got very far in atmospheric physics text books, otherwise he would know that his statement (updated Dec 9th with longer quotation on request):
T is proportional to P and P is known from observation to decrease with increasing altitude. It follows that the average T has to decrease with altitude. This decrease from the surface to the average infrared emission altitude around 4000 m is 33 oC. It will be about the same even if we increase greenhouse gases by 100%.
– was very incomplete. How is it possible not to know the most important point about the inappropriately-named “greenhouse” effect with a PhD in Climatology? Or even no PhD and just a slight interest in the field?
What determines the average emission altitude?
The “opacity” of the atmosphere. See The Earth’s Energy Budget – Part Three. Clearly Jelbring doesn’t know about it, otherwise he would have brought it up – and explained his theory of how doubling CO2 doesn’t change the opacity of the atmosphere – or the average altitude of radiative cooling to space.
Gilbert adds in his section:
I was immediately amazed at the paltry level of scientific competence that I found, especially in the basic areas of heat and mass transfer. Even the relatively simple analysis of atmospheric temperature distributions were misunderstood completely.
Where is Gilbert’s evidence for his amazing claim?
Gilbert also derives the equation for the lapse rate and comments:
It is remarkable that this very simple derivation is totally ignored in the field of Climate Science simply because it refutes the radiation heat transfer model as the dominant cause of the GE. Hence, that community is relying on an inadequate model to blame CO2 and innocent citizens for global warming in order to generate funding and to gain attention. If this is what“science” has become today, I, as a scientist, am ashamed.
I’m amazed. Hopefully, everyone reading this article is amazed.
The derivation of the lapse rate is in every single atmospheric physics textbook. And no one believes that radiative heat transfer determines the lapse rate.
And the important point – the Climate Science 101 point – is that the altitude of the radiative cooling to space is affected by the concentration of “greenhouse” gases.
Actually understanding a subject is a pre-requisite for “debunking” it.
Many people read blog articles and comments on blog articles and then repeat them elsewhere.
That doesn’t make them true.
Science is about what can be tested.
What would be a worthwhile “debunking” is for someone to take a well-established atmospheric physics textbook and point out all the mistakes. If they can find any.
It would be more valuable than just “making stuff up”.
Elementary Climate Physics, Prof F.W. Taylor, Oxford University Press (2005)
Handbook of Atmospheric Science, Hewitt & Jackson, Blackwell (2003)
An introduction to atmospheric physics, David Andrews, Cambridge University Press (2000)
Atmospheres, R.M. Goody & J.C.G. Walker, Prentice-Hall (1972)
Some Coolness Regarding Global Warming, Lindzen, Bulletin of the American Meteorological Society (1990)