Guest Post by Willis Eschenbach.
For all of its faults, the IPCC (Intergovernmental Panel on Climate Change) lays out their idea of the climate paradigm pretty clearly. A fundamental part of this paradigm is that the long-term change in global average surface temperature is a linear function of the long-term change in what is called the “radiative forcing”. Today I found myself contemplating the concept of radiative forcing, usually referred to just as “forcing”.
So … what is radiative forcing when it’s at home? Well, that gets a bit complex … in the history chapter of the Fourth Assessment Report (AR4), the IPCC says of the origination of the concept (emphasis mine):
The concept of radiative forcing (RF) as the radiative imbalance (W m–2) in the climate system at the top of the atmosphere caused by the addition of a greenhouse gas (or other change) was established at the time and summarised in Chapter 2 of the WGI FAR [First Assessment Report].
Figure 1. A graph of temperature versus altitude, showing how the tropopause is higher in the tropics and lower at the poles. The tropopause marks the boundary between the troposphere (the lowest atmospheric layer) and the stratosphere. SOURCE
The concept of radiative forcing was clearly stated in the Third Assessment Report (TAR), which defined radiative forcing as follows:
The radiative forcing of the surface-troposphere system due to the perturbation in or the introduction of an agent (say, a change in greenhouse gas concentrations) is the change in net (down minus up) irradiance (solar plus long-wave; in Wm-2) at the tropopause AFTER allowing for stratospheric temperatures to readjust to radiative equilibrium, but with surface and tropospheric temperatures and state held fixed at the unperturbed values.
In the context of climate change, the term forcing is restricted to changes in the radiation balance of the surface-troposphere system imposed by external factors, with no changes in stratospheric dynamics, without any surface and tropospheric feedbacks in operation (i.e., no secondary effects induced because of changes in tropospheric motions or its thermodynamic state), and with no dynamically-induced changes in the amount and distribution of atmospheric water (vapour, liquid, and solid forms).
So what’s not to like about that definition of forcing?
Well, the main thing that I don’t like about the definition is that it is not a definition of a measurable physical quantity.
We can measure the average surface temperature, or at least estimate it in a consistent fashion from a number of measurements. But we can never measure the change in the radiation balance at the troposphere AFTER the stratosphere has readjusted, but with the surface and tropospheric temperatures held fixed. You can’t hold any part of the climate fixed. It simply can not be done. This means that the IPCC vision of radiative forcing is a purely imaginary value, forever incapable of experimental confirmation or measurement.
The problem is that the surface and tropospheric temperatures respond to changes in radiation with a time scale on the order of seconds. The instant that the sun hits the surface, it starts affecting the surface temperature. Even hourly measurements of radiative imbalances reflect the changing temperatures of the surface and the troposphere during that hour. There is no way that we can have the “surface and tropospheric temperatures and state held fixed at the unperturbed values” as is required by the IPCC formulation.
There is a second difficulty with the IPCC definition of radiative forcing, a practical problem. This is that the forcing is defined by the IPCC as being measured at the tropopause. The tropopause is the boundary between the troposphere (the lowest atmospheric layer, where weather occurs), and the stratosphere above it. Unfortunately, the tropopause varies in height from the tropics to the poles, from day to night, and from summer to winter. The tropopause is a most vaguely located, vagrant, and ill-mannered creature that is neither stratosphere nor troposphere. One authority defines it as:
The boundary between the troposphere and the stratosphere, where an abrupt change in lapse rate usually occurs. It is defined as the lowest level at which the lapse rate decreases to 2 °C/km or less, provided that the average lapse rate between this level and all higher levels within 2 km does not exceed 2 °C/km.
This is an interesting definition. It highlights that there can be two or more layers that look like the tropopause (little temperature change with altitude), and if there is more than one, this definition always chooses the one at the higher altitude.
In any case, the issue arises because under the IPCC definition the radiation balance is measured at the tropopause. But it is very difficult to measure the radiation, either upwelling or downwelling, at the tropopause. You can’t do it from the ground, and you can’t do it from a satellite. You have to do it from a balloon or an airplane, while taking continuous temperature measurements so you can identify the altitude of the tropopause at that particular place and time. As a result, we will never be able to measure it on a global basis.
So even if we were not already talking about an unmeasurable quantity (radiative change with stratosphere reacting and surface and tropospheric temperatures held fixed), because of practical difficulties we still wouldn’t be able to measure the radiation at the tropopause in any global, regional, or even local sense. All we have is scattered point measurements, far from enough to establish a global average.
This is very unfortunate. It means that “radiative forcing” as defined by the IPCC is not measurable for two separate reasons, one practical, the other that the definition involves an imaginary and physically impossible situation.
In my experience, this is unusual in theories of physical phenomena. I don’t know of other scientific fields that base fundamental concepts on an unmeasurable imaginary variable rather than a measurable physical variable. Climate science is already strange enough, because it studies averages rather than observations. But this definition of forcing pushes the field into unreality.
Here is the main problem. Under the IPCC’s definition, radiative forcing cannot ever be measured. This makes it impossible to falsify the central idea that the change in surface temperature is a linear function of the change in forcing. Since we cannot measure the forcing, how can that be falsified (or proven)?
It is for this reason that I use a slightly different definition of the forcing. This is the net radiative change, not at the troposphere, but at the TOA (top of atmosphere, often taken to mean 20 km for practical purposes).
And rather than some imaginary measurement after some but not all parts of the climate have reacted, I use the forcing AFTER all parts of the climate have readjusted to the change. Any measurement we can take already must include whatever readjustments of the surface and tropospheric temperatures that have taken place since the last measurement. It is this definition of “radiative forcing” that I used in my recent post, An Interim Look at Intermediate Sensitivity.
I don’t have any particular conclusions in this post, other than this is a heck of a way to run a railroad, using imaginary values that can never be measured or verified.
w.
Willis says: “Thanks, mkelly. I see you and other folks above making the argument that since the downwelling longwave radiation doesn’t do what y’all expect it to do, it must not exist,…”
Willis you often get annoyed with folks who don’t quote you or put words in your mouth. I have never said that it does not exist I have said and maintain that it has not power to do anything. ie work. So please don’t think or say that I said it does not exist. The question is can it do anything and I say no.
Frank,
“…the IPCC assumes that (to a first approximation) the lapse rate remains constant so that…”
Yes. But the added CO2 is not constrained by the lapse rate because this gas is created ex nihilo. Emulate its temperature on the lapse rate is an arbitrary operation. The value obtained (radiative forcing) is therefore also arbitrary.
Stephen Wilde says:
December 13, 2012 at 11:35 am
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The cloud example is a difficult example and proves next to nothing because one cannot separate the various mechanisms that may be at play, and thereby correctly ascribe cause and effect.
The cloud is an example of the classic greenhouse, ie., it really is akin to the glass roof in that it hinders convection thereby trapping warm(er) air. So whilst one may feel less cold on a cloudy night, one does not know whether this is due to the points you raise to which I would add the obstruction of convection (which would otherwise be more efficiently cooling the body of air immediately above the ground), or whether as Willis argues there is more DWLWIR.
Curious George says:
December 13, 2012 at 10:40 am
What argument are you talking about? Details, friends, the devil is in the details.
w.
Frank says:
December 13, 2012 at 11:36 am
Sure, you can calculate it … but is it correct? That’s the recurring question, we have no answer yet. As Shakespeare put it:
You go on to say:
It’s the “best system we have”? Sez who? You? Color me unimpressed. We need to start with something we can actually measure. If you want to develop theoretical values from that, fine. But:
• If you can’t measure it, you can’t falsify it.
• If you can’t falsify it, it’s not science.
• If it’s not science, how can it be the best system we have?
I hear people say this all the time. The temperature at the surface of the earth ranges from about 134°C to – 90°C, a swing of about 200°C. The solar forcing goes from zero to a thousand watts per square metre in the tropics every day.
What part of that says “small percent changes in forcing” to you?
There is a further problem with this, which is that in some cases the averages are totally deceptive. I discussed this in “The Details Are In The Devil“. In some cases, there may be no relationship between forcing and temperature. See my previous post, “An Interim Look At Intermediate Sensitivity“. In that case, not only is the linear approximation incorrect. Any putative relationship is incorrect.
w.
Well nowhere in the earth climate system, is anything IN EQUILIBRIUM.
“””””…..The radiative forcing of the surface-troposphere system due to the perturbation in or the introduction of an agent (say, a change in greenhouse gas concentrations) is the change in net (down minus up) irradiance (solar plus long-wave; in Wm-2) at the tropopause AFTER allowing for stratospheric temperatures to readjust to radiative equilibrium, but with surface and tropospheric temperatures and state held fixed at the unperturbed values……””””
In particular, given that the earth rotates, so that no point on earth ever is in thermal equilibrium. or radiative equilibrium, so this definition is BS.
Moreover, there is no known way to hold either surface or tropospheric temperatures or “state” fixed at any value let alone any unperturbed value.
Who are these people who think it is ok for them to simply make up their own physical laws, and make comlex systems obey their silly ideas ?
mkelly says:
December 13, 2012 at 11:50 am
mkelly, If you would quote my entire sentence, rather than selectively quoting me as you have done, you would note that I actually said (emphasis mine):
I said that you and others were making one of two arguments, EITHER that DLR doesn’t exist, OR making the argument that it does not have any power to warm things.
Obviously, you are included in the OR clause … so I did not misquote or misrepresent you in the slightest. As you say, you claim that measurable downwelling longwave radiation, which obviously contains energy (that’s how we measure it), has no power to do anything at all. Which is exactly how I described your argument.
Now, this is obviously some new kind of radiation, because every other kind of radiation that I’ve ever heard of has the power to do something. Generally speaking, for example, all radiation warms whatever absorbs the radiation.
But you have a brand new kind of radiation, one that contains energy and yet does not warm what it is absorbed by, it has no power to do anything …
So where does the energy go when such radiation hits the earth? It can’t be destroyed. Your claim is that it is not turned into heat as everyone else might think, including myself … so where does it go? It’s not turned into light, or mechanical motion, and according to you it’s not turned into heat … so where is the energy that was contained in the downwelling radiation?
Regards,
w.
Its morning here now, and even though I haven’t had my coffee yet…
It appears Figure 1 is based on wet lapse rate.
If you take the tropical (pink) line.. its surface value is 20C (ignore where the numbers are, they are badly printed) That line crosses the grid again at -30C at 9km so the slope is 5.5C/km
Same slope with the polar (blue line) but isn’t polar air mostly dry ?
Still.. the point sits that using 20km as TOA is really pretty ridiculous.
richard verney says:
December 13, 2012 at 12:05 pm
I am not “arguing” that there is more downwelling longwave radiation under clouds than under a clear sky. That is a measurable fact, and has been measured many times, both during the day and the night. It is not due, as you postulate, to the “obstruction of convection”. Heck, many clouds are created by convection, they are areas of increased rather than decreased convection, and despite that, they are sources of increased downwelling radiation … go figure.
Finally, we know it is not just interrupted convection because of the speed of the phenomenon. Just like when a cloud covers the sun it immediately becomes cooler (radiation), the same is true of night-time winter clouds. As soon as a cloud covers the night sky, the surface immediately becomes warmer. This is the sign of radiation, not convection.
Look, guys, this stuff is not theory. This part of climate science is measurable, testable, and is even detectable by our own senses. There are good arguments against the conventional consensus theory. The idea that clouds don’t warm winter nights through increasing DLR is not one of them. Nor is the idea that DLR somehow magically does nothing when it is absorbed by the surface, the idea that the energy in the downwelling radiation just disappears. All of that is just wishful thinking.
w.
Comment from Ryan Dec 13th 2012 6.40am …..Good comment Ryan . Well said.
richard verney said:
“So whilst one may feel less cold on a cloudy night, one does not know whether this is due to the points you raise to which I would add the obstruction of convection”
I agree, Richard.
Suppression of convection facilitates downward conduction.
It cannot be anything to do with DLR because if it were the effect would be the same from both high and low clouds yet we know it is not.
I don’t see it as anything to do with DLR in any event because the solar throughput is unhindered at equilibrium. At equilibrium solar shortwave in must equal longwave out at top of atmosphere.
Solar shortwave comes in and planetary longwave goes out and at equilibrium they are always equal.
What matters is how the atmosphere intervenes and that is a constant related to mass. gravity and insolation and nothing else.
PE + KE = Constant.
Only mass, gravity and insolation set that constant.
The atmosphere shuffles KE and PE through the speed of adiabatic processes as necessary to maintain that constant.
If the radiative characteristics of individual atmospheric components vary so as to disrupt the balance between solar shortwave in and longwave out then the atmospheric heights change to redistribute KE and PE to negate the imbalance.
The constant being set by mass, gravity and insolation, any other factor such as the radiative characteristics of individual constituents of the atmosphere can only affect the proportion of KE relative to PE.
The more the atmosphere expands from more GHGs the more PE there can be and the less KE (cooling) and the more the atmosphere contracts from less GHGs the less PE and the more KE (warming).
GHGs might cause the atmosphere to expand but if they do that then PE increases relative to KE and there is an equal and opposite cooling effect due to the reduction in KE.
If they cause the atmosphere to contract then KE increases relative to PE and there is an equal and opposite warming effect due to the increase in KE.
That is the true Thermostat Hypothesis and Willis’s version is correct as far as it goes but it does not extend to the entire globe which is where it fails.
“Heck, many clouds are created by convection, they are areas of increased rather than decreased convection, and despite that, they are sources of increased downwelling radiation ”
Really ?
Clouds created by convection as compared to clouds formed beneath an inversion layer result in air flowing in from surrounding sunlit regions to feed the uplift.
No increase in DLR there.
The argument seems to be based on average temperatures.
Willis: What argument are you talking about? Details, friends, the devil is in the detail.
The red, blue, and green lines in Fig. 1 are all averages – I may be wrong. Has IPCC ever considered temperature variations in space or time? I thought Willis might know.
Willis Eschenbach says:
December 13, 2012 at 12:52 pm
“So where does the energy go when such radiation hits the earth?”
First if you did not indend for me to be included in the group of folks that say the radiation for CO2 does not exist then I with draw my comment.
It is called reflection. You assume it is absorbed.
Just because radiation strikes a body does not mean it is absorbed and turned into thermal energy (heat).
I have said before if you or others can write a radiative heat transfer equation showing how CO2 warms the surface of the earth I’ll happily accept that. ie makes the surfaced go from 255K to 288K.
Ummm.. clouds are where the convective flow stops.
If you stop the convective flow, the convective flow below is forced to slow down.
Upward energy transfer is thus slowed down.
Think of a big heavily laden truck going up a hill on a one lane road, with many cars behind that want to go faster.
(since heat cannot be effectively conducted down
Some posts have been a little off topic, but that is no doubt because one can hardly add to Willis’s closing comment. It is only too true that one can’t have any particular conclusions given the use of imaginary values that can never be measured or verified.
I am in the mkelly camp that the issue is not whether DWLWIR exists, but rather it is one of whether DWLWIR has sensible energy/the ability to do real work in the Earth environment.
The key to AGW is the behavoir of DWLWIR and water. The reason for this is threefold. First, it is the oceans that control the weather. Second (and this is related),the latent heat content of the oceans dwarfs the latent heat content of the atmosphere. Third, the absorption of DWLWIR in water is very different to that in dry air (such that the behavoir of DWLWIR over the oceans is different to that over land). IR cannot penetrate water to any significant degree such that water acts as an IR block. Almost all IR is absorbed within 10 microns, with about 40% of all DWLWIR being absorbed within 1 micron and 60% within 3 microns. Sunlight can penetrate water to great depths. This is fundamental.
The power from sunlight can warm water; it does not immediately cause the top micron layers to burn off/evaporate but instead the energy penetrates to depth slowly heating a vast volume of water at depth. IR is very different since approximately 60% of all IR is absorbed within 3 microns. This means that energy in IR does not heat a vast volume of water at depth, but instead it is concentrated and heats a relatively small volume at the very top 1 to 3 micron layer. Since the energy is not dissipated, but concentrated, the very top microns surely must burn off.
If one considers the amount of DWLWIR that is, according to Trenbeth/AGW proponents, hitting the oceans, as a matter of the absorption characteristics of water, the energy in this (assuming that DWLWIR can perform sensible work) would lead to the top micron layer quickly evaporating. If this was happening, then there would be 10s of metres of rainfall annually, which there is not. The fact that there is not such an amount of rainfall suggests: (i) the characteristics of absorption of IR in water is wrong (extremely unlikely) such that IR is not completely absorbed in the first microns but can infact penetrate many metres, (ii) DWLWIR does not exist or not in the quantity postulated by AGW proponents, or (iii) DWLWIR lacks sensible energy. It is a signal but cannot perform real work in the conditions encountered in Earth’s environ.
Until one can witness DWLWIR performing real work such as burning off dew, or melting ice, questions quite obviously arise as to whether it does (or does not) possess sensible energy.
PS. If one looks at the temperature profile of the oceans, the top few microns are cooler than the top 15 microns such that the direction of heat flow is up towards the surface, not down towards the deeper ocean.
PS. In my last post where I use IR, I mean LWIR. The wavelength is very important to the characteristics of absorption.
One can generally state the Forcings Theory as,
The Earth’s climate warms/cools from changes in the net radiation balance at a hypothetical contiguous shell that surrounds the climate.
TOA would fit the contiguous shell surrounding the climate criteria. And the tropopause would, as you point out, seem to fail the contiguous criteria.
Ignoring heat from the Earth’s interior, the Forcings Theory, as stated above, would appear to be a priori true. But being a priori true, doesn’t make it science.
Firstly, we cannot measure (at our hypothetical shell) the radiative source for most radiative forcing changes. Therefore cannot measure the change in a particular forcing.
Secondly, the theory gives us no criteria to determine whether something is a radiative forcing or not. Which means there may be yet undiscovered forcings, as GCRs were a few years ago.
All in all, I have trouble considering the Forcings Theory as properly scientific.
The graphic showing a smooth variation in troposphere height from equator to poles is wrong.
There are discontinuities between the equatorial, mid latitude and polar tropopauses. The jet streams occur there.
mkelly says:
December 13, 2012 at 1:32 pm
I assume nothing of the sort. I know it is absorbed. The average absorptivity of the earth’s surface at the relevant frequencies is greater than 95%. In a previous post, I said:
So we know for a fact that only a bit of it is reflected, a few percent. Thus, your claim that it is reflected is falsified. Again, these are measurements, not theory.
True, and in the case of the earth more than 95% of it is absorbed and turned into thermal energy.
Sure, be glad to. See my previous posts, The Steel Greenhouse, and People Living In Glass Planets.
All the best,
w.
richard verney says:
December 13, 2012 at 1:40 pm
Richard, like mkelly you are postulating an entirely new class of radiation, radiation which contains no energy. Until you have some evidence that such a bizarre creature exists, I suspect that most folks will have the same reaction as mine … I’ll believe it when you show me such radiation, or any serious scientific claim that such energy-free radiation exists.
Until then, infrared radiation contains energy, get used to it. Your job is to explain what happens to that energy if it is not absorbed by the ocean. You can’t get out of it by simply making up a fantasy about energy-free radiation.
See my post above for an explanation about why DLR won’t melt ice, and despite that, it contains energy, and why the world is warmer with DLR than without DLR.
Richard, in my post “Radiating the Ocean“, I listed four reasons why people’s theory that DLR can’t warm the ocean is wrong. I closed by saying:
So there is the hurdle you need to get over in order to sustain your claim that DLR can’t warm the ocean. You need to refute all four of them if you want to get any traction.
w.
I don’t know of other scientific fields that base fundamental concepts on an unmeasurable imaginary variable rather than a measurable physical variable.
Historically, most of them have done that aplenty. Conceptual and definitional clarity have usually followed decades of confusion. Consider the fundamental concept of “ergodic”, described in Lawrence Sklar’s book “Physics and Chance”, or just about any history of atomic theory.
Possibly the most famous imaginary is the “body in uniform motion”.
Willis writes a strawman argument “Go buy an infrared lamp, put it over a pan of water, and see what happens.”
You have just made DLR > ULR which isn’t the case for the ocean. You’ve fallen into the precise trap that you’ve argued all along doesn’t matter regarding whether something is cooling more slowly or actually “warming”.
Willis,
Maybe I can get a bit of traction over DLR “can’t warm the ocean” I suppose anything in nature is possible but what you are contending here is that a trace gas wafts around in the air above the ocean waves and warms the water beneath more than otherwise by the sun. Call me a stickler for not introducing amounts and figures but when thinking about all this I get a feeling of insignificance and impossibility, and so should you.