Guest Post by Willis Eschenbach
OK, a quick pop quiz. The average temperature of the planet is about 14°C (57°F). If the earth had no atmosphere, and if it were a blackbody at the same distance from the sun, how much cooler would it be than at present?
a) 33°C (59°F) cooler
b) 20°C (36°F) cooler
c) 8° C (15°F) cooler
The answer may come as a surprise. If the earth were a blackbody at its present distance from the sun, it would be only 8°C cooler than it is now. That is to say, the net gain from our entire complete system, including clouds, surface albedo, aerosols, evaporation losses, and all the rest, is only 8°C above blackbody no-atmosphere conditions.
Why is the temperature rise so small? Here’s a diagram of what is happening.
Figure 1. Global energy budget, adapted and expanded from Kiehl/Trenberth . Values are in Watts per square metre (W/m2). Note the top of atmosphere (TOA) emission of 147 W/m2. Tropopause is the altitude where temperature stops decreasing with altitude.
As you can see, the temperature doesn’t rise much because there are a variety of losses in the complete system. Some of the incoming solar radiation is absorbed by the atmosphere. Some is radiated into space through the “atmospheric window”. Some is lost through latent heat (evaporation/transpiration), and some is lost as sensible heat (conduction/convection). Finally, some of this loss is due to the surface albedo.
The surface reflects about 29 W/m2 back into space. This means that the surface albedo is about 0.15 (15% of the solar radiation hitting the ground is reflected by the surface back to space). So let’s take that into account. If the earth had no atmosphere and had an average albedo like the present earth of 0.15, it would be about 20°C cooler than it is at present.
This means that the warming due to the complete atmospheric system (greenhouse gases, clouds, aerosols, latent and sensible heat losses, and all the rest) is about 20°C over no-atmosphere earth albedo conditions.
Why is this important? Because it allows us to determine the overall net climate sensitivity of the entire system. Climate sensitivity is defined by the UN IPCC as “the climate system response to sustained radiative forcing.” It is measured as the change in temperature from a given change in TOA atmospheric forcing.
As is shown in the diagram above, the TOA radiation is about 150W/m2. This 150 W/m2 TOA radiation is responsible for the 20°C warming. So the net climate sensitivity is 20°C/150W-m2, or a temperature rise 0.13°C per W/m2. If we assume the UN IPCC canonical value of 3.7 W/m2 for a doubling of CO2, this would mean that a doubling of CO2 would lead to a temperature rise of about half a degree.
The UN IPCC Fourth Assessment Report gives a much higher value for climate sensitivity. They say it is from 2°C to 4.5°C for a CO2 doubling, or from four to nine times higher than what we see in the real climate system. Why is their number so much higher? Inter alia, the reasons are:
1. The climate models assume that there is a large positive feedback as the earth warms. This feedback has never been demonstrated, only assumed.
2. The climate models underestimate the increase in evaporation with temperature.
3. The climate models do not include the effect of thunderstorms, which act to cool the earth in a host of ways .
4. The climate models overestimate the effect of CO2. This is because they are tuned to a historical temperature record which contains a large UHI (urban heat island) component. Since the historical temperature rise is overestimated, the effect of CO2 is overestimated as well.
5. The sensitivity of the climate models depend on the assumed value of the aerosol forcing. This is not measured, but assumed. As in point 4 above, the assumed size depends on the historical record, which is contaminated by UHI. See Kiehl for a full discussion.
6. Wind increases with differential temperature. Increasing wind increases evaporation, ocean albedo, conductive/convective loss, ocean surface area, total evaporative area, and airborne dust and aerosols, all of which cool the system. But thunderstorm winds are not included in any of the models, and many models ignore one or more of the effects of wind.
Note that the climate sensitivity figure of half a degree per W/m2 is an average. It is not the equilibrium sensitivity. The equilibrium sensitivity has to be lower, since losses increase faster than TOA radiation. This is because both parasitic losses and albedo are temperature dependent, and rise faster than the increase in temperature:
a) Evaporation increases roughly exponentially with temperature, and linearly with wind speed.
b) Tropical cumulus clouds increase rapidly with increasing temperature, cutting down the incoming radiation.
c) Tropical thunderstorms also increase rapidly with increasing temperature, cooling the earth.
d) Sensible heat losses increase with the surface temperature.
e) Radiation losses increases proportional to the fourth power of temperature. This means that each additional degree of warming requires more and more input energy to achieve. To warm the earth from 13°C to 14°C requires 20% more energy than to warm it from minus 6°C (the current temperature less 20°C) to minus 5°C.
This means that as the temperature rises, each additional W/m2 added to the system will result in a smaller and smaller temperature increase. As a result, the equilibrium value of the climate sensitivity (as defined by the IPCC) is certain to be smaller, and likely to be much smaller, than the half a degree per CO2 doubling as calculated above.
Willis
…Again, folks seem to think that a colder object cannot radiate heat to a warmer object. It most definitely can. The constraint from the Second Law is only that the net flow has to be from the warmer to the colder object. It says nothing about the individual flows except that the flow from warm to cold has to be greater than the flow from cold to warm……….
A cold object can radiate to a hotter object.
It cannot radiate HEAT.
Heat has the thermodynamic property of the capacity to do Work.
Ask yourself if this applies to the above statement.
Look at the definition of HEAT in any physics textbook.
Anna V,
I totally agree with you that there is a lot of confusion because of semantics.
In climate science heat and heat radiation are sometimes used as synonyms.
This is sloppy language and creates statements that apparently violate the 2nd law. If one applies the correct language everything is fine.
Per example one reads sentences like:
“all bodies at non-zero temperature radiate heat according to their temperature…”
Such sentences are wrong and incomplete. In physics heat is defined as energy transport from warm to cold. Therefore such sentences need to read:
“all bodies at non-zero temperature radiate heat radiation according to their temperature and emissivity”
If physics is phrased correctly and the word radiation is used, confusion is minimized.
I agree with your analysis.
Best regards
Guenter
Willis,
Where is TOA in a world without an atmosphere?
Bryan says:
You may be right about the technical definition. These sort of things are why I have never been a big fan of thermodynamics and always try to think in terms of the underlying statistical physics. However, as Guenter Hess notes, what you are then quibbling over is just semantics. It does not in any way change our argument.
For example, here is a discussion by retired meteorology professor who is really militant on these issues of semantics and pedogagy: http://www.ems.psu.edu/~fraser/Bad/BadGreenhouse.html However, note that unlike you and G&T, he doesn’t jump to the conclusion that because the semantics are arguably not perfect, therefore the phenomenon does not exist. He just argues for a better way to describe the phenomenon.
Invariant says:
Based on the “forcings” in GISS climate model,
http://data.giss.nasa.gov/modelforce/,
we may erroneously get the impression that the global temperature would be completely constant in a world without humans. This is particularly peculiar since we know that Milankovitch cycles, ocean cycles and other cycles may lead to severe fluctuations – it is usually not the case that the criterion of thermal equilibrium is satisfied.
Well, if you erroneously get that impression, it is your own erroneous conclusion. Hansen et al. very well understand that there are forcings that occur from natural causes too. In fact, that is how they have arrived at one estimate of the climate sensitivity: They have looked at the estimated forcings during the Ice Age – interglacial cycles (triggered by the Milankovitch cycles of which you speak) and at the resulting temperature change. Forcings and temperature change due to volcanic eruptions like Mt. Pinatubo in the early 1990s provides another piece of empirical data to estimate the climate sensitivity.
You are confusing two different things here:
(1) Changes in temperature due to changes in natural forcings (such as the ones that I have listed above).
(2) Changes in temperature due to internal variability.
The latter are NOT assumed not to exist and, in fact, there has been quite a bit of study of such internal variability using climate models and comparing to the real world. Unfortunately, however, this can be hampered a bit by the fact that we don’t have very accurate estimates for forcings in the past, particularly during times when the forcings were fairly small (e.g., changes in solar forcing over the last couple thousand years) and, of course, our estimates of the temperature changes themselve is more difficult once we go back to before the instrumental record.
We know quite accurately (within about 10% or so) the radiative forcing due to a given increase in CO2. We can also estimate the radiative forcing due to past events such as the last glacial maximum and the Mt Pinatubo eruption. This allows us to calculate what the effect of CO2 should be. So, in fact, it is the past climate changes…particularly the significant ones for which we can get the best estimates of temperature change and forcings…that allow us to estimate how large a change in climate will be produced by the known radiative effect of increasing greenhouse gases.
Willis Eschenbach says:
Willis,
I don’t think you have really disposed of the question at all. In fact, you haven’t really addressed the questions from the last post: I.e., I still don’t understand what your argument is. Are you claiming (1) that the ~4 W/m^2 number includes the effects of feedbacks such as the water vapor feedback, or (2) that it doesn’t but somehow the water vapor feedback doesn’t change this number?
Also, how do you feel that an estimate of forcing discussed in the way that Gregory et al. define it (by this regression to zero temperature change) could possibly include the effects of the water vapor feedback, which only operates when there is a nonzero temperature change?
And, I still don’t understand the mechanism by which you imagine the IPCC would claim that a ~4 W/m^2 change in the TOA radiation would lead to such a large surface temperature change. The only mechanism that I could see for that happening is if there were a huge amplification of the surface temperature relative to that higher up in the troposphere and, in fact, we know that the prediction is for the amplification to go the other way (although on a global scale it is not that large).
When you find yourself arguing against what is clearly a fallacious argument…particularly one that you think has been embraced by a very large community of scientists, that is a sign that you may be arguing against a “strawman” that you have created rather than their actual argument. I am afraid that this is indeed true in this case.
Joel
You may be right about the technical definition. These sort of things are why I have never been a big fan of thermodynamics and always try to think in terms of the underlying statistical physics. However, as Guenter Hess notes, what you are then quibbling over is just semantics. It does not in any way change our argument…….
The matter of whether one is a big fan of one branch or physics or not we must use the language developed within the discipline or it will lead to all sorts of confusion.
For instance I have never been completely comfortable with Quantum Mechanics yet I use its methods and language until some better explanation comes along.
I hope that in your new paper you will use language that is consistent within the Framework of Physics after all that is what the article is meant to be addressing.
> Unfortunately, however, this can be hampered a bit by the fact that we don’t have very accurate estimates for forcings in the past, particularly during times when the forcings were fairly small (e.g., changes in solar forcing over the last couple thousand years) and, of course, our estimates of the temperature changes themselve is more difficult once we go back to before the instrumental record.
Thanks Joel for comments. I am honestly trying to figure out what is your point of view – disagreements pave the road to progress!
Now, from what you state, do you argue that any change in global temperature need to be caused by an internal or external force?
Joel,
I agree with Bryan.
Semantics in this context is very important, since your statement implied to the reader a violation of the 2nd law of thermodynamics.
I made my statement because I find the confusion between heat and heat radiation or thermal radiation in popular books about climate change written by prominent physicists like Schellnhuber and Rahmstorf.
Such a confusion suggests to many scientists that the grasp of thermodynamics by the author, who uses the technical words wrongly, is not sufficient to talk about issues like global warming with expertise.
I do not assume that Rahmstorf or Schellnhuber do not know this. However, I do think one should strive to phrase the physics correctly.
G&T refuted wrong statements like yours and in that they were right in some particulars.
You in turn tried to refute G&T in turn with the same wrong statement they already refuted. This is a waste of time. Therefore, lets strive to phrase correct statements about physics.
By the way I am a big fan of thermodynamics classical and statistical. Both branches augment each other and are necessary to describe the physical world within any field of science.
Best regards
Guenter
Joel,
I would argue that transitions from one climate state to another do not have to be caused by any particular change in an external driver. In driven, non-equilibrium systems such changes may occur even though a specific cause can not be identified. If the temperature is not in equilibrium, the right hand side of the heat balance is non-zero,
m c dT/dt = Qin – Qout
and the temperature may change even though Qin and Qout is constant. In fact the temperature may change both for constant and variable values of Qin and Qout, but not if the difference, Qin – Qout, is identically equal to zero.
Most of the arguments I have seen from the AGW community seems to assume that there is always equilibrium, in order for the temperature to change, something has to change it…. This is clearly nonsense, in particular when the AGW community argues that something has to have caused the warming from the little ice age. Well, do they argue that there was equilibrium during the little ice age in 1750 when the world was much colder? If there is also equilibrium today this clearly does not make sense since the earth is warmer today… We know from the heat balance that the last term Qout is temperature dependent (Stefan Boltzmann radiation), so it’s impossible that two different temperatures at the same time can be the equilibrium temperature for our planet! Then the question is, given that the temperature has changed a lot the last 1000 years,
http://pages.science-skeptical.de/MWP/MedievalWarmPeriod1024×768.html
would it be possible to argue that the climate behaves as an oscillator, with normal fluctuations in temperature around equilibrium?
m c dT/dt = Qin – Qout
Look at the heat balance; wouldn’t it be fantastic if the temperature fluctuations would be zero? A perhaps more realistic result would be, given the Milankovitch cycles, ocean cycles and other cycles, that the temperature would oscillate a couple of Kelvin?
What is your gut feeling Joel? That the temperature fluctuations are small or large?
(The html link was corrupted!)
The question to Joel is, given that the temperature has changed a lot the last 1000 years,
http://pages.science-skeptical.de/MWP/MedievalWarmPeriod1024x768.html
would it be possible to argue that the climate behaves as an oscillator, with normal fluctuations in temperature around equilibrium?
m c dT/dt = Qin – Qout
Look at the heat balance; wouldn’t it be fantastic if the temperature fluctuations would be zero? A perhaps more realistic result would be, given the Milankovitch cycles, ocean cycles and other cycles, that the temperature would oscillate a couple of Kelvin?
What is your gut feeling Joel? That the temperature fluctuations are small or large?
Invariant: Yes, it is quite possible that there has been a negative internal fluctuation in temperatures over the last century that has partially masked the warming due to greenhouse gases which otherwise would have been larger.
Actually, I am being somewhat facetious in the above. However, my point is that internal variability doesn’t only occur in one direction. And, more important than that is the fact that saying that internal variability exists doesn’t repeal the fact that climate responds to forcings too…and that we have estimates for its sensitivity to such forcings.
And, by the way, there is quite a bit of work within the climate science community in characterizing internal variability…so it is not like it is something that they haven’t thought about, or that the climate models themselves don’t show. And, as I understand it, the estimates are that the internal variability is pretty small.
What evidence do you have for such numbers? And, why are you including Milankovitch cycles at all…Those provide a forcing; they are not internal variaibility.
Invariant: Yes, it is quite possible that there has been a negative internal fluctuation in temperatures over the last century that has partially masked the warming due to greenhouse gases which otherwise would have been larger.
OK. Agreed!
Actually, I am being somewhat facetious in the above. However, my point is that internal variability doesn’t only occur in one direction.
Sure! Oscillations go both ways, just like a pendulum.
And, more important than that is the fact that saying that internal variability exists doesn’t repeal the fact that climate responds to forcings too…and that we have estimates for its sensitivity to such forcings.
OK. Agreed!
And, by the way, there is quite a bit of work within the climate science community in characterizing internal variability…so it is not like it is something that they haven’t thought about, or that the climate models themselves don’t show
OK. I think I have to learn your language, it is internal variability I should state when I mean internal oscillations not caused by an (external) force.
And, as I understand it, the estimates are that the internal variability is pretty small.
Now, this is interesting. What is regarded as large and small interests me a lot. Compared to what? What is the evidence for this? And is it easy to tell internal variability from increased CO2 or other external variations? Sometimes I tend to listen more to what people have experienced in historical times than dubious climate reconstructions…
“Comparatively rapid variations of climate, of the order of a century, have presumably always occurred…”
Climate Through the Ages (1950) C E P Brooks. http://www.archive.org/download/climatethrouchth033039mbp/climatethrouchth033039mbp.pdf
(p. 379)
What evidence do you have for such numbers?
Well, I have no experience in climate science, however I have a Ph.D. in Physics with specialization in non-equilbrium thermodynamics, and I suspect that it is unlikely that internal fluctuations (as you like to call them) are negligible. I do not regard a couple of Kelvin as much since the climate never has a chance to reach equilbrium.
And, why are you including Milankovitch cycles at all…Those provide a forcing; they are not internal variaibility.
I know, but I think the internal fluctuations may be triggered by external fluctuations. Think of an harmonic dissipative oscillator RLC circuit with many resonsance frequencies that is driven by oscillations on many frequencies due to Milankovitch cycles and/or oscillations between
1. day and night,
2. summer and winter,
3. ice ages and warmer periods
The fact that the equilbrium temperature is not fluctuating more than 287 ± 1-2 K is quite impressive. A process engineer would be very happy with a regulator that manages to keep the temperature that stable…
Joel Shore (07:13:15)
Cite? (Please don’t cite climate models, I’m looking for evidence …)
Joel Shore (07:27:58)
The number Hansen quotes is obtained by doubling the CO2 in a model, and then holding all other conditions the same until the surface temperature stops changing. Presumably, this includes the effects of all feedbacks such as water vapour, as all modern climate models include them. So I am claiming (1).
I think that you misunderstand the situation. The CO2 was doubled, increasing the forcing in the model. The modelled surface temperature then started to rise, with all of the relevant feedbacks that implies. The model was run until there was no further temperature change. At that point, the net change in TOA forcing (and surface temperature) was calculated.
So it is not a situation of a zero temperature change, as you seem to think. The CO2 was doubled, surface temperature started to rise, and the model was run until the temperature stopped rising.
Heck, I don’t know what mechanisms the IPCC claims. All I know is that they claim that a doubling of CO2 leads to an equilibrium TOA forcing change of 3.7 W/m2, and that the doubling will result in a temperature change of 3°C. Hansen (op cit) says the doubling leads to an equilibrium change of 3.95 ± 0.11 W/m2, and a surface temperature change of 1.96 ± 0.02°C.
You’ll have to be more clear about what you think is a “fallacious argument”. The IPCC numbers basically agree with Hansen’s numbers. The IPCC says an increase in forcing of 3.7 W/m2 (a doubling of CO2) will lead to a 2 – 4.5°C temperature increase. Hansen says an increase in forcing of 3.95 W/m2 (a doubling of CO2) will lead to a 2C temperature increase.
Where is the fallacy?
lgl (02:51:47)
The more relevant question is, how much TOA forcing (downwelling longwave radiation) is there in a world without an atmosphere. The answer, of course, is zero.
Joel and Willis,
I do not doubt that the calculations of shells and temperatures are correct. Of course there is a “greenhouse effect”, we are here, aren’t we?
The classical thermodynamic view of “reservoir1” and “reservoir2” and the second law should be working on a ball with an atmosphere whether there is an extra heat source or not. Otherwise the Clausius formulation of the second law is defied.
My point is that talking of “back radiation”, adding watts/m^2 all over the place is not within classical thermodynamics, it mixes in quantum statistical terms and leads to confusion and I suspect double counting in the famous energy budgets.
The chicken in the oven
http://www.vermonttiger.com/content/2008/07/nasa-free-energ.html
being an illustration of double counting.
So it is semantics, but it is easy to make logical errors when the semantics is confused.
Willis Eschenbach (17:32:57) :
The relevance is that you put the 0 W at surface altitude and the 150 W at 6 km altitude in your equation.
And the 3.7 W is without feedbacks.
anna v
“I suspect double counting in the famous energy budgets.”
There is double counting. That’s how feedback loops work. If 59% of the LW from surface is back radiated, the resulting gain is 1/(1-0.59)=2.44 and the 200 W solar input becomes 490 W at the surface.
By the way, Willis, the Hansen et al. paper is very clear that the forcing definition used by the IPCC does not include feedbacks other than those due only to the STRATOSPHERIC temperature change:
@ur momisugly Joel Shore:
Models could only simulate temperatures in the 1990s by adding forcing from GHGs. Why does Earth return to pre-Pinatubo temperature so quickly if lags and feedbacks are involved in GHG forcing? ~.4C swing both directions in a matter of 3 years. Does this not suggest climate seeks to stabilize?
And, as I understand it, the estimates are that the internal variability is pretty small.
Could you please be a little more specific. I would really appreciate to know what is the current state of the art knowledge here. Does it mean that internal variability may cause the temperature to fluctuate something like T = 287 ± 0.4 K?
invariant,
the current state of knowledge? That’s been summed as “natural variation? we don’t need no stinkin’ internal variability!”
Of course, this is the same crew that presumes constant albedo in order to estimate sensitivities. Well, constant expect for the usual man-made surface changes.
seems like the closest to measuring albedo for any time period (about 20 yrs) came up with peak to peak variations of around 10%. That’s about 10w/m^2 average.
ooops! sorrry – that’s 10w/m^2 averaged p-p power difference for that event.
cba (04:34:41) :
Sure. However, I would very much like to know what they think, not necessary to determine if it makes sense, but merely to figure out what is going on inside their head. I do not think most of the climate scientists deliberately are cheating, and I think it is fortunate that Joel is contributing to WUWT.
So, with state of the art knowledge, I really mean what most of the scientists developing climate models think! Possibly Mojib Latif think internal variability is larger, however, that’s not what I intend to find out, what is the opinion of the main stream climate scientists?
I think this is relevant for the whole climate sensitivity discussion too; imagine that we knew that the internal variability was T = 287 ± 1.6 K with a characteristic cycle length of ~330 years. Then we could argue that the sensitivity of the climate would be less – it is harder to influence an oscillating system than a system at (or close to) equilibrium.
Internal variability is what destroys farmers into bankruptcy. The condition of the Pacific Ocean, combined with both the Arctic Oscillation and the Jet Stream can cause the inland northwest area of the US to freeze sewer tanks. Or allow us to grow something. Not a small percentage of crops are planted in the fall or once very few years, so a deep freeze will kill these kinds of plants. And if these weather pattern variables are oscillating in the cold mode and in tandem for a few years, you can kiss your farm subsidies, let alone your crops, goodby. It is a decidedly no small thing and exposes the fact that armchair and Ivory tower climate warming believers haven’t a clue about the strength of internal variability, in one season, and over several seasons.
Addendum, internal variability cannot be “averaged”. Internal variability is a climate zone specific entity. Some zones are stable to variability, and some are not. A calculated average lulls everyone into unpreparedness. And many deaths. Anyone here who is willing to state such a mathematical calculation as a single application to climate modeling is guilty by association to such nonsense and engages in dangerous propositions.