Guest Post by Willis Eschenbach
Of late there has been a lot written about the effect of “black carbon”, a.k.a. “soot”, and also “brown carbon”, a.k.a. wood and dung smoke, on the climate. Me, I think it’s worthwhile controlling black and brown carbon solely because of the health effects. Inhaled soot and wood smoke kill a lot of people every year. So reducing atmospheric black and brown carbon is an example of the “no-regrets” actions I have been advising that we should take. It is of value whether or not black carbon affects global climate.
And city dwellers are familiar with the phenomenon that when soot falls on snow, it absorbs sunlight, warms, and speeds the melting of the snow. In the country, people spread firewood ashes on frozen walkways to melt the ice. So black carbon tends to melt snow and ice, and thus reduce snow and ice albedo, and thus warms the climate. How much? Unknown, but estimates say black carbon is a definite factor in the Arctic warming.
However, there is one major misconception out there about the effect of black carbon on climate. It shows up in a recent editorial by Richard Kerr in Science magazine.
A Quick (Partial) Fix for an Ailing Atmosphere
Science 13 January 2012: , Vol. 335 no. 6065 p. 156 , DOI: 10.1126/science.335.6065.156
The world’s air could use a quick scrubbing. So a group of scientists has come up with 14 practicable approaches to doing just that. The researchers say the selected cleaning methods, described on page 183, would more than pay for themselves in lives saved and crop yields increased while cutting global warming to boot. “Technically, it can be done,” says atmospheric scientist Mark Jacobson of Stanford University in Palo Alto, California, who was not involved in the work. “It’s a question of will power.”
Scientists and policymakers alike have long known how, in principle, to get a quick start on cleaning up the atmosphere: Stop the gush of short-lived pollutants. Carbon dioxide will remain in the atmosphere for centuries, warming the world all the while, but pollutants like soot and methane remain airborne just a few weeks and a decade or so, respectively. Stop their emissions and their concentrations would promptly start dropping, sharply.
And that would be a good thing. Inhaled soot, also called black carbon, kills or debilitates millions of people each year, while soot in the atmosphere tends to warm climate, mainly by absorbing more sunlight.
It is the last statement, “soot in the atmosphere tends to warm climate, mainly by absorbing more sunlight”, that is in error. I can show this by means of a curious thought experiment, by taking black carbon to extremes.
The logic of their claim goes like this. The earth receives a global 24/7 average of 342 W/m2 at the top of the atmosphere. Of this, about 107 W/m2 is reflected back into space. Black carbon is very much like an ideal blackbody, it absorbs just about all of the light that hits it. The claim is that black carbon in the atmosphere absorbs the incoming solar radiation, so it cannot be reflected back to space. In addition, it also absorbs sunlight reflected from the ground and prevents it from escaping to space. So it intercepts and absorbs sunlight in both directions.
As a result, the system has to end up warmer than it is at present.
And to be fair, that all sounds eminently logical. We end up with more energy in the system, the atmosphere ends up warmer, because the black carbon is absorbing both more sunlight and more reflected sunlight. “Simple physics”, as the AGW folks are fond of saying.
So, here is the thought experiment. Suppose we have a planet just like the Earth, that receives a global 24/7 average of 342 W/m2 at the top of the atmosphere and reflects about 107 W/m2 back into space
We start adding black carbon to the atmosphere. We note that as Richard Kerr says, the black carbon absorbs more and more of both incoming (solar) and outgoing (reflected solar) radiation. Just as their logic says, there’s less and less energy reflected back into space.
We add more and more black carbon, slowly absorbing more and more sunlight and reflecting less and less sunlight. Finally we have added so much black carbon that it forms a shell of solid black carbon entirely surrounding the planet, say 20 kilometres above the surface. This shell is not reflecting anything at all, it is absorbing all the sunlight.
What happens to the temperature of the planet? This is the extreme case of black carbon in the atmosphere, and so it will tell us what the net effect is of adding black carbon to the atmosphere.
Well, we know that the shell has to radiate the same amount of energy that it receives, both inwards and outwards. Since the shell is the only thing heating the planet, that means the planet must be at the same temperature as the shell.
And what temperature would that be? Well, it would be the blackbody temperature sufficient to radiate 342 W/m2, which is … wait for it …
5.5°C or 42°F
This is well below the current temperature of the planet, which is usually taken to be about 14-15°C, or 58°F.
And this means that black carbon in the atmosphere cools the planet.
So where did the logic go wrong?
Their logic went wrong by not considering the effect of atmospheric black carbon on the poorly named planetary “greenhouse effect”. The greenhouse effect works because sunlight strikes the surface. When that energy is radiated back out towards space, some of the energy is absorbed by the atmosphere.
About half of that energy is radiated from the atmosphere back to earth, while the rest is radiated back to space. As a result, the earth ends up warmer than it would be without “greenhouse” gases in the atmosphere.
But when atmospheric black carbon absorbs the solar energy, only about half of the absorbed energy is radiated down to the surface, with the rest radiating upwards towards space.
And as a result, the surface only receives half the radiant energy from the sun that it would have gotten if the black carbon were not there.
In other words, atmospheric absorption of solar energy by any aerosols or molecules, including black carbon, reduces the efficiency of the greenhouse effect. Instead of the surface receiving energy from both the sun and the atmosphere, when black carbon intercepts the sunlight, the surface receives energy solely from the atmosphere.
For the greenhouse effect to work, the sun has to strike the surface. Any solar absorption in the atmosphere reduces the greenhouse effect, and in the extreme, total solar absorption in the atmosphere reduces the greenhouse effect to zero.
And as a result, as the thought experiment shows, adding black carbon (or anything that absorbs sunlight) to the atmosphere cools the planetary surface.
I cannot let this go by without expressing my displeasure at the use of bad science in pushing public policy. As Richard Kerr has just amply demonstrated, the understanding of climate even among scientists is still far too poor to serve as a base for any kind of policy decisions.
w.
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Joel Shore says:
February 9, 2012 at 9:28 am
Indeed, that is the question. I have shown that it doesn’t hold over the period of a day. If it doesn’t work over a day …
Ah. Sorry, I thought that couldn’t be your explanation.
As I have shown here and here, Joel, you don’t need a lapse rate to have a greenhouse. You don’t even need an atmosphere.
As a result, it is clear that the lapse rate is the result rather than the cause of the greenhouse effect.
Finally, you say that the cooling will start when “the atmosphere is no longer being warmed from below and cold from above”. But that process is not an either-or thing. What you are describing is the loss of efficiency of the greenhouse effect, and that cooling starts as soon as the carbon is added.
Either way, Joel, whether it will be more or less forcing, what he is saying is that you cannot use TOA forcing to estimate the warming.
No, Ramanathan doesn’t know that what is more important is TOA balance. That is just the oft-repeated assertion that ∆T = λ ∆F. You and Ramanathan keep trying to assume that, when it is what the AGW supporters have tried and failed to establish.
In addition, he doesn’t even know if the TOA balance from carbon is positive or negative, the errors are too large.
But I am overjoyed that you finally, after all these years, seem to be agreeing that the surface temperature is NOT a slavish function of the TOA forcing. Let me explain why.
According to Ramanathan, the changes from BC are an increased forcing of 2.6 W/m2 for the atmosphere, and a decreased forcing of 1.7 W/m2 for the surface, giving a net TOA forcing of 0.9 W/m2.
So lets suppose that a slightly different substance, I’ll call it “almost black carbon”, has almost the same effect as black carbon, except that it doesn’t warm the atmosphere quite as much. Suppose it only warms the atmosphere by 1.7 W/m2.
Now, that is a perfectly physically feasible and possible outcome … but that means that there won’t be your claimed TOA rebalancing, because there’s no change in TOA forcing. And that in turn means that
∆T ≠ λ ∆F
Ponder on that situation, my friend. Black carbon repartitions the energy between the surface and the atmosphere. But once you allow for the possibility of repartitioning, it means that surface temperature is decoupled from TOA forcing, and the canonical equation of the field is shown to be wrong.
I have shown evidence that clouds respond, not to black carbon, but to any change in temperature. The thing about the cloud governing mechanism is that its parameters are not set by the forcing. They are set by the surface temperature. I used to see this from my porch, looking out over the tropical Pacific ocean. As soon as a hot spot develops anywhere in my field of vision, a cloud pops up to cool it down.
It’s not run by the forcing. It doesn’t matter what is causing the warming, the slow warming of the sun over millions of years, the warming of the day, or the warming from black carbon. When the het spot develops, the clouds appear to cool it down. If just clouds aren’t enough, then thunderstorms develop and dump mega-tonnes of cold water to chill things out.
You know me, Joel, I’m always for intelligent thinking. The example of black carbon repartitioning of forcing between the surface and the atmosphere falsifies the claim that ∆T = λ ∆F. In other words, surface temperature is not simply a function of TOA forcing. What are your intelligent thoughts on that?
Again you are neglecting the effect of partitioning. Not all of the energy entering the tropics raises the surface temperature. Some merely passes through the system, from equator to poles, and is rejected at the cold end of the massive heat engine that is the climate.
The question is the partitioning. All of the energy, as you point out, has to leave the planet to maintain the overall TOA energy balance. But that requirement does not uniquely determine the surface temperature. It depends on how much of that energy is heating the surface and how much of the energy is just passing through.
One way to consider this is the idea of “greenhouse efficiency” or alternatively “greenhouse multiplier”. There are various ways to measure this, but it measures how much (in blackbody radiation terms) the system is able to jack the surface temperature above the expected theoretical S-B temperature. For simplicity, let’s use a multiplier calculated as (blackbody radiation from current temperature) divided by (Incoming solar after albedo). Incoming solar is after albedo is about 235 W/m2, and current surface temperature is about 390 W/m2, so the multiplier of the whole greenhouse system, dogs, cats, and all, is 390 / 235 = 1.66.
Now, as you might imagine there are a host of things that affect that multiplier. One is how much outgoing radiation is intercepted by the atmosphere. Another is how much incoming radiation is intercepted by the atmosphere. And of course, both of those can change on both short and long time scales.
And when that happens, as the black carbon example establishes, the surface temperature can change without the TOA forcing changing. When the greenhouse system gets less efficient, surface temperature drops and atmospheric temperature rises.
I believe I have demonstrated above that all three are significant.
My bad, reading too fast, read “conduction” in place of “convection”.
But you miss the point. The BC example shows that changes in internal distribution of the energy can occur on an ongoing basis with no change to the TOA radiation. It is not the be-all and end-all of the system.
The climate is a huge natural heat engine. It does a stupendous amount of work driving the circulation of the ocean and the atmosphere. Like any heat engine, it has a hot (tropics) and cold (poles) end. Like any heat engine, it does not utilize all of the energy passing through it, some merely goes through and is rejected at the cold end.
The oddity of natural heat engines is that they are always running as fast as they possibly can given the physical constraints. The are always adapting and changing to maximize the sum of throughput plus turbulence.
In the case of the climate, it is also a governed system, with the governor being the hourly and daily evolution of the clouds and thunderstorms. The clouds are a throttle, that regulates the incoming energy.
You AGW folks keep wanting to claim that changes in the operating temperature of this huge complex heat engine are a linear function of changes in forcing. But the forcing varies over a very wide range on an hourly, daily, monthly, yearly, and long term basis … and despite that, the operating temperature of the system changes very little. It’s not set by the forcing, Joel.
The operating temperature of a natural heat engine running as fast as it can (as all of them do) is set by the physics of wind and wave and temperature and cloud formation. It is not a function of forcing.
Off to work, gotta pound nails, take big pieces of wood, cut them into smaller pieces, and assemble them into a structure …
My very best to you,
w.
Willis Eschenbach says:
February 9, 2012 at 10:55 am
mkelly says:
February 9, 2012 at 7:56 am
Pertaining to the longwave IR thermal radiation would you show a radiative heat transfer equation using the surface and CO2, please? Assuming surface to be 255 K to start.
Sounds like you have some point you want to make. How about you just make it, and skip the Socratic questions? It might be faster, particularly since I have no clue what you are trying to get to.
Thanks,
w.
I ask for a radiative heat transfer equation straight up. That is the point. I have asked Joel Shore (you know Joel) he has declined. I have asked Mr. Connelly, I think you know him, also and he declined. I have asked a fair number of people on different sites for the equation and no one will show how radiation from atmosphere heats the surface via a standard radiative heat transfer equation.
Thanks in advance.
Willis Eschenbach says:
I’m not sure what this means. I don’t know how you would even try to measure the global climate forcing and resulting temperature change over the period of one day.
Yes, you do need a lapse rate to have a greenhouse. It is discussed very clearly in Ray Pierrehumbert’s book (p. 148 if I remember correctly). If the temperature of the radiating level is the same as the temperature of the surface, then there is no greenhouse effect. [And, of course, Nikolov and Zeller just rediscovered this by putting convection into the simple shell (or “steel”) greenhouse model in such a way that it (incorrectly) drives the two temperatures to be equal and not surprisingly found that the greenhouse effect went away.]
But, yes, you are correct that the lapse rate is also the result of the greenhouse effect. What happens is that the radiative greenhouse effect would alone set up a lapse rate that would even exceed the observed lapse rate; however, since lapse rates steeper than the adiabatic lapse rate are unstable to convection, convection occurs and lowers the lapse rate back down to the appropriate adiabatic lapse rate.
No…because the thing currently limiting the lapse rate is convection. If you start to warm the upper troposphere and cool the surface by radiative forcings, what will happen is not that the lapse rate will significantly decrease but rather that convection will decrease to compensate and the lapse rate will remain about the same.
Such decoupling cannot really occur because of the lapse rate in the troposphere being limited by convection. I am not claiming that there can’t be any variability with the nature of the forcing (as there are complexities such as having both moist and dry adiabatic lapse rates), but in general the coupling is pretty strong, much stronger than the coupling of the surface radiative forcing to the surface temperature. This is talked about very nicely in a calculation done by L. Danny Harvey in his book “Global Warming: The Hard Science”.
And, are you claiming that the phenomenon of heating of the surface sparking convection, leading to these clouds and thunderstorms, is not included in climate models? I find that hard to believe. I am certainly almost sure that it is included in numerical weather prediction models. I know that climate models are operating on coarser resolution but they still certainly are going to include this effect in some way.
So, again, you are predicting a significant change in lapse rate in a troposphere where the lapse rate is pretty much pegged to be near the adiabatic lapse rate by convection.
You are confusing different things here. The climate system has a large amount of thermal inertia (particularly due to the oceans, although even the atmospheric thermal inertia is significant on the diurnal time scale). So, forcings on shorter time scales tend to get damped out. However, that does not mean that this will happen to a forcing on very long time scales, i.e., low frequencies.
Hope the building went well.
Cheers,
Joel
mkelly says:
In my experience, what you’ve asked for are things that show that you don’t understand how radiative transfer works in the general case where radiation actually travels through a medium (as it does through an atmosphere) as opposed to simplified situations such as solids where all of the radiation is essentially either reflected or absorbed at the boundary. If you want to read about how such situations are dealt with, here is one starting point: http://en.wikipedia.org/wiki/Radiative_transfer A lot of this stuff goes beyond my expertise and way beyond what probably even anybody who has the expertise can explain to you in the simple soundbite that you seem to desire.
I don’t get all this malfeasance over a harmless bit of good old black gold.
Black coal on the ground doesn’t assume a different electromagnetic spectrum, by its composition, as the energy around it interacts with single atoms and molecules, its behaviour also depends on the amount of energy per quantum (photon) available.
Solid, liquid or gas, mass cannot retain more photons then the energy balance around it allows. Hence, Co2 cannot add heat by its composition to the atmosphere.
I thought is was akin to the universal nature of things. Now that there are other perspectives on how the climate works, the planetary harmonics, solar isolation, galactic energy flows, a complex coupled atmosphere/ocean system, are being seen in a new light.
Not to mention Nikolav & Zeller knockout, United Theory Of Climate hypotheses. A killer punch to AGW, if there ever was going to be one.
Who would think, the force of pressure was the enclosure regulating energy flow through the atmosphere? Seems better than having a roof over my head, there’s blue sky above now. I wonder if Baron Fourier owned a greenhouse?
———————————————————————————————————————
The pressure of the atmosphere and bodies of water, has the general effect to render the distribution of heat more uniform. In the ocean and in the lakes, the coldest particles, or rather those whose density is the greatest, are continually tending downwards, and the motion of heat depending on this cause is much more rapid than that which takes place in solid masses in consequence of their connecting power. The mathematical examination of this effect would require exact and numerous observations. These would enable us to understand how this internal motion prevents the internal heat of the globe from becoming sensible in deep waters.
General Remarks on the Temperature of the Terrestrial Globe and the Planetary Spaces; by Baron Fourier.
—————————————————————————————————————-
Joel Shore says:
February 9, 2012 at 6:13 pm
mkelly says:
I ask for a radiative heat transfer equation straight up. That is the point. I have asked Joel Shore (you know Joel) he has declined.
In my experience, what you’ve asked for are things that show that you don’t understand how radiative transfer works in the general case where radiation actually travels through a medium (as it does through an atmosphere) as opposed to simplified situations such as solids where all of the radiation is essentially either reflected or absorbed at the boundary. If you want to read about how such situations are dealt with, here is one starting point: http://en.wikipedia.org/wiki/Radiative_transfer A lot of this stuff goes beyond my expertise and way beyond what probably even anybody who has the expertise can explain to you in the simple soundbite that you seem to desire.
Joel you don’t pay attention to the things I have told you in the past. I have my old college heat transfer book and use it for light reading sometimes. I told you that I used it to get my estimate of CO2 emissivity at 1 atm and 288K. (Hottel charts) I asked you what you would use for emissivity of CO2 under the same conditions. You and others fail to answer but still accept that CO2 will transfer heat back to the surface. The emissivity of CO2 at these conditions is a critical component of the transfer equations.
No matter what the complexity of the issue it still comes down to two requirements for heat transfer 1. a path 2. a TEMPERATURE gradient. You seem to miss that point always. If T1 = T2 then Q is zero.
If you admit your expertise is short on this then say so and stop telling others they are wrong or don’t understand. As far as I know I have never stated anything not inline with the text book I learned from.
mkelly says:
As we have told you at least 50 times before, there is no such thing as an emissivity for a gas. You have to specify the amount of gas and you have to specify the EXACT wavelength to many significant figures to talk about such a thing…because the amount of absorption or emission you get from a gas depends on the optical thickness of the gas and the optical thickness depends on both the amount of gas and very sensitively on the wavelength since absorption / emission lines are typically very narrow.
Everybody understands it…but you seem to use that fact incorrectly to draw wrong conclusions.
mkelly says:
The difference between us is explained by the Dunning-Kruger Effect ( http://en.wikipedia.org/wiki/Dunning_kruger_effect ). I understand enough to know what I don’t know; you apparently do not.
Your 20km high carbon eggshell is not a good model for where soot is really found in the atmosphere, and as such the conclusions you draw are misguided at best. As Zeke has mentioned, soot is unlikely to enter the stratosphere (where your hypothetical eggshell resides). More than 50% of re-radiated energy from low soot will be trapped because there is something above it to absorb that energy.