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.
1DandyTroll says:
Because calculations show that the rate of heat transfer to the surface is simply too small to be significant. In particular, thermal conduction is a slow way to transfer heat. Here is a calculation (actually a nice problem for 1st year physics students) based on the typical geothermal gradient of 22 C per km and a typical thermal conductivity of granite rock of 3 W/(m*K). The result is a rate of heat flow of 0.066 W/m^2. ( http://en.wikipedia.org/wiki/Geothermal_gradient )
If you compare that to the 4 W/m^2 of radiative forcing one gets from doubling CO2 levels, you can see that this heat flow corresponds to about a 1% increase in CO2 levels. And, note that this is looking at the total value of the heat flow. Variations in this average value of the heat flow will be smaller still.
You say:
“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.”
==========
And as long as they think the Earth gets to be 33 degrees Celsius, or Kelvin, warmer than the 255 K the Sun can provide just because the surface gets back half the energy it emits –
I say: “the understanding of climate, especially among scientists, is going to stay too poor to serve as a base for any kind of policy-, or any other decisions.
Let’s not forget the effect black carbon has on glaciers in the Himalyas that was noted back when Glaciergate was in the news. For example, see
http://wattsupwiththat.com/2010/02/03/lbnl-on-himalayas-greenhouse-gases-alone-are-not-nearly-enough-to-be-responsible-for-the-snow-melt/
which opens with
Does the carbon shield have enough energy to heat the surface 20 Km below?
Heat rises ir doesn’t exactly sink unless the whole space becomes saturated, but then it would still be colder at the surface ‘an the top.
How about your thought experiment with the BC shell at 1m above the surface?
With the normal greenhouse effect operating mostly above the shell, I’ll bet the surface temperature is increased (due to the albedo change).
Willys say: “No, I haven’t forgotten that, Jan. It doesn’t happen. If the planet is warmer than the shell it will lose energy to the shell until they are in thermal equilibrium. The same will happen if it is cooler than the shell, it will warm until equilibrium.”
Well, have you thought about how that stream of energy from the warm part to the cold part will happen? Basically heat transfer can happen in three different ways, conduction, convection and radiation.
Since air is a very good insulator, we can eliminate the conduction part when we talk about long atmospheric distances since the effect would be negligible.
If I understand you thought experiment correctly, with the air so full of black carbon that all radiation is immediately absorbed, we can also eliminate the radiation element.
Then we only have the convection element back, i.e. the moving air. And then if you move a volume unit of air up to a lower pressure, the temperature falls according to the thermodynamic laws. This is causing the lapse rate effect with cooler air in the height.
This is all on the precondition that we have a real world condition with a turbulent atmosphere. You link to a thought experiment with a cylinder of non-moving gas. You are right that if you have such a perfectly insulated and air tight cylinder, the gas will not move, and the temperature will be equal all over. But it is hard to imagine that such non-moving air conditions can exist on a planet. The different energy input on day and night side is just one of the factors which will create an imbalance which again will make the air move and create a turbulent system.
@Steve Garcia
Did anyone claim that it was warmer where these glaciers are retreating? Remember Arctic ice in 2007? All that noise about AGW’s litmus proof? The air was not warmer, was it? It was warm water pushing in through the Bering Strait and the multi-year ice being blown past the northern tip of Greenland, drifting south and melting. Just because ice disappears is no proof of systemic warming. If people were not so bent on looking for confirmation bias, rational explanations would be easier to find.
Paul Kelly says:
February 8, 2012 at 5:01 am
Paul, you are correct that in your experiment you have “replaced the earth’s surface with a perfect black body”.
But we’re not talking about surface carbon. We’re talking atmospheric carbon. Up in the sky, you know, above our heads. Not replacing the surface.
Remember what both Ramanathan and I agree on. Atmospheric carbon warms the atmosphere, but it cools the surface. When the atmosphere absorbs absorbs a photon of solar radiation, the atmosphere warms but the greenhouse multiplier effect of that photon is lost forever, so the surface cools. There is a bit more energy in the system, due to lower albedo. However, it goes to the atmosphere, not the surface, because the greenhouse efficiency has decreased.
my best to you,
w.
Wasn’t this tested during the First Gulf War when Saddam set all the Kuwaiti oil wells on fire (not him personally and not all of them). Regardless, didn’t the models of the time (constructed to estimate the effect of GNW) predict a cooling effect and were they not proven wrong when nothing much really happened?
“peeke says:
February 8, 2012 at 12:11 pm
Incoming is visible light. Outgoing is IR. No mystics, nothing to do with Hansen either. The way you seem to think thermodynamics work refrigerators can’t exist.
peeke says:
February 8, 2012 at 11:58 am
Won’t BC function as condensation cores, and thus effectively increase rather then decrease the albedo of earth?”
—
Peeke, so putting all that together one would get cooling of atmosphere. By this mechanism;
Incoming Solar 100%
Reflected from surface 4%
” ” atmosphere 6%
reflected by clouds 20%
Absorbed by clouds and atmosphere 19%
Available at surface 51% 100%
Radiated to atmosphere from surface 21% Distribution of UWR
Radiated directly to space from atmosphere ( 6%) after themalisation.
radiation absorbed by atmosphere 15%)
Heat absorbed in clouds from surface 23%
Convection force of rising air 7%
Radiated directly to space from clouds & atmosphere 64%
Radiated directly to space from surface after
radiation absorbed by atmosphere 6% 100%
Increasing albedo would reduce force available to convection and heat absorption in clouds. Cooling.
Next.
This didn’t come out to well.
Radiated to atmosphere from surface 21%
Radiated directly to space from atmosphere (6%)
radiation absorbed by atmosphere (15%)
Distribution of UWR from surface.
Willis says:”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.
Could you be more specific as to the word “energy”?
Oh by the way peeke, it can also follow that mass extinction of megafauna and flora, can occur by rapid increase in albedo, upper atmospheric disturbances lost to space, and a decrease in pressure affecting biochemical absorptions to such a extent, whole biological systems failed and became unsurvivable in a completely different atmospheric pressure.
Volcano’s may have very well exterminated the dinosaurs but not by greenhouse.
Troposphere would cool initially whilst upper atmosphere would warm losing more mass to space. With a of gradual increase in Earths near surface temperature as pressure increases over times-scales. Just as is the geological record since the last glacial, with a couple of little joy rides in between.
Get ready for another joy ride as the Suns isolation, and planetary harmonics, cause a loss of atmosphere from recent climate anomalies.
Next.
Joel, good to hear from you.
Joel Shore says:
February 8, 2012 at 5:11 am
All you have done is repeat the crazy mantra that the surface temperature is determined by the TOA radiation and the TOA radiation alone. You can’t assume that, Joel, that’s what you are trying to prove, that the incredibly complex climate is perfectly linear in the form of
∆T = λ ∆F
and you have given us nothing to support the validity of your presumed equation. Nor, despite my requests, has anyone given me an example of a complex natural flow system where the operating conditions are a linear function of the inputs. A river is a good place to start.
In addition, even that claim doesn’t “explain the mechanism”. I say BC is cooling now, and it will be cooling no matter how much carbon you add. One mechanism
You say there will be a switchover. You say BC is warming now, but that at some point as the concentration increases it will cease to be warming and start cooling. That’s the part you haven’t explained. How and when does that happen?
I don’t believe that because of Occam. I believe it because I have produced a lot of evidence saying it’s so. I have shown, for example, that during an average tropical day, climate sensitivity is high in the morning, low around noon, and sometimes goes negative in the afternoons. If you think that is at all representable as an average, you’re not the scientist I believe you to be. Remember that the “narrow range” you are discussing goes from -80°C in Antarctica to 40°C in the deserts.
I don’t think it will be monotonic. I do think if you are proposing that the effect of adding carbon will be warming early and cooling late you need to explain how, where, and why the changeover will occur.
Man, talk about selective quoting, you should be up for some kind of prize. Ramanathan’s next sentence continues:
Ya think? He’s saying, you cannot ignore the reduction in greenhouse efficiency. He’s saying it “implies” that but we can’t simply do that. In fact, he shows exactly how that 0.9 W/m2 is split between the atmosphere and the surface.
Again with the “TOA determines the surface temperature” nonsense. Did you ever hear of clouds? You guys all claim that if there is a change in the TOA, the only thing that can re-balance the equation is increasing temperature. In fact, there are three other possibilities.
The first one is what we’ve just seen Ramanathan and I both explain independently. TOA radiation can go up while the surface radiation (and thus temperature) goes down.
The second is that clouds can decrease the amount of incoming energy. It only takes a trivial change in the clouds to completely counterbalance a doubling of CO2.
The third is that the system can increase the throughput, the amount of energy that is simply transported from the equator to the poles.
That’s three mechanisms, Joel. Three. Three mechanisms that decouple TOA forcing from surface temperature. So please, stop with the “TOA determines surface temperature” nonsense.
Finally, you imply I am ignoring conduction. What conduction do you think is relevant to this discussion, and how am I ignoring it?
Best regards,
w.
Here’s a link to a NOVA I saw that concluded the opposite of the study:
http://www.pbs.org/wgbh/nova/sun/
Philip T. Downman says:
February 8, 2012 at 5:51 am
The difference is that CO2 is transparent to visible light, where much of the solar energy is located.
Black carbon, on the other hand, intercepts the sunlight and prevents the greenhouse effect from occurring.
w.
Hu McCulloch says:
February 8, 2012 at 7:58 am
Hu, good to hear from you. However, in such a case there would be no adiabatic lapse rate. The planet would be at the same temperature as the shell, and the atmosphere would be isothermal. See the Jelbring thread.
w.
mkelly says:
February 8, 2012 at 3:56 pm
Not sure what you’re asking. It’s energy. It exists in various forms. In this discussion we’re talking about longwave (infrared) thermal radiation, as well as sensible heat.
w.
“‘Black carbon, on the other hand, intercepts the sunlight and prevents the greenhouse effect from occurring.””
Hi Willis, good to see you’re cutting them up here. No need to answer but, would it be insubordinate if I suggested that:
“”Black carbon, on the other hand, intercepts the sunlight and prevents the atmospheric illumination/enhancement effect””.
Markus Fitzhenry says:
February 8, 2012 at 6:18 pm
Thanks, Markus. It would definitely be incomprehensible to me if you suggested that, as I know of nothing called the “atmospheric illumination/enhancement effect”.
w.
“”Willis Eschenbach says:
February 8, 2012 at 7:58 pm Thanks, Markus. It would definitely be incomprehensible to me if you suggested that, as I know of nothing called the “atmospheric illumination/enhancement effect””.
Funny that, I still trying to get my head around the fact there is a greenhouse effect, if black coal cools.
@Markus Fitzhenry,
“Peeke, so putting all that together one would get cooling of atmosphere.”
That depends. A rise in CO2 levels of the atmosphere causes more heat to be trapped and more BC causes albedo to increase. What I wanted to say is that I think the albedo change may very well be far more important than any other effect.
“Next”
I am frightfully sorry if I don’t seem to understand this, but what do you mean by that?
Willis says: “Not sure what you’re asking. It’s energy. It exists in various forms. In this discussion we’re talking about longwave (infrared) thermal radiation, as well as sensible heat.”
w.
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.
Thank you for your prior response.
Willis Eschenbach says:
You can always linearize a function about a point if you look over a small enough range. The question then becomes what the range is over which the approximation that it is roughly linear holds.
Yes…I have explained it. You just aren’t listening to the explanation: I have said that as you increase black carbon, you increase the TOA radiative balance and hence you cause warming of the troposphere. That warming should translate to warming down at the surface provided that there is sufficient heating from below and cooling from above to maintain the lapse rate at the adiabatic lapse rate.
Where the switch from warming to cooling happens is when the black carbon shell gets so thick that the atmosphere is no longer being warmed from below and cold from above sufficiently to maintain the lapse rate at the adiabatic lapse rate.
Alas, your quoting is selective too. If you read the next sentence after that, he says: “For example, GCMs suggest that the reduction of sea ice and snow albedo by BC is three times as effective as CO2 forcing for global average surface warming.” So, no, he is not saying that the BCs are likely to cause surface cooling…He is in fact saying that they may warm the surface more dramatically than would be predicted by assuming the same sensitivity to forcing as for CO2.
No…Ramanathan does not say that. He does say that surface radiation goes down but he does not say that this leads to a lower surface temperature because he knows that what is more important is the TOA energy balance (or, to put it another way, that a decrease in convection can compensate for a decrease in surface radiation).
Well, if you want to make the claim that clouds do counterbalance things in the case of black carbon, then it would be helpful to show some evidence for this. However, I would also note that your thought experiment didn’t include changes in clouds either (although I suppose clouds may be irrelevant in the sort of bizarre extreme that you went to where the carbon extends to above the clouds, completely blocking out the radiation from getting down to the clouds). At any rate, I don’t see why we should consider your thought experiment of taking the atmosphere to a ridiculous extreme as more definitive in determining the effect of black carbon in the current climate than we should consider intelligent thinking about the effect of black carbon on the TOA radiative balance.
That is not relevant to the global energy balance at the top-of-the-atmosphere. You would still have BC causing a radiative imbalance that has to be compensated by warming.
…Only one of which could even plausibly cause a decoupling significant enough to be important, and very doubtful that any of them will change the sign from warming to cooling.
Convection, not conduction. You are so focused on the surface radiative balance that you are ignoring the fact that changes in the radiative balance between the surface and the troposphere can easily be counteracted by changes in convection. That is why what is important at the end of the day is the top-of-the-atmosphere radiative balance, at least as long as you are in the regime where the heating and cooling distribution is sufficient to spark convection in the troposphere.
mkelly says:
February 9, 2012 at 7:56 am
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.