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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A veritable “Edison Cage” for energy as it were. The solution to the freshman physics E&M homework of what is the electric field inside the ball given that the electric field outside the ball is X. The answer of course is zero, which incidentally implies zero net energy transport within the sphere.
“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.”
EXACTLY.
Willis,
well said and dead on. Thanks!
After we fix the soot in the arctic issue, we could move on to Saharan dust. It’s one of the confounding issues in forecasting Atlantic hurricanes – when dust is blowing off the African coast, it absorbs sunlight and warms the atmosphere. Also, the reduction in sunlight reduces the oceanic warming, so sea surface temps rise more slowly than without dusty weather.
The result is reduced convection and reduced tropical storm formation. While it is not responsible for the decline in tropical storm activity over the last few decades, we might be able to bring TS activity back to normal by taking better care of the eastern Atlantic! 🙂
Note – see smiley face? I’m just kidding. We don’t need to baby our hurricanes.
Willis, is there any recourse here? How about submitting a dissertation to ‘Science’ explaining just what you did here and ask them, ‘What gives’? This is basic stuff.
While “black carbon” may well have the radiative absorption described, it is my understanding that airborne particulate matter – aerosols – have a net cooling effect on the surface by reducing the amount of solar reaching the ground … hence why volcanic eruptions cause net cooling
I would also think the airborne “black carbon” – while it may well be a good “black body” from an absorption standpoint, also still has to exist in its environment – and that environment is inherently cold – so while black carbon may absorb the energy, it is unable to store it as the battle between thermal masses – pitting airborne particulate, even when warmed by solar, against the vastness of the atmosphere, is no contest, and any warmth absorbed would seem to be quickly sucked away and diluted by the atmosphere
This is completely incorrect. The important flux is the one at the tropopause and any extra absorption by BC below the tropopause is basically equivalent to lowering the surface albedo. So, yes, black carbon does warm the system.
Note too that ‘brown carbon’ is something completely different (volatile organics), not soot.
When will the “average” madness cease – it is simply wrong to say the Earth receives 342 W/sq m average 24/7.
This simply lets the AGW crowd get away with their claims.
The atmosphere provides a protection from the intense solar radiation, convection in the atmosphere and evaporation from the ocean act as an “air-conditioner” removing the heat from the surface to the upper atmosphere and preventing the Earth from ever reaching the blackbody temperature that the solar constant or 70% of it or even 51 % ( as the FPCC claim heats the surface ) is capable.
51 % of the solar constant ~698 W/sw m – is associated with a temperature of ~333 K or 60 degrees C.
This has never been measured as air temperature on Earth though 50 degrees C is probably a believable result.
Given the IPCC state ~20% is absorbed by the atmosphere on the way in the temperature should be even higher – and we can artificially raise the temperature locally by preventing convective cooling such as in a glasshouse or your car.
The atmosphere keeps the surface temperature down during the day.
When the strong convection effects cease at night radiative cooling slowly lowers the surface temperature – at a slower rate and if the site of interest is close to the ocean the cooling is moderated even more.
I am undecided if I even believe CO2 can increase the Earth’s atmospheric or surface temperature because every quantu of radiation emitted results in a lower energy state for the emitter. During the day convection is removing heated air from the surface much more than the radiative effect.
I am still of the mind that backradiation is an example of perpetual motion because there seems to be no account for the fact that emission of radiation results in a decrease in the energy state of GHG molecules – but I could be wrong.
Simpler experiment requiring no thought, just a fact:
Mt. Tambora. 1816. Soot all over the world.
Coldest year in the historical era of measurement.
“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. ”
Wrong, right, and wrong. Soot is short-lived, but so are CO2 and methane, which have half-lives of 5-7 years, not the 200-1000 years the IPCC and NASA would like to claim. The annual rise and fall of CO2 in the Mauna Loa data bespeaks the high turnover of CO2. So, they are all short-lived and, once again, the climate “scientists” are lying to the people as well as other scientists.
CO2 and water vapor are only greenhouse gases according to the climate science definition. Actually, as these gases can absorb IR and convert it to heat, they can just as well do the reverse and other molecules are perfectly able to hand them heat energy. So, during the day they might add a bit of energy, but during the night they act as IR leaks, bleeding IR to space. It’s like having many small holes in the greenhouse glass ceiling. During the day, they will hardly make a difference, but during the night, the cooling will be noticeable.
Nitrogen and oxygen gases are the real greenhouse gases, as they are heated by conduction from the Earth’s warmed surfaces and, once heated, have no way to lose the heat besides convection or passing it off to CO2 and water vapor. Near the surface, it’s a safe bet that the main flow is heat energy to IR and NOT the IR to heat that everybody appears to fear.
As climate models do not appear to have a night time, it’s also a safe bet that the one way outward flow of energy is not in the energy budget. Another FAIL!
Ashes on the sidewalk melt snow for the same reason that calcium chloride on the sidewalk melts snow: the ionic solutes in the ash lower the freezing point of the snow.
Willis: It is fine to go to extremes and see what happens but one should not necessarily fool oneself into believing you can predict all points in between. So, even if you are right about the extreme case, it may be that in the current climate state an increase in black carbon would have a net warming effect.
And, as Neil points out (by looking at the top-of-the-atmosphere radiation balance), there is good reason to believe that in fact it would. Your arguments might hold once the absorption profile got so extreme that the lapse rate was no longer limited by convection. But, right now, the lapse rate in the troposphere is limited by convection…And so, if you add black carbon in the troposphere and increase the absorption in the top-of-the-atmosphere radiation balance, then that would cause the temperature in the atmosphere to increase and then increase will propagate down to the surface via the lapse rate. (Adding black carbon to the statosphere is different…That may well have a cooling effect on the surface.)
Our ancestors lived around fires in caves for hundreds of thousands of years. Ventilation was very primitive, if existed at all. Undoubtedly, they have been breathing in a lot of soot (“brown” or “black” — this doesn’t matter). Too much soot (as well as too much of anything) is bad for health, of course. But I think that its effect on our health is exaggerated, as are many things these days. Scaremongering is as widespread in modern health care as it is in “climate science.”
Footnote: this comment is for WUTW readers in general, not for Mr. Eschenbach personally. I am not interested in Mr. Eschenbach’s opinion, and will not respond to him unless he apologizes abjectly and publicly for his foul personal attacks on his critics, for his cowardly censorship, and for blatantly breaking the rules of this forum.
“Neil says…”
Huh? The carbon is high in the atmosphere – the atmosphere has a strong absorption gradient due the temperature dependence of the water vapor saturation point. Once you get to the top of the troposphere the radiation is much more likely to radiate out than in because of the gradient and the geometry. Any energy absorbed at the top of the troposphere is essentially radiated back to space. I could integrate a one dimension model to prove this (or a three dimension model if you really want accuracy) for say a point at the 10000 m altitude to prove this.
What is Mr Feht talking about? Did I miss something?
Wood ashes are best used on the driveway, the grit gives extra traction. Never use on the walkway as it gets tracked into the house. Soon to dry, and airborne ash and soot it becomes. GK
Simple way to think about it: the greenhouse effect is because there is an “in” window (visible wavelengths) and an “out” window (microwave), and CO2 blocks the out but not the in, letting heat build up. Soot in the air blocks the “in” window.
Interesting thought experiment, and I’ll have to do a bit more thinking about it.
A few things off the top:
1) The effects of black carbon on melting snow and ice are particularly strong, and so of course, at lower levels of black carbon (where sunlight can still penetrate to the ground) we get an amplified effect in Arctic areas from a little bit of black carbon being around. The notion of taking an extreme case of creating a solid shell of black carbon surrounding the planet doesn’t prove anything. The effect of black carbon at the extreme might be non-linear, such that a shell of black carbon that was 95% opaque to sunlight might be completely different that one that was 99% or 100% (i.e. would could get net warming up to 95%) and then the effect is essentially flat from 95 to 99%, and then reverses dramatically from 99 to 100% to a cooling effect.
2) I’m am wondering about the internal heat generated by the Earth if there is an external shell of black carbon 20 Km up in the atmosphere? Over time, this internal heat would warm up the Earth under the black carbon, as no heat would flow from the cooler Earth to the black carbon shell until such time as the Earth under the shell was warmer. Thus, even if the geothermal energy released by the Earth under the black carbon shell was only .1 w/m2, it would not flow to the much warmer black carbon shell, and would just be trapped, and over millions of years, the atmosphere and surface under the shell would get warmer and warmer, until some equilibrium was reached with the black carbon shell. This highlights the difference between a geothermally active planet like Earth versus a simple dead rock in space. The Earth has significant “body heat”, with a 5000C to 7000C interior or core temperature, and the black carbon shell would trap that heat bubbling up from that 5000C, until such time as the surface and atmosphere under the black carbon shell reached the same temperature or higher as the black carbon shell.
The result: The estimate of 5.5C surface temperature is probably off.
higley7 says:
February 7, 2012 at 6:30 pm
CO2 and water vapor are only greenhouse gases according to the climate science definition. Actually, as these gases can absorb IR and convert it to heat, they can just as well do the reverse and other molecules are perfectly able to hand them heat energy. So, during the day they might add a bit of energy, but during the night they act as IR leaks, bleeding IR to space.
______
Interesting notion, but seems to go against observations. The warmest nights in the Arctic (without the passage of a warm front) are ones with a low stratus cloud deck . Thus, if you took two nights identical in every regard except for the amount of cloud cover, the clear sky night would be cooler than then cloudy night. The clouds trap LW and radiate it back toward the ground. Not seeing how this is acting like an IR “leak” to space.
Interestingly enough, extremely black carbon is also extremely heavy carbon, at least as far as gasses go, which means that its extremely unlikely to escape the troposphere. As has been already mentioned, black carbon below the tropopause effectively decreases the surface albedo, as it absorbs incoming solar radiation that is re-emitted as long-wave and interacts with greenhouse gases in the tropopause similar to surface radiation.
Generally, when you have a bright idea that makes smart folks like Ramanathan look stupid, its bears stepping back and thinking it through, as one of you is going to be wrong.
“”J Storrs Hall says:
February 7, 2012 at 7:12 pm
Simple way to think about it: the greenhouse effect is because there is an “in” window (visible wavelengths) and an “out” window (microwave), and CO2 blocks the out but not the in, letting heat build up. Soot in the air blocks the “in” window””
That’s too simple, in widows and out widows? the whole of atmosphere is a opened window, the pressure inside is greater than outside.
How can co2 turn it’s back on incoming but catch the outgoing? Hansen mystics at work, no doubt.
Willis
Black carbon (soot particles) don’t float around very long – they’re heavy! And not gases. They tend to fall to the surface, darkening it. They are on the surface…
“And this means that black carbon in the atmosphere cools the planet”
Um, NO it does not.. It reduces the 0.3 albedo (in visible wavelengths, energy reflected from the sun) of the planet, meaning more energy into the climate to be radiated as IR, which means higher temperatures to radiate that energy out. That’s about as basic as the science gets.
Regardless of your GHG issues, cleaning soot out of the atmosphere is a good idea just from reducing lung disease. Simple, relatively cheap – and the GHG effects are simply a combined bonus.
“R gates says;
The warmest nights in the Arctic (without the passage of a warm front) are ones with a low stratus cloud deck . Thus, if you took two nights identical in every regard except for the amount of cloud cover, the clear sky night would be cooler than then cloudy night.”
Bit of a shame that thermodynamics comes along a blows a wind over snow-cover at night, totally obliterating your fairy tale of identical nights. Oh that’s right, the models don’t give much credence to things like thermos, so reality can’t be right, R gates only argues partially.
I’ve spoken to you about that before Mr R gates, now you are trying my patience.
Tell me please R gates, does near surface barometric pressure increase or decrease during cloud formation? Work it out as a conundrum against Co2 radiative forcing.
I have to agree with Joel and Neil here. The thought experiment seems a bit contrived. I don’t know that the assumption of a solid sphere of carbon at 20km is valid. Perhaps it is. However, it may be more appropriate to have the sphere at 2km with much of the atmosphere still above it. That would have the effect of lowering the Earth’s albedo and raising temperature. It seems that the location of the carbon is critical to determine its net effect.
I can also produce another thought experiment that leaves the Earth’s temperature completely independent of the shell’s temp. Imagine I coat the Earth with perfectly reflective paint, lowering its emissivity to zero. Then I have effectively removed it from the radiative universe, and it’s temperature as measured by direct contact will be totally independent of what’s happening in the carbon shell presuming there is no conduction/convection to transfer heat between the two. I don’t think this is a valid or useful state but it does show a danger of taking a thought experiment to an extreme.