Guest post by Ben Herman and Roger Pielke Sr.
We have received a further question on our post:“The Greenhouse Effect” by Ben Herman and Roger Pielke Sr.
The question is summarized by the following text
Anyway my question refers to the common example of taking away the atmosphere and observing a cold surface. But as I understand it, the mean daytime surface temperature on the moon is over 100 C, with no greenhouse effect. The mean nighttime temp drops to -150 C. http://www.solarviews.com/eng/moon.htm
This is important to note, because encouraging a popular picture in which the presence of the atmosphere only warms the surface takes all the convection and fluid dynamics out of the discussion, and that’s where all the important complexities are.
Isn’t it more the case that the atmosphere both warms and cools the surface, depending on circumstances? The IR absorption of H2O and other GHG’s warms the surface relative to what it would otherwise be, but as the lunar case shows, convection and turbulent mixing cools the surface relative to what would happen without an atmosphere. Take away the atmosphere and you take away both warming and cooling mechanisms.
We have reproduced the substance of our follow up answer below.
Predicting the surface temperature indeed involves the interaction of the atmospheric and ocean turbulent sensible and latent fluxes, long- and short- wave radiative fluxes and interfacial fluxes between the surface and the atmosphere. I have been urging for years to move away from the surface temperature to characterize global warming and cooling (and replace with ocean heat content changes in Joules) because the surface temperature is such a limited sample of the heat content changes of the climate system as well as involving these complicated feedbacks.
On the Moon, there is, of course, no atmosphere, so its surface temperature results from the difference between the surface long wave radiative emissions, the amount of solar radiation absorbed and reflected, and the conduction of heat into and out of the surface. The effect of the atmosphere on Earth is to mute the diurnal (and seasonal) temperature range as a result of the turbulent fluxes, and other effects (such as clouds and precipitation). These atmospheric effects, for example, result in lower daytime and higher nighttime temperatures from what they otherwise would be. I presume this is the cooling and warming effects that you refer to. However, even with these effects, the surface is clearly warmer than it would be without the CO2 and water vapor IR absorption bands.
But the reasons are that the atmosphere scatters back to space some sunlight, and takes up some of the surface heating through conduction, and mixes it it by convection and turbulence. Also, the relatively rapid rotation of the earth on its axis does not permit the daytime side to reach equilibrium before it starts nighttime cooling. As a result, daytime temperatures on earth are cooler than they would be with no atmosphere, and warmer at night than with no atmosphere.
Of course, the Moon, with no atmosphere, still has to have basically the same effective radiating temperature as does the Earth. This should be
[sigma *Tmd**4 + sigma* Tmn**4]/2 = sigma*Te**4 where Tmd is the daytime temperature of of the Moon, Tmn is the night time temperature of the Moon, and Te is the effective radiating temperature of the Earth.
The fact that the daytime time temperature is warmer than the Earth’s temp is simply a result of the fact that the Moon is not in an equilibrium state – it warms up during the daytime and cools down at night, just as does the Earth. However the warming during day and cooling at night must balance each other or the Moon ( and the Earth) would be steadily heating up or cooling down over time. The daytime warming occurs because the outgoing IR cannot balance the absorbed solar during the day. The nighttime cooling occurs because the outgoing IR is greater than the non-existing solar at night. The existence of a partially absorbing atmosphere does, as you stated, keep days cooler and nights warmer.
Also, the length of a day on the Moon is 29.5 earth days, almost a full Earth month. Therefore the daylight side of the Moon heats due to solar radiation, for half a month. Then when it’s night, it cools for another half month. Thus the daytime and nighttime temperatures are much more extreme. There is no greenhouse effect on the Moon, of course, and if the Moon’s day was the same 24 hours as an Earth day, its day and night temperatures would not vary as much but its radiative equilibrium temperature would be the same.
Update #2 John Nielsen-Gamon has alerted us to more information on the Moon’s radiative temperature. John e-mailed
I read your blog post on Greenhouse Part 2. I also recently came across the Science of Doom web site; it seems to be of very high quality. You might want to link to http://scienceofdoom.com/2010/06/03/lunar-madness-and-physics-basics/ [on] your post to direct the reader to further details on the radiative temperature of the Moon.
Update – corrected text (underlined) h/t to Gerald E. Quindry
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RE: Nick says:
July 29, 2010 at 3:21 pm
Theo:
Its mixing ratio (grams per kilogram of air) is constant throughout the atmosphere, except when you get beyond the stratosphere where that goes to hell. Hence why it is a “well-mixed gas”.
_____
Nick mat be very wrong. There is a detailed paper by the U.S.A.F. dated about the late 60’s that has measured the CO2 concentration vertically and it is not at a constant p.p.m.. As altitude increases the concentration of CO2 in the atmosphere decreases. I originally had expected CO2 to have settled mostly out soon after the top-of-troposphere but the decrease is not that marked, however, it is there and a great amount has settled due to CO2’s molar mass compared to the other components. I’ll try again to relocated that study and if successful will post it here. If I remember correctly, that paper showed a drop of something like 30-50 p.p.m. at that date up to about 80 km but that is just by memory and is not to be trusted 🙂 .
Maybe Nick will post his source paper of the data that he bases that conjecture on so we can compare results and sources.
RE: cal: (July 29, 2010 at 2:37 pm) “The height at which CO2 emits is already close to the tropopause which is the lowest temperature in the atmosphere.”
In the tropics, I believe, the tropopause is above about 90 percent of the atmosphere. I believe this must represent the altitude at which there is insufficient remaining clear-air dissolved water vapor [I make this unusual distinction because there are many people who mistakenly think the term ‘water vapor’ means fog] and CO2 in the upper atmosphere to prevent the escape of most the outward radiation emitted from these trace gases to outer space. As gaseous water is the primary earthshine spectrum-blocking/emitting agent in our atmosphere, I think the net mass of this component remaining in the upper atmosphere is most important factor determining the level of the tropopause.
Each gas has its own set of unique molecular vibration frequencies at which it will absorb or emit radiation. Thus any gas is the best blocker of its own radiation.
I note that Venus has two cold regions in its upper atmosphere. Perhaps the first of these is like the tropopause of the Earth where trace gases become too thin to block their own radiation going out and the second level, much higher, is where CO2, the primary gas, finally thins out to the point where its own unique radiation can escape to outer-space.
It may be that the lower tropopause levels of the Earth and Venus both indicate the altitude above which the trace gases become insignificantly thin and atmospheric heating is dominated by the absorption/emission spectra of the primary components of the atmosphere.
Wayne, thanks very much. I look forward to learning more.
Theo Goodwin:
Can’t seem to relocate that ~1970 paper on CO2 concentration with altitude yet but here are some very interesting papers from about a decade ago.
This one is in detail of co2 cooling and chemistry in upper atmosphere specifically in relation to solar sun spot cycle position (minimum or maximum) as the energy flux is sizeable and CO2’s role in the cooling and flexes greatly on the sun’s activity at the moment in shifting. Very deep analysis. Relies much on some of Jean Lean’s work. Will take some time to absorb.
Response of Ionosphere and Thermosphere to Extreme Solar Conditions
http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA425778
http://uap-www.nrl.navy.mil/uap/7641/publications/2001%20GRL%20Discovery.pdf
Still searching.
Theo Goodwin:
This is getting close, but this was Australia’s RAAF measurements in the early 70’s for nine years, not U.S.A.F. or possibly it was the Navy. The U.S. paper had a very similar table by altitude vs. CO2 ppm but in thousands of feet, not kilometers.
ATMOSPHERIC CO2 CONCENTRATIONS – THE CSIRO (AUSTRALIA)
MONITORING PROGRAM FROM AIRCRAFT FOR 1972-1981
at http://cdiac.ornl.gov/ftp/ndp007/, see .DOC and .PDF, data in .DAT
However, these measurements were all made within the convection mixing lower troposphere where you would expect the air to be well mixed. In the U.S. study it was the 40-60 thousand feet, maybe even 80,000 feet, were the readings showed the drop I mentioned. Anyone else good at digging through the search engines? It fell in my lap six month’s ago and now it’s in hiding, doesn’t that always happen! I give.
Theo:
This shows, ignoring the ~15 ppm variances, the randomly and evenly mixed distribution of CO2 per NASA in only two dimensions: 🙂
http://spacemath.gsfc.nasa.gov/weekly/NASA1.pdf
Nick Stokes writes
Simple way to think about it: increase CO2, increase the effective radiating level’s altitude. To remain in equilibrium, air at that altitude increases in temperature so it emits at the effective temperature. Assuming the lapse rate remains constant in this scenario, the surface will warm by the same amount. This is not really realistic, as the lapse rate will change, its sign depending upon how things like static stability and the water vapor feedback play out.
I think you have your physics wrong. If the temperature at that level increases the amount of energy radiated will increase. In order to maintain the earth’s energy balance the surface will have to cool. I also do not understand the basis for the assertion of your second sentence. To remain in equilibium with what? If the level where the tropopause starts is increasing as you say (my understanding is that the changes are small and disputed) the only way this can happen is for the temperature to continue to fall beyond the current circa 230K where it stops fallling before increasing – eventually to several thousand degrees in the thermosphere. Is there evidence of this? I would also be interested in your sources for what you state in your last sentence which, I have to admit, I do not understand.
The math for the lunar temperatures in a 29.5 day is rather simple. The lunar day at 29 1/2 days is about 708 hours.
At dawn, the moon is still cooling. Even though it may below 165 Kelvin, sunlight at a 90 degree angle gives effectively zero energy. It continues to cool for another 3 hours past dawn. It then warms continuously for the next 12 days, 6 hours, or until 5 days past noon. Peak heating in degrees Kelvin happens more than halfway through the morning, about 4 days 15 hours from dawn. I should heat up at slightly more than one degree Kelvin for about 78 consecutive hours, even though the peak heating should be only about 1.06 Kelvin per hour. After the peak, it cools through sunset and all night, or 17 days, 6 hours.
On Earth, high-low differences are typically 5-20 degrees Kelvin, with the higher numbers in mountains and deserts. Figuring 8-10 hours heating and 14-16 hours cooling, and saying 10 degrees Kelvin in 10 hours, Earth and Moon heat and cool at about the same rate when the Moon is close to the Earth’s temperature.
Thus, simple math indicates the hypothesis that the Moon heats faster than the Earth is incorrect. The Earth’s near-surface air can and does heat up faster when placed in a greenhouse, and about the same (factor of half to a factor of two) in typical weather.
Of course, ocean temperatures fluctuate less, due to specific heat, convection, clouds, evaporation and the fact that sunlight usually penetrates several meters in water.
Oh, and as it turns out, it is much more difficult to come up with a simple model for Earth’s daily temperature variations than I expected. The most common problem I had was getting the temperature at +24 hours to be equal to temperature at 0 hours, with actual temperatures and actual temperature ranges and using math and physics to calculate the changes. Most of my simple models predict less day-night difference than actually occurs, and that is without evaporation and infrared blocking. My hats off to the weather computation guys.
The temperature distribution on the lunar equator follows a Lambertian profile [ cos^1/4(x)] where x is the angle wrt local noon. Based on the Clementine mission (max ~380K, min ~200K).
BRIGHTNESS TEMPERATURES OF THE LUNAR SURFACE: THE CLEMENTINE LONG-WAVE INFRARED GLOBAL DATA SET. S. L. Lawson and B. M. Jakosky, Laboratory for Atmospheric and Space
Physics, University of Colorado, Boulder, CO 80309-0392 (lawson@argyre.colorado.edu).
A simple way of looking at the effect of the atmosphere, I believe, is to first picture the heating signal produced by the sun as something like a half-wave rectified AC signal — a positive half sine-waves. The Moon or the Earth without an atmosphere would respond to this signal with minimal filtering similar to a simple resistor-capacitor filter.
Adding the atmosphere to the Earth greatly increases the low-pass filtering, increases reflectivity, and provides a randomly acting, pulsed convective temperature-regulation system. That temperature regulation system, I believe, is dependent on the trace Earthshine absorbing/emitting (aka greenhouse) gases in the atmosphere with gaseous water being the most important of these.
That’s accurate but misleading. The day/night temparture swing is about 300K. The first 200K of heating and cooling happens very quickly – an almost vertical rise from shortly after sunrise and vertical fall shortly after sunset.
You can see it graphed here:
http://www.ilovemycarbondioxide.com/pdf/Greenhouse_Effect_on_the_Moon.pdf
Wayne,
Thanks so much. It looks very interesting. I have to go study now.
Re discussion of CO2 distribution, etc
1) Don’t have link but a recent satellite poduct shows considerable variation in concentration around the globe.
2) With a dispersed gas (molecule per 2600 atmo molecules) surely the targets for IR to ‘hit’ a CO2 m are comparatively few.
3) Of those that hit, half gets reradiated out to space anyway.
4) 3/4 of the radiation back boumces off the ocean and heads back up again to run the gauntlet back toward space.
5) If the CO2 is not uniformly distr. Then log relation between concentration and absorption would diminish the GHG effect per unit in areas of higher conc and greatly reduce it in areas of lean conc (by the inverse log effect).
I’d be happy to be corrected in my thinking.
Dave Springer says:
July 30, 2010 at 7:02 am
http://www.ilovemycarbondioxide.com/pdf/Greenhouse_Effect_on_the_Moon.pdf
____
That’s a good amount of information in that paper, especially in the list of references at the bottom (and they are all live and easy to access links). Thanks.
Theo Goodwin says:
You are confused by what is meant by the statement that CO2 is well-mixed in the atmosphere. What it means is not that the concentration is (approximately) the same in terms of, say, number of molecules per unit volume as you go up but rather that the concentration is the same in term of the fraction of the air molecules that are CO2 molecules.
In fact, oxygen is well-mixed in the atmosphere also. The reason that the concentration (in O2 molecules per unit volume) decreases as you go up is that the pressure decreases…i.e., the density of the air itself is decreasing; however, the proportion of air molecules that are O2 molecules stays about the same. [I just recently flew from Cusco, which is at 11000 feet, to Lima, which is close to sea level, and the empty plastic water bottle that I had was quite dramatically crushed by the change in pressure / density between those 2 altitudes.]
What generally determines whether a gas is well-mixed in the atmosphere or not is the rate at which it added or removed from the atmosphere due to sources and sinks relative to its total concentration (and, also to some degree, how uniformly those sources and sinks are distributed). While it is true that the oceans absorb and emit quite a bit of CO2, it is also true that there is quite a bit of CO2 in the atmosphere (in comparison to some other trace gases…I know 400 out of every million may not seem like that much). It is also true that the sources and sinks of CO2 are not too non-uniformly distributed. And, there are some detectable variations in CO2 concentrations across the globe (and presumably altitude-wise) too although they are relatively small…i.e., on the order of only a percent or two.
Gary Pearse says:
July 30, 2010 at 10:19 am
Re discussion of CO2 distribution, etc
1) Don’t have link but a recent satellite poduct shows considerable variation in concentration around the globe.
2) With a dispersed gas (molecule per 2600 atmo molecules) surely the targets for IR to ‘hit’ a CO2 m are comparatively few.
3) Of those that hit, half gets reradiated out to space anyway.
4) 3/4 of the radiation back boumces off the ocean and heads back up again to run the gauntlet back toward space.
5) If the CO2 is not uniformly distr. Then log relation between concentration and absorption would diminish the GHG effect per unit in areas of higher conc and greatly reduce it in areas of lean conc (by the inverse log effect).
I’d be happy to be corrected in my thinking.
Just as well, you’re wrong on all five points!
Indeed. To all who understand it it becomes apparent what role the atmosphere plays on the earth. It’s overwhelmingly important effect is giving us 14psi of pressure at the surface which raises the boiling point of water enough so that liquid water can exist on the surface.
The oceans cover 70% of the surface with an average depth of 4000 meters. This is far, far beyond the optical depth of the ocean and water has a tremendously high heat capacity in both sensible and latent form.
Tallbloke in another thread stated the consequence beautifully in the fewest words I’ve seen:
“The sun heats the oceans, the oceans heat the atmosphere, the atmosphere radiates it away into the deep cold of space.”
The atmosphere has almost inconsequential heat capacity compared to the ocean. It is a mere one thousandth of the heat capacity of the oceans.
Everything else is pretty much just minor details compared to the big picture summarized so well by tallbloke.
Gary Pearse says:
July 30, 2010 at 10:19 am
Re discussion of CO2 distribution, etc
1) Don’t have link but a recent satellite product shows considerable variation in concentration around the globe…..
_____________________________________________
The uniform CO2 distribution and the long (100 yr) residence time for CO2 in the atmosphere are two key points in the warming theory and therefore will be defended at all costs.
I find this experimental information interesting….
WHEAT: “The CO2 concentration at 2 m above the crop was found to be fairly constant during the daylight hours on single days or from day-to-day throughout the growing season ranging from about 310 to 320 p.p.m. Nocturnal values were more variable and were between 10 and 200 p.p.m. higher than the daytime values….”
“Plant photosynthetic activity can reduce the Co2 within the plant canopy to between 200 and 250 ppm… I observed a 50 ppm drop within a tomato plant canopy just a few minutes after direct sunlight at dawn entered a green house (Harper et al 1979)”
And then there is how the CO2 is measured at Mauna Loa… Talk about cherry picking!
“4. In keeping with the requirement that CO2 in background air should be steady, we apply a general “outlier rejection” step, in which we fit a curve to the preliminary daily means for each day calculated from the hours surviving step 1 and 2, and not including times with upslope winds. All hourly averages that are further than two standard deviations, calculated for every day, away from the fitted curve (“outliers”) are rejected. This step is iterated until no more rejections occur.”
If you want the other side of the story so you can weigh both sides check out this web site run by a couple of scientists. http://www.co2web.info/
clicking on the points will bring you to their well written scientific papers.
This particular pdf looking at the dogma and politics behind the 70 years of CO2 measurement as well as the science. It is a very interesting read. http://www.co2web.info/ESEF3VO2.pdf
“I know 400 [ppm CO2] out of every million may not seem like that much”
It actually isn’t that much. The major gases of the atmosphere are nitrogen, oxygen, and argon at 78%, 21% and 1% respectively. The exact numbers fall just a hair short of 100% for those three gases. What remains are trace gases.
One of the trace gases has to be the largest. It happens to be carbon dioxide at 0.04%.
While some of the trace gases have great biological impacts their macroeffects in climate regulation are as minimal as they seem to be.
Speaking of atmosphere composition the above are for completely dry air which just never happens in the troposphere. In the troposphere water vapor is not a trace gast and handily exceeds argon by a factor of three – about 100 times more of it than carbon dioxide.
It also has much wider long wave infrared absorption bands as compared to CO2.
A big fallacy I see repeated over and over by CO2 warmists is that when CO2 absorbs LWIR energy in its absorption bands it emits it in it absorption bands.
This is not how it works in a cold dense gas. When CO2 absorbs energy it its absorption bands it causes nearly instantaneous collision with another molecule, the vast majority of which are nitrogen, oxygen, and water vapor. The kinetic energy in the collisions is radiated in continous blackbody spectrum with the peak frequency determined by the sensible temperature of the gases.
Thus what happens as the ocean radiates in long wave infrared at night approximately 8% of the energy is absorbed by CO2. This absorption takes place very near the surface as the optical depth of CO2 to radiation in its absorption bands is a matter of hundreds of feet. If you look down at earth from space at night you won’t see any CO2 spectral (emissive) lines. You will see CO2 absorption lines.
The real travesty with anthropogenic CO2 warming is that more CO2 only increases the optical depth without adding any significant insulating effect. Because the optical depth is so short (hundreds of feet) the change makes little difference because convection effectively mixes air quite well over that short of a distance.
So while one can make a case that the first 100ppm in the atmosphere might raise the average temperature a degree or two (water vapor doing the lion’s share of the insulating work because there’s 100 times as much of it near the surface with similarly short optical depth, and much broader absorption bands that, adding insult to injury, overlap CO2’s absorption bands significantly) one cannot make a case that adding more changes the situation much. Except of course for biological imperatives… plant growth ceases between 100 and 150ppm CO2.
RE: Dave Springer says: (July 31, 2010 at 9:00 am) “One of the trace gases has to be the largest. It happens to be carbon dioxide at 0.04%”
I believe the concentration of invisible gaseous water (water ‘vapor’) usually clocks in somewhere from 3% to 4%. (Source: DOE, NETL FAQ.) This trace gas, I believe, is the primary Earthshine absorbing and emitting (greenhouse) gas in the atmosphere.
Dave Springer says:
There is more to the issues than just heat capacity. The atmosphere…or more precisely the infrared-active gases that make up only a small portion of the atmosphere…regulate the amount of radiation from the earth’s surface that escapes into space and thus play a very important role in climate.
The importance of increasing CO2 stems from its raising the effective radiating level. And, it is the wings of the absorption band that are less saturated that play the most important role.
Look, the amount of radiative forcing caused by an increase in CO2 is not controversial. It is around 3.8 W/m^2 (plus or minus maybe 10% at most). Roy Spencer agrees with this; Richard Lindzen agrees with this; I presume that Roger Pielke Sr. does too.
All your non-quantitative arguments here are just noise that does nothing to change that fact.
Dave Springer says:
July 31, 2010 at 9:28 am
Speaking of atmosphere composition the above are for completely dry air which just never happens in the troposphere. In the troposphere water vapor is not a trace gast and handily exceeds argon by a factor of three – about 100 times more of it than carbon dioxide.
There are plenty of places in the troposphere where this is not true.
It also has much wider long wave infrared absorption bands as compared to CO2.
Actually it doesn’t, it has a much sparser spectrum with larger gaps between the lines than in the case of CO2 (the cartoon spectra you often see on line don’t show this).
A big fallacy I see repeated over and over by CO2 warmists is that when CO2 absorbs LWIR energy in its absorption bands it emits it in it absorption bands.
This is not a fallacy it’s the way gas phase spectra are.
This is not how it works in a cold dense gas. When CO2 absorbs energy it its absorption bands it causes nearly instantaneous collision with another molecule, the vast majority of which are nitrogen, oxygen, and water vapor. The kinetic energy in the collisions is radiated in continous blackbody spectrum with the peak frequency determined by the sensible temperature of the gases.
The collision part is true but nitrogen, oxygen, and water vapor do not radiate as blackbody spectra.
Thus what happens as the ocean radiates in long wave infrared at night approximately 8% of the energy is absorbed by CO2. This absorption takes place very near the surface as the optical depth of CO2 to radiation in its absorption bands is a matter of hundreds of feet. If you look down at earth from space at night you won’t see any CO2 spectral (emissive) lines. You will see CO2 absorption lines.
Where on earth did you get this from, it’s also untrue.
The real travesty with anthropogenic CO2 warming is that more CO2 only increases the optical depth without adding any significant insulating effect. Because the optical depth is so short (hundreds of feet) the change makes little difference because convection effectively mixes air quite well over that short of a distance.
So while one can make a case that the first 100ppm in the atmosphere might raise the average temperature a degree or two (water vapor doing the lion’s share of the insulating work because there’s 100 times as much of it near the surface with similarly short optical depth, and much broader absorption bands that, adding insult to injury, overlap CO2′s absorption bands significantly) one cannot make a case that adding more changes the situation much. Except of course for biological imperatives… plant growth ceases between 100 and 150ppm CO2.
More errors, apart from the first sentence which was partially true the whole post was wrong.
Joel Shore writes:
“You are confused by what is meant by the statement that CO2 is well-mixed in the atmosphere. What it means is not that the concentration is (approximately) the same in terms of, say, number of molecules per unit volume as you go up but rather that the concentration is the same in term of the fraction of the air molecules that are CO2 molecules.”
Thanks for a clear, concise answer that is right to the point. Could you please write an introduction to AGW and post it here? 🙂
So, why do folks talk about it being “well mixed?” For me, “well mixed” is a Red Herring. What should interest climate scientists is where it is and at what concentration. If we are to know its effects, we have to know where it is. Something tells me that climate scientists have not been really keen on the empirical part of this work.