Guest Post by Willis Eschenbach
OK, a quick pop quiz. The average temperature of the planet is about 14°C (57°F). If the earth had no atmosphere, and if it were a blackbody at the same distance from the sun, how much cooler would it be than at present?
a) 33°C (59°F) cooler
b) 20°C (36°F) cooler
c) 8° C (15°F) cooler
The answer may come as a surprise. If the earth were a blackbody at its present distance from the sun, it would be only 8°C cooler than it is now. That is to say, the net gain from our entire complete system, including clouds, surface albedo, aerosols, evaporation losses, and all the rest, is only 8°C above blackbody no-atmosphere conditions.
Why is the temperature rise so small? Here’s a diagram of what is happening.
Figure 1. Global energy budget, adapted and expanded from Kiehl/Trenberth . Values are in Watts per square metre (W/m2). Note the top of atmosphere (TOA) emission of 147 W/m2. Tropopause is the altitude where temperature stops decreasing with altitude.
As you can see, the temperature doesn’t rise much because there are a variety of losses in the complete system. Some of the incoming solar radiation is absorbed by the atmosphere. Some is radiated into space through the “atmospheric window”. Some is lost through latent heat (evaporation/transpiration), and some is lost as sensible heat (conduction/convection). Finally, some of this loss is due to the surface albedo.
The surface reflects about 29 W/m2 back into space. This means that the surface albedo is about 0.15 (15% of the solar radiation hitting the ground is reflected by the surface back to space). So let’s take that into account. If the earth had no atmosphere and had an average albedo like the present earth of 0.15, it would be about 20°C cooler than it is at present.
This means that the warming due to the complete atmospheric system (greenhouse gases, clouds, aerosols, latent and sensible heat losses, and all the rest) is about 20°C over no-atmosphere earth albedo conditions.
Why is this important? Because it allows us to determine the overall net climate sensitivity of the entire system. Climate sensitivity is defined by the UN IPCC as “the climate system response to sustained radiative forcing.” It is measured as the change in temperature from a given change in TOA atmospheric forcing.
As is shown in the diagram above, the TOA radiation is about 150W/m2. This 150 W/m2 TOA radiation is responsible for the 20°C warming. So the net climate sensitivity is 20°C/150W-m2, or a temperature rise 0.13°C per W/m2. If we assume the UN IPCC canonical value of 3.7 W/m2 for a doubling of CO2, this would mean that a doubling of CO2 would lead to a temperature rise of about half a degree.
The UN IPCC Fourth Assessment Report gives a much higher value for climate sensitivity. They say it is from 2°C to 4.5°C for a CO2 doubling, or from four to nine times higher than what we see in the real climate system. Why is their number so much higher? Inter alia, the reasons are:
1. The climate models assume that there is a large positive feedback as the earth warms. This feedback has never been demonstrated, only assumed.
2. The climate models underestimate the increase in evaporation with temperature.
3. The climate models do not include the effect of thunderstorms, which act to cool the earth in a host of ways .
4. The climate models overestimate the effect of CO2. This is because they are tuned to a historical temperature record which contains a large UHI (urban heat island) component. Since the historical temperature rise is overestimated, the effect of CO2 is overestimated as well.
5. The sensitivity of the climate models depend on the assumed value of the aerosol forcing. This is not measured, but assumed. As in point 4 above, the assumed size depends on the historical record, which is contaminated by UHI. See Kiehl for a full discussion.
6. Wind increases with differential temperature. Increasing wind increases evaporation, ocean albedo, conductive/convective loss, ocean surface area, total evaporative area, and airborne dust and aerosols, all of which cool the system. But thunderstorm winds are not included in any of the models, and many models ignore one or more of the effects of wind.
Note that the climate sensitivity figure of half a degree per W/m2 is an average. It is not the equilibrium sensitivity. The equilibrium sensitivity has to be lower, since losses increase faster than TOA radiation. This is because both parasitic losses and albedo are temperature dependent, and rise faster than the increase in temperature:
a) Evaporation increases roughly exponentially with temperature, and linearly with wind speed.
b) Tropical cumulus clouds increase rapidly with increasing temperature, cutting down the incoming radiation.
c) Tropical thunderstorms also increase rapidly with increasing temperature, cooling the earth.
d) Sensible heat losses increase with the surface temperature.
e) Radiation losses increases proportional to the fourth power of temperature. This means that each additional degree of warming requires more and more input energy to achieve. To warm the earth from 13°C to 14°C requires 20% more energy than to warm it from minus 6°C (the current temperature less 20°C) to minus 5°C.
This means that as the temperature rises, each additional W/m2 added to the system will result in a smaller and smaller temperature increase. As a result, the equilibrium value of the climate sensitivity (as defined by the IPCC) is certain to be smaller, and likely to be much smaller, than the half a degree per CO2 doubling as calculated above.
Hmmm – Isn’t the moon pretty much earth without air? The temperature there is entirely radiative to surface dwellers (the few that have dwelt), and the soil temperature is dependent upon it’s exposure to the sun. In shadows it is damned cold – I’d wager colder than 40 something degrees.
I think your science on this is not robust, or my understanding of what you mean by black body located in our celestial toroid is flawed.
For a real chart showing thermal balance go look up figure 2.3 Principles of Atmospheric Physics and Chemistry. Goody 1996
The back radiation term is pure bs. It is tied in with the nonsense argument of the atmospheric reradiation of 1/2 up /1/2 down. Absolute rubish
Wiki Answer to: “What is the temperature on the moon?”
The average daytime temperature on the Moon is around 107°C (225°F), but can be as high as 123°C (253°F).
When an area rotates out of the sun, the “nighttime” temperature falls to an average of -153°C (-243°F).
253 F
-243 F
_______
10 F
Don’t know if that helps. 8 degrees is pretty close.
dp (20:46:32)
I’m not sure what your point is here. The moon experiences huge temperature swings because it rotates so slowly. As a result, the temperatures are very dependent on local topography. Recent results from the Diviner satellite show that there are areas on the moon which never see the sun, and are at a temperature of ~ 40K. None of these are true of the earth.
My calculations are based on a blackbody using the Stefan-Bolzmann equation. This equation allows us to convert between radiation intensity and temperature. If I have made a mistake in my calculations, please let me know.
enough (20:51:43)
Sorry, you have not given enough information for me to respond … plus you misspelled “rubbish”. If you post and link the figure you refer to, we can discuss it. In the interim, you might read the Kiehl/Trenberth paper referred to above.
I find this analysis be very important. Thanx
Willis, I think he is talking about a figure numbered 2.3 in this book:
http://www.amazon.com/Principles-Atmospheric-Physics-Chemistry-Richard/dp/0195093623
You can get it used for only $50.00!
Without an atmosphere there would be no oceans, ice, snow or plant life to affect albedo, so the albedo of the Earth should be more similar to that of the barren Moon. It would seem reasonable and logical to expect the high and low temperature variations on an atmosphere-less, barren, waterless Earth to more closely resemble those of the Moon. Am I missing something here?
“Lunar Surface Temperatures
Temperatures on the Lunar surface vary widely on location. Although beyond the first few centimeters of the regolith the temperature is a nearly constant -35 C (at a depth of 1 meter), the surface is influenced widely by the day-night cycle. The average temperature on the surface is about 40-45 C lower than it is just below the surface.
In the day, the temperature of the Moon averages 107 C, although it rises as high as 123 C. The night cools the surface to an average of -153 C, or -233 C in the permanently shaded south polar basin. A typical non-polar minimum temperature is -181 C (at the Apollo 15 site).
The Lunar temperature increases about 280 C from just before dawn to Lunar noon. Average temperature also changes about 6 C between aphelion and perihelion.
Marvin Ostrega
Reference: Heiken et al. Lunar Sourcebook: A User’s Guide to the Moon. Cambridge: University of Cambridge Press, 1991.”
Willis Eschenbach (21:04:42) :
My calculations are based on a blackbody using the Stefan-Bolzmann equation. This equation allows us to convert between radiation intensity and temperature.
I would have said 20C, not 8C…
The link about the manifold ways in which thunderstorms cool the earth appears not to be working. Pity – I really wanted to read it.
>>
In the interim, you might read the Kiehl/Trenberth paper referred to above.
<<
The link isn’t working (for me). Which paper? KT1997? Or the update, TFK2009? I made an infinite layer model and the back radiation doesn’t match KT1997, but it comes close. That 40 W/m^2 for the atmospheric window may be bogus. KT1997 doesn’t calculate it correctly. It may be 80 W/m^2 or 87 W/m^2, depending on how you define “cloudy.”
Jim
enough (20:51:43)
Ok, I found the Figure 2.3 you referenced:
Other than minor differences, my numbers agree with that figure. The difference is that your diagram only shows the net flows, while mine shows all flows. In other words, both are correct, and they don’t disagree with each other.
I don’t want this to devolve into an argument about the global energy budget. For my purposes, I’m only using two figures from the diagram, the TOA radiation and the surface albedo. Your diagram is not detailed enough to show either of those. So although it is interesting and correct as a diagram of net flows, it is not relevant to my calculations.
I keep reading a number of .05-.09C of CO2 warming and that may indeed be right.
less than .5C or a factor of TEN! decade vs century?
Thanks for the post, id bet is was a lot of work!
You will note that the closer we come to the TRUTH the more they attack, without sources, or logic.
Tim L
How of the incoming energy from the Sun is converted into atmospheric and oceanic convection?
None, according to Kielh and Trenberth.
Which is amazing.
Climate physics is a fascinating subject.
dp (20:46:32) : “Hmmm – Isn’t the moon pretty much earth without air? The temperature there is entirely radiative to surface dwellers (the few that have dwelt), and the soil temperature is dependent upon it’s [sic] exposure to the sun. In shadows it is damned cold – I’d wager colder than 40 something degrees.
“I think your science on this is not robust, or my understanding of what you mean by black body located in our celestial toroid is flawed.”
Your understanding is flawed across the board, and your prose is impenetrable. What do you mean by “radiative to surface dwellers?” Where did you come up with “our celestial toroid?”
A thing you’ve raised to ponder is does the moon radiate solar heat as fast as it absorbs it? Well, obviously yes, at some temperature it does, and necessarily into that part of the sky not filled with sunlight. (And I’m perfectly happy to accept regional variances in temperature owing to maria vs disrupted lunar surfaces.) As would an airless earth. Actually, so too would an atmospheric earth as Venus demonstrates.
Since we’re talking about energy balance here – clearly the moon is now radiating back to space as much energy as it receives after all these billions of years, there being no mechanism for storage and transport as there is on earth, the current energy level, the black body temperature of the moon, allowing for the rotational gradient, is it really that close to earth’s temperature which is moderated by atmospheric and oceanic energy distribution? My problem is I don’t see how black body temperature translates to an embracing thermal experience as provided to living things by the atmosphere and oceans.
If what you say is true it is really quite profound as it suggests our global temperature is a matter of albedo, no?
I think this first part is questionable. Nothing wrong with your division of 20/150 mathematically, just whether it means anything.
If you take a fixed albedo and increase the radiative forcing at the surface you can calculate the increase in temperature without feedbacks. You obviously know how to do this..
(For people who don’t, you can see more at The Earth’s Energy Budget – Part One and at the end of CO2 – An Insignificant Trace Gas – Part Seven )
So your calculation is basically saying that the response of the climate system from no atmosphere to current status is a linear model.
I know that of course, we can’t assume the same albedo. I see your comments on the various aspects of climate response, don’t know what to think about those yet.
Rightly or wrongly to assume no climate through to current climate is linear seems way way out there!
Perhaps you are aiming at a parody of GCMs producing a linear response?
I find their linear response hard to believe but perhaps you could say that if you look at one small part of a big curve, the slope is linear or can be approximated linear close to that area..
Jim Masterson (21:31:33)
Link fixed, thanks for alerting me.
w.
Great post, Willis.
Maybe I missed it, but it should also be stated that, as a new point number 7, the general circulation models are also woefully lacking in accounting for the multi-decadal oscillations of the oceans, including, but not limited to the PDO and the AMO, among many others.
But that point on the importance of cooling with tropical thunderstorms, poorly understood, can not be overemphasized!
Dr. Spencer and Lindzen and others are cracking that block….and so little is known. But you could not be more right. Thunderstorms…are magnificent (albeit ephemeral) players in the earth’s climate.
They boil in atomic-bomb-scale local and mesoscale fury…to heights up to the tropopause…and we wonder how they can bring down airlines (Brazil to France, last year).
Then they fade away in cirrus wisps the next day….all of that heat escaping through an open “window” in the atmosphere…
Thanks again for this post.
Chris
Norfolk, VA, USA
enough (20:51:43)
Bingo! Spot On.
Willis Eschenbach
It’s pretty late here and I would like to debate your so called diagram. So a couple of things now and more tomorrow. Backradiation as well as feedbacks are pseudoscience. There is no real physical basis for back radiation. As enough(my feelings exactly) stated it’s nonsense and simply not true.
The holy grail of the black/grey body is inadequate to analyse the earth’s weather and climate. Does the earth look like a black/grey body? The warmers have concocted a heady brew from this as the diagram shows. Forget Kiehl/Trenberth they are climate quacks. Take clouds for example, according to the diagram 76w/m2 is not only reflected by the clouds, but also by aerosols and the atmosphere. Really? How is the number 76 arrived at? Clouds most certainly absorb the suns energy. Where is the figure for that? Another thing, with clouds constantly forming and dissipating across the planet, is this an averaged figure for the entire surface? Are all the numbers in the diagram static and unchanging or subject to WIDE variations?
It all looks like an add up the numbers exercise. My BS detector goes off the charts whenever I look at that diagram. Its a mess. So please explain to me your understanding of backradiation and how it occurs and I’ll debunk it.
By the way, in your post at 21:04:42 you misspelled Boltzman. Pretty easy to leave a letter out, eh.
Let’s try it and find out. 🙂
scienceofdoom (22:09:37)
I make no assumption of linearity at all. What I’m doing is figuring the average sensitivity of the system as a whole. In fact, I point out that the equilibrium sensitivity is going to be different from the average sensitivity, and list some reasons why the equilibrium sensitivity will be smaller than the average.
Sometimes my birdfeeder has hawks circling above it looking for easy pray. One is them is Eschenbach’s hawk. a subspecies of Cooper’s hawk; both of which are far too uncommen
‘Sometimes my birdfeeder has hawks circling above it looking for easy pray. One is them is Eschenbach’s hawk. a subspecies of Cooper’s hawk; both of which are far too uncommen’
LOL – I have hawks visiting my feeders too at times.
Nature is a bummer for science.
The Moon is very different to Earth, which makes the simple comparisons of pundits above worthless.
1) It is 3,743 km in diameter versus earth’s 12,756 km;
2) Earth is over 1000 deg C at the top of the mantle, which is a mere 5km below the seabed in the deep ocean, & about 50km under the land surface.
3) Moon rotates once each 27 & a bit days, Earth rotates every 24 hours.
4) Earth has lots of volcanic activity, which brings heat to the surface. None has been detected on the Moon, yet.