Guest Post by Willis Eschenbach
Today I came across an IPCC figure (AR4 Working Group 1 Chapter 2, PDF, p. 208) that I hadn’t noticed before. I’m interested in the forcings and responses of the climate models. This one showed the forcings, both at the surface and at the top-of-atmosphere (TOA), from the Japanese MIROC climate model hindcast of the 20th century climate.
Now, do you notice some oddities in these two figures? Here’s what caught my eye.
The first oddity I noticed was that the surface forcing from the long-lived greenhouse gases (LLGHG) was so small compared to the top-of-atmosphere LLGHG radiative forcing. At the end of the record, the TOA forcing from LLGHG was just over two watts per square metre (W m-2). The surface forcing from LLGHG, on the other hand, was only about 0.45 W m-2. I don’t understand that.
This inspired me to actually digitize and measure the surface vs TOA radiation for a few of the components. For each W m-2 of TOA radiative forcing from a given source, the corresponding surface forcing was as follows:
Aerosol Direct: up to 15 W m-2 (variable)
Land Use: 1.5 W m-2
Volcanic Eruptions: 0.76 W m-2
Solar: 0.72 W m-2
Cloud Albedo: 0.67 W m-2
LLGHG: 0.21 W m-2
With the exception of the Aerosol Direct these relationships were stable throughout the record.
I have no idea why in their model e.g. one W m-2 of TOA solar forcing has more than three times the effect on the surface as one watt of TOA greenhouse gas forcing. All suggestions welcome.
The next oddity was that the sum of the radiative forcings for “LLGHG+Ozone+Aerosols+LandUse” is positive, about 1.4 W m-2. The surface forcing for the same combination, on the other hand, was strongly negative, at about -1.4 W/m2. The difference seems to be in the Aerosol Direct figures. It seems they are saying the aerosols make little difference to the TOA forcings but a large difference to the surface forcings … which seems possible, but if so, why would “Land Use” not show the same discrepancy between surface and TOA forcing? Wouldn’t a change in land use change the surface forcing more than the TOA forcing? But we don’t see that in the record.
In addition, the TOA Aerosol Direct radiative forcing changes very little during the period 1950-2000, while the corresponding surface forcing changes greatly. How can one change and not the other?
The next (although perhaps not the last) oddity was that the total surface forcing (excepting the sporadic volcanic contribution) generally decreased 1850-2000, with the total forcing (including volcanic) at the end of the period being -1.3 W m2, and the total forcing in 1950 being -0.6 W m-2 … why would the total surface forcing decrease over the period during which the temperature was generally rising? I thought perhaps the sign of the forcing for the surface was the reverse of that for the TOA forcings, but a quick examination of the corresponding volcanic forcings shows that the signs are the same. So the mystery persists.
In any case, those are the strangenesses that I found. Anyone with ideas about why any of those oddities are there is welcome to present them. What am I missing here? There’s some part of this I’m not getting.
In puzzlement,
w.
PS – I’m in total confusion regarding the albedo forcings that go all the way back to 1850 … if I were a suspicious man, I might think they just picked numbers to make their output match the historical record. Do we have the slightest scrap of evidence that the albedo changed in that manner during that time? Because I know of none.
PPS – Does anyone know of an online source for the surface and TOA forcing data in those figures?
LazyTeenager says:
June 5, 2011 at 8:01 am
—-
The ice, being a pretty good insulator, will always be somewhere between the temperature of the air and the temperature of the water. When artic air gets down to -50F, what temperature do you think the ice and the water get to?
“Considering Cloud cover has decreased by 4% during the satellite period resulting in a large 0.9w/m2 positive forcing it seems strange to me that the model shows the cloud albedo having a very constant decline over the century resulting in a negative 0.6w/m2
”
Does anyone happen to have the references for this?
I saw one reference that showed a lowering forcing from albedo in the last 20 years, but it was just whether it was increasing or decreasing and to tell the truth this would fit that graph – (kind of). But that in itself would be huge and would add to my source material greatly.
To explain what this means….
If you combine this with the forcing from LLGHG…
You get 1.4 (LLGHG by itself) W/m2
– 0.9 W/m2
=
0.5 W/M2 which is very small in comparison to say what is shown here.
And if you subtract out the assumed negative there…
you get -0.1 W/M2 for long-lived GHG.
Of course, this would seem to show that its possible that the CO2 is completely over-run with negative feed-backs that actually make CO2 make the planet cooler. (from just cloud impacts.)
Of course, this does not include the rest of stuff such as aerosols, etc, but the point still remains that this is a very large issue to say the least. And I tend to agree with the assessment that there is no way we know what the clouds were like in say 1850. That initial point is just simply put a guess that may not even be educated in the least. The conclusion obviously is that no one still knows what clouds do, and without that information the models are still worthless and no matter how fast of computers we use, they will still be worthless until we figure out the mechanisms for clouding.
But then again, I think we all have been saying this as sceptics for years…the cloud cover issues have not been taken into consideration with the models and therefore as such fine-tuning the CO2 effects is nearly impossible without knowing what drives cloud formation in the first place.
I still have no idea myself what the actual effect of additional CO2 is. But I am willing to bet its a very small part of the energy equation compared to say solar or cloud cover. And I am also not willing to bet the economy on terrible ideas for energy. Small steps are fine, such as better efficiency…but huge steps such as wind boondangles…screw that.
Willis: Try this 1981 Ramanathan paper. The role of ocean-atmosphere interactions in the C02 climate problem. V Ramanathan – J. Atmos. Sci, 918 (1981) http://www.cfa.harvard.edu/~wsoon/ChristopherMonckton08-d/Ramanathan81.pdf
See Figure 2 for the change in radiative forcing for 2X CO2 with height. The overlap between the absorption of water vapor and carbon dioxide becomes more important lower in the atmosphere. At wavelengths where water vapor absorbs 9 out of 10 photons emitted by the surface, doubling CO2 produces only a small change in outgoing radiation.
If you double the concentration of an absorber like CO2, how much can that reduce transmission? If 98% of the photons are already being absorbed at a particular wavelength, doubling the absorber will increase absorption to 99%. If 1% of the photons are being absorbed, doubling the absorber will increase this to 2%. Neither of these changes produces a big decrease in transmitted energy. If 50% of the photons are being absorbed at a wavelength, doubling the absorber will increase absorption to 75% and reduce transmission by 25%. The biggest change in radiative forcing upon doubling CO2 occurs at wavelengths where about half of the photons are able to escape to space. scienceofdoom.com/2011/03/12/understanding-atmospheric-radiation-and-the-“greenhouse”-effect-–-part-nine/ especially comment 1.
Also see: judithcurry.com/2010/12/11/co2-no-feedback-sensitivity/
<LazyTeenager says June 5, 2011 at 8:01 am
JerOme reckons
__________
itself, which is pretty much always warmer than the ice,
__________
and what do you think the temperature of the water under the ice is Jerome?
I bet you, based on some well known physics, that it’s the same temperature as the ice.”
Is that the well known physics that ice exists because it is colder than water?
Obviously if the water were as cold as the ice it would be ice, the ocean would be frozen to the bottom.
Obviously open water is warmer than ice, otherwise it would be ice (on the surface).
Lazy indeed! (Recommended study: high school physics.)
There seems to be much confusion over the term “Radiative Forcing” (RF). It is defined at http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-2.html . It has nothing to do with absorption of photons from the surface. It also has nothing to do with the Top Of The Atmosphere (TOA). To paraphrase, it is the imbalance at the TROPOPAUSE resulting from changes in emissions from the atmosphere to space.
I have a lot of problems with this. Firstly, the Tropopause is a very variable beastie. In Polar Latitudes it’s altitude is about 8.5km. At 40Deg Latitude it is around 11km. In the 30N to 30S region it is about 17km. The significance of this is that in Polar latitudes, over 30% of the atmosphere is above the tropopause, and over 20% of the atmosphere is above the Tropopause outside the 30N to 30S region, within which 10% of the atmosphere lies above the Tropopause.
A photon emitted by a CO2 molecule has to evade the overlying CO2 molecules to successfully escape to Space. We know that at the Surface, 50% of photons will be absorbed within 1m, 25m and 50m for wavenumbers 670, 650 and 700 respectively. I’m not sure where that translates to in the upper atmosphere, but I would think it to be well above the Tropopause. And a doubling of the gas concentration simply moves the emission height further out. In the stratosphere, where higher = warmer.
I think all this means:
1. I am uncertain that the change in stratospheric temperatures has been correctly calculated. It would be nice to take a dekko at the back of the envelope.
2. The variability in height of the Tropopause means that the “Radiative Forcing” is highly latitude dependant. It will be much, much greater in the equatorial band , and negligible, if not negative, in the high latitudes. It would be nice to see the calculations.
3. The temperature of the Surface does not depend on “Radiative Forcing” at all. It depends on “Surface Forcing”. The inattention paid to this quantity is puzzling. No-one cares what the temperature of the tropopause is. Everyone is talking about Surface Temperature – so why aren’t we discussing that quantity, concentrating on the changes AT THE SURFACE?
Can’t put my finger on the ref, but have just seen a density calc that says the average distance between CO2 molecules at sea level is 3.9m, and at half that pressure is 4.9m.
So absorption within 1m seems “infinitely improbable.”
Brian H said:
“Can’t put my finger on the ref, but have just seen a density calc that says the average distance between CO2 molecules at sea level is 3.9m, and at half that pressure is 4.9m.”
CALCULATION OF DISTANCE BETWEEN CO2 MOLECULES AT THE SURFACE
Volume of CO2 molecules in 1m^3 of Air: ~400mL (400ppmV)
Volume of CO2 at STP containing ~6 x 10^23 molecules: 22400mL
Thus number of CO2 molecules in 1m^3 of air at STP = ~ 10^22
Average distance between CO2 molecules = ~0.05um
Colin Davidson says:
June 6, 2011 at 5:11 pm
Like you, I have huge problems with their definition. In addition to the ones you identified, you can add that it is a quantity which is not directly physically measurable … which in itself should be enough to disqualify it as a useful tool for describing the climate.
In addition, it ignores the radiation from above the tropopause.
w.
“In addition, it ignores the radiation from above the tropopause.”
I have been unhappy for some time. I can’t square the tabled absorption figures for CO2 with the claim that the majority of emissions from CO2 to space are coming from below the Tropopause. Take the least active of the 3 wavenumbers I have cited, wavenumber 700. At the surface, 50% of photons are gone within 50m (the table says 2atmcm, which equates to about 50m), ie 0.5% of the atmosphere. At 17km, the equivalent amount of atmosphere is around 500m – a photon emitted to space from 17km has only a 50% chance of surviving the first 500m of its travel. And there’s all this overlying gas (another 9ish% of the atmosphere) also radiating.
I think that even at the equator, the emissions in the main CO2 bands (and we are talking only of about 18W/m^2 emitted by CO2 to Space) must mostly be from the Stratosphere. And if that is the case the main effect will be cooling, not warming…
And I agree – by using the qualifier “after allowing for stratospheric temperatures to readjust to radiative equilibrium”, there seems to be no necessity to quantify what happens in the Stratosphere.