Aug 2, 2014 at 2:21 PM | Nullius in Verba

Can you not give a rough summary on what controls the re-emission time?

"Can you not give a rough summary on what controls the re-emission time?"

Yeah. The lifetime of a transition between two states depends on the extent to which the time-dependent Hamiltonian of the molecule perturbed by an EM wave couples the wavefunctions of the 'before' and 'after' states, or to put it another way, the extent to which the 'before' and 'after' motions overlap when projected in the 'direction' (in an abstract vector algebra sense) of the oscillatory wave. The lifetime of a state depends on the lifetimes of all the possible transitions it can undergo, which all happen in parallel, and tends to be dominated by the shortest of these. Did you look up the stuff on Fermi's Golden Rule?

Or perhaps it's easier just to think of it as one of those quantum things.

"Reverting to CO2, I am still not clear that thermalisation can take place in a non-bounded system and would love to see the experimental evidence for this."

The experimental evidence for thermalisation is that things get warmer when you shine a light on them, as the energy is absorbed. If it wasn't absorbed, but re-emitted in the same form it arrived, that would be scattering rather than absorption. What do you mean by "bounded" and why do you think it would make a difference?

Ronaldo who said anything about it being an analogy. I was merely pointing out that energy is partitioned amongst translational, rotational and vibrational components when you heat the water and pan. It is exactly the same for the CO2. A photon is absorbed by a molecule raising the vibrational quantum level of that particular molecule. At some time in the future that energy might be lost be emission of a photon, or it might be thermalised by distribution into rotational and translational modes. You seem to think that energy cannot be converted from vibrational to translational modes and this is a misconception. As NiV says consider the molecules are continuously bumping into each other and transferring energy.

I don't know what the characteristic time for thermalisation is and this will depend on pressure, composition of the gas phase etc. but from memory I think it is on the order of micro to tens of micro seconds.

Rhoda

The toa radiation budgets are known and measured. They are the outward long wave radiation and its counterpart, the downward long wave radiation (aka back radiation).

For a good introduction try Ira G!ickstein's article on Emission Spectra at WUWT.

Something of relevance here

http://hockeyschtick.blogspot.fr/2014/08/paper-finds-decrease-of-ir-radiation.html

which I've posted on unthreaded too.

"when the noise of the water signal must dominate?"

I'm not sure I'd call it noise when it is the dominant effect. You would have to assume that variations in CO2 could influence the amount of H2O in the atmosphere (liquid or gas) so you couldn't really separate the two anyway even if you could measure the effect.

Rhoda

That's right. The total area under the black body curve is proportional to the total energy flux. The area enclosed above the OLR line around 15 micrometres and below the black body curve is the proportion redirected by CO2. If you know the total outward radiation energy flux you can use the relative areas to calculate the relative energies. There are a few subtleties......

Spectral Radiance units are Watts per square metre per steradian per cm. A steradain is the area of a circle on the surface of a sphere which subtends an angle of one radian. As a rule of thumb, a steradians is about 1/10 of the surface area of a sphere.

Converting radiance to watts/m^2 at TOA is rather beyond my pay grade. I will think about it. Perhaps Nullis in verba can help.

Rob Burton

The general view is that higher CO2 leads to higher temperatures which lead to higher water vapour.

The higher water vapour leads to reduced direct outward radiation. However when you add in the effect of higher water vapour on cloud cover it gets more complex. More cloud of all types is expected.

High cloud has a net warming effect because it retains IR more than it increases albedo. Low cloud has a net cooling effect because its albedo is larger than its IR retention.

The exact overall effect? Consider it work in progress.

Entropic man
Any comment on this actual research rather than modelling? Researchers say that (I've highlighted the key word)

A trend analysis was applied to a 14-yr time series of downwelling spectral infrared radiance observations from the Atmospheric Emitted Radiance Interferometer (AERI) located at the Atmospheric Radiation Measurement Program (ARM) site in the U.S. Southern Great Plains. The highly accurate calibration of the AERI instrument, performed every 10 min, ensures that any statistically significant trend in the observed data over this time can be attributed to changes in the atmospheric properties and composition, and not to changes in the sensitivity or responsivity of the instrument. The measured infrared spectra, numbering more than 800 000, were classified as clear-sky, thin cloud, and thick cloud scenes using a neural network method. The AERI data record demonstrates that the downwelling infrared radiance is decreasing over this 14-yr period in the winter, summer, and autumn seasons but it is increasing in the spring; these trends are statistically significant and are primarily due to long-term change in the cloudiness above the site. The AERI data also show many statistically significant trends on annual, seasonal, and diurnal time scales, with different trend signatures identified in the separate scene classifications. Given the decadal time span of the dataset, effects from natural variability should be considered in drawing broader conclusions. Nevertheless, this dataset has high value owing to the ability to infer possible mechanisms for any trends from the observations themselves and to test the performance of climate models.

http://journals.ametsoc.org/doi/full/10.1175/2011JCLI4210.1

"The general view is that higher CO2 leads to higher temperatures which lead to higher water vapour."

There is quite a bit of observational evidence that both cloud and water vapour dropped during the late 20th century when both CO2 and temperature were increasing. Reduced cloud would have warming tendencies too.

"The exact overall effect? Consider it work in progress."

I definitely agree with this summary.

Mike Jackson

The logic of the increasing cloud hypothesis is fairly simple. A warmer atmosphere can hold a greater quantity of water vapour. Convect that atmosphere and as it rises and cools more water vapour condenses out and you get more low cloud.

Under more humid conditions such convective cooling also dumps more latent heat and drives the energetic convection which generates cumulonimbus clouds. These transport more water into the stratosphere, hence more high cloud.

This is still work in progress. Conventional wisdom was that the lower cloud would increase faster, making increased cloud cover a net cooling feedback. This was included in the CMIP5 models run in 2007.

Sherwood et al 2014 suggested that the extra water would transfer to higher altitudes, giving a greater proportion of high cloud and a net warming effect.

Monitoring cloud has given different results from different techniques, mainly due the difficulty of measuring multiple cloud layers from the surface or from orbit. Because of the large confidence limits it is not yet possible to deduce long term trends in different types of cloud cover from the data to date.

I'm probably too late for this post, but I see many questions. I'll pick a few and add comments.

1. The spectrum of radiation at different heights - there are extracts from Grant Petty, A First Course in Atmospheric Radiation in Understanding Atmospheric Radiation and the “Greenhouse” Effect – Part Ten.

2. The thermalisation time is the order of nanoseconds. This is a simple physics basics problem - velocity of molecules given by the Maxwell–Boltzmann distribution and the density of molecules provides the mean free path.
The result is that energy from absorbed photons by water vapor, CO2, CH4 and other radiatively-active gases is shared with the local atmosphere, not scattered.

3. "And then there's the photons. Apparently they don't just get absorbed and re-emitted, they thermalize O2 and N2, they in turn energise other CO2 or H2O molecules, they get absorbed and re-emitted all the way up until they make their inevitable way out. Now, why does it matter if they do that a gazillion times or 1.5 gazillion. They leave the planet pretty quick either way. What gets warmed up more because of the extra density of CO2? All the energy leaves. It is an open system, there is nothing to stop it."

The calculation of radiative transfer doesn't track photons. If you want to understand radiative heat transfer don't think about photons - that's just my suggestion. But you don't see photon tracking in any of the equations. I know people trying to provide conceptual insight talk about photons. I believe it doesn't help.

The calculation of radiative transfer calculates emission and absorption through the atmosphere and relies upon knowing the temperature profile, the concentration profile of GHGs and the absorption and emission properties (which are well known with a few million absorption lines recorded in the HITRAN database).

What causes warming is less energy radiated from the climate system. Ein - Eout = energy stored. I can point you to the equation (eqn 16) in the link just provided and say "there you go", or give an analogy.

Analogies are problematic and can be criticized. So I'll just point you to the equation, which is from fundamental physics, and has been proven and accepted for 60+ years. Nobel prize winner Subrahmanyan Chandrasekhar wrote the book in the 1950s.

4. "If you subscribe to the view that an unvalidated computer model is nothing more than an illustration of a hypothesis, you then have to conclude that the greenhouse effect is simply not understood. The absence of answers to rhoda's questions provides confirmation."

There are analogies and there are equations. Atmospheric physics textbooks give simple models to help the student learn. They probably weren't designed to help people who don't understand heat transfer and have a fundamental distrust of climate science. Anyway, people teaching are often not great at it.

If you want to gain insight into how "something" absorbing and re-radiating can increase the surface temperature of a body heated from inside - then there are simple shell models. If you want to know the physics, there's a set of equations. The real equations have nothing to do with blackbody shells. You can only solve these equations numerically. You can't get an analytic solution to the equation. That's true of most real world physics and engineering. The equations may be true but the solution requires a numerical approach.

This is not quite how most people think of "computer models". Instead, think of "computer models" as a hierarchy. They solve equations. Some equations are difficult to solve even with supercomputers - e.g., the ones involving turbulence. Some equations are simple to solve even if you can't calculate the results in your head. Like the equations of radiative transfer.

In the absence of feedbacks the calculation of radiative transfer and how it changes with more or less GHGs is a simple but computationally expensive task. I give some examples in Visualizing Atmospheric Radiation – Part Two and later parts in the series.

Calculating feedbacks is the difficult part.

5. "Scienceofdoom is simply a school teacher with an AGW bias and a strong copy and paste habit. I don't think I'd regard him as the guru that some seem to."

Fascinating. Which school did I teach at? What kind of skeptic are you to report this kind of invented information? However, I'm definitely not a guru. You are right about that. I'm a skeptic, therefore, there are no gurus. I try to understand climate science and explain and evaluate it. Opinions are useless.

What can be demonstrated from theory and experiment? This is the only thing that matters.

6. "What is this resistance to convection you talk about? IMHO most of the heat redistribution is happening in the tropics. There are massive vertical flows there every day. Transporting H20 in vapour form up to where it can dump latent heat way above the tropopause.
Why does the height of the radiative balance layer vary with co2 concentration? I though it was 5km because that's half way up the atmosphere, by mass. Or halfway up the troposphere, by coincidence or not. Why does more CO2 mean it isn't halfway any more? Or was the 50% pressure alt just a coincidence too."

Latent heat isn't generally dumped way above the tropopause. The tropopause is where convection stops. Water vapor condenses at a range of heights. The altitude of clouds gives these points away. Mostly well below the tropopause.

The height of radiative balance varies with CO2 concentration because emission of radiation depends on the opacity of the atmosphere. The 5km is an invented number - invented as a teaching tool. Averages are useful teaching tools.

The opacity of the atmosphere is completely - and strongly - dependent on wavelength. The atmosphere absorbs 95% of radiation in 1m at 14.98um so the important height is very high up in the stratosphere. Increasing the concentration will probably increase the emission by a tiny amount (because the stratospheric temperature increases with height). At a wavelength where the atmosphere absorbs 50% of radiation in 10km the important height is about 5km and a 10% change will move this effective height up a significant amount and reduce the temperature, and therefore, intensity, of emission. If the atmosphere absorbs 1% of radiation in 10km then the important height is about 100m and a 10% change won't have that much effect.

The sum of all these changes (the "integral") is what the radiative transfer equations calculate.

7. "Well done Martin, you have demonstrated that not one of those outfits can provide an explanation that stands examination. There is no trapped heat. Outgoing equals incoming, over time."

Explanations are people trying to turn equations into something conceptual. Some people do a good job. Some people do a bad job. Some people are given website access and don't even understand the basics.

Don't read stuff in the media, that's my advice.

"Outgoing equals incoming over time" - is 100% correct. The question - the important question - is what is the relationship of the surface temperature to the outgoing radiation. Trapped heat is (approximately) related to temperature. There's lots of trapped heat in lots of places. If there wasn't it would be very cold.

When some material property changes, the way that new equilibriums are formed is by changes in temperature. This is what you find when you have to solve first year heat transfer problems. If you make insulation thicker and have internal heating, then the temperature rises. That's trapped heat. Outgoing still equals incoming. But the outgoing heat is leaving from the outside of the insulation and it takes a higher temperature inside (when the insulation is thicker) to get the same outgoing heat transfer.

That was an analogy to the climate. Analogies don't prove anything. If it hasn't helped I can only apologize.

Refer to the equations.

I see my link to the equations of radiative transfer failed.

http://scienceofdoom.com/2011/02/07/understanding-atmospheric-radiation-and-the-%E2%80%9Cgreenhouse%E2%80%9D-effect-%E2%80%93-part-six-the-equations/

And trying to make a html link: Understanding Atmospheric Radiation and the “Greenhouse” Effect – Part Six – The Equations

SoD thanks for the explanations. I wonder if you would clarify for me whther my earlier question was nuts or sensible. People here seem to think the former. The question was:

if at height h in the stratosphere the number of CO2 molecules per cubic meter is some nominal X, do you accept that after doubling the % CO2 in the atmosphere h will increase for the same X? It all hangs on this.

"It all hangs on this."

Aug 8, 2014 at 11:14 AM | Unregistered Commenterraff

Everything else being equal. Which it isn't. So it doesn't hang on that.

Raff

Yes. The number of CO2 molecules per unit volume at height h will double if atmospheric CO2 concentration doubles.