Saturday, March 17, 2018

A Simple Model for Why the Greenhouse Effect Warms the Surface


While working on the answers to Judge Alsop's second question a very simple model that explains what is happening occurred to Eli about the third,

3.  What is the mechanism by which infrared radiation trapped by CO2 in the atmosphere is turned into heat and finds its way back to sea level?
The thought goes back to the early days of thermodynamics when it was realized that heat flows and interrupting or slowing a flow while maintaining constant delivery rates requires increasing the pressure head of the pump

Heat from the Sun flows to the Earth's surface at a constant rate determined by its ~6000 K black body temperature.  The Earth's surface transforms the visible light from the sun into ~290 K IR emission which escapes to space.  The flow of energy from the Sun to the Earth has to EXACTLY (them's Nikolov caps folks) match the flow of energy from the Earth to space.

Greenhouse gases function as a regulating valve.  If their concentration increases, the valve restricts the energy flow and the Surface has to pump harder to maintain the flow.  If the concentrations decrease the pressure the pump is delivering decreases.  

The operating mechanism of the valve is simple. The higher the mixing ratio (concentration) of greenhouse gases, the more absorbing the atmosphere is at frequencies that the greenhouse gases can absorb. The optical density of the atmosphere at those frequencies sets the level at which each greenhouse gas can emit to space without being re-adsorbed, i.e. it sets the level below which emission is blocked.  The rate of emission from the level at which the greenhouse gas IR emissions can reach space thus rises with concentration.  Since the temperature decreases with altitude, the higher the effective level, the slower the emission, the more the valve closes.

OK, make a copy of this and take it to your festive dinner.  Haul it out when Uncle Ralph starts.


21 comments:

lifeisthermal said...

OMG, you climate-satanists are so funny. First the blankets and now a pump. Do you ever question yourself? How come you never ask yourself:
Why do I need to explain cold air with blankets and pumps, when air is not blankets and pumps?
We already have fully functional theories for cold gases and heat sources, and they say the opposite of what gh-theory say.

First, blankets/insulation:
https://en.m.wikipedia.org/wiki/Thermal_insulation

"Thermal insulation provides a region of insulation in which thermal conduction is reduced or thermal radiation is reflected rather than absorbed by the lower-temperature body."

See? You need to prevent absorption to retain heat.

How about you using a reference from physics once in a while, instead of making stuff up?

Second, pumps:

Pumps do work, if co2 is a valve, it has to produce an opposing force, which is also work. The first law says that only heat and work can increase temperature, are you saying that co2 does work?
Since you are mentioning pumps...

Here, have some second law:
"Heat cannot spontaneously flow from cold regions to hot regions without external work being performed on the system"
https://en.m.wikipedia.org/wiki/Second_law_of_thermodynamics

So, does co2 do work on the system?
Because it can only be work, because heat is defined as:

" heat refers to the energy that is transferred from a warmer substance or body to a cooler one."
https://en.m.wikipedia.org/wiki/Heat

Well, it seems as I nuked your "theory" to dust.

Talking about nukes, I'll copy paste something interesting I posted elsewhere:


"In the equation E=mc² we find the units m=kg and c=m/s. The unit N, used for forces, is kgm/s. So, E=N=kg(m/s)². This also means that E/c²=N/(m/s)²=kg. Also, we know that N/(m/s)²=W/m²

Gravity on earth is kgx9.8m/s, same units as mc². So sqrtE=9.8N/(m/s)=kg And E=g²=9.8²N/(m/s)²=96N/m²=96W/m²=kg

The force of gravity, g², acting on 1m² has the power 96W/m². Gravity obeys the inverse square law, so the source power is 4x96W/m²=384W/m². This is equal to the average surface temperature of earth at 287K.

The sun irradiates earth at 1360.8W/m². Earth with the mass m receives Solar heat at the speed c, earth simultaneously emits heat at the speed c in all directions.

So E=mc²=m x T⁴ x TSI.

If 4g²=sigma x T⁴_surface, then this must be valid: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elesph.html

TSI/8g²=(4/3)/(4/3), with g=9.78(equatorial).

With support of electric field theory, is it correct that E/c²=sigma x T⁴=N/m²=kg, for earth?

Is E=mc² actually a mass placed in a radiation field with incoming heat at speed c, while simultaneously emitting heat at speed c?

Is Earth a spherical conductor in an inductive field, where the temperature is the heat transfer from thermal resistance to the energy flowing in a magnetic force field? The unit N/m2 is used for pressure, stress and thermal resistance. If E=mc2, then N/m2 =g2 is the gravitational unit of charge, in the global state TSI/(4/3)=4/3*8g2.

Can earth be defined as an optimized finite model of a heat engine in a constant thermal field?

If temperature and voltage acts equally as finite potentials for a current of energy, is thermal energy really electricity? Or, is electricity really a product of electromagnetic heat radiation?"

The greenhouse theory is one of science greatest embarrassments, just accept your loss. Deal with it. Your climate-satanist-blanket is burning, switching to pumps won't help you. Save your face and get off the stupid-train.

William Connolley said...

> The flow of energy from the Sun to the Earth has to EXACTLY (them's Nikolov caps folks) match the flow of energy from the Earth to space.

This isn't true, as you know.

Second, you already *have* a simple model, remember? It's http://rabett.blogspot.co.uk/2017/10/an-evergreen-of-denial-is-that-colder.html

Also, I thought we'd long ago agreed that language like "trapped" is unhelpful, and anyone using that phrase should have it pointed out to them why it is unhelpful. Is there some reason that judges get a free pass?

So the correct answer is "your question is somewhat confused. If what you're trying to ask is 'why do GHG's like CO2 warm the surface' then the answer is 'because they increase downwelling radiation'; or in simpler terms, 'because the surface is warmer if heated by sun+atmos, rather than just sun alone'".

> the Surface has to pump harder to maintain the flow

Notice this doesn't get you the answer you want. If your "pump" is purely down-thermal-gradient then yes the sfc has to warm, but you haven't added that step. But equally plausibly (within your analogy) the atmosphere might just "work harder" (whatever that might mean) and sfc temperature stay the same.

EliRabett said...

Simple models are never complete

William Connolley said...

Is that an answer? It doesn't make sense to me. Why replace a simple, fundamentally physically correct model with a no-simpler-at-best fundamentally physically incorrect one?

Barton Paul Levenson said...

lifeisthermal: OMG, you climate-satanists are so funny.

BPL: Not as funny as you science deniers.

Windchasers said...

Gravity on earth is kgx9.8m/s, same units as mc²

Uhhh... these are different units. kg*m/s is different from kg*m^2/s^2. And the units for gravitational force is neither of these.


If temperature and voltage acts equally as finite potentials for a current of energy, is thermal energy really electricity?


No.

Or, is electricity really a product of electromagnetic heat radiation?"

Also no.

I don't mean to be insulting, but you're messing up a lot of high school-level physics here. I posit that if your scientific ideas have you contradicted by 99% of the world's scientists, you might have misunderstood some things.

EliRabett said...

Because Weasel grandpa didn't pass his physics qualifiers.

Nick Stokes said...

I think the more correct analogue is not pressure but entropy. I tried to develop a budget based on entropy transport here; the most recent, with other links, is here. The general idea is that a flux Q of heat passing through a material at T K, has an entropy transport Q/T. Sunlight arrives with low associated entropy; you could say that flux Q leaves the sun associated with entropy flux Q/6000. Every time it is transferred to a medium at lower temperature, entropy is gained. And in steady state entropy, like heat, must all be exported with outgoing IR.

There is a constraint there. For a flux Q, entropy flux is maximised if it is radiated from a black body at uniform T given by Stefan-Boltzmann, Q=&sinma;T^4. That max entropy flux is Q/T=&sinma;T^3. But if the emission happens at varying temperature, entropy flux is less. The max emission corresponds to snowball earth. Anything that impedes export means less entropy can be created internally. GHGs partition export between a atmospheric window component at about 288K and a emission layer component at about 225K.

If less entropy is exported, less can be created. At the surface, the amount created is approx Q/Ts-Q/T_sun. To reduce this, Ts, surface temperature, has to be higher.

marcoclimate said...

"Uhhh... these are different units."

I explained that to lifeisthermal before on rabett, but he appears to be completely impermeable to such facts.

I've seen some first year students with equally embarrassing skills in getting units right, but at least they *are* embarrassed when it is pointed out. Lifeisthermal just repeats the same mistakes over and over again...

CapitalistImperialistPig said...

Analogy sweepstakes: I give the edge to the Stoat, mainly because the "EXACTLY" was an unfortunate own goal. Every simple analogy has its flaws, though, and in the case of the Stoat, the problem is lack of explanatory power. Why, exactly, should increased IR opacity increase downwelling radiation? The answer has to due with opacity and the source function and already it gets complicated, mainly because the energy flow in the troposphere is mainly convective.

I still like the blanket analogy, since it is simple, familiar, and gets the energetics right. Or you could just refer the Judge to the first twelve pages of Chandrasekhar's Radiative Transfer.

CapitalistImperialistPig said...

I extend my sympathies to those who try to instruct or correct lit, but he is better ignored. He is the intellectual equivalent of a perfectly white body. No information penetrates or is emitted.

andthentheresphysics said...

Analogies are always imperfect. My own preference when it comes to the greenhouse effect is to think in terms of energy balance. The system will tend towards a state in which the amount energy leaving matches the amount coming in (per unit area per unit time). The presence of greenhouse gases (GHGs) in the atmosphere prevent the surface from radiating directly to space. Consequently, in order for the system to attain energy balance, the surface has to be warmer than it would be in the absence of GHGs in the atmosphere.

Brad Schrag said...

Your units are completely bonkers in your dissection of E=mc^2

Right side is kg(m/s)^2 = m(kg m/s^2) = Nm = joule

See how that worked, ended up with units for energy, not Wm-2. This is very basic stuff, don't try thermo until you understand how to use units properly. It's not that thermo is that difficult but there is an obvious lacking of basics on your part.

Brad Schrag said...

Intellectual white body. That's great.

andthentheresphysics said...

I think that getting the units wrong was something highlighting in this interesting talk about the various letters that physicists typically get from people claiming to have overthrown Einstein's theories, or found a new theory for something alread well understood.

William Connolley said...

Speaking of which, when is Eli going to write down the equations for his model?

Brad Schrag said...

"But equally plausibly (within your analogy) the atmosphere might just "work harder" (whatever that might mean) and sfc temperature stay the same."

Source of energy for the majority of the atmosphere is the surface, since atmosphere is miserly transparent to incoming shortwave. If the atmosphere is going to do more work and remain in equilibrium then it must receive more energy to do so. Surface must warm to increase the work capacity of the atmosphere. If regions of the atmosphere where temperature isn't dictated by the surface we see that the increase in co2 is causing cooling (stratosphere). Energy input hadn't increased but emission has. Source of work is then the change in temperature.

CapitalistImperialistPig said...

Another thing to like about the blanket analogy: Under local thermodynamic equilibrium, a not bad approximation in the IR, both radiative and convective transfer satisfy diffusion type equations, just like heat transfer through a blanket. Increasing the IR opacity is equivalent to decreasing the effective diffusion coefficient (increasing the effective thermal resistivity).

Oale said...

Please don't be too harsh (like using violence and causing physical harm) to the first commenter. He's just applying for a government job and this is his first loyalty check. We all need to do this under Pruitt.

EliRabett said...

The point dear Weasel is NOT to write down equations, but to convey an idea.

EliRabett said...

and: Wavenumbers are not units of energy or frequency but they are used for both (being related by a constant). Drives organikers crazy