Technical Discussions

[parmenides3]

But that's wrong, isn't it? The LW radiation is converted to heat, and because the molecule has heat it emits radiation. The process isn't, as implied here, that the molecule has some sort of capacitance; it is entirely because the molecule has heat , and no other reason.

Perhaps I am being a little too pedantic . . .

***

Anyway back to the thread topic . . .

Has it been demonstrated (in the lab) that the sort of radiation that the Earth emits specifically heats up, say, CO2 at a faster rate than, say, nitrogen? This is, after all, the crux of the matter.

I think you've got it a bit wrong, here VP: the LW radiation is the heat, surely? Put simply, heat goes up, is absorbed, heat is radiated.

Back to the topic; Nitrogen has no 'greenhouse' effect; some of its compounds do. CO2 is 20 times more efficient at absorbing upwelling LWR than it is at blocking/absorbing downwelling SWR. Some of the other 'GHG's, i.e., methane, are much more powerful than CO2, but there is much less of them in the atmosphere.

To my next question: can we agree that CO2 is one thing which 'holds' heat within the atmospheric system? (Is this simple enough?)

Please don't think I'm being patronising here; I'm still trying to get at what we can find consensus on.

:)P

[VillagePlank]

I think you've got it a bit wrong, here VP: the LW radiation is the heat, surely?

If radiation is equivalent to heat then how can solar radiation pass through the earths atmosphere virutally untouched? Surely if this was the case then by virtue of conduction the atmosphere would heat directly from the incoming solar radiation?

I understand it as being an electromagnetic wave (ie energy) Where contact is made energy is transferred and the subject is heated by this process. Does a charge have a temperature?

In the case of the Earths atmosphere, the earth heats in response to the radiation from the sun, and convection, and conduction heat the atmosphere. The earth, like any other body which has heat, also emits radiation which heats the GHG's. They in turn radiate, as they should do, in complete agreement with the known laws of physics. Effectively, the Earth has two forms of incoming radiation - the sun, and the atmosphere. Therein lies the 'Greenhouse' effect.

Back to the topic; Nitrogen has no 'greenhouse' effect; some of its compounds do. CO2 is 20 times more efficient at absorbing upwelling LWR than it is at blocking/absorbing downwelling SWR. Some of the other 'GHG's, i.e., methane, are much more powerful than CO2, but there is much less of them in the atmosphere.

That is the point of my question. I am well aware that Nitrogen is not considered a GHG; so, I asked is there any laboratory studies that demonstrate this? If there are (I strongly assume there are) can anyone provide a link?

To my next question: can we agree that CO2 is one thing which 'holds' heat within the atmospheric system? (Is this simple enough?)

Please don't think I'm being patronising here; I'm still trying to get at what we can find consensus on.

No I don't agree. Again, implying some form of capacitance process that simply isn't there. I don't think you can simplify this, I'm afraid. There are notions being banded around that simply are not true. I think it is highly important that if you want to understand the atmosphere and especially global warming then one needs to understand that it's all about the radiation emitted from a body which has heat.

Edited March 7, 2007 by VillagePlank

[parmenides3]

If radiation is equivalent to heat then how can solar radiation pass through the earths atmosphere virutally untouched? Surely if this was the case then by virtue of conduction the atmosphere would heat directly from the incoming solar radiation?

No: Longwave radiation = heat, shortwave radiation = light. The gases in the atmosphere absorb some of the sun's radiative energy, and reflect some more back into space, but it has a different frequency to the radiation which upwells from the surface. CO2 (and other GHGs) are more efficient at absorbing LWR than SWR. To add to the complexity, I think it has something to do with pressure and temperature differential, which is why a lot of effort is put into looking at the upper troposphere/lower stratosphere, where the balance of influences is critical.

You can look for the nitrogen links yourself; I do have other things to do, honest!

I am worried that our personal discussion is starting to get technical and may encourage some readers to lose the will to live.

I still want to establish more general agreement on a basic idea; is CO2 a 'greenhouse gas'? I don't disagree with you that it's important to understand the physics, but here, on this 'naysaying' thread, I want to know what people do & don't think, and what any 'naysayer' is willing to agree on.

:)P

[Devonian]

No: Longwave radiation = heat, shortwave radiation = light. The gases in the atmosphere absorb some of the sun's radiative energy, and reflect some more back into space, but it has a different frequency to the radiation which upwells from the surface. CO2 (and other GHGs) are more efficient at absorbing LWR than SWR. To add to the complexity, I think it has something to do with pressure and temperature differential, which is why a lot of effort is put into looking at the upper troposphere/lower stratosphere, where the balance of influences is critical.

You can look for the nitrogen links yourself; I do have other things to do, honest!

I am worried that our personal discussion is starting to get technical and may encourage some readers to lose the will to live.

I still want to establish more general agreement on a basic idea; is CO2 a 'greenhouse gas'? I don't disagree with you that it's important to understand the physics, but here, on this 'naysaying' thread, I want to know what people do & don't think, and what any 'naysayer' is willing to agree on.

:)P

Erm..."Infrared radiation is popularly known as "heat" or sometimes "heat radiation," since many people attribute all radiant heating to infrared light. This is a widespread misconception, since light and electromagnetic waves of any frequency will heat surfaces that absorb them...."

All radiation has an 'heating' effect I think.

[VillagePlank]

Erm..."Infrared radiation is popularly known as "heat" or sometimes "heat radiation," since many people attribute all radiant heating to infrared light. This is a widespread misconception, since light and electromagnetic waves of any frequency will heat surfaces that absorb them...."

All radiation has an 'heating' effect I think.

Spot on, Devonian. Radiation is not heat. It is the interaction with radiation with other bodies that give heat. As your post says, if a substance absorbs a particular frequency of radiation then it will heat (I think!) SW radiation from the sun is not easily absorbed by the atmosphere so it (mainly) passes straight through. It is, however, absorbed by the earth, which then heats.

Edited March 7, 2007 by pottyprof

[BrickFielder]

What we are really talking about is planetary albedo and how much energy goes in and out of the earth.

Clouds play a big part

Nasa measurements of outgoing energy

CDC Map room comparing outgoing energy

CO2 Science perhaps a little biased

The earths energy budget

[parmenides3]

A quick note on Brick's previous post in the other thread: another nice collection, thanks. I'd warn people about the CO2 Science site, though; it has a reputation as a disinformationist site which cherry picks and misrepresents the science and the scientists, so the truth or accuracy of some of the material on it might be questionable (that's the polite description).

So far, we are struggling to agree what is meant by a 'greenhouse gas'. Some of the posts/links seem to make this relatively clear, some less so.

Can we say: ' A 'greenhouse gas' is a trace gas present in the atmosphere which absorbs infra-red radiation which upwells from the earth's surface, heats up, then emits radiation. Some of the emitted radiation is directed within the atmosphere or back toward the earth. The net effect of the trace gases in the atmosphere which act in this way is to 'balance' the earths heat budget.' ?

:)P

[Iceberg]

It might be worth saying that the heat level is constant/balanced because only so much absorbsion can take place by the Greenhouse layer.

[Devonian]

The net effect of the trace gases in the atmosphere which act in this way is to 'balance' the earths heat budget.' ?

:)P

Humm, I know* what you mean but there would be a balance ghg's or not?

*well, I think I know

[parmenides3]

Iceberg: I am presuming you are right. I think it has to do with pressure and temperature differential, again. Anyone disagree?

Dev: Yes. Without the GHGs, the balance would be sustainable by an ice-covered earth. The climate on which life depends requires the presence of GHGs to increase the overall heat content of the system. I believe that the 'contemporary' (last several hundred million years) climate is 'balanced' about 5C either side of 15C, though variations can exceed these values during glacial and interglacial extremes.

:)P

[VillagePlank]

P3, Yes, very close to a consensus opinion, there; only sticky point for me is that some of the gas sourced radiation is emitted into space, and one would expect it to be of equal proportions, generally.

Dev, he simple climate model I posted on the other thread, if you change the earth's effective emissivity to 1 (loses everything it gains) then it shows a stable temperature of about -18C. If you trap everything (e=0) then we have a stable temperature of 1160C. Yikes!

It is also worth stating that a change to e of just 0.022% is enough to increase the mean surface temperature in this model by 2.6C. Try e=0.59

It's a simple model, by shows the sensitivity our climate is to emissivity.

Does anyone know the formula for change in emissivity to CO2 atmospheric proportions?

Edited March 7, 2007 by VillagePlank

[parmenides3]

Does anyone know the formula for change in emissivity to CO2 atmospheric proportions?

This might prove to be a bit tricksy. You can probably find the formula (equation?) for the heat budget, and there is definitely a formula for the response of the system to CO2 concentration (climate sensitivity), but the way you ahve framed the question makes it hard to know exactly what we're looking for. As we're trying to avoid making any assumptions at this stage, i'm presuming it isn't the latter (climate sensitivity).

:)P

[Stratos Ferric]

It might be worth saying that the heat level is constant/balanced because only so much absorbsion can take place by the Greenhouse layer.

yes, though that "so much" is for a constant "greenhouse layer". The argumet is that if you change the quantity and make-up of that layer, so you change the physics; in the same way that if you give me a bigger bucket then I can carry more water.

[Devonian]

P3, Yes, very close to a consensus opinion, there; only sticky point for me is that some of the gas sourced radiation is emitted into space, and one would expect it to be of equal proportions, generally.

Humm, if a ghg emits in all directions, and it does, then effectively half goes up and half down? It's that bit that goes down that matters*. We have to realise the gh effect is not a huge effect relative to the Sun (Sun heats from about -270C to about -18C ghg's the rest, 33C or so) but that a small change to ghg's causing another 1C GH effect (plus feedbacks, the bit that's really disputed) is, climate wise, a darn lot.

*Well, it's more complicated I think, nutshells and all that.

[VillagePlank]

Humm, if a ghg emits in all directions, and it does, then effectively half goes up and half down? It's that bit that goes down that matters.

Yes, I agree.

[VillagePlank]

Found a source for absorptivities and emissivity calculations. Might take me a while . . .

[parmenides3]

!Gulp! Good luck, VP.

:)P

[parmenides3]

Thanks very much to Paul (Pottyprof) for a great job of merging the threads. I'm a bit busy right now, but I'm looking forward to seeing what people come up with later.

:)P

[raritas]

Hi

Has anyone noticed the cold anomaly (which has sustained for a while) where the oceanic conveyor goes north at the equator, next to Florida.

If the ocean is slowing due to the lack of cold columns falling (the oceans momentum motor)(up north), this would be where it will show?

The equator retains more heat and the medium which normally carries the heat north is reduced up to be the North Atlantic Drift?

It is possible that a trigger mechanism/point could shut off the flow quicker than thought, as this is fairly unknown ground?

Does anyone know over what time period the anomalies are calculated? A week/month/year?

If, by 'chance', it continues or extends further north (the purple area on the sea temp anom chart , in free data) we could be

witnessing the actual shutting off of the North Atlantic Drift.

Interesting ... maybe... temperatures in Europe would be affected by May if it were so.

Maybe its a blip? Or a precursor to a future reduction in flow?

Anyway more importantly....... we will have more snow should this be the case.

[Hiya]

Humm, if a ghg emits in all directions, and it does, then effectively half goes up and half down?

That isn't complicated enough for what you are trying to prove/explain. Be more technical everyone.

[parmenides3]

Blimey, Dave! I think you'll find the cold anomaly is in the wrong place. Strangely, there's a response of a kind in the link I'm about to post.

This is clearly jumping the gun in terms of the discussion we're having about what we mean when we say CO2 is a 'greenhouse gas', never mind what might follow that, but it is a good piece of technical writing on the subject: http://tamino.wordpress.com/2007/03/06/fast-co2/#more-179

Back to the subject in hand; Are we agreed that, though it is a misleading term, CO2 is, in the common parlance, a greenhouse gas?

What does this mean; it means that its presence in the atmosphere is an important part of why the earth's atmosphere (and surface) is the temperature that it is. Any objections?

:)P

[Iceberg]

Another thing to add.

Think of greenhouses gases as a rainbow, each colour/band represents a different gas.

Each band will absorb a slightly different frequency of Longwave radiation with a small overlap between them, hence the band of water vapour although by far the largest band doesn't block a lot of heat, again hence the importance of the smaller quantities of GHG like CO2.

[Admiral_Bobski]

Back to the subject in hand; Are we agreed that, though it is a misleading term, CO2 is, in the common parlance, a greenhouse gas...that its presence in the atmosphere is an important part of why the earth's atmosphere (and surface) is the temperature that it is. Any objections?

Okay, I'll take the bait! I'm not going to mince words over "degrees of influence" or "to what extent" or any of that stuff. A direct answer to a direct question, then we can see where this discussion takes us:

Yes; CO2's presence in the atmosphere has some relevance to Earth's temperature.

Now what?

C-Bob

[parmenides3]

I like the way you cautiously phrase your agreement, C-Bob: not planning to get hijacked, are you?

Unless anyone else wants to disagree, the next issue sounds simple, but is likely to end up being far from it, if the discussion of 'heat' and radiation is anything to go by.

If CO2's presence in the atmosphere is connected to earth's temperature, in the sense that it contributes positively, does more CO2 in the atmosphere imply more temperature? Trying to keep it simple (impossible, impossible); if x amount of something = y temperature, then does x+n amount = y+(unknown, but related to n) temperature?

Try to bear with me. Correct and adjust as you see fit.

:)P

[parmenides3]

Don't you just love the internet? Just for us: '20th century changes in surface solar irradiance in simulations and observations': http://www.agu.org/pubs/crossref/2007/2006GL028356.shtml

Ho, hum. :)P