Technical Discussions

[parmenides3]

Is CO2 a greenhouse gas?

Does the climate depend, at least in part, on the presence of CO2 in the atmosphere?

Has either of the two above been 'proven'?

These are the most basic questions of physics relating to the atmosphere. Where is the confusion?

[VillagePlank]

(i) Is CO2 a Greenhouse Gas.

No. Absolutely Not. The Greenhouse is a misnomer, and has nothing to do with atmopsheric science. A greenouse inhibits convection - and this is not the way the atmopshere works. It is a nickname, but it's a bad one. It's a pedants point, I admit freely, but if you want to read more, look here, and particularly here.

(ii)Does the climate depend, at least in part, on the presence of CO2 in the atmosphere?

Yes. Absolutely correct.

(iii) Proof of (i) and (ii)?

It's almost lay science that (i) is incorrect, but the correlation implied in (ii), to whatever degree, I suspect is beyond a reasonable doubt.

I think the argument is the extent of cause and effect of (ii)

Edited March 6, 2007 by VillagePlank

[Admiral_Bobski]

Does the climate depend, at least in part, on the presence of CO2 in the atmosphere?

Can you rephrase that? The answer depends upon what you mean... You could have "climate" without any CO2 being in the atmosphere, but that would leave the whole respiration/transpiration thing a bit stuffed, so you might have to exclude any kind of organic life from that world.

Life certainly depends, to some extent, on there being CO2 in the atmosphere (certainly the more complex forms of life), but climate...I'm not so sure...or do you mean "our existing climate"? If this is what you mean then, yes - without CO2 you have no life, and without life you have a different atmospheric composition and, therefore, a different climate. That's not to say that CO2 has a great part to play in climate change, necessarily, but its absence has a knock-on effect.

Note that I'm not talking about a small increase or reduction in CO2 - I'm talking about a complete absence (or, I suppose, over-abundance, like 30% of total atmospheric composition). But this is Life related, not temperature related.

Confused!

C-Bob

[BrickFielder]

Is CO2 a greenhouse gas?

Does the climate depend, at least in part, on the presence of CO2 in the atmosphere?

Has either of the two above been 'proven'?

These are the most basic questions of physics relating to the atmosphere. Where is the confusion?

:)P

Is CO2 a greenhouse gas?

Yes in isolation from gravity, clouds , plants ,sealife etc. The affects in our atmosphere are a rather complicated calculation on interacting variables. For example greenhouse gas traps warmth which produces cloud which reflects light which can cool the air. Warmer seas mean more sealife which absorbs more co2 and produces more oxygen. The calculation is complex non linear and certain aspects are often aproximated (Gravity wave affects in particular) in climate models. The theory is that CO2 abosrbs heat and reflects heat out again in all directions. Heat reflected back downwards contributes to

Does the climate depend, at least in part, on the presence of CO2 in the atmosphere?

Almost certainly ,to what extent and significance is debateable. If I asked a climate scientist to explain the limitations and possible errors involved in his climate models , you would understand that climatology is not an exact science, with probabilities and margins of error of prime importance. The questions should be is it an important factor and what is the major cause( land use and the reduction of iron dust falling on the pacific with subsequent reduction in plankton may be the major cause) of its increase.

Has either of the two above been 'proven'?

Neither is proven one way or the other. Consensus of opinion and probabilites tend to point us in a particular direction, while scientist own admitted model limitations make us slightly unsure of the amount of error in their calculations. Quite clearly action is required on climate and ecological balance untill we really do have a finite numerical understanding of the implications of mans actions , which I think is a more wide reaching requirement than the short term and easy targets that politicians aim at.

[Admiral_Bobski]

It is possible to change the question to; 'Does the presence of CO2 in the atmosphere serve to prevent the loss of energy in the form of heat to space?' is this adequate? It might also server to help you C-Bob, with your question. Perhaps they amount to the same thing. I imagine I was intending to refer to the climate of the world as we know it - ie, the one in which life is at least possible, which has the present broad chemistry that has developed over time.

I thought that's probably what you meant, but it's always worth clarifying these things!

Well, as I know you are aware, CO2 is not solely responsible for the prevention of the loss of energy in the form of heat to space. It would be possible to have some kind of "greenhouse effect" (or whatever the more appropriate term is) without CO2 being there. The degree of variability in Earth's climate as a result of the presence of a given quantity of CO2 is a more complicated question, especially when taking Life into consideration, with all of its associated feedbacks and cycles.

To keep the current variety of flora and fauna on this planet alive, yes, we need CO2 in the atmosphere - at least some CO2. I don't know how little Life could get by with, I don't know how much would be too much, but that's more from a physiological standpoint than a climatological one. So I'm still not entirely sure what you mean by "does the climate depend on CO2"...it's an essential part of an atmosphere required to sustain the majority of macroscopic life forms, but is it essential to climate...?

In answer to the first question, yes - CO2 is a "greenhouse gas", in that it traps heat in an otherwise static environment. In the real world it certainly has these properties, but that doesn't prove it is as pivotal in Climate Change as it is supposed to be - too many other factors to be able to conclusively say that it is.

I'll stop rambling now!

C-Bob

Edited March 6, 2007 by Captain_Bobski

[parmenides3]

Have we made a little bit of progress?

It seems that we can agree that 'CO2 is a 'greenhouse gas'; in other words, it's presence in the atmosphere has a positive effect on temperature. Any objections to this?

[AtlanticFlamethrower]

It seems that we can agree that 'CO2 is a 'greenhouse gas'; in other words, it's presence in the atmosphere has a positive effect on temperature. Any objections to this?

Carbon dioxide is a greenhouse gas. As far as I'm aware, nobody has debated this. It would be like me asking you if you believe that radiation from the sun is variable over time. It's a simplistic question that would belittle you.

Edited March 7, 2007 by pottyprof

[VillagePlank]

No the atmopshere (hence CO2 and others) does not trap heat. If it did the temperature would be steadily rising. It, in the main, loses heat at the same rate at which it gains it.

Edited March 7, 2007 by VillagePlank

[Iceberg]

Nobody is saying that people that don't believe in AGW are ignorant.

And I feel that we really need to move away from this right/wrong black/white argument, nobody is saying that anybody is wrong to not agree with the AGW theory. It's a theory you can agree and disagree as you like.

Just felt I needed to make myself clear above just in case we get any more statements of it's not fair.

But If you claim x,y,z i.e GW is due to natural cycles then's it's quite right for somebody to challenge that statement.

If we argee that CO2 is a greenhouse gas that might cause warming, how should we go about measuring the effects of our increase in CO2 ?

[parmenides3]

Carbon dioxide is a greenhouse gas. As far as I'm aware, nobody has debated this. It would be like me asking you if you believe that radiation from the sun is variable over time. It's a simplistic question that would belittle you.

Perhaps you'd like to ask a more specific question to the HGW naysayers?

AF: People debate this,'simple' point all the time. I'm trying to establish a baseline, here, on what can be agreed on. Also, the answer is not that obvious to some. I have a purpose. Trust me.

VP: You say the atmosphere does not 'trap heat'. Do clouds trap heat? Is a proportion of the heat radiated away from the earth's surface retained in the atmosphere?

Iceberg; you're jumping the gun a bit; please be patient with me.

:)P

[VillagePlank]

Is a proportion of the heat radiated away from the earth's surface retained in the atmosphere?

No.

The energy radiated from the Earth surface is converted to energy in the atmosphere thus modifying the temperature of the atmosphere. Because the atmosphere (as a body) has a temperature it will give off radiation uniformly (for simplicities sake) both to space, and back to Earth.

By observation, the radiation that the atmosphere gives off is NOT the same as that which the surface does. There is no 'retention', nor 'reflection' involved with the Earth's radiating energy (if it were retained or reflected then we'd see the same spectral composition radiating from the atmosphere as we do radiating from the Earth)

I think this is quite an important point; I am sure that most will argue it's a point for pedants . . .

Edited March 7, 2007 by VillagePlank

[Hiya]

I think someone needs to post up some links or an explanation of how carbon dioxide "works" so that we're all reading off the same hymn sheet, there are a few people who either don't understand or don't fully understand and thats whats causing the continuation of some niggling issues in the past few pages.

If no one does it by the time I get home from uni and work (5pm) I'll do it.

I'm talking about a technical explanation, not an overview, cause that won't help.

Edited March 7, 2007 by Hiya

[VillagePlank]

For fun, lets all play with the simplest of simplest climate models. If you want to up the CO2 to increase reduce the effective earth emissivity (this value is how much energy in total leaves the surface/atmosphere system), if you want more sun then increase the solar constant. Have fun!!

I've looked for a source for the CO2 link to emissivity, but can't find one - does anyone else know where one is? Also I can't find projected solar 'constant' projections. Both would be interesting to run through this model and graph, I think.

(Note: this is extremely simple. Beyond simple - it's meant to be fun, not educational, though I'm sure some the latter will occur)

SimpleClimateModel.xls

Created from here

Edited March 7, 2007 by VillagePlank

[Devonian]

No the atmopshere (hence CO2 and others) does not trap heat. If it did the temperature would be steadily rising. It, in the main, loses heat at the same rate at which it gains it.

Then why are the Moon and the Earth (effectively in the same place relaitve to the Sun) so differnet?

Well, ghg's that's what. Clearly the Earths temps hasn't been steadly rising, but, then again, neither have, until now, ghg's conc been rising - at least over the long (geological term).

Now, the physics - gulp. Bodies do both recieve and give out em radiation. The sun at several thousand degress, Earth, actually, at about -18C. -18C is the Earth's temperature from space, but not at it's surface. That's is ghg's for you. Effectively they impead upwelling radiation and the effect of that here on earth is to raise temperatures lower down.

I think and unless someone knows better/can explain the basics better

[VillagePlank]

Devonian, see my latter post, for a fuller explanation of my post you quoted. 'Greenhouse' gases, btw, do not act in the manner you state.

Edited March 7, 2007 by VillagePlank

[Devonian]

Devonian, see my latter post, for a fuller explanation of my post you quoted. 'Greenhouse' gases, btw, do not act in the manner you state.

Well, how do they act? I know it wasn't a full explaination - I'm not going to copy out a text book - but was it fundamentally wrong? I like to learn and the physics of the GH effect are difficult (at least in my case) to really get a grip on and to then simply explain.

Edited March 7, 2007 by Devonian

[VillagePlank]

Well, how do the act? I know it wasnt a full explaination - I'm not going to copy out a text book - but was it fundamentally wrong? I like to learn

Yes, the notion of a layer in the atmosphere acting like the glass in a greenhouse is fundamentally wrong.

Here's the basic steps in the atmosphere

(i) Radiation from the sun hits the Earth surface. For brevity I shall ignore cloud reflectivity despite invitations to be drawn on this

(ii) The sun's radiation is coverted to heat at the surface. Effectively the Earth, itself, heats up

(iia) By conduction the air close to the surface heats up

(iii) Any body that has heat gives of radiation: different bodies give off different wavelengths of radiation

(iv) That radiation, for simplicity, is radiated to the atmopshere

(v) The atmosphere coverts that radiation to heat

(vi) The atmosphere has heat so it gives of radiation some of it to the surface

(vii) The radiation given of from the atmosphere is NOT the same radiation that left the earth's surface. There is no retention, nor reflection involved.

A greenhouse heats because convection of air inside is limited by the glass, radiative forcing only being apparent initially when the ground inside the greenhouse is being heated which in turns heats the air.

The literay presence of a greenhouse effect is simply to communicate the concept of something below being heated. It has no relevance in atmospheric physics.

The notion of CO2 increases is that changing the CO2 composition of the atmosphere will modify the wavelength of radiation emitted by the atmosphere thus increasing the heating effect (I think - I'm a bit fuzzy on this)

Edited March 7, 2007 by VillagePlank

[Devonian]

Yes, the notion of a layer in the atmosphere acting like the glass in a greenhouse is fundamentally wrong.

Correct me if I'm wrong but where did I mention greenhouses??? EDIT: hang on are you cricising or agree with me????

Here's the basic steps in the atmosphere

(i) Radiation from the sun hits the Earth surface. For brevity I shall ignore cloud reflectivity despite invitations to be drawn on this

(ii) The sun's radiation is coverted to heat at the surface. Effectively the Earth, itself, heats up

(iia) By conduction the air close to the surface heats up

(iii) Any body that has heat gives of radiation: different bodies give off different wavelengths of radiation

(iv) That radiation, for simplicity, is radiated to the atmopshere

(v) The atmosphere coverts that radiation to heat

(vi) The atmosphere has heat so it gives of radiation some of it to the surface

(vii) The radiation given of from the atmosphere is NOT the same radiation that left the earth's surface. There is no retention, nor reflection involved.

A greenhouse heats because convection of air inside is limited by the glass, radiative forcing only being apparent initially when the ground inside the greenhouse is being heated which in turns heats the air.

The literay presence of a greenhouse effect is simply to communicate the concept of something below being heated. It has no relevance in atmospheric physics.

Simplified, but I'll agree. Now, how does the GH effect work and what does adding ghgs do?

Edited March 7, 2007 by Devonian

[VillagePlank]

Correct me if I'm wrong but where did I mention greenhouses???

... they impead upwelling radiation and the effect of that here on earth is to raise temperatures lower down.

That is the physics of a greenhouse and not the atmosphere.

Now, how does the GH effect work and what does adding ghgs do?

I'm working on that bit

Edited March 7, 2007 by VillagePlank

[Devonian]

That is the physics of a greenhouse and not the atmosphere.

Then it's my bad explaintion. I KNOW it's nothing to do with greenhouses OK? Anyway, what do, colloquially, ghg's do? Well, they abosorb radiation and then re-emit it again - in all directions? Some therefore goes down, and....

So, in a (colloquial) way, ghg's DO impead the upwelling of radiation - no?

Edited March 7, 2007 by Devonian

[VillagePlank]

How does the GH Effect work? Well, my simplest possible explanation is that the Earth has two sources of incoming radiation. The atmosphere, and the sun. Thus keeping the surface layer warmer.

How do 'GHGs' modify that? I'm working on that bit.

So, in a (colloquial) way, ghg's DO impead the upwelling of radiation - no?

No I just don't accept that. It's different radiation that is emitted by the atmosphere.

[Devonian]

No I just don't accept that. It's different radiation that is emitted by the atmosphere.

Oh, I see, that's your problem. For the time being I'll stick with what I said.

OK, the Earth radiates 'long wave' radiation. Without ghg's that radiation would just escape, with ghg's some of it , as I said, is absorbed by said ghg's and then reradiated, in all directions some therefore downward, and that downward bit does what to the surface or atmosphere below...warms it . As I understand it...see fig 2 here

Now, work to do

Edited March 7, 2007 by Devonian

[VillagePlank]

Oh, I see, that's your problem. For the time being I'll stick with what I said.

OK, the Earth radiates 'long wave' radiation. Without ghg's that radiation would just escape, with ghg's some of it , as I said, is absorbed by said ghg's and the reradiated, in all directions some therefore downward, and that downward bit does what to the surface or atmosphere below...warms it . As I understand it...see fig 2 here

As I understand it, the gases convert the earths outbound radiation more readily, thus heat more. I am particulary woolly on the process here, so I hope you'll understand my rather vague response, here.

The heat of these gases then emits (it does not reradiate - it is not the same radiation) - by all sorts of known laws - radiation simply by the mere concept that any body that has heat emits radiation. The radiation from the earth has already been converted. It has already gone. Disappeared. None left. Not reflected. Not Rerediated.

The effect is that of a greenhouse - something below heats up. We could have called it the "inverse bunsen-burner principle" because it has the same effect. Now there's a thought . . .

[edit] I am avoiding clouds, here [/edit]

Please understand, that although my recent post seem pedantic, I am trying to go back to first principles in order to come to a reasoned conclusion for myself.

My first criticism is the misnomer of the 'greenhouse' which is an entirely inaccurate analogy.

Edited March 7, 2007 by VillagePlank

[parmenides3]

This is the explanation from the site VP linked to above, climateprediction.net . It should do to clarify the phenomenon we are trying to describe, which is the existence of heat within the atmosphere. Quoting seemed easier than re-writing. Sorry if it's a bit long.

In the nineteenth century various scientists (such as Joseph Fourier) explained that the atmosphere can, like an ordinary greenhouse, retain energy radiated into it from outside. The greenhouse analogy isn't very exact, but the name certainly stuck.

In the 1860s John Tyndall explained that certain gases, including water vapour and carbon dioxide (CO2), don't affect visible light but absorb longer wavelength radiation (infrared, heat). He suggested that these gases insulate the Earth.

The actual process works like this (see figure 2): visible incoming sunlight either gets reflected (for example by clouds, or aeroplanes), or passes unhindered through the atmosphere, and gets absorbed by the surface of the Earth, thus heating it. The Earth radiates heat from the surface back into the atmosphere, where it can pass back into space, or get reflected again, or, because it has now got a longer wavelength than before, it can get absorbed by the water vapour, carbon dioxide, methane and other greenhouse gases which are present in the atmosphere. As the water vapour/ methane/ carbon dioxide molecules absorb the longwave radiation, they heat up, and in turn re-radiate long wave radiation in all directions. Some is lost to space, but some of it also gets radiated back to the surface, again warming it.

This naturally occurring process helps keep the Earth warm enough for liquid water to exist. Without greenhouse gases, the average temperature at the Earth's surface would reach only -17ºC, approximately 33ºC colder than it actually is!

Now, what if the concentrations of these insulating gases increase? We might expect the process described above to intensify. In fact, this is just what the Nobel Prize-winning Swedish chemist Svante Arrhenius did in 1896. By knowing how CO2 absorbs heat radiation from the surface of the Earth, he calculated what would happen if the amount of CO2 in the atmosphere were doubled. He estimated that a doubling of CO2 would lead to an average global surface temperature increase of 2 °C. This is consistent with modern predictions.

This approach, while still a handy first guess, considers the climate system in the absence of any feedback processes. Feedbacks are processes in which outputs from the process have an effect on the inputs to that same process. Sometimes feedback processes act to offset or inhibit a change (negative feedback), and sometimes they act to amplify a change (positive feedback). Examples of negative feedback include the maintenance of your body temperature: when you get too warm, you trigger various mechanisms (e.g. perspiration) to cool you down and vice versa. A common example of positive feedback is often associated with amplified music or speech, when the microphone is placed too close to a loudspeaker... someone speaks/ sings/ plays into the microphone, the noise is amplified, and comes out of the speaker. If some of this amplified noise goes back into the microphone, it gets amplified again etc. etc. and the end result is a deafening whine.

There are many examples of feedbacks in the climate system. If the atmosphere gets warmer, ice melts. Ice reflects a lot of incoming solar radiation, so if it melts, less gets reflected, more gets absorbed by the Earth and the atmosphere gets warmer; a positive feedback. On the other hand, if there is more carbon dioxide in the atmosphere, some plants grow faster, absorbing more carbon dioxide and eventually reducing its amount in the atmosphere; a negative feedback.

Because of the complexity of the climate system, due to the presence of feedbacks within it, we need to try to represent the whole system as thoroughly as possible in order to simulate the likely changes. We need to be able to understand how and where feedbacks act, and how large they are.

:)P

Side note: in searching google on 'correlation between CO2 and earth emissivity' (34,800 hits), this was one of the first sites I checked out. I have no idea of it's validity or anything else, but the argument struck me as at least rational and clear, even though I suspect there may be an oversight in the scineitific analysis. To me, this represents a good example of 'naysaying' about AGW: it doesn't shout its case, but tries to show how certain assumptions may not be tenable. As such, it contradicts to a certain extent the long post above. Worth a read, I feel: http://www.chemcept.co.uk/global.htm

:)P

Edited March 7, 2007 by parmenides3

[VillagePlank]

As the water vapour/ methane/ carbon dioxide molecules absorb the longwave radiation, they heat up, and in turn re-radiate long wave radiation in all directions.

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.

Edited March 7, 2007 by VillagePlank