Model CO2 as Greenhouse Gas: Tips & Results

[Rickeroo]

Thanks Sylas.

With the correlation being .735, would that be enough to say that the comparision is relevant, or at least something to be looked at further?

There are enormous fluxes of carbon in and out of the atmosphere from vegetation, and temperature is likely to have an impact on that, rather than the other way around.

Would that suggest that temperature leads carbon, at least to some degree?

 

[sylas]

Thanks Sylas.

With the correlation being .735, would that be enough to say that the comparision is relevant, or at least something to be looked at further?

It's enough to be suggestive; worth looking at. I would not be at all surprised to see some kind of temperature related effect, but as I said, it's a bit of a guess. I suspect that if we hunted through the literature on the carbon cycle we'd find some consideration of such effects. I don't know off the top of my head and I haven't take time to look.

Would that suggest that temperature leads carbon, at least to some degree?

Sure. If you look at the Mauna Loa data, you should see that the total atmospheric CO2 looks like a tilted sine wave. There is a very strong annual flux of CO2 in and out of the atmosphere every year, and then a steady continuous increase going on all the time as well.

In a way, the Earth "breathes". The effect is seasonal, and it arises mostly (I think) from changes in the way vegetation takes in and emits CO2 between winter and summer. The total flux of CO2 involved is huge.

However, it is not cummulative. The carbon taken into vegetation is released again later. There's a continual cycle of carbon between atmosphere, vegetation, soil and ocean, going on all the time. The human input is a bit different, because we are basically acting as a way for carbon from geological reserves (fossil fuels) to make its way into the carbon cycle, and this leads to a gradual increase in carbon in all parts of the carbon cycle: the atmosphere and ocean especially.

Basically, the carbon cycle consists of several "reservoirs" of carbon, each with a different total capacity, and with carbon fluxes between them. Here's a diagram, from an online textbook: http://www.uwsp.edu/geO/faculty/ritter/geog101/textbook/earth_system/biogeochemical_cycles.html .) The numbers are the capacities of the reservoirs, and the total amount of carbon moving between them annually.

What human emissions do is add 5.5 GigaTonnes per year into the atmosphere. Over a century, this has resulted in a large increase in total carbon in the atmosphere, ocean and terrestrial reservoirs. But at the same time, there is about 90 Gigatonnes per year going each way between ocean and atmosphere, and about 120 Gigatonnes per year each way between atmosphere and vegetation/soil on land. Temperature effects can shift the balance of the reservoirs a bit, enough to make the net atmospheric increase rise or fall a bit, and I would guess this is the main reason for the correlation you have observed.

Cheers -- sylas

 

[Rickeroo]

Thanks Sylas. Yes, the sine wave at Manua Loa makes perfect sense with the seasonal vegetation level, as does the net addition of CO2.

It also makes sense that temperature would have an effect of CO2 transfer or absorption, something to be looked at anyway.

My next task will be to correlate the temperature with the rise in CO2, and to correlate the melting ice with the rise in sea level.

 

[Richard111]

silas - thank you for your comments and advice way back in post #155.
First I must admit I am not the originator of that thought experiment. I read it on a blog first, but sadly did not record the url. Later I attempted to work out the mass of the atmosphere on 1sq/m at standard pressure and found my answer was about right. This chuffed me no end, so I attempted to calculate the mass of global CO2 and got it wrong.

Minor correction here: CO2 is about 0.04% by volume; so you have to scale by 44/29 (the molecular weight of CO2 and the average molecular weight of air) to get pretty close to 6 kilograms.

Your correction improved my calculation but not enough yet. I was attempting to calulate the global mass of CO2. There are 10^6 square meters in a square kilometer so we have 6 x 10^6 kg/km^2.
From this link: http://www.net-comber.com/worldarea.html I selected 510,072,200 km^2 as the total global surface area and arrive at 3.06 x 10^15 kg. (umm.. still something wrong)

Towards the end of your post you mention dealing with the atmosphere in slabs and integrating the temperature changes, well, its 55 years since anyone last attempted to teach me calculus, so I am a lost cause there.

A point for clarification; in our column of well mixed gasses, as we progress upwards with a constant lapse rate, we not only have less temperature, we also have less density so the total mass of CO2 per "slab" will also be less. Therefore I feel we must take into account reduced mass as well as temperature.

I would like to get hold of the following book but it is not available in my local library. Might be in the Uni library. I will have to wait until Amazon offers used copies at much reduced prices. A short critique at:

http://climatesci.org/2006/05/05/co2h2o/

Relative Roles of CO2 and Water Vapor in Radiative Forcing
Filed under: Climate Change Forcings & Feedbacks, Climate Change Metrics — Roger Pielke Sr. @ 6:09 am
In the second edition of our book

” Cotton, W.R. and R.A. Pielke, 2006: Human impacts on weather and climate, 2nd Edition, Cambridge University Press, New York, in press ”

 

[shredder666]

before I make my views on this, how would current rate of change in global temperature affect the rate of which major greenhouse gases such as water vapour from the ocean, methane in garbage dumps, and CO2 trapped in soils, are released?

 

[sylas]

Your correction improved my calculation but not enough yet. I was attempting to calulate the global mass of CO2. There are 10^6 square meters in a square kilometer so we have 6 x 10^6 kg/km^2.
From this link: http://www.net-comber.com/worldarea.html I selected 510,072,200 km^2 as the total global surface area and arrive at 3.06 x 10^15 kg. (umm.. still something wrong)

That sounds pretty much exactly correct. That's what is given in wikipedia's Carbon Dioxide article. (Wikipedia is an unsafe source for this forum, but it's okay as a confirmation of your calculation.)

Note that people often speak of the mass of carbon in the atmosphere, which would be 12/44 times the mass of carbon dioxide. This corresponds to about 8.2 * 10¹⁴ kg, or 820 Gigatonnes. The carbon cycle diagram I've just posted gives 750; but that may just be an older value, corresponding to about 355ppm CO2 in about 1990.

A point for clarification; in our column of well mixed gasses, as we progress upwards with a constant lapse rate, we not only have less temperature, we also have less density so the total mass of CO2 per "slab" will also be less. Therefore I feel we must take into account reduced mass as well as temperature.

Quite so. However, we often use pressure as the altitude co-ordinate, which doesn't have that problem. This makes all sorts of calculations more straightforward.

I would like to get hold of the following book but it is not available in my local library. Might be in the Uni library. I will have to wait until Amazon offers used copies at much reduced prices. A short critique at:

http://climatesci.org/2006/05/05/co2h2o/

I can confirm for you right away the main conclusion. H2O is easily the most important gas in our atmosphere for giving the greenhouse effect. I've noted this a couple of times in the thread. An increase in humidity has a very strong effect; much more than a similar increase in carbon dioxide.

This is, in fact, the reason why "water vapour feedback" is such an important part of the more complex question of climate sensitivity. The amount of water in the atmosphere is mostly a function of temperature.

Industry emits huge amounts of water vapour into the atmosphere. Ironically, many pictures trying to show a picture of pollution are actually showing discharges of water vapour. A picture of CO2 emissions is much more boring, because it is invisible.

But the effect of human H2O emissions is almost nil on atmospheric water vapour. Anything extra we add comes out again almost immediately, because the water cycle is so rapid. So you really can't hope to increase humidity just by adding water. The best way to increase the water content of the atmosphere is simply to heat things up somehow. That's why carbon dioxide, despite being a smaller part of the total greenhouse effect, is what is forcing the changes. The warming effect of carbon is amplified by the effects of additional water from this feedback. See our previous discussion on "Planck response" and feedback. There are a lot of other effects to consider as well. Water vapour will reduce the lapse rate, which is a negative feedback; and changes to cloud can reflect sunlight (negative feedback) and also absorb infrared even more strongly than gaseous vapour (positive feedback). It looks like we may be pulling apart some of the scientific literature on this question as the thread progresses.

Cheers -- sylas

 

[Richard111]

Water vapour will reduce the lapse rate, which is a negative feedback; and changes to cloud can reflect sunlight (negative feedback) and also absorb infrared even more strongly than gaseous vapour (positive feedback). It looks like we may be pulling apart some of the scientific literature on this question as the thread progresses.

When water vapour reaches dew point and starts to condense on whatever CCN's are available, there is a drop in air pressure. I believe this can result in fierce updraughts within large cumulus clouds. You can see this effect here in Pembrokeshire. The "Finger of God" extending upwards from the cloud tops. Very impressive and a warning to any aircraft to keep clear. I would assume a lot of energy would be transported upwards even while the cloud is accumulating energy from the sunlight above and longwave radiation from below. At night I assume the "feedbacks" will change due to lack of solar input.

I feel I must acquire more understanding of the "greenhouse effect" of water vapour and liquid water (clouds, fog) and ice crystals (cirrus clouds) in the atmosphere and the effect on positive/negative feedback. Possibly, then, an understanding of the "feedback" due to increasing CO2 will be more clear to me.

So back to my imaginary 1m^2 column of air and a dry adiabatic lapse rate of 3C per 1000 feet and assuming the air temparature has stabilised from about 2 meters above surface level I expect the air temperature at 10,000 feet (plus 6 feet or so) to be some 30C cooler.

Now consider the air in 1000 foot slabs/layers, each layer 3C cooler than the layer below and that a net transfer of heat will only flow from hotter to cooler. We must also bear in mind that each layer has less mass than the layer below. The flow of energy is upwards. It appears only the bottom layer of a 1000 feet or so seems to have any feedback to the surface even as the net flow is upwards. It has been established that increasing the water vapour content does not effect the dry adiabatic lapse rate therefore any increase in CO2 also has no effect in dry air.

Sea surface temperatures appear to range from a minimum of -2C to a maximum of about 33C. A much smaller variation than on land and also less inclined to change sharply over short time periods. Seeing that slightly more than 70% of the Earth's surface is water I thought this might be a good place to start. In my attempts to gain some knowledge about water I have been looking at the Water Absorption Spectrum page on Martin Chaplin's site.

I must confess I find this site very heavy going, but extremely interesting. I never knew water could take on so many different molecular configurations which seem to be responsive to different temperature regimes. Every change seems to have its own spectral response. Quite awesome.

On the above page is a graph titled The visible and UV spectra of liquid water

http://www1.lsbu.ac.uk/water/images/watopt.gif

You can see clearly how light and some UV can penetrate quite deeply into clear water. (I read somewhere that you can get sunburn under water and thought Huh!) The area of the graph I am trying to get to grips with is the IR region. From about 3µm to 100µm. Here penetration seems limited. If I read that correctly I fail to see how downwelling IR from any source can possibly provide any significant heating into water. From other literature (haven't found it on Chaplin's site) I read that IR reacts with surface molecules of water to increase the rate of production of water vapour. How this may be quantified I haven't clue.

So to satisfy my curiosity I will suspend a shielded IR source over a measured quantity of water and try to record any temperature change. The IR source, still to be obtained, will be a circular slab of steel or cast iron of about 2kg mass and the shield will be a small drum such that airflow past the source is minimal but heat radiated downward will have a clear path to the water surface. Should be interesting. I will post the result in due course.