Global Warming and Electromagnetic Radiation

[parmenides3]

AF: you are correct; I should have inserted the second conditional (could). Note thought hat I am not suggesting anything definitive here; it's just an interesting paper.

I'd be surprised if there was no lag of CO2 behind temp in the past, because it stands to reason that the natural processes which produce CO2 would have to experience a change in conditions to stimulate a change in output. It also seems reasonable to assume that the initial changes in T are caused by changes in the relationship of Earth's surface to the Sun, in particular, obliquity. However, it looks like no single Milankovitch forcing is potent enough in itself to stimulate the kind of climate shift that happens at the start and end of full glacial/interglacial periods; there needs to be a combination of positive changes.

As to what causes the 'tipping point'; the only clear suggestion at the moment is that the changes in T stimulate a phase shift in ocean circulation patterns, which in turn releases CO2 (as a result of increased overturning of the bottom ocean, where CO2 (& possibly clathrates) are trapped). Being a GHG, the extra CO2 encourages the entire system to store a small but significant extra amount of energy/heat, thus starting the feedback/forcing process. If the paper puts this theory to the test, by suggesting that the T - CO2 link is less clear than this, or even that the T rise/phase shift requires the extra CO2 feedback, then it makes an important contribution to our understanding of climate processes, which in turn may have implications for how we expect the climate to respond in the future to the current forcings.

In the meantime, I'll try to find out more about the constraints on climate sensitivity, in other words, why CO2 increases only connect to a certain amount of warming and no more (note the deliberate omission of the causal link, there).

:)P

[Admiral_Bobski]

Just a quick post to 1) bump this thread up in the hopes of rekindling the passion in this part of the debate , and 2) post this link:

http://www.physicalgeography.net/fundamentals/6f.html

This link could be useful if we are to pursue the mathematics of the CO₂ problem. Of course, there's a possibility that I'm the only person vaguely interested in this, in which case I apologise...but at least I won't lose the link now!

CB

EDIT - can I also check with Hiya, does the CO₂ IR spectrum tell us that the CO₂ molecule only absorbs radiation at around 0.5µm and 2.4µm? And are the 80% and 20% the relative amounts of energy absorbed at each of these wavelengths? Cheers

And while I'm at it - to save myself a bit of work(!) - can anyone tell me the approximate altitude at which the majority of the atmospheric CO₂ is accumulated?

Edited March 20, 2007 by Captain_Bobski

[Hiya]

Just a quick post to 1) bump this thread up in the hopes of rekindling the passion in this part of the debate , and 2) post this link:

http://www.physicalgeography.net/fundamentals/6f.html

This link could be useful if we are to pursue the mathematics of the CO₂ problem. Of course, there's a possibility that I'm the only person vaguely interested in this, in which case I apologise...but at least I won't lose the link now!

CB

EDIT - can I also check with Hiya, does the CO₂ IR spectrum tell us that the CO₂ molecule only absorbs radiation at around 0.5µm and 2.4µm? And are the 80% and 20% the relative amounts of energy absorbed at each of these wavelengths? Cheers

And while I'm at it - to save myself a bit of work(!) - can anyone tell me the approximate altitude at which the majority of the atmospheric CO₂ is accumulated?

If you are concerned with the near IR range, there are more absorptions than that. Where did you get the 0.5µm from?

What you could say along the lines of what you have said is that there are two absorptions at ~2.7 (double peak) and 4.2µm with the latter having an ~80% absorbance.

If thats too simple for what your upto I can go into more detail.

[Admiral_Bobski]

If you are concerned with the near IR range, there are more absorptions than that. Where did you get the 0.5µm from?

What you could say along the lines of what you have said is that there are two absorptions at ~2.7 (double peak) and 4.2µm with the latter having an ~80% absorbance.

If thats too simple for what your upto I can go into more detail.

Thanks for that, Hiya - I'm obviously reading the darned thing all wrong! (The small peak is at around 500cm^-1 - is that not 0.5µm?) There again, I don't believe I've ever had the pleasure of an IR spectrum before, so it's no wonder I'm muddled! Still, the figures you've given me should, hopefully, be what I'm after. Now I need to know where all that CO₂ is and I'm all set to do some calculations!

Cheers

CB

PS - What are the other absorptions?

[Hiya]

Thanks for that, Hiya - I'm obviously reading the darned thing all wrong! (The small peak is at around 500cm^-1 - is that not 0.5µm?) There again, I don't believe I've ever had the pleasure of an IR spectrum before, so it's no wonder I'm muddled! Still, the figures you've given me should, hopefully, be what I'm after. Now I need to know where all that CO₂ is and I'm all set to do some calculations!

Cheers

CB

PS - What are the other absorptions?

nah tis not.

Wavenumbers (nu bar) (cm^{-1) = 1/wavelength (cm)}

^{Wavelength (cm) / 100 = wavelength (m)}

^{1µm = 1e-6m}

^{so 500 wavenumbers = 20 microns}

^{IR spectra are not a pleasure believe me!}

^{There are 3 IR active modes for carbon dioxide, the ones in my last post cover the absorptions in the near-IR I believe. Have a look in here http://www.astrochem.org/CO2H2O.html you might find something useful.}

^{Intresting article of releavence http://www.nsf.gov/news/news_summ.jsp?cntn...187&org=NSF}

^{I'd guess the carbon dioxide would probably be in the upper troposphere.}

[Admiral_Bobski]

nah tis not...IR spectra are not a pleasure believe me!

I'd guess the carbon dioxide would probably be in the upper troposphere.

Thanks for explaining that (and that's what I get for not reading the graph properly - my eyes read "wavenumber" but my brain read "wavelength" - doh!). And thanks for the links; I'll check them out later on

I'm thinking upper troposphere, too - better check I've got relative abundances and altitude numbers, though!

Back later,

CB

[Admiral_Bobski]

By the way, to anyone who hasn't worked out where I'm going with this, let me explain...

The website I linked to previously has various details on absorption and emission of radiation, including graphs showing the distribution of wavelengths and relative intensity emitted from both the Sun and the Earth.

Now, I'm not talking about adhering strictly to details, and nor am I talking about an analysis of the entire Earth's climatological system, but...

It should be possible to estimate the amount of energy radiated from the Earth in the wavelengths that CO₂ absorbs (and re-emits). It should be possible to work out an average density of CO₂ molecules in the atmosphere. And it should be possible to work out how much of that energy is re-emitted back towards the Earth.

Now, this is all paper-napkin maths, but it should be possible to estimate an actual figure for the CO₂ forcing from first principles - I know someone, somewhere, must have done calculations like this, but one never sees the calculations, just the final figure. Is the figure quoted actually accurate? Would our paper-napkin calculation be in the ballpark? If our figure is out by orders of magnitude then someone, somewhere, has got something wrong.

No, I'm not claiming to be smarter than the scientists and mathematicians, but this kind of exercise is extremely useful for understanding flaws in our logic and reasoning, as well as being educational and - dare I say it?! - interesting.

CB

[Hiya]

Excellent, I look forward to the results!