[Bored chemist]

shows the oxygen absorption spectrum

No
It shows the oxygen and ozone absorption.
The Ozone massively dominates.

The O2 molecule isn't polar, it hasn't got a "handle" for IR to hold onto and it doesn't absorb IR.

[alancalverd]

So, how do they make the place warmer than it was a thousand years ago?

They don't. It's the water that changes things significantly, just like it has done every 100,000 years, as far as we know.

[alancalverd]

The Ozone massively dominates.

and as long as the sun shines and there's oxygen in the stratosphere, the ozone will continue to dominate where water doesn't.

The O2 molecule isn't polar, it hasn't got a "handle" for IR to hold onto and it doesn't absorb IR.

Scarcely relevant since H2O absorbs or reflects so much of the IR spectrum and has 300 times as much heat capacity as all the other consitituents of the atmosphere.

[Bored chemist]

and as long as the sun shines ...

You will still have been wrong to say

shows the oxygen absorption spectrum

And you will still have been wrong if there's ever no O2 in the air.

300 times as much heat capacity as all the other consitituents of the atmosphere.

Gas        Specific heat capacity at constant pressure (J kg-1K-1)   
Air                           993   
Argon                   524   
Carbon dioxide   834   
Carbon monoxide   1050   
Helium                   5240   
Hydrogen           14300   
Nitrogen                   1040   
Oxygen                    913   
Water vapour            2020   

Are you muddling latent heat with heat capacity, or are you just something like ten thousand fold wrong?
(Given that air is roughly 1% water and 99 % other stuff).

[alancalverd]

You mustn't ignore the fact that water is unique in changing state in the atmosphere, appearing as gas, liquid and various forms of solid, with very large latent heat exchanges between phases and a very large range of content from almost none to 5% by volume of gas, and the distribution in all three dimensions and phases is necessarily chaotic but bounded. It is also unique in transferring very large amounts of energy between the solid/liquid surface and the atmosphere, and determining the albedo at all levels. 

Including hydrogen and helium in your table of gases might make it relevant to the greenhouse effect on Jupiter but these gases are depressingly absent from the stuff I breathe.

[Bored chemist]

You mustn't ignore the fact that

I didn't- it was you who tried to lump it in with heat capacity.

And, the weather forecasters also don't ignore it- they are quite good at predicting rain.
They also consider it in climate modelling- for exactly the reasons you give.

So what point did you think you were making?

Including hydrogen and helium in your table of gases might make it relevant to the greenhouse effect on Jupiter but these gases are depressingly absent from the stuff I breathe.

When you come back down to this planet, you will find about 5ppm of helium in the air. The hydrogen concentration is about a tenth of that.
BTW, neither of them is a greenhouse gas.

[evan_au]

The O2 molecule isn't polar, it hasn't got a "handle" for IR to hold onto and it doesn't absorb IR.

Could you explain something for me, please?
- Comparing O₂ and CO₂...
- Both have a linear shape
- Both are symmetrical, so there is no overall electric dipole
- And yet CO₂ interacts more strongly with IR than O₂?

Is there an internal electric dipole in CO₂, or additional vibration modes (eg bending)?

[Bored chemist]

Infrared absorption is related to molecular vibration (and, to some extent, rotation but ...).
When an oxygen molecule O2 vibrates there's never a dipole.
There are a number of ways a CO2 molecule can vibrate.
If it bends then that gives it a dipole. If it vibrates in a way where the carbon stays still but the oxygens move symmetrically in and out there's no dipole change, so that vibrational mode doesn't absorb IR.
If it vibrates where the oxygens stay more or less still, but the carbon bounces between them then that has a change in dipole and it emits IR (and absorbs it).

https://en.wikipedia.org/wiki/Infrared_spectroscopy#Number_of_vibrational_modes

Obviously, hydrogen H2 has no dipole and it is still unpolarised when it stretches so it can't contribute to a greenhouse effect (even on Jupiter)
Technically, the half deuterated version HD can.
https://www.nature.com/articles/166563a0
Helium has even fewer options.

[alancalverd]

Here's an interesting spectrum

https://en.wikipedia.org/wiki/Sunlight#/media/File:Solar_spectrum_en.svg

The difference between the "space" spectrum and the "sea level" spectrum is massively dominated by the absorption of water, with CO2 very much an afterthought in the tail.

But don't let the facts spoil a profitable hypothesis.

[alancalverd]

Anyway, back to the ice cores.

If we ignore the CO2 lag and suppose that sudden increases of CO2 were responsible for sudden temperature changes, those of a curious nature would ask what caused those sudden bursts of CO2?   

Obviously, volcanic activity. Which projected massive amounts of CO2 and dust into the atmosphere. So we look at the ice cores and see....that the dust maxima mostly coincide with temperature and CO2 minima.

Bloody Russians.   

[chiralSPO]

Here's an interesting spectrum

https://en.wikipedia.org/wiki/Sunlight#/media/File:Solar_spectrum_en.svg

The difference between the "space" spectrum and the "sea level" spectrum is massively dominated by the absorption of water, with CO2 very much an afterthought in the tail.

But don't let the facts spoil a profitable hypothesis.

Exactly! The water part of the spectrum is saturated. That's why changes in water concentration don't have as significant an effect. On the other hand, where CO₂ absorbs, the spectrum is NOT yet saturated, and therefore will be related to concentration. Also, I see these spectra are overlaid with the blackbody radiation of incoming solar radiation. I would highly recommend comparing to the blackbody spectrum of the earth too. You will find that the frequencies of IR that interact strongly with CO₂ make up a very small portion of the incoming energy, and a significant portion of the outgoing.

outgoing.png (162.06 kB . 700x348 - viewed 4487 times)

[Petrochemicals]

Due to the convective nature of the water cycle, what frequencies does water emit radiation at during condensation? Whilst I understand water condensation may conduct energy to the air around it and thus the gaseous emission frequency will prevail, is the condensate frequency different.

[Bored chemist]

The difference between the "space" spectrum and the "sea level" spectrum is massively dominated by the absorption of water, with CO2 very much an afterthought in the tail.

Do you remember me saying this?

I'm sure I have seen you failing to properly understand the idea of a saturated transition as you seek to explain why CO2 isn't important to climate change.
Well, that argument is much more nearly valid for water vapour.
So the change in net solar gain with water vapour in the air is smaller.

[Bored chemist]

, what frequencies does water emit radiation at during condensation?

There's a law of physics which says that things (almost always) emit radiation at the same wavelengths that they absorb it.
So, the emission spectrum of the liquid water will look the same as the absorption spectrum.

https://en.wikipedia.org/wiki/Kirchhoff's_law_of_thermal_radiation

[alancalverd]

Exactly! The water part of the spectrum is saturated. That's why changes in water concentration don't have as significant an effect.

So you say there is no positive feedback mechanism? And clouds don't affect surface temperature? You'd have a problem telling a meteorologist, whose career depends on knowing a bit about atmospheric water.

[Bored chemist]

So you say there is no positive feedback mechanism? And clouds don't affect surface temperature?

I think you will find that what we say is... what we said.

Only MarkPawelek is naive enough to think that there's no positive feedback.
There are at least 3 major pathways for it
1 Ice is reflective
2 Methane trapped as hydrates would be a very potent greenhouse gas
3 water vapour

[alancalverd]

So the water absorption spectrum isn't saturated, but Chiral says it is. It's very difficult to challenge a consensus where there isn't one!

[Bored chemist]

So you say there is no positive feedback mechanism? And clouds don't affect surface temperature?

Clouds provide a negative feedback mechanism.
Perhaps you should establish a consensus with yourself.

[evan_au]

the cyclic fine structure of the Mauna Loa data

This is a seasonal pattern.

Since it is less than 11 years, it is not talking about climate.
- For cycles of 1 year, you have to look for factors impacted by Earth's annual orbit around the Sun, rather than weather or anthropogenic greenhouse gases.

Obviously, volcanic activity

I don't see how volcanic activity can produce semi-periodic results.

There have been suggestions that some of the Milankovitch cycles could/should drive some of the Earth's climate behavior in semi-periodic ways.
- One of the more surprising suggestions was that the angle of Earth's orbit relative to the plane of the ecliptic varies over long periods. If Earth's orbit were aligned with the ecliptic, there would be more zodiacal dust hitting the Earth about every 100,000 years.
- Perhaps increased fine dust in the upper atmosphere could affect the dynamics of solar absorption?

See: https://en.wikipedia.org/wiki/Milankovitch_cycles#Orbital_inclination

[alancalverd]

Quote from: alancalverd
the cyclic fine structure of the Mauna Loa data
This is a seasonal pattern.

Yes, but it's wrong! The Mauna Loa CO2 peaks quite sharply in the northern summer, when anthropogenic emission is minimal, so there must be something out there which generates more CO2 than human activity, and more when the temperature rises.

Quote from: alancalverd
Obviously, volcanic activity

I don't see how volcanic activity can produce semi-periodic results.

Neither do I, but those who say CO2 has been the historic driver of temperature have generally offered volcanic activity as the source of those sudden rises in CO2. I might accept that by sheer coincidence there have been huge peaks of volcanism almost exactly every 100,000 years and of almost identical magnitude, if only the dust traces supported that hypothesis.

Problem with the dust traces is that whilst they mostly peak fairly close to temperature minima, there is no clear lead-in. If dust caused low temperatures (and we know that is true in the short term for volcanic dust), you'd expect  to see the dust level rise before the temperature started to drop, but it's almost as though nothing happens until the temperature is very close to a minimum, whereupon the dust level suddenly rises then drops again. 

However I look at the Vostok data, it only seems to make sense  if water is the driver of temperature, and biological activity generates more carbon dioxide  when the temperature rises. Why the shape of the dust trace? I'm not sure, but if the planet is very cold, most of the water will be in the expanded ice caps so you won't get much rain falling in the unfrozen areas. Desertification, dust bowl, reduced albedo, and the cycle restarts.