How does Carbon Dioxide increase global temperatures?

[SteamyTea]

2 minutes ago, A_L said:

CO₂ is a strong absorber of infrared radiation

I get that, but the man on the Clapham omnibus won't.

It is why I have been trying to find a decent 'mechanical' description, people understand that.

The best I can come up with at the moment is that a photon is like a hammer, they come in different sizes and weight.

A molecule is like a nail, the larger the molecule, the larger the 'head'.

So it is possible to hit a large nail with a small hammer, but it does not do much, but hit a small nail with a large hammer, it does a lot.

Now my analogy is breaking down as I am not sure if a large hammer is infrared or ultraviolet.

Maybe light is a bunch of hammers, and only one needs to hit a nail to get it moving.

Probably why there are no simple 'mechanical' descriptions, it just does not work like that.

 

[Ed Davies]

1 hour ago, A_L said:

Try this :-

 

CO₂ is a strong absorber of infrared radiation. It is then re-emitted. Think of the CO₂ in several layers which absorb the same amount of infrared transmitted through it. The lowest layer re-transmits 50% back to the ground and 50% to the second layer which then absorbs and retransmits 50% back to layer 1 and 50% on to layer three (and so on). So an increase in CO₂ increases retained infrared radiation. Thus the temperature rises.

 

That's true as far as it goes but such a tiny part of the story that stating it like that is wildly misleading, so it's a pity it's such a widely used explanation.

 

The dominant mechanism for heat transfer up through the lower atmosphere is by convection of sensible and latent heat. This can be seen because the lapse rate (the rate at which temperature decreases with height) is set by the dry or wet adiabatic lapse rates (i.e., the rate that dry or saturated air cools with expansion). Eventually the heat transferred up from the ground has to go somewhere and, because space is pretty good at stopping convection and conduction, it has to go by radiation. It does this by being radiated from greenhouse gasses from fairly high up the atmosphere. Obviously radiation to space happens from all sorts of layers but it's helpful to think of it just radiating from one average layer. As the concentration of greenhouse gasses in the atmosphere increases this effective radiation layer rises in the atmosphere though stays at the same temperature to maintain the constant radiation power. There's now more atmosphere below it for the adiabatic lapse rate to work over so the surface temperature increases.

 

This way of looking at it was first published by Nils Ekholm in the Quarterly Journal of the Royal Meteorological Society in January 1901 in a paper titled “On The Variations Of The Climate Of The Geological And Historical Past And Their Causes”.

[epsilonGreedy]

2 hours ago, Ed Davies said:

Eventually the heat transferred up from the ground has to go somewhere and, because space is pretty good at stopping convection and conduction, it has to go by radiation. It does this by being radiated from greenhouse gasses from fairly high up the atmosphere.

 

 

There is a hole in your explanation. In order for these greenhouse gasses in the upper layers of the atmosphere to radiate out energy into space they first have to capture heat radiated upwards from lower in the atmosphere. In the absence of this point you give the impression that CO2 hovers over the main body of the atmosphere waiting to be warmed by convected heat transfer and then the CO2 acts as a heat export layer by taking over transport of energy out into space at the point where convection ceases to function due to a thinning atmosphere.

 

This sounds a little bonkers because such a mechanism describes CO2 as the opposite of a greenhouse gas.

[epsilonGreedy]

13 hours ago, SteamyTea said:

I get that, but the man on the Clapham omnibus won't.

 

 

You are going far too deep trying to explain photon impacts and molecular resonance to the man on the Clapham omnibus.

 

Just explain it this way: Planet earth is like a cold blooded lizard which generates negligible internal heat. Only the sun really warms the earth but just above the earth's lizard skin the temperature of outer space is more than  200 degrees below freezing. Fortunately the earth has a few thin duvet covers called the atmosphere. The thickest duvet is water vapour and this is topped up with the CO2 and Methane duvets.

 

For the past 2 million years the earth was a chilly place where ice ages are the norm. Human civilization has florished over the past 10,000 years during a brief inter glacial warm period triggered when the earth wandered a bit closer to the sun and warmed a tad ending the last ice age. Scientists are a little puzzled as to why the earth has not started to cool as we are due to fall into a new ice age. The halt in the typical temperature drop into the next ice age seemed to coincide with humans inventing agriculture which increased the thickness of the methane duvet. Despite being warmed a little by the thicker methane duvet the earth has been cooling for a few thousand years just slower than expected.

 

With the earth's climate teetering at the edge of the next ice age mankind invented the industrial revolution and over the last 200 years the tog value of the thin CO2 duvet has increased by 30% and halted the downward temperature decline into the next ice age. This is fortunate because it will buy humans a few extra thousand years to work out how to manage the climate to prevent the next ice age. If the earth lapsed into a new ice age billions of humans would die.

 

 

Edited January 2, 2020 by epsilonGreedy

[Ed Davies]

12 hours ago, epsilonGreedy said:

In the absence of this point you give the impression that CO2 hovers over the main body of the atmosphere waiting to be warmed by convected heat transfer and then the CO2 acts as a heat export layer by taking over transport of energy out into space at the point where convection ceases to function due to a thinning atmosphere.

 

Sorry if you got the impression that I meant that was the main mechanism but it is part of what happens. If there were no greenhouse gasses in the lower atmosphere there would still be the greenhouse effect as heat would be transferred to the layer of greenhouse gasses in the upper atmosphere both by direct radiation from the surface and via convection and conduction in the otherwise transparent layer of gasses in the lower atmosphere.

 

Look at it another way: the effective radiative temperature of the Earth as seen from space (e.g., an astronaut on the Moon pointing their IR thermometer at the Earth) is set by the amount of solar radiation absorbed by the Earth (in turn derived from the solar “constant” and the albedo of the planet as seen from the direction of the Sun) and the emissivity of the effective radiating layer in the atmosphere (which is smeared out in height due to radiation randomly making it past higher layers and being of wavelengths which aren't absorbed so much, including wavelengths which are directly radiated to space from the surface). The temperature of the surface is then set by the temperature of that effective radiative layer increased by the effects of the lapse rate below the layer down to the surface. My point is that the effects of adiabatic cooling dominate in determining that lapse rate and radiation backwards and forwards between layers in the lower atmosphere is a secondary consideration.

 

12 hours ago, epsilonGreedy said:

This sounds a little bonkers because such a mechanism describes CO2 as the opposite of a greenhouse gas.

 

Nope, remember that the emissivity of a material is equal to its absorptivity, you can't have one without the other.

 

Professor Mike Merrifield is probably better at explaining this than, particularly with the advantage of animations and gestures.

 

 

[joe90]

@epsilonGreedy what an elegant description, even I can understand that!!!

[Ed Davies]

12 hours ago, epsilonGreedy said:

when the earth wandered a bit closer to the sun

 

Nope, it's the same distance as always, on average.

 

Yes, maybe agriculture caused a bit of warming though I'd like to see some references that say it was due to methane rather than carbon dioxide.

 

It's controversial whether or not the next dip in the Milankovitch cycles would cause an ice age. The consensus now is that they won't for quite a while: https://en.wikipedia.org/wiki/Milankovitch_cycles#Present_and_future_conditions “Earth's orbit will become less eccentric for about the next 100,000 years, so changes in this insolation will be dominated by changes in obliquity, and should not decline enough to permit a new glacial period in the next 50,000 years.”

 

Most importantly, our current CO₂ emissions are way greater than anything needed to hold off the start of any new ice age for quite a while.

[Ed Davies]

2 minutes ago, joe90 said:

@epsilonGreedy what an elegant description, even I can understand that!!!

 

Yes, elegantly simple. Just complete bullshit.

[SteamyTea]

1 hour ago, Ed Davies said:

Yes, elegantly simple. Just complete bullshit.

Yes.

I have never been happy with the 'blanket' description, or the greenhouse one, for that matter.

 

I am still working on a hammer hitting something analogy.

 

[joe90]

13 minutes ago, SteamyTea said:

 

I am still working on a hammer hitting something analogy.

Yes I could understand anything that involves a hammer?

[SteamyTea]

17 minutes ago, joe90 said:

Yes I could understand anything that involves a hammer

So imagine a hammer being a particle of light.  If it is ultra violet light, it is very small, infra red, large.

Now you have a line of nails that have been part pushed into a bit of timber.

With the small hammer, you might hit one or two of those nails, at once.

Large hammer, you can hit 5 or 6 at once.

So the small hammer, the ultra violet light, can easily pass by a nail and miss it, but the large hammer, the infra red light, is almost certainly going to hit some nails.

Those nails are the atoms of different molecules.  The more atoms in the molecule, he more likely it will be hit, especially if the hammer is large.

So a CO₂ molecule is quite small, 3 atoms, but there is a lot of them, a methane atom is larger, 5 atom, but there are less of them.  At best, the hammer can hit all 3 atoms in CO₂.  At best the large hammer could hit all 5 atoms in the CH₄. 

If the hammer does make contact, it is slowed and the kinetic energy is converted to thermal energy.  If it totally misses the molecule, it just carries on, either hitting another molecule, or off into space.

 

How does that sound.  It may need a but more editing to make it shorter, but not got the time to write less at the moment.

[joe90]

Just watched the Merrifield clip above and that made sense to me. The description of Venus and runaway heating was interesting but pleased to hear that we are a long way from that (yet!).

[SteamyTea]

23 minutes ago, joe90 said:

Just watched the Merrifield clip above and that made sense to me

Still does not explain how CO₂ causes warming, just the effects increasing it has.

Though it is good to see that he myth busts the greenhouse analogy.

 

[epsilonGreedy]

7 hours ago, SteamyTea said:

Large hammer, you can hit 5 or 6 at once.

So the small hammer, the ultra violet light, can easily pass by a nail and miss it, but the large hammer, the infra red light, is almost certainly going to hit some nails.

Those nails are the atoms of different molecules.  The more atoms in the molecule, he more likely it will be hit, especially if the hammer is large.

...

7 hours ago, SteamyTea said:

 

How does that sound.  It may need a but more editing to make it shorter, but not got the time to write less at the moment.

 

This over simplifies the situation and skips a key point in the alarmist/skeptic debate. CO2 only interacts with a sub section of the infrared energy escaping from the earth. Methane and water vapour do the same in other segments of the infrared spectrum. When the infrared radiation spectrum is observed from space chunks of it are missing and these chunks are signatures of the three main greenhouse gases interacting with the whole infrared spectrum radiating from the earth.

 

Skeptics argue most of the energy that CO2 can capture is already absent at current levels of CO2 and more CO2 will capture proportionally smaller amounts of energy.

[epsilonGreedy]

22 hours ago, Ed Davies said:

Yes, elegantly simple. Just complete bullshit.

 

 

Much of what I posted was communicated in the most convincing pro alarmist climate change presentation I have seen.

 

The geologist nearly convinced me about climate change by first conceding the validity of most of the skeptic points of dispute.

• Yes CO2 levels have been sustained at 2 or 3 times current levels in the past 500 million years and the oceans did not boil away and indeed earth's biosphere positively flourished in high CO2 conditions.
• Yes we have been experiencing regular clockwork ice ages for millions of years, predictable orbital variations and resulting variations in the sun's heat striking earth are hugely influential in understanding ice ages and warming periods.
• Yes photosynthesis evolved in a geological period when CO2 was much higher and thus it is correct to characterize present CO2 levels as a state of CO2 deprivation from a biological point of view.
• Yes CO2 levels plummeted to an historic low in the last ice age and simple extrapolation indicates that in another ice age or two photo synthesis and life on earth could be snuffed out as the earth's biosphere continues to lock further CO2 (also known as plant food) in rock strata.
• Yes the Minoan, Roman and Medieval warm periods are historical realities unrelated to human generated CO2 but they are relatively minor climatic wobbles from the perspective of a geologist and are most likely explained by the invention of agriculture and rising CH4 which is a significant by-product.
• Yes the world was a touch warmer 2000 to 3000 years ago.
• Yes 300 years of medieval warmth did not melt the Greenland Ice cap illustrating how much thermal inertia and resilience there is in the whole system.

But, and this is a big geological BUT, the record shows that when earth has experienced CO2 levels of where it appears to be heading in the next few centuries the climate could possibly probably flip back to something that preceded the recent series of ice ages. The earth's biosphere would continue to flourish in higher temperatures plus high CO2 and alligators might swim around the coast of Antarctica once again.

 

The principal point of concern would be the inevitability of rising sea level hundreds or thousands of years in the future.

 

Edited January 3, 2020 by epsilonGreedy

[Temp]

C02 levels have certainly been higher in the past but the sun wasn't as bright then and apparently that makes a big difference..

 

https://skepticalscience.com/co2-higher-in-past.htm

 

Quote

 

Another important factor is the sun. During the Ordovician, it would have been several percent dimmer according to established nuclear models of main sequence stars. Surprisingly, this raises the CO2 threshold for glaciation to a staggering 3000 ppmv or so.
 

 

 

A winter duvet is fine in winter but summer is arriving and even a few blankets will be too much.

Edited January 3, 2020 by Temp

[Ed Davies]

12 hours ago, epsilonGreedy said:

Skeptics argue most of the energy that CO2 can capture is already absent at current levels of CO2 and more CO2 will capture proportionally smaller amounts of energy.

 

Which, yet again, entirely misses the point that it's the height in the atmosphere at which the absorbed (and convected) heat is re-emitted that matters.

 

Also, the bands which are captured are not discrete. They are overlapping and smeared out. With more CO₂ more energy is captured in the edges of the bands.

 

Also, also, it's well understood that increasing amounts of CO₂ have proportionally smaller effects. That's completely implicit in the way in which climate sensitivity is discussed in terms of the temperature increase for a doubling of CO₂: it's not specifically doubling from pre-industrial (270 to 280 ppmv to 540 to 580 ppmv), it's any doubling say from the last glacial maximum of 180 ppmv to 360 ppmv or the next doubling from around 550 ppmv to 1100 ppmv.

 

11 hours ago, epsilonGreedy said:

But, and this is a big geological BUT, the record shows that when earth has experienced CO2 levels of where it appears to be heading in the next few centuries the climate could possibly probably flip back to something that preceded the recent series of ice ages. The earth's biosphere would continue to flourish in higher temperatures plus high CO2 and alligators might swim around the coast of Antarctica once again.

 

Indeed, it's entirely possible that a warmer Earth with more CO₂ would overall be “better” in the sense of sustaining more life. But with 7+ billion people currently on the planet right now the adaptation needed to deal with the change would likely be much more harmful in the short term (next few decades to centuries).

[Ed Davies]

21 hours ago, Ed Davies said:

Just complete bullshit.

 

To be clear, I wasn't (just) swearing here: I was using “bullshit” in the sense described here.

[SteamyTea]

It does amaze me that anthropogenic climate change deniers tend to think that those of us that believe, through the science, that we are changing global temperatures, have never heard of all the counter arguements.

But that is moving away from what I need to know, which is a description of how molecules change energy types.

[Temp]

13 hours ago, epsilonGreedy said:

Skeptics argue most of the energy that CO2 can capture is already absent at current levels of CO2 and more CO2 will capture proportionally smaller amounts of energy.

 

Think that partly confuses energy and temperature. Capturing less energy does not necessarily mean a smaller temperature rise. It means a smaller _rate_ of temperature rise. Temperatures keep rising until there is no net inflow of energy. 

 

It's actually the relationship between the surface temperature and the energy lost into space that needs to be considered. Eg how big an increase in surface temperature is required to increases the energy lost to space and restore net zero energy flows?

[Temp]

13 minutes ago, SteamyTea said:

But that is moving away from what I need to know, which is a description of how molecules change energy types.

 

Do you mean how does matter such as the surface of the earth convert visible light to infra red?

 

Think that's mostly to do with temperature and the way photons work. The energy a photon has is determined by its frequency or equivalently it's wavelength.

 

The sun is literally white hot (radiates in the visible spectrum).  The surface of the earth is colder so energy it radiates is mostly in the infrared spectrum. If you heat up some steel the light it emits starts as infra red and changes to visible light as its temperature increases.

 

https://en.m.wikipedia.org/wiki/Photon_energy

 

 

[SteamyTea]

10 minutes ago, Temp said:

Do you mean how does matter such as the surface of the earth convert visible light to infra red?

No.

I am after a simple explination, preferably a mechanical one, that describes how molecules absorb and emit different wavelengths of light.

Why should some molecules not absorb UV but absorb IR.

For that matter, why should snow, which is cold, and made from water, reflect UV and not absorb IR.

It seems a simple enough question to me, but hard to get an easy to understand answer.

[Ed Davies]

16 minutes ago, SteamyTea said:

It seems a simple enough question to me, but hard to get an easy to understand answer.

 

It's only quantum mechanics, of course there should be a simple explanation. ?

[SteamyTea]

31 minutes ago, Ed Davies said:

It's only quantum mechanics, of course there should be a simple explanation

Feynman replied, “Hey buddy if I could explain what I won the Nobel prize for in 2 minutes, it wouldn’t be worth winning the Nobel lyrics for would it!”

 

But was overhearing a conversation today about the the recent MET Office data release.

The daughter, probably late 30s was chatting to her Mother about how it was the second hottest dacade on records, within minutes, the Mother was explaining that the world is always getting hotter, as the Bible said about the flood.

Was a conversation I wanted to join in, but felt best not to.

 

[A_L]

2 hours ago, SteamyTea said:

that describes how molecules absorb and emit different wavelengths of light.

An individual molecule may have several vibrational states which each require different wavelengths of light because the energy of the absorbed photon (and therefore the wavelength) must be the same as the change in energy needed to move between the vibrational states. e.g. a water molecule as three vibrational modes, 1. where the two O-H bonds change length in unison (symmetric stretch) 2.where they oscillate out of phase with each other (asymmetric stretch) 3. where the H-O-H bond angle oscillates.

Different molecules absorb at different wavelengths simply because their vibrational states are different and require different energies.

 

2 hours ago, SteamyTea said:

Why should some molecules not absorb UV but absorb IR.

Absorption at UV wavelengths requires electronic transitions within an atom. Some molecules e.g. H₂O simply do not have constituent atoms with the necessary transitions.

 

2 hours ago, SteamyTea said:

For that matter, why should snow, which is cold, and made from water, reflect UV and not absorb IR.

Ice definitely absorbs IR at a slightly longer peak wavelength than liquid water. Since water cannot absorb UV it must reflect/transmit it