Atmospheric CO2 Levels and Ice Core Determinations of Same - RB

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Atmospheric CO2 levels and Ice Core Determinations of Same Russ Babcock November 7, 2023 The following discussion regarding the validity of Ice-Core-derived atmospheric CO2 levels all started with the question: "If increasing CO2 were natural, why did it not occur in previous interglacials?" This question was posed by a critic in response to my explanation of where the current increase of atmospheric CO2 concentrations comes from. Let's start with that explanation: Where does man's CO2 go if nature is the main source of the increase in CO2?

We might want to consider that CO2 is fluxing back and forth between the atmosphere and the ocean surfaces all the time. Equilibrium will be attained when the amount fluxing in one direction is equal to the amount fluxing in the other direction. Assuming no changes to any other conditions except the addition of more CO2 to the atmosphere (including from burning fossil fuels), this will set up a net flux from the atmosphere to the ocean, in accordance with Henry's Law. Henry's Law states that, at equilibrium, the solubility of a gas in water is directly proportional to the partial pressure of that gas in the atmosphere above the water.

That net flux will reduce to zero, when the same amount going in one direction is equal to the amount going in the other direction. THAT happening will be in strict accordance with Henry's Law. All while this fluxing is happening between the surface layers of the ocean

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and the atmosphere, there is considerable chemistry going on in the ocean that involves the newly immigrated CO2 from the atmosphere. Namely: CO2 + H2O <------------> H2CO3 <-----------> H+ + HCO3- <-------------> H+ + CO3= . These reactions will tend to drive the pH down as more and more CO2 dissolves. All of these reactions tend to re-establish and maintain their own equilibriums - all concurrently. Carbonic acid (H2CO3) is a weak acid, so unless something else is neutralizing the newly created H+ ions, these reactions won't proceed very far in the direction shown above (left to right). BUT, all while this is happening, the ocean is well buffered at about pH 8.1, by virtue of both soluble and relatively insoluble, basic carbonate salt sinks. So this buffering effectively allows more CO2 to dissolve than would otherwise be the case (as in distilled water for example).

You can probably see by the above, that the concentration of CO2 in the ocean will go up as more CO2 is added to the system, but when the new equilibrium is established to account for the additional CO2 to the system, that concentration will be extremely close to what it was before the addition of more CO2 to the system. When we do the math of all the chemical equilibrium equations, and account for the [CO2atm] / [CO2aq] relationship dictated by Henry's Law, you will see it to be the case. So, in summary then, the CO2 added to the atmosphere from outside the atmosphere/ocean "system" sets up a net flux of CO2 from atmosphere to ocean in response to the increased partial pressure of CO2, all in accordance with Henry's Law. Keep in mind that the only species of CO2 in the gas phase (atmosphere) is CO2, while CO2 exists in the aqueous phase (ocean), not only as CO2, but also as HCO3-, CO3=, and H2CO3.

I trust that this helps to visualize what is happening when CO2 is added to the atmosphere of the atmosphere/ocean system from outside the system.

However, the current increase in atmospheric CO2 that we are actually witnessing is from within the system. It is well understood that as oceans have been slightly warming over the last few centuries, the solubility of CO2 decreases, like that of any gas, thus setting up a flux of CO2 in the other 2

direction - from ocean to atmosphere. This is all in accordance with a slight change in Henry's constant (because it is temperature dependent), thus setting up a new and higher [CO2]atm / [CO2]aq ratio at equilibrium. The entire atmosphere/ocean system is NEVER at equilibrium, but Nature is always tending toward it.

The above describes only the surface layers of the ocean and does not include any interactions with the substems below that. I.E It's an extreme simplification.

Critique No. 1 This does not explain a very simple CO2 budget from human emissions that shows that only half of the CO2 emissions show up in the atmosphere.

About 50% are naturally sequestered. Nature is taking a huge amount of CO2 OUT of the atmosphere and not adding to it. #1 unanswered question: If increasing CO2 were natural, why did it not occur in previous interglacials?

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Answer to Critique No. 1 1. CO2 levels from thousands, 10's of thousands, 100's of thousands of years ago, are all based on ice core proxy data. A whole lot of assumptions (masquerading as facts) and statistical manipulations take us from the actual measurements in the ice cores to the derived atmospheric CO2 concentrations.

2. A graph of the stock market with x axis points a year apart misses the peaks and valleys that show up with x axis points a day apart, just as the graphs of CO2 levels derived from ice core data grossly blur the peaks and valleys over the millenia.

3. Ice core data does not properly take into account, diffusion of CO2 through ice over thousands, 10's of thousands, and 100's of thousands of years. Diffusion too, will smooth out the peaks and valleys over time.

4. We know next to nothing about air currents, ocean currents, temperature profiles in the oceans from thousands of years ago. Just wild assed guesses imo, or they were simply ignored. Yet, all could easily affect localized air temps, ocean temps, air CO2 levels, and ocean surface CO2 levels. And what about oceans pH's? We don't know what they were either, and they also affect ocean solubilities of CO2 which in turn affect atmospheric partial pressures of CO2.

In summary, we're looking at such long ago past periods through an extremely opaque lens. I suppose the info is there, but there's nowhere near enough detail to conclude that the atmospheric CO2 levels in the interglacial periods were as indicated by ice core analysis.

So, as to your question: "If increasing CO2 were natural, why did it not occur in previous interglacials?", I ask you, how do you know for sure that it did not occur in previous interglacials?.

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Then we come to the graph you included that showed both accumulated emissions from burning fossil fuels and atmospheric CO2 concentrations from 1960 to 2020. A few facts make this graph almost useless to make the point that you're trying to make.

1. CO2 is being added (fossil fuel emissions) from outside the atmosphere/ocean system to the atmosphere. This new CO2 wants to create a CO2 flux from the atmosphere to the ocean.

2. The ocean surface layer has been warming since the peak of the Little Ice Age, and as a result, wants to create a CO2 flux from the ocean to the atmosphere. Opposite direction!

3. It's obvious even from your graph, that the effect of the warming ocean is greater than the effect from fossil fuel emissions. If all the fossil fuel emissions stayed in the atmosphere, and if the oceans hadn't been warming for so long, we'd be seeing the rate of atmospheric CO2 increasing at double the rate it is now. You say so yourself, when you admit that "only half the CO2 emissions show up in the atmosphere". What you seem to be misunderstanding is WHY that is so.

4. We are not at equilibrium in terms of where Henry's Law is taking us, but we are clearly moving in that direction. If we were to suddenly reduce fossil fuel emissions to nothing, but keep everything else the same, we'd continue to see atmospheric CO2 levels rise until we DO reach equilibrium BECAUSE the warming oceans will still want to gas off CO2. Who knows how much of it is coming from deeper ocean levels (different subsystems with different dynamics)? It is far from being intuitively simple. Near chaos in a never-end quest for equilibrium. That's Mother Nature!

Critique No. 2 - including the response to it, point by point The critique comments are in black font. The responses are below each of the points made, and they are in blue font.

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1. Ice core CO2 measurements are not proxy's, they are direct measurements of CO2, CH4, N2O and recently human-made CFC's in ancient air with the same equipment as direct measurements in the atmosphere, including a 20 year overlap with direct measurements at the south pole.

With one drawback: the air is a mix of 8 years to 560/600 years, depending on the local snow accumulation.

There are no statistical manipulations or assumptions involved, except a firn densification model to calculate the start and end of the closure time of the enclosed air bubbles. The latter is confirmed by accurate measurements in the different layers of firn until full closure.

The actual measurement of CO2 contained in the bubble is indeed direct, and probably very accurate. THAT is not the proxy part of the story. The assumptions made in order to conclude that the amount of CO2 in that bubble is the same as it was when the bubble first closed 800,000 years ago IS the proxy part of the story. Not being familiar with the process involved in ice core analysis, I did a bit of reading about it. After reading https://www.pnas.org/doi/10.1073/pnas.94.16.8343, I found it impossible to have sufficient faith to think that the assumptions and calculations made through the use of modeling techniques, that the present day value of the measurement reliably reflects the value it was 800,000 years ago. Way too big a leap of faith for me. We're talking temperatures and pressures that take CO2 through its triple point, where the gas becomes liquid for goodness sake. How does one accurately model what has happened over 800,000 years under conditions like that? Ice cores might be good at revealing trends, but certainly not actual values.

To the non-geologists among this crowd, and rather than me trying to explain my lack of faith, please read the article I linked above. It is well written, and easily understandable. I believe you will come to a similar conclusion. As Chris Schoneveld said in another email of another thread, "When considering ice cores we are dealing with geological time scales and 6

I have a big problem accepting the low variability of CO2 in ice cores during interglacials when so many major factors are at play."

2. Even the current increase of 120 ppmv over 170 years time would be visible in the worst resolution Vostok ice core (600 years) as an un normal peak of 30 ppmv.

To make your math work, you must be assuming that the current increase of 120 ppmv happened suddenly 170 years ago. That did not happen. In fact, the "abnormal peak" would be much less than 30 ppmv, because the 120 ppmv increase was gradual over 170 years, not sudden. That just helps to make my point - i.e. the obliteration of peaks and valleys.

3. Diffusion was theoretically calculated from a melt layer in the "warm" Siple Dome ice core and only broadens the resolution from 20 to 22 years at middle depth and to 40 years at the bottom of the core. No problem at all.

That plays zero role in the much colder inland cores like Vostok and Dome C. Moreover, if there was much diffusion, the about 8 ppmv/K seen between glacial and interglacial periods would fade over time, which is not the case at all.

Key words "theoretically calculated". Just another way of saying "manipulated". Time can't be scaled up like that, especially when we don't consider or even know what else happened during that time. We don't even know what we don't know.

The "8 ppmv/K seen" was also determined by the same methodology, same theory. How's that different from using a word in the definition of that same word?

4. We don't know much about past oceans, but we know the CO2 levels over the past 800,000 years with 560 years resolution and that shows a reasonable correlation between ice core isotopic temperatures (mainly from Antarctic temperatures where oceanic water vapor condensed to snow) and lagged CO2 levels.

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Semantics? - We know the CO2 level trends over the past 800,000 years.

We do not know the actual CO2 levels in detail over the past 800,000 years.

We should not present them as if we do.

About your question: Any 120 ppmv peak over 170 years would be noticed in every ice core as an unnormal increase beyond the normal 8 ppm/K in/decrease over the past 800,000 years.

Noticed? Probably. But the amplitude of the peak would be dampened, especially so, if the peak amplitude didn't last throughout the time the bubble represents. I wouldn't even trust the value of the peak even if it was wider than the time between the opening and closing of the bubble, because I have no faith that the CO2 level in the bubble at the time of measurement was the same as it was 800,000 years ago.

Second part: 1. True. The observed net sink rate is directly proportional to the extra CO2 level above the equilibrium levels over the past 800,000 years at about 2% net sink rate of the pCO2 difference. See further for the details.

Sorry, I don't know what you're saying here. But it sounds like we're in agreement on this one?

2. True but very modest: the 8 ppmv/K for Antarctic temperatures translates into about 16 ppm/K for global temperatures or about 13 ppmv since the LIA to reach a new equilibrium with the atmosphere. That is all.

Far from the 100 ppmv increase since 1958, caused by the 180 ppmv human emissions over the same time frame...

There is an exact formula to calculate the pCO2 in/decrease of seawater, based on ten thousands of seawater samples, by Takahashi. That gives the same value.

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I don't buy a word after "True". The formula you refer to must be assuming that we not only know the surface ocean temperature differences over the period, but that we also know how much CO2 migrated from lower ocean levels to the surface ocean layer over that same period. We DON'T know that. The ocean is part of Earth's atmosphere/ocean system, but the ocean consists of many subsystems, each with many but unique and variable parameters that are constantly in flux within themselves, and between adjacent subsystems. I doubt that these climate models even consider such detail. And the devil is always in the details.

3. Can't be right. If the pCO2 increase in the atmosphere is higher than the pCO2 increase in the ocean surface, then the net flux is from the atmosphere into the oceans, not reverse.

Correct, but in my "what if" scenario, I did NOT say that the flux reverses.

What I said was, and I quote myself is: "If all the fossil fuel emissions stayed in the atmosphere, and if the oceans hadn't been warming for so long, we'd be seeing the rate of atmospheric CO2 increasing at double the rate it is now." You missed the IF parts. I'm trying to tell you that all the fossil fuel emissions CANNOT and DO NOT stay in the atmosphere, and also in this "what if" scenario, the pCO2 is NOT increasing so there is no increased flux from the ocean. The reason the increase of [CO2]atm would be double is purely because the scenario impossibly calls for 100% of the emissions to stay in the atmosphere. The point I'm trying to make is that some fraction of the increase to the atmosphere comes from fossil fuel emissions (I say 2% of it, certainly not 50%), so the rest of the increase must come from somewhere else, and Henry's Law conveniently tells us that that somewhere else is the ocean, BECAUSE it has been warming since the peak of the Little Ice Age. The rest of your reasoning is rather strange: if all human CO2 remained in the atmosphere ánd the oceans were a net source, then the increase in the atmosphere would be larger than that by human emissions alone. The fact that the increase is smaller is proof that the oceans (and plants) are net sinks, not net sources...

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I presume that by "human CO2", you mean fossil fuel emissions.

NO, I'm not saying that at all. I'm saying that the increase to the atmosphere would double because instead of seeing an increase equivalent to 50% of the fossil fuel emissions, we'd be seeing an increase equal to 100% of the fossil fuel emissions. That's double. And NOT strange.

4. Indeed we are far from equilibrium now: 120 ppmv above (!) equilibrium, which for current average sea surface temperature is around 295 ppmv, not 415 ppmv as is observed. If human emissions suddenly stopped, the oceans would continue to absorb CO2 at the same rate in the first year, a little less the second year, etc... in ratio to the pCO2 difference with the equilibrium, until equilibrium is reached with an observed half life time of about 37 years...

Never hope that the deep oceans are involved: the pCO2 at the deep ocean temperature is only 150 ppmv, good to kill all trees and other C3 cycle plants...

I trust your numbers, but at such high pressure as at many miles deep, the prevalent species of CO2 is not CO2. Not by a long shot. Whatever amount of CO2 migrates upward will be replenished by more prevalent species, such as H2CO3, through the magic of chemical equilibrium. But you make a good point. We should somehow educate the media, the politicians, and some of the oil companies (esp in Canada) that the purposeful sequestration of CO2 (carbon capture) should be deemed illegal in every country in the world.

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