Calculating atmospheric CO2 levels from ice cores

Can I have a fact-check, please, Bob?

I’ve just read this which questions the accuracy of historical CO2 levels as measured by ice cores. I don’t have access to the paper it cites. Can someone please fact-check this? I rather doubt it’s disputing the measured CO2 levels - that would be absurd - but rather the atmospheric CO2 calculated from those measurements.

I think that it does not matter that the bubbles inside the ice can exchange CO2 with the ice itself. According to Fick’s law there is a partitioning of various solutions in multiphase systems like this, which depends on the chemical potential or fugacity (these are essentially the same thing). The point is that if there is an equilibrium of CO2 concentration in ice and in water and in air when the samples formed, then what’s in the bubbles will continue to represent the concentration at the time of formation, unless the entire system can effectively exchange CO2 with newer systems. So, if you left that ice core out in the freezer warehouse long enough, its CO2 levels will change. But, then, it will sublime away, too.

By the way, fugacity seems to be one of the most inconsistently understood and defined concepts in the chemical engineering world. I would up having to get multiple professors talking with one another to negotiate a concensus definition when getting patents for sorbent systems. Perhaps this innocent thread will now death spiral into a debate about fugacity?

I’m not entirely sure I understand that. You’re saying that they can caulclate how much of each atmospheric gas migrates from the bubbles to the ice for a given temperature and pressure? And from that they can calculate what the atmospheric concentrations would have been? How long does it take for this to change when the extracted ice core is stored under different temperature and pressure?

This is a good question, so I think I’ll give it a bump. If no one answers by tomorrow, I’ll see if I can’t dig out the original paper cited in the OP and give it a read - I should caution that I’m not a chemist, so it would probably be best if someone else interpreted it, but I can give it a shot if no one else does.

I never replied because this is circumstantial and doesn’t factually answer the OP, but this should get you going in the right direction. Or if you’re like me, it may be enough to conclude there’s really nothing valid enough in what that blog link says to put any more effort into it.

The paper he quotes is co-authored by “Stauffer, B” in 1977. I did a little searching for his name (aka Bernhard Stauffer from Climate and Environmental Physics of the University of Bern) and, among other things, found:

So this guy pretty much invented the method for reading CO2 accurately from ice cores. He’s also written/cowritten some papers about CO2 levels. I’d suggest Atmospheric CO2 Concentrations over the Last Glacial Termination. Follow the footnotes to other papers like “Processes affecting the CO2 concentrations measured in Greenland ice” and others. It seems pretty clear that the scientists know what they’re doing.

Here is what annoys me. The blog in the OP posted a small blog entry quoting a 30 year old abstract and claiming it “takes the legs out from under the whole global warming theory” but never bothered to really learn anything about the subject they were talking about or even make an attempt to see if anything new had happened in the last 30 years. They just selectively find a sentence that they like and proclaim global warming to be dead.

Thanks for replying, Fubaya, I wouldn’t want to go it alone. :slight_smile:

Anyway, the confluence of three factors bothers me about the quote cited in the OP:
[ul]1. The quote comes only from the abstract.[/ul]
[ul]2. The work cited is rather old (1978).[/ul]
[ul]3. The issue of the journal the paper is in is apparently not available online.[/ul]

(I should note that neither #2 nor #3 would be enough by themselves to make me suspicious, but the combination of them together gets me there.)

For the first issue, it’s unusual to see just the abstract from the article quoted. For any readers (I know many people reading this are, so my apologies) unfamiliar with scientific writing, the abstract is a very short summary of the work, its central point, and its significance. It’s just the “hook” to get you to read the paper, really. The details are what’s really significant, and they’re inside the paper, not in the abstract usually. So why didn’t the blogger quote some significant phrase from the “meat” of the paper? I don’t know, but I shouldn’t even have to ask the question - that’s why it’s suspicious.
For the second issue, it’s not necessarily bad that the paper is old. However, the authors have published much more recent work. I was able to download Bernhard Stauffer’s “Atmospheric CO[sub]2[/sub] concentrations over the last glacial termination.” From Vol. 291, issue 5501 of Science in 2001.

This does not sound like the work of someone who thinks:

Instead, it sounds like someone who has a definite opinion that Antarctic ice cores are better than Greenland ice cores for determining ancient CO[sub]2[/sub] concentrations - which is almost completely the opposite of saying the air bubbles are not related to the original concentrations.
For the third issue, my access may be different from that of others operating at an institution with a different subscription, but http://www.ingentaconnect.com tells me that only recent issues of the Journal of Glaciology are available online:

And now that I read the post completely, it seems that An Englishman’s Castle hasn’t even read the article attached to the abstract himself:

I have to go with Fubaya’s assessment: this is an ideological opposition to global warming that has taken the trouble to look scientific, without any of the actual reading of sources to see if the science says what he thinks it does. Very intellectually dishonest.

I am entertaining the thought that the paper from the 70s may still be accurate. Maybe he (or they-- his name just stuck out) found that bubbles didn’t work back in the 70s, but later found a better way to get samples. I only skimmed some of the papers but I didn’t see any mention of bubbles and I don’t really understand how they get CO2 now, but I don’t feel like going any deeper. I’m actually pretty interested in ice cores but I’ll put my money on the science dudes without attempting to learn all the technical methods behind CO2 extraction.

Speaking of taking the legs out from under the whole global warming theory… Flipping through radio channels today, I heard Rush Limbaugh say that Mars has 95 times as much CO2 as earth, so it should be extremely hot, but the “global warming wackos” don’t want you to know that Mars is a cold planet. Even now, hours later, I literally cannot form words to describe how insanely stupid that is.

Thanks.

I agree that it’s possible, but at the end of the abstract there’s a hint:

It’s also possible that instead of finding an alternative to bubbles we now know what the solubility and diffusion constants of CO[sub]2[/sub] in ice are as a function of temperature, correct?

Hopefully he’s published some methodological work that follows up on this and is more recent than 1978. I’ll see if I can dig any up.
I hope you don’t mind, Quartz, we may have answered your question, but I’m still interested in the topic. :slight_smile:

No problem; it can be very interesting when someone says, “Hang on a moment…”

Sadly, for me often a “moment” can mean days to weeks. :wink:
However, in this case I overlooked something I should have checked. The article cited above has a methodological appendix: http://www.sciencemag.org/cgi/content/full/291/5501/112/DC1

The CO[sub]2[/sub] being measured does indeed come from air bubbles in the ice core.

There are sources of uncertainty in that production of CO[sub]2[/sub] can occur in the air bubble under certain conditions - measurements of calcium and hydrogen peroxide can help determine how great production of CO[sub]2[/sub] in a given core might be.

Syncing the record with other cores and with diatom deposits from that time period allows the establishment of common events which are atmospheric, rather than local to the air bubble since its deposition in the ice.

There may be more in the rest of Stauffer’s work that describes how the problem from the 1978 paper was addressed, but this does give us some ideas of modern methodology.

I too was curious about this work. The oddity to me is that the relationship between (air age - ice age) and CO2 should exist at all, I don’t see the mechanism …

w.

The problem with basing any predictions from ice samples is that there aren’t any ice samples in the middle of the Atlantic Ocean. Greenland is subject to North American weather patterns and does not represent the planet as a whole.

Not sure what you mean by predictions, but CO2 levels would be the same in Greenland as in the rest of the world. But they know that whatever weather/climate information they get from ice cores is only good for that area. It’s just another piece of the puzzle. If, for example, you find that Greenland was much warmer at a certain time and data from around the world for the same time period shows sea levels were higher, tropical plant fossils were farther north, and Foraminifera from oceanic core samples show warmer ocean currents, you can figure out the global climate during that period.

The data used in things like the UN report are based on mutliple studies which use different original sources like ice, tree rings, coral, sediments, etc.

http://en.wikipedia.org/wiki/Paleoclimatology

My WAG is that the mechanism is that when a specific parcel of ice is added onto a glacier, it is frozen either as snow compressed by the weight of other snow and ice on top of it, thus incorporating air that was between snowflakes into the ice as air bubbles, or as melted snow on the surface of the glacier that then freezes as ice, which would also incorporate air bubbles. The air trapped at the time of freezing is then sequestered further and further away from the atmosphere as the glacier grows.

If the glacier shrinks, the air bubble is released to the atmosphere and we’ll never find it in an ice core.
If the above is true, the air should be frozen at the same time the ice does (since the ice is the only thing keeping it from escaping to the atmosphere,) and its CO[sub]2[/sub] content should be at least that of the atmosphere at the time of freezing. Creation of CO[sub]2[/sub] through chemical reactions in the ice is possible and mentioned above in the portions of the article that I quoted. Breaking down CO[sub]2[/sub] in the ice is extremely unlikely due to the combination of the low free energy state of CO[sub]2[/sub] and low temperatures inside ice.

I’m operating off memory for that, so I’m pretty confident a search of the relevant literature will turn up minor corrections to my explanation - hopefully no major corrections though. :wink:

I’m afraid that I am completely confused by this question, Magiver. What predictions are based on ice samples?

As far as I know, none. :confused:
You may be thinking about how ice samples are used to quantify paleoclimates, that’s what the work discussed above in the thread deals with. Note the title: “Atmospheric CO2 concentrations over the last glacial termination”, Stauffer and his co-authors are talking about thousands of years in the past - out to 420,000 years ago in the paper cited, not into the future.

This is also unclear to me. Who ever said Greenland represented the planet as a whole? The papers we’re looking at discuss the methods of extracting air from ice and measuring its CO[sub]2[/sub] content. CO[sub]2[/sub] is pretty well mixed in the atmosphere and will not be very different in Greenland vs. Antarctica (although there will be small differences.) Sage Rat alludes to a different methodology, that of constructing a paleoclimate over the entire planet using multiple sources. To this point, all the papers discussed here have only been presenting one source, not an entire paleoclimate.

OK, some further research. I downloaded the Vostok data, and the relationship between (ice-age minus air-age) is quite strong, especially in the older samples (R^2 = 0.87, older half of dataset, and 0.82, full dataset).

The reason for this is rooted in a 1991 paper by Barnola which spelled out a formula for calculating how long it takes for the ice bubbles in the firn to close completely. This formula uses the temperature, inter alia, to calculate the closeout date.

Since the CO2 content is related to the temperature, and the closeout date is a function of the temperature, they are related.

What I haven’t found out is what they used as a proxy for the temperature in say 276,000BC … my research continues. I will report back if I find anything else. The oddity is that the Vostok (ice-age minus air-age) data is much more closely related to Vostok CO2 levels than to the Vostok ∂O18 levels, which are usually taken as a temperature proxy. Curious. Perhaps they used CO2 levels as a temperature proxy in some fashion, dunno.

w.

From what I understand the ratio of heavy to light isotopes is used to determine temperature in ice cores. If you can, for example, relate δ[sup]18[/sup]O values to temperature, is it possible to relate [sup]14[/sup]CO[sub]2[/sub] or C[sup]18[/sup]O-O values to temperature?

Could you elaborate on how it is more closely related?

Thanks,
:slight_smile:

I was under the impression that global warming predictions were linked to CO2 levels and that ice samples were prevalent in this research. My mistake. Carry on.