A couple of days ago WUWT carried a story, talking about intense cold in Antarctica, carbon dioxide, and the icecap of Mars. This one passage stirred up a significant debate:
According to Weather Underground, Vostok, Antarctica is forecast to reach -113F on Friday. That is four degrees below the freezing point of CO2 and would cause dry (CO2) ice to freeze directly out of the air.
It seemed (at the time) a reasonable statement. The freezing point of CO2 is -109.3 degrees Fahrenheit (-78.5 degrees C). There’s been mentions of this supposed phenomenon of CO2 freezing out of the air before on other blogs and websites. One of the best examples was even an entry in the website “ask a scientist” where the question of CO2 freezing out of the air was posed, and the answer from an Argonne National Laboratory scientist seemed to indicate that CO2 could indeed precipitate as a solid from the air if the temperature was low enough at Earth’s south polar ice cap, specifically at Vostok Station, which holds the record for the lowest surface temperature recorded on Earth at −89.2°C (−128.6°F)
Certainly, at least some of the carbon dioxide in the atmosphere at the poles does freeze out during the winter. However, there is not enough frozen out to accumulate to any extent at the present.
David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory
So, it seemed possible. But as WUWT commenters soon pointed out, temperature is only part of the equation needed to deposit CO2 as a solid from the free atmosphere at that temperature.
Soon we were discussing gas laws, phase diagrams, and partial pressures. The debate mainly centered on whether or not this phase diagram for carbon dioxide applied to 1 atmosphere of pressure of pure CO2 versus simply 1 atmosphere of pressure independent of the purity of the gas.
The author of the post, Steven Goddard wrote in comments:
The phase diagram shows unambiguously that the equilibrium state of CO2 at one atmosphere at 113F is solid. The freezing point of CO2 is -109F at 1 atmosphere.
The PDF referenced doesn’t translate well to the blog size format, but this less detailed phase diagram for CO2 does fit and was mentioned in comments also:
Since many of us know from experience that with ice, be it water ice or CO2 (dry) ice, that a phase change can occur directly from solid to gas (sublimation). It seemed reasonable to conclude that the reverse could be possible, going from a gas to a solid as long as the temperature was below the “triple point” of CO2 as well as the freezing point at 1ATM.
The freezing point/sublimation point of CO2 at 1ATM is at -78.5C (-109.3F). In the situation described in the forecast for Vostok station, the temperature was forecast to reach below the freezing point for CO2 at -80.5 C (-113F ). It seemed reasonable then to concludes that CO2 would freeze right out of the air, much like frost does from water vapor. Plus we had a statement from a scientist at a National Laboratory saying it was possible also. What’s not to like?
One small detail: partial pressure.
The concentration of CO2 in the free atmosphere is very small. Thus the partial pressure of CO2 in the atmosphere is about 0.0004 atmospheres. But wait there’s more. Vostok station is at a high elevation, 3288 meters above sea level (10,787 feet) and the atmosphere is thinner. Thus the partial pressure of CO2 is even lower.
Commenter George E. Smith summed it up pretty well with this paragraph:
At -78.5 deg C (-109F), that equilibrium occurs at a partial pressure of CO2 of 760 mm Hg, one atmosphere. Below that pressure, there isn’t enough abundance of CO2 molecules in the vapor phase for collisions with the solid surface to occur at a fast enough rate to make up for the ones that escaped; so the solid CO2; dry ice, will continue to sublimate.
Basically, there are so few CO2 molecules in the free atmosphere, sublimation rules over deposition as a solid. Yes some CO2 may deposit on a surface at at -80.5 C (-113F ), but it would quickly sublimate back into the free atmosphere, and thus accumulation would not occur.
Meanwhile WUWT reader Ric Werme had written to Dr. David Cook of Argonne National Lab to ask about his original opinion he wrote for “ask a scientist” web site. Ric reports he responded with this:
Ric,
You are correct. In my attempts at being simplistic I made a mistake in my answer to “Freezing CO2″ on the Ask-A-Scientist page. -57 C is the boiling point of CO2. The freezing point of CO2 at atmospheric pressure is -78.5 C (-109.3 F). If the temperature reaches -113 F at Vostok, Antarctica, some carbon dioxide might freeze out of the air, assuming that the carbon dioxide vapor pressure drops to its saturation vapor pressure.
The vapor pressure must reach the saturation vapor pressure for dew or frost to form. This happens at the dew point or frost point temperature, which is dependent on atmospheric pressure and the absolute amount of vapor in the air. As atmospheric temperature increases, the dew/frost point temperature increases. As atmospheric pressure increases, the vapor pressure increases. At very low temperatures, the dew/frost point temperature is very low.
When the temperature of the surface (whether grass or a car window) is below freezing, frost will usually form instead of dew, although water can be super-cooled and not produce dew, fog, or clouds in some cases. Surfaces on the Earth cool off sooner than the air, so dew/frost will normally form on them before fog (water or ice) forms in the air.
The temperature being at “freezing” or below does not imply that frost will form on surfaces or in the air. The vapor pressure must be high enough (saturation vapor pressure) and the temperature low enough (the frost point temperature) for frost to form.
So it seems, Dr. Cook (and our own Steve Goddard) made the basic and simple error of not taking vapor pressure into account. Given our human experience with the everyday freezing of water, we don’t often think about it. I didn’t catch it either initially, nor did some WUWT commenters.
It does demonstrate though, how little CO2 there is in our atmosphere, we can’t even precipitate it to solid under any natural condition of earth.
But, even with the debate apparently settled, the CO2 freezing question was still all in the realm of opinions and phase diagrams. Some people really wanted to see some empirical proof. Some thoughts on experiments were tossed about.
Enter WUWT reader Dr. Thomas Thatcher of the University of Rochester who had not only an idea for an experiment, but the means with which to carry it out. He had a lab freezer which would “maintains -80˚C (-112˚F) in my lab, and it can be set as low as -86˚C (-122˚F).”.
He proposed that he could use that freezer to do a test with dry ice:
The argument, as far as I can tell, is that at the atmospheric partial pressure of CO2, dry ice at -113F will sublimate faster than it forms (which may be different than how a pure CO2 atmosphere would behave). I am in a position to test this, as described above.
…
Based on the arguments presented here, the two postulated outcomes are,
1) significant loss of mass, as the sublimation rate exceeds the deposition rate
2) no change, or negligible gain in mass.
(I suspect that any gain in mass will evaporate on the short walk from the freezer to the balance.)
It’s admittedly an imperfect experiment. But I expect the outcome will be rather obvious; the dry ice will be gone in the morning. We’ll see.
He conducted his experiment overnight between Thursday and Friday, and writes:
The freezer is a VWR brand ultralow temperature upright freezer, similar to models shown here.
http://www.vwrsp.com/catalog/product/index.cgi?catalog_number=14230-120&inE=1&highlight=14230-120
It is set to -86C, the temperature typically rises 1-3C when opened, and recovers in about 30 minutes. (Factory temperature calibration was NIST-traceable but it has not been recalibrated since it was installed here.) The samples were loaded at 4:30 pm and removed at 9:30 am, so the freezer will have been largely undisturbed during that time.
The interior is mostly filled with stainless steel racks that hold cardboard boxes for storing biological samples. I placed the test samples in two boxes on the bottom shelf at the rear of the freezer, the coldest zone and closest to the temperature probe.
One sample was placed in an open box with extra holes cut to allow air circulation. The other sample was placed in small zip top plastic bag inside a cardboard box. The samples were weighed by difference before being placed in the freezer and after removal in the morning. Additional weighings were taken to estimate the amount of sublimation during the weighing procedure and the amount of water that might condense on the boxes, but these amounts proved insignificant next to the overall results.
The samples were placed in the freezer at 4:30pm (reading -82C) and removed at 10:00am (reading -83C).
Open container, start weight 36.5g dry ice, end weight 0g, amount sublimated 100%.
Zip-top bag, start weight 27.6g dry ice, end weight 25.3g, amount sublimated 8.3%
Proving, I think, that CO2 will freeze and remain frozen at below -78.5C if the partial pressure of CO2 is near 1 ATM, but the CO2 will rapidly sublimate is the partial pressure of CO2 is near atmospheric normal.
And he concludes:
Bottom line, 40g of dry ice placed in an open container at -82C completely sublimated overnight, while 27g of dry ice placed in a zip top bag retained 90% of its mass. This proves two things, first, that the temperature of the freezer did not exceed -78.5C for any appreciable period of time, and second that yes indeed, the partial pressure of CO2 is the key to the problem.
Best of all, he sent photos of the experiment he conducted:
Thanks to everyone who participated in the debate, including Ric Werme for his correspondence help and especially Tom Thatcher for conducting the experiment and taking photos.
We all learned something, we had a little fun, some online yelling occurred, and some egos were bruised. Overall though it was worthwhile that this myth of “CO2 snow at Vostok station” was finally put to rest.
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If the temperature of the dry ice doesn’t change, the partial pressure of CO2 is unchanged.
That should read “vapor”, not “partial”, pressure. I am also having problems keeping them straight!
Only had time to glance at the first post but great outcome.
Best Science Blog – by a long way!
Maurice Garoutte (08:51:42) :
I propose a home experiment to show how CO2 levels can be the result of global warming rather than the cause. I know the science blogs talk a lot about the solubility of CO2 in the ocean as a function of temperature; this just brings the concept home.
1. Go to the refrigerator, take out and open two cans of soda.
2, Pour a little out of each can into glasses to verify that both have the same levels of CO2 while cold.
3. Put one of the open cans back in the refrigerator and leave the other on the kitchen table.
4. Wait six hours.
5. Pour a little of each can into glasses and note the level of fizz in each.
6. Note that the can that was on the kitchen table lost more dissolved CO2 than the can from the refrigerator.
7. Theorize whether the extra CO2 from the can on the table kept the kitchen warm, or whether the warm kitchen caused more CO2 to come out of solution.
Please don’t try this experiment with beer. The result would be the same but it would be… well just wrong.
TERRIFIC.
Wish Ms. Jackson at the EPA had conducted this experiment before designating CO2 a “dangerous pollutant”, with all that portends.
@ur momisugly John M
Our comments crossed in moderation. I did mispeak.
Thanks for your clarification – that answers my other question. The partial pressure of CO2 goes up with the partial pressure of N2, etc. So increasing the overall pressure raises the temperature where the partial pressure is in equilibrium with the vapor pressure, i.e. the frost point.
The effect is small, but if the atmosphere cools, the pressure at ground level rises, and so does the frost point, a little. Right?
>>>•Carbon Dioxide (CO2): 95.32%
>>>Possibly more CO2 in Mar’s atmosphere than in Earths atmosphere.
We’re not going to have a runaway warming on Mars, are we?
.
I’m probably a kook, but I love phase diagrams.
neill (11:09:43) :
“Wish Ms. Jackson at the EPA had conducted this experiment before designating CO2 a “dangerous pollutant”, with all that portends.”
I wish Ms. Jackson could be prosecuted for fraud in calling CO2 a dangerous pollutant, but I’m sure her defense in court would be that you can’t use an english dictionary to define “pollutant.”
Experiment? In a global warming context, my heavens, that is so…..so….so
so Scientific!
The ignomy. How will you ever live it down?
Ive got a question. Given that carbon has such a love for sharing itself, how much of the ‘melted’ dry ice went into the air as Co2 and how much of it was left as a residue on the racks and floor of the freezer? I have worked with a few productions that used masses of dry ice, the result was white powdery stuff everywhere the fog bank went. Granted we caused the effect by dunking dry ice into hot water so it could be a water/ice residual… just wondering.
KBK (11:13:01)
Now you’re going to get me to go all weaselly on you. Will the pressure be lower? Yes…”all other things being equal.”
Of course, all other things are never equal. (I’ll try not to use “on the other hand”.)
In this case, the system is not a closed one, and will respond to everything else that’s going on, including winds and air currents. More importantly though, it will respond to neighboring air pressure and the effect of temperature drop on the local air pressure will be swamped out by the response imposed by the sea of surrounding air.
But let’s say for the sake of argument that we can treat a “chunk” of air of constant volume near the ground in isolation from the rest of the atmosphere. If the temperature drops from 0 °C to -5 °C (32 °F to 23 °F, or more importantly, 273.15 K to 268.15 K, which is the temperature scale that counts here), that would correspond to a drop in pressure of 0.018 atm (1-268.15/273.15) or about a quarter of a psi.
Based on the dew point conversion chart I linked to earlier, I would estimate that the change in dew point from that type of pressure change would be less than a tenth of a degree F. Note again, that’s a distinct upper limit with the unnatural constraint that the chunk of air is independent of its surroundings. (I think we’re starting to get to the difference between reading a phase diagram and modeling the climate.)
Hope that helps.
This experiment is about weather, not climate.
So, is there anything here that can help us with the various Ice Core data. ALL of them, well, except for the scatter plot that I belive Beck and Jaworaski published, look suspiciously like a plot of depth vs CO2. A the temperatures and pressures encountered, what would happen to air trapped in snow as the depth and pressure increases? I’ve not seen this explained anywhere on the web, and I’ve looked.
REPLY: Phil. did indeed make some valuable contributions, but behaved very badly.
Really, how?
That, and I don’t believe in rewarding bad behavior. There was too much labeling of people by some commenters, and it was entirely unprofessional and unnecessary. We really don’t do anyone any favors when we revert to this level while trying to educate and enlighten online. – Anthony
By implication here and directly elsewhere you have accused me of ‘labelling people’, I did not do so.
By the way Anthony you said “If it turns out the statement is wrong, and some empirical proof can be presented, I’ll retract and/or amend the article.”, however the offending statement is still there.
Good job. I would like to point out that, while this may be a basic chemistry lesson, climate studies cover so many disciplines of science (meteorology, geology, paleontology, astronomy, chemistry, biology, and many more) that few, if any, of us will have even basic mastery of all of them. Many times a scientist in one field will have need of expertise in another field, and we should not be impatient with having to explain some basic concepts. An expert in solar magnetic fields may have little need for knowing the details of phase diagrams.
The fact that a reproducible experiment can put us all on the same page must not be underestimated. I have seen arguments on other sites by some who were clueless as to what even constituted an experiment – up to and including the belief that the output of computer models was the same as experimental results. In one instance someone posited that a CO2-warming experiment wasn’t needed because the models predicted there wouldn’t be a measurable temperature change in that situation, oblivious to the possibility that the model might be wrong (and a temperature change WOULD be detected) and what the implications of that would be. Models may help us determine what questions we may want to research, but they are not science.
I don’t expect those who are not chemical engineers to fully grasp all of this, but I do expect the climate-modeling scientists to understand and follow the basics of physics. That they do not is apparent, and that is of grave concern in the ongoing debate over Global Warming via climate models.
This is simply high school chemistry not rocket science – there is very little to grasp it is very elementary stuff. People are lazy that’s all – so they make assumptions, make comments and don’t bother checking. I find it embarrassing that some people would think this is akin to rocket science.
They used to teach this in Grade 11 in Canada and even I can remember Dalton’s, Charles and Boyle’s Laws. Please let’s not make a mountain out of basic stuff.
FWIW: I think it would be more interesting to add a post to explain to lay people why the Sky is Blue and why Sunsets are Red. Lord Rayleigh was a pretty sharp fellow along with Charles and co.
I suppose what I’m interested, in, is “the behavior of atmospheric gases at arctic temperatures and increasing pressures in a semi-permeable substrate.”
@Alan Bates:
True, as long as you grasp the importance of partial pressure in the phase diagrams, what I did was not really an “experiment” as much as it was a demonstration. In fact, I added the zip-top bag when I realized that filling the bag with CO2 should preserve the dry ice. Still, it took me several passes through the comments to finally “get it”, and I hope that there is value in a simple demonstration with pictures.
@Skeptic Tank, if you open a container of liquid CO2 (under pressure, of course) to normal atmospheric temperature, some of it will boil away to CO2 gas. It takes heat to do that (the heat of vaporization) which is pulled out of the remaining liquid so that some of it will solidify. It will all, of course, sublimate eventually.
@pkatt, probably water ice. In our lab we also have large dewars of liquid nitrogen (-196C, I think). When we draw off the liquid nitrogen, frost forms on the steel transfer hose. I would expect that as long as that hose gets below -140C, some of the frost will be CO2. The problem is that most of it will be water ice and it will be difficult to measure the CO2 fraction without special equipment.
REPLY: about -140C, but it may be such a thin powder that it is unobservable, since there is so little CO2 in the atmosphere.
– Anthony
Thanks Anthony,
so as my comment in the earlier thread, it was a question of at what temperature it happens not that it can’t happen. It is unlikely to get that cold even in the deepest ice age?
M White (04:18:56) :
(and Ralph Ellis)
“Possibly more CO2 in Mars’s atmosphere than in Earths atmosphere.”
Lots more. If you assume 6millibar surface pressure on Mars(it can go up to more than 10mB) and the partial pressure of CO2 on Earth is 0.6mB you get a factor of 10. But because the surface gravity on Mars is 0.38g there must be 2.63 times as many molecules to create any given pressure. So depending on the pressure at the Martian surface there is 26 to 44 times as much CO2 over every square meter on the Martian surface as there is on Earth.
Clearly Mars must be sweltering!(just kidding)
Seriously, in Mars we have a nice natural laboratory to explore the consequences of lots of CO2 in the atmosphere without a lot of confounding factors. The numbers I’ve found indicate that the warming effect of the CO2 on Mars is 5 to 10deg C. I don’t know whether this is just a poor estimate with wide error bands or meant to describe differences at different locations. Note that compared to Earth, Mars has almost the same length of day, almost the same axial tilt, has a year about twice as long and receives half the insolation at the top of the atmosphere.
Also conveniently, the CO2 levels vary during the Martian year by a factor of nearly 1.7. Can anybody tease out the effects of the changing CO2 levels on the surface temperature of Mars? There’s got to be at least a scientific paper in this if not a PhD.
The facebook script that I use (Facebook provided) for reposting WUWT stories does not seem to work on this post. Something must have changed in the data format.
Here is the script (saved as a bookmark in Firefox):
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Atmospheric pressure really isn’t the issue. The issue is how much CO2 is in the atmosphere. An easier way of thinking about it is to pretend that CO2 is water. If we pretend CO2 is water than Earth’s atmosphere is very “dry”. It has extremely little CO2. Mars has a very “wet” atmosphere or a lot of CO2 by proportion to the total gasses.
Now what happens to regular water ice in an extremely cold by extremely dry environment? It evaporates. We see that in the “dry valleys” in Antarctica. The air is so dry that the ice evaporates without going through the liquid phase.
The same thing is happening with CO2. In terms of CO2, the earth’s atmosphere is extremely “dry” and frozen CO2 would evaporate even if the temperature were well below the freezing point of CO2. The experiment that had the dry ice in a bag in effect created an atmosphere very “humid” in CO2 and so the ice did not evaporate.
I believe that is the easiest way to put it into terms most people can understand.
Jeremy (13:42:45) :
Too many of us were victims of “relevance” in the 60’s and 70’s. World History? Irrelevant. Classical Languages? Irrelevant. French, Spanish and German? They all speak English. Irrelevant. Philosophy? Irrelevant, this is the 20th Century, Man! Science? Nothing left to learn, they’re just tying off loose ends. Irrelevant. Learning to think for yourself? Don’t you want to fit in? Irrelevant.
Unfortunately, this CO2 episode on this blog has really lowered the value of the whole blog. Steven Goddard made a wrong statement about the basic CO2 chemistry and physics. It would have been much better if he admitted his error straightaway, rather than trying to prove his (wrong) point with more and more bizarre posts.
I understand that he is a regular contributor to this blog, but did you really have to create a “scientific experiment” to save his face as if there was any doubt about the CO2 phase diagram? Equally well, you could have made an experiment to check if water really freezes at 0 C or if water boils at 100 C.
As somebody already said above, this is really basic stuff, my 14 year old daughter is doing similar demonstrations (not scientific experiments) at school.
WUWT is my favorite blog. I am skeptic about everything unless I see the real data. There is a lot of good information on this blog. However, in my opinion more background check is needed before CO2 freezing kind of stuff is published.
The fact that we have another post about CO2 behaving just the way hundreds of scientists have shown many years ago (and school children in proper educational systems are demonstrating every day), is lowering the credibility of this site.
Anthony, you are doing a great job with this site, please do not give any more ammunition to the AGW side with these “let’s measure the water boiling point again” posts.
Sincerely,
Jari
I can see it now; GE/NBC get the contract to build giant co2 assist scrubbers at both poles.
Flanagan (10:17:33) :
rephelan :
I don’t see why I would be next. I think I behave quite peacefully. Moreover, I was right about the CO2 deposition :0)
I actually expected Anthony or Charles to snip my post, but since they didn’t, let me explain. You are a polite troll, but a troll nonetheless and you contribute almost nothing to the discussion here. Your serial references to that French blog? Tamino, Stoat and even RC are more informative. I still retain enough French to deduce that much. You post references to charts that are not self explanatory and expect the rest if us to say OOHHH!!!!. You cited a social science paper on the effect of non-ideological information’s impact on perceptions of global warming….(sorry, I can’t find the reference right now, but I did download it) and incorrectly….. no, deliberately misrepresented, the results to suggest that AGW advocates were more intelligent than denialists. The number of times I’ve said to myself “maybe the little bugger has something this time….” I’m tired of searching out obfuscation and dishonesty. Get honest, or if Anthony decides to hold a vote on who gets snipped first…..Tsai-jian, ben-dahn.