Last year, Antarctica reached -135ºF, which is 27ºF below the freezing point of CO2 at atmospheric pressure. This is cold enough to freeze CO2 right out of the air.
There has been some long standing confusion about this because we do not find dry ice in Antarctica, except in their ice-cream machine.
There are different concepts which people confuse related to the partial pressure of a gas. Consider water vapor. Temperatures can drop below freezing, without frost accumulating on your windshield. This is because the number of molecules sublimating is equal to the number of molecules freezing. Until the temperature drops below the dew point or frost point, ice will not accumulate. The dew point/frost point is a function of the partial pressure of water, which is also a function of the humidity. The humidity has almost no effect on the freezing point.
Put in simple terms, ice does not accumulate at temperatures above its dew/frost point, because it is evaporating just as fast as it is freezing. When the temperature drops below the dew/frost point, more molecules are freezing than are sublimating.
The same thing is true with CO2. At 0.0004 mole fraction of the atmosphere, CO2 has a very low partial pressure, so it won’t accumulate at -135ºF. That doesn’t mean that CO2 molecules aren’t freezing – it simply means that they are sublimating at the same rate as they are freezing, so there is no net buildup.
Partial pressure is a statistical measure which has no meaning to the behavior of any individual molecule. It does affect the numbers of molecules which are freezing. It doesn’t affect the freezing point.
I thought Antarctica could only get that cold during the Southern winter, i.e. June-September. Or is this higher in the atmosphere and not at the surface ?
The coldest temperatures were registered during the winter months, in 2010 and last year,
“Newly analysed Nasa satellite data from east Antarctica shows Earth has set a new record for coldest temperature ever recorded: -94.7C (-135.8F).
It happened in August 2010 when it hit -94.7C (-135.8F). Then on 31 July of this year, it came close again: -92.9C (-135.3F).”
http://www.theguardian.com/world/2013/dec/10/coldest-temperature-recorded-earth-antarctica-guinness-book
At 14-15 micron wavelength, that at which CO2 supposedly “back radiates” and re-heats the Earth, the temperature is -80C. So, if so-called “back radiation” from CO2 could do any possible heating, it would be only in Antarctica at locations where the surface temperature was below -80C.
We have been through this 100 times. All matter above absolute zero radiates. A colder object doesn’t warm a warm object, but it slows the loss of heat from it, compared to an absolute zero object. Your blanket is 70 degrees. You are 98.6 degrees. How can a 70 degree object possibly heat a 98.6 degree object?
A colder object (the sky) doesn’t warm a warm object (earth), but it slows the loss of heat from it, compared to an absolute zero object (space).
I’m sure you still don’t get it.
I didn’t know that the coldest spots on earth get below the freezing point of CO2. I guess CO2 forms the ice caps on Mars since its atmosphere is 95% CO2… a higher partial pressure.
The density of CO2 in Mars atmosphere is about 14X higher than on earth, so yes you are correct.
The temperature at the poles on Mars is so low that there is very little sublimation in the winter, but there is in the summer. Mars’ axis tips like earth’s, so when the north pole tips towards the sun, all the CO2 sublimates and moves to the south pole, where it snows CO2. The partial pressure is the same all around Mars, and both poles are below the freezing point, but one pole is colder and too cold to sublimate as fast as it freezes.
?? Could this explain the low CO2 coming out of the last ice ages??
The low CO2 coming out of RECENT ice core testing is an artifact of the test method, the CO2’s diffusion through ice and politics.
Of special interest: “…before 1985, the ice cores were showing values much higher than the current atmospheric concentrations (Jaworowski et al. 1992b).”
For the nitty gritty on whys and wherefores of the testing procedures read page 4 The Truth About Ice Cores
I should note “gas differentiation” is well known to chemists. It is the basis for gas chromatography. A similar method of separation of mixtures is called liquid chromatography so none of this was unknown territory. Both methods were being taught in University in the late 1960s
I believe the truth about CO2 levels and sea level rise will be the last to be revealed after the great AGW scam finally ends.
The present data seems completely corrupted and meaningless in both cases.
Thank-you Steven.
Science that can not explain itself, within the parameters of the known universe, is not science.
Of course the ‘known universe’ falls within what Richard Feynman speculated on what it is to ‘know’.
Thanks for the very good review of “partial pressure”.
(Old chemistry humor: “If you’re not part of the solution, you’re part of the precipitate.”)
A favorite of this old chemist.
Gee Steve, when you actually decide to more than a few words together in the one post, you can be remarkably coherent …
Even I understood this one.
So you admit you were wrong in the below?
http://wattsupwiththat.com/2009/06/13/results-lab-experiment-regarding-co2-snow-in-antarctica-at-113%C2%B0f-80-5%C2%B0c-not-possible/
I still think your use of the words ” freeze right out of the air” is misleading though, it gives the impression of CO2 snow which rapidly sublimates. In fact you do not get any snow at all, never mind an accumalation.
Andy
When I go out to my car on a cold January morning with the temperature well below freezing and find that there is no frost on my car’s windshield, I never think to myself that “Wow, water is freezing right out of the air,” I think to myself, “Yep, we didn’t get down to the dew point last night.”
What’s the minimum number of molecules needed to call something a solid? Or a crystal? For water, six might be a good number. I suspect on those dry mornings, I don’t get clusters of six water molecules.
If you want to say we do, go right ahead, but please make it clear not many people are on that bandwagon.