Bob Armstrong

People don't understand that CO2 is one of the reasons why the asserted radiative equilibrium temperature of Earth is claimed to be ~ 255K , about 23K below the ~ 278.6K graybody temp in our orbit . CO2's absorptivity=emissivity bands cool , not warn the planet .
The hypothesis is that more CO2 raises the altitude at which it is finally sparse enough to radiate to space w/o jut bumping in to another CO2 molecule . Due to the gravitational >< kinetic adiabatic temperature gradient , it's cooler higher so radiates less , cooling the planet less . Happer &
van Wijngaarden , eg: upendsthat argument

https://cosy.com/y21/Sun.Dec,20211212.html#PlanetaryTemperature , do , that the effect is insignificant at these already optically saturated at a few molecules per 10k of air levels to high altitude .

Tim adds:

Certainly Mars - with an atmosphere that is 95% co2 - is colder than it should be. It is generally blamed on the thinness of the atmosphere but why is the atmosphere thin? Much of it is frozen out as dry ice. IF co2 is a greenhouse gas whenever the atmosphere thickens (which it frequently does) the planet should warm leading to a runaway greenhouse effect. It doesn't. Instead the thicker atmosphere kicks up dust and cools the planet back down. Who is to say the co2 isn't just cooling Mars as it increases (Mars' atmosphere ranges from 7 to 15 millibars at "sea level".)

Bob replies:

Mars is not colder than it should be . It's pretty close to it's SB temp as are all the inner planets except Venus due to its massive atmosphere ( nothing to do with spectrum ) .
I think the accepted reason for Mars's thin atmosphere is that it doesn't have sufficient gravity to hold on to one .
Tim responds:

, I would say Mars is colder than it should be if we assume carbon dioxide is a greenhouse gas. You are correct; it's where it should be given the amount of radiative heating it receives. But one must wonder why it isn't HOT during the day; the Moon certainly gets hot enough, although it's day is much longer.

I would point out that Mrs had a much denser atmosphere in times past, and there is evidence of running water. https:// news.asu.edu/ 20221018-hydroge nrich-first-atm osphere-mars-in ferred-clays-it s-surface / and https:// www.sciencedaily .com/releases/ 2017/10/ 171002114214.htm Mars was unlucky; it lost it's magnetic field, thus allowing the solar wind to strip much of it's atmosphere.

BUT if carbon dioxide were so powerful a greenhouse gas, why isn't Mars enjoying a thicker atmosphere now? There are vast amounts of both water ice and carbon dioxide frozen at the polls, and much of Mars is lousy with permafrost. It's not that the atmosphere is so thin so much as that a lot of it is frozen. While it is unclear how much thicker the atmosphere could be if Mars were as warm as the Earth, it clearly would not be anywhere nearly as thin - and that would mean it wouldn't be nearly as cold.

In fact Mars' atmosphere does thicken on occasion as the planet warms but then dust storms cause it to cool again and drop back out.

In my opinion Mars disproves the whole notion of carbon dioxide warming, or at least seriously hurts it.

I agree; Venus is so hot because it's atmosphere is so dense, not because of the composition. If it were nitrogen I suspect it would be just as hot at that immense pressure. And Venus is different in other ways; it's slow, retrograde rotation probably helped it retain atmosphere, and it was and remains highly volcanic, spewing out gas as fast as the solar wind can strip it. Couple that with gravity akin to Earth's and you have a recipe' for a dense hot atmosphere.

I wonder; most extrasolar systems show "Hot Jupiters", gas giants near their primaries. I suspect Venus was following along that course of development early on but something stopped it. If Venus were a "super Earth" would it have continued to suck up interplanetary gas and become a Hot Jupiter?

Posted by: Timothy Birdnow at 10:31 AM | Comments (1) | Add Comment
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