On 20 veebr, 09:17, Logan Kearsley <chronosur...@[EMAIL PROTECTED]
> wrote:
> On Feb 19, 11:12 pm, Bryan Derksen <bryan.derk...@[EMAIL PROTECTED]
> wrote:
>
> > Logan Kearsley wrote:
> > > On Feb 18, 6:12 pm, Bryan Derksen <bryan.derk...@[EMAIL PROTECTED]
> wrote:
> > >> If it is cold enough for CO2 to start freezing out on the
antistellar
> > >> pole, then the atmosphere is already demonstrably not capable of
> > >> sufficient heat transport thaw frozen CO2 back there.
>
> > > It's demonstrably not capable of sufficient heat transport to thaw
> > > frozen CO2 given not-necessarily-permanent current conditions. That
> > > doesn't mean it can't warm up again.
>
> > No, but with CO2 absent from the atmosphere you'll have to warm it up
> > again via some mechanism other than greenhouse effect.
>
> Well, obviously.
>
Why? Why not greenhouse gases other than carbon dioxide?
Like methane? Boiling point lower than that of carbon dioxide.
Imagine... over time, methane concentration in atmosphere slowly
increases, the general temperature rises... till the dark side gets
warm enough to evaporate the carbon dioxide. Runaway greenhouse effect
follows - first the carbon dioxide evaporates, then ice seats and
oceans thaw.
(The cycle has a return side, too: once the oceans are open,
photosynthetic production increases. Small quantities of free oxygen
are released into atmosphere and the surface layer of ocean, while
deep ocean remains anoxic and dead organic matter sediments there. The
free oxygen rapidly removes the methane from atmosphere...)
>
>
> > > Or dust condensing out of the atmosphere- a
> > > particularly large volcanic eruption might temporarily freeze the
> > > planet. And I don't know how stable it would be, but I can imagine a
> > > cyclic situation where an evaporating ice cap could induce
planet-wide
> > > dust storms such as are seen on Mars, which then cool the planet and
> > > cause the cap to re-condense, after which the dust settles and it
> > > starts to warm up again.
>
> > But with the CO2 gone you don't get any of the warming that it might
> > have been contributing before the freeze. According to
> > <http://web.uccs.edu/geogenvs/ges100-online/Chapt4.doc>
without the
> > greenhouse effect Earth's average temperature would be -15 C whereas
the
> > current average is 15 C. If Earth was a tide-locked planet balanced
> > close to the point of having its CO2 freeze out, and something dropped
> > the temperature enough to trigger it, to recover you'd need to
increase
> > the heating of the planet enough to overcome that 30 degrees C
> > temperature deficit that you're no longer getting from the greenhouse
> > effect. If you've got snowball conditions to deal with the albedo will
> > be boosted, too, making it even harder.
>
> > Personally, I think the "CO2 collapse" scenario their models predicted
> > sounds quite plausible.
>
> I find it perfectly plausible. I just don't think that it must
> *always* be a permanent condition.
> For my current purposes, though, I think ensuring that it *is*
> permanent may be the best solution for how to get geologic activity
> without increasing greenhouse gas content and warming the planet up-
> if anything extra that gets spewed out of a volcano just precipitates
> out on the darkside, that ought to be just as good as carbonate
> sequestration, no?
>
> That works out nicely for the tidelocked planet scenario, but leaves
> me wondering about the high-tilt planet scenario. Perhaps that one can
> be saved for later.
>
> I wonder, though, what, if anything, it would do to the planet's
> geology to have carbon continuously leached out of the mantle and not
> replaced by subduction.
>
> > Reversing it could be an interesting
> > terraforming scenario, you could perhaps set up orbital mirrors and
try
> > to raise the antistellar point's temperature enough to get the
> > greenhouse effect going again.
>
> That makes for a nice story idea- planet looks like a prime
> terraforming prospect if you just set off a few nukes on the ice cap,
> and then you discover the psychrophilic natives....
>
> -l.
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