> > http://www.scotese.com/climate.htm
> > This shows clearly a geological history of global temperature.
> > Note the plateau at 22 degrees C. These times included ANY time when
> > the atmospheric CO2 exceeded approximately 600 ppm, including millions
> > of years when it ixceeded 2000 ppm with no additional corresponding
> > warming whatsoever. What source to you use to imply that that is
> > either innacurate or irrelovent? If we are planning to expend the
> > herculean efforts involved in a 550 ppm stabilization (again, I am
> > sceptical that 25% current emissions would produce that) and 600 ppm is
> > the response cieling, then what's the point??
> That's an awfully crude diagram to be basing that much importance on. The
> paleoclimate
> evidence isn't really that obliging regarding global mean surface
> temperature.
As opposed to what? Paleoclimate is I will grant you, not very
good for accuracy or precision, but taking it to be +- 2 degrees C
still pretty clearly indicates the plateau.
> You may want to have a look at an alternative representation of this data.
> http://www.globalwarmingart.com/wiki/Image:Phanerozoic_Climate_Change_Rev_png
Okay, that also pretty clearly shows the diminishing forcing
effects. not as dramatically as the on I presented, but then again, it
is a wiki piece.
> Note that image only claims a rough proxy for tropical sea surface
> temperature.
Nor did I ever claim it to be anything else. I am inclined to
make the same mistake you are, that of being pretty confident of my
information on a subject that is both divisive and understudied.
> You may also wish to consider that events that may be too short to capture
> on a half-billion year time scale graph (never mind one obviously drawn
> freehand, more of a cartoon than data) can be plenty long enough to make
> matters very nasty for humans.
Well, yes, however, if co2 concentrations in excess of 600 ppm
produced higher temperatures, then it would show on that graph in pink
neon. The fact that there's a plateau
> Finally, if your model of things is correct, we really ought to stop
> emitting immediately, because a 7 C rise in mean surface temperature is not
> something to shrug off.
correct, however, I don't see any means to prevent it, given that
even the optimistic stabilization scenarios show 550 at 25% of current
emissions. there's no way we can go below that emissions case, and I
don't even see how it's possible to get down to that level without
giving up most of the progress from the last 200 years. when
discussing what we SHOULD do, we should first look at both what we CAN
do.
> > > Simply because there are a great deal of factors at
> > > > work other than carbon. Venus isn't a fair comparison due to several
> > > > factors, among them, 1) it is closer to the sun.
> > > Not close enough. Do you understand the relationship between the
> > > Stefan-Boltzmann law and planetary surface temperature? Again this is
> > > first-year stuff.
> > Yes, I understand the concepts involved in blackbody radiation,
> > and in radiative forcing. It is nonetheless a fact that once the
> > atmosphere is completely opaque at the indicated range of wavelengths,
> > adding more opacifier doesn't result in additional warming.
> Then why is Venus warmer than Mercury?
venus has an atmospheric thickness
> > Us old guys are partial to Wallace and Hobbs, "Atmospheric Science, an
> > > Introductory Survey" 1977 but there are plenty of alternatives. I
> > understand
> > > that there is a new edition of W&H as of 2006.
> > > 2) Our moon has
> > > > been shown to have gravitationally "skimmed" our atmosphere such that
> > > > there is a very great deal less total volatile volume to work with on
> > > > earth.
> > > News to me. Are you making that up? What does that have to do with
> > anything
> > > if so? And what do you mean by "volatile"?
> > No. gasses leak from the atmosphere when the average temperature
> > velocity is greater tthan 1/10 of escape velocity. For the earth, the
> > moon produces a very significant reduction (circa 15%) in that escape
> > velocity which in turn increases the amount of atmospheric leakage.
> Supposing I grant this point. I find it plausible but not especially
> relevant. You didn't explain why it has anything to do with the matter at
> hand.
Because an atmosphere that is 9 times as thick as our own has a
greater ability to trap heat. Also because tidal friction under that
kind of pressure is nontrivial. if we had an atmosphere ad thick and
dense as venus' our surface would be kinda warm too.
> However,
> > accepting it as a valid source, I still don't see a stabilization
> > mechanism defined in your reference, merely a comparison of different
> > "stabilization scenarios", and a bald assertion that these are indeed
> > stabilization scenarios. What mechanism produces the carbon
> > sequestration that you and they assert will remove the annually added
> > co2 from the atmosphere?
>
> The equilibration is similar to the preindustrial equilibration to mean
> volcanic sources. Many processes speed up when a reagent's concentration is
> increased. It's not surprising; eventually the concentration settles to
> where it would be if there were more volcanos.
Yes, however, we've reduced the ability of several of those sinks
to effectively uptake and respond, so I am unsure if the historical
uptake mechanisms will still be able to cope in the same manners.
> the global land use currently in play
> > prevents that mechanism from being the addition of more forest land,
> > and the ocean under warming conditions is a source of co2, not a sink.
>
> Ah, only if you hold atmospheric CO2 constant. It's a sink if you increase
> CO2 holding temperature constant. Eventually concentration wins.
> I am oversimplifying here and don't want to get into it any further.
>
> The trouble with your approach is you put too many balls in the air for me
> to pursue all of them.
The problem with your approach is that it's a full system.
Talking about carbon emissions without discussing energy is kinda like
buying a car without checking the gas mileage, you can do it, but it
won't produce good results. Same with talking about energy neglecting
economics. Same in fact with talking about co2 without discussing
clouds, which we've done, but we'll leave off that one for now.
> It seems to me your argument (which peculiarly seems perfectly happy with a
> 7 C increase in mean temperature, albeit on an unspecified time scale)
> remains based on the idea that the greenhouse effect saturates.
I never said I was happy with it, in fact, I said that it's going
to take everything we've got to cope with it. I also said that there
isn't any way to avoid it, and that wasting resources trying will
guarantee a lot of death when it happens anyway. kinda like if the
volcano is going to blow next year. Do you attempt to cool off the
volcano, or do you evacuate the people? never in all of history has
cooling off the volcano worked, so it's a better use of resources to
move out the valuables and let'er blow!
> Suppose we postulate that the CO2 "saturated" temperature of the Earth is
> 22C, ie, 295 K. Now the orbit of Venus is at 67/93 of the earth's orbit, so
> that by the square law it receives (93/67)^2 as much irradiation per unit
> area. Even leaving aside albedo, which would incline in favor of the
> argument, by Stefan-Boltzmann law the temperature of Venus should go as the
> fourth root of the irradiation, or as the square root of (93/67) * 295 = 347
> K, not even enough to boil water, less than 100C. So what then would account
> for the actual surface temperature in excess of 400C?
That's funny, I did that same math 1 hour ago.
The difference lies in the thickness of the atmosphere. In
talking about the blackbody radiation, you are talking of surface
temperature (surface in this case being the top layer of the
mesosphere). That's where the radiation is emitted, so venus at the
top of the atmoshere should have a temperature (and in fact does) of
roughly 1.5 times our own. The next variable to consider is where the
heat is input, in this case, the heat input is 9 times as deep as in
our atmosphere, and slightly LESS in quantity, due to the albedo you
mentioned. so, we're heating the crust of venus to the point where the
temperature, linearly (roughly) decreasing from crust to the top of the
atmosphere produces the energy balance that is required.
Where the greenhouse effect comes into play is in effectively
increasing the linear temperature gradient. Insolation produces the
strongest warming effects at the surface of the planet. Now radiative
heat transport through gases is based on localized temperature
differences, thus if you can transport 1 joule/second through 1 meter
of atmospheric depth with a given concentration of ghgs, you can only
transport .5j/sec with a higher concentration for a given temperature
difference. so the temperature difference goes up to compensate, you
can transport the same joule if the temperature difference is twice as
high.
So, based on that, the surface of venus should have a temperature
of approximately 1053 degrees c (9*the difference in temperature
between our own mesosphere and the venerian one) why doesn't it?
Because co2 is a FAR less potent ghg than is water vapor, especially
when you consider the evaporation cycle and it's ability to limit the
transport of heat into the upper atmosphere, so the venerian greenhouse
effect is *today* far less effective per meter of atmospheric depth
than our own due to the absence of water vapor effects and the limits
of co2 as a ghg.
Note that I've totally neglected convective effects here. that's
because they are chaotic and would tend to diminish the greenhouse
effectiveness (thus bringing the surface temperature down).
Do you have any evidence that the temperature on the venus surface
would be lower if it were 5% co2 instead of 95%?
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