From the European Association of Geochemistry, a claim that looks to be little more than paleo-dowsing. Though, ya gotta love the silly claim that Earth would have hit a runaway greenhouse effect like Venus, had it not been for some mountains forming, sucking up all the CO2. Plus we’ve seen the Earth hit 5000PPM CO2 in the past, and it didn’t turn into Venus. This (Figure 1) from this post at the Met Office.
Of course it all just more model output, there’s no real earth science going on -all guesswork, no actual measurements.
How Earth avoided global warming, last time around
Geochemists have calculated a huge rise in atmospheric CO2 was only avoided by the formation of a vast mountain range in the middle of the ancient supercontinent, Pangea. This work is being presented to the Goldschmidt geochemistry conference in Sacramento, California.
Around 300 million years ago, plate tectonics caused the continents to aggregate into a giant supercontinent, known as “Pangea”. The sheer size of the continent meant that much of the land surface was far from the sea, and so the continent became increasingly arid due to lack of humidity. This aridity meant that rock weathering was reduced; normally, a reduction in rock weathering means that CO2 levels rise, yet in spite of this CO2 levels – which had been falling prior to the mountain formation- continued to drop, eventually undergoing the most significant drop in atmospheric CO2 of the last 500 million years. This phenomenon has remained unexplained, until now.
Now a group of French scientists from the CNRS in Toulouse have produced a model which seems to explain this contradiction. The period coincides with the rise of a vast series of mountains in the interior of Pangea, the “Hercynian” mountains”. These mountains arose in a wide belt, running from what is now the Appalachians, through to Ireland, South-Western England, through Paris and the Alps into Germany, and on further East.
According to team leader, Dr Yves Godderis (CNRS, Toulouse, France):
“The formation of these mountains meant that the rock weathering, which was threatening to slow to a walk through much of the supercontinent, was able to continue. The steep slopes of these Hercynian mountains produced physical erosion. Occurring in a humid equatorial environment, this physical erosion promoted rock weathering and removing CO2 from the atmosphere”.
He continued, “We believe that it is this which led to the dramatic drop in atmospheric levels of CO2. We estimate that if it hadn’t been for the formation of the Hercynian mountains, the atmospheric CO2 levels would have reached around 25 times the pre-industrial level, meaning that CO2 levels would have reached around 7000 ppm (parts per million). Let me put that into a present-day context; the current atmospheric CO2 levels are around 400 ppm, so this means that we would have seen CO2 rise to a level around 17 times current levels. This would obviously have had severe effects on the environment of that time. But the formation of the mountains in fact contributed to the greatest fall in atmospheric CO2 in the last 500 million years”.
The team believes that even if the mountains had not formed and CO2 levels rose sharply, this would not have led to a runaway greenhouse effect as happened on Venus, because the increasing temperatures would have led to rocks being ultimately weathered, heat compensating for the scarcity of water. Rock weathering would have removed CO2 from the atmosphere, thus stopping the rising temperatures.
“So it would eventually have been self-correcting” said Dr Godderis, “but there’s no doubt that this would have stalled Earth’s temperature at a high level for a long, long time. The world would look very different today if these mountains had not developed when they did.
This is a new model which explains some of the events in the 80 million years following the start of the Carboniferous period, and of course the ideas need to be confirmed before we can be sure that the model is completely accurate. The take-home message is that the factors affecting atmospheric CO2 over geological periods of time are complex, and our understanding is still evolving”.
Robertvd says: June 12, 2014 at 12:25 am
Venus is a newcomer in the solar system and it is slowly cooling down and speeding down its rotation velocity…
Stephen Skinner says: June 12, 2014 at 12:28 am
“… and speeding down its rotation velocity. ”
Can it go any slower?
Good question. Is retrograde slower than zero?
johnmarshall says: June 12, 2014 at 1:36 am
Venus, tropopause 70K above the surface, surface atmospheric pressure 92bar, insolation less than half that of earth due to very high albedo, (0.67) atmospheric lapse rate 10.2C/km surface temperature over 700K due to ADIABATIC COMPRESSION.
We had a post many years ago discussing the proposition that adiabatic compression was responsible for the high Venusian surface temperature, but one or two wise and learned commenters (the usual ones, as I recall) made well-reasoned and convincing arguments that adiabatic compression was not involved. The fact that the atmosphered rocky bodies in the solar system, Venus, Earth, Mars, and Titan, all fit the adiabatic temperature prediction was doubtless coincidence.
A runaway greenhouse involving positive CO2 feedback has the temperature going up to boil away all the oceans, and the water vapor getting dissociated up at the top of the atmosphere and losing the hydrogen to space. Trouble is, that doesn’t fit Venus. We have darn little evidence there ever was liquid water on Venus. No ocean basins, no water erosive features, maybe some deuterium in the atmosphere that could have been dumped by the same comets we suspect doused Earth, but nothing otherwise.
The temperature at the 1 bar level in Venus’ 96.5% CO2 atmosphere runs just under the boiling point, and is right about where our 0.04% CO2 atmosphere would be were we in Venus’s orbit. Move along, nothing to see here.
The most interesting thing to me about Venus’ atmosphere is that at that temperature and pressure, the CO2 is a supercritical fluid, where the density of liquid and gas are the same. That density is pretty impressive, too. Air runs about 2½ pounds per cubic meter, but on Venus, the CO2 runs 147 pounds.
supercritical fluid video
Johnmarshall says:
” The venusian atmosphere is under continual compression. It is not stratified and isothermal but under continued convectgion. Surface winds are monumental.
The atmosphere is so thick it is debatable if any insolation actually makes the surface to heat it. It is all adiabatic.”
It is under constant and unchanging compression. It is not being compressed to a smaller volume which is required for compressional heating.
“Surface winds are monumental”
Not according to the few probes that have landed there. They found virtually calm conditions. The strong winds are at high altitudes.
“The atmosphere is so thick it is debatable if any insolation actually makes the surface to heat it.”
In that case how come it was possible for the Venera probes to photograph their surroundings? The light level was fairly low, but it wasn’t dark.
“It is not stratified and isothermal but under continued convectgion.”
Indeed. And the convection is driven by what, if not solar heating? Geothermal heat?
“It is all adiabatic”
No atmosphere is “all adiabatic”. There is the sun on one side, the ground below and space all around you know.
MikwMCmillan says:
“The fact that the atmosphered rocky bodies in the solar system, Venus, Earth, Mars, and Titan, all fit the adiabatic temperature prediction was doubtless coincidence.”
No coincidence there. They are all convecting atmospheres which are expected to cool with altitude at the local adiabatic lapse rate (which depends on atmospheric composition). Incidentally this breaks down on Mars when there are global dust storms. Then the higher layers are warmer due to solar heating of the dust and low insolation at ground level.
Is this the solution the greens have been looking for – build more mountains?
So there are actually three differing opinions-
1- The Team has one opinion, but the science is not quite settled as yet.
2. We have the ‘Model’, that was tuned by the “team” to present the required outcome.
3. Then we have reality. That is the main problem apparently. That reality thing always appears to be way too stubborn to bend to the wishes of the Soothsayers, the bone-pointers and Magic-oil merchants.
Coincidentally, just yesterday I posted the following on the Tips and Notes page:
* * * * * *
Is it time to revisit the ‘runaway warming’ hypothesis for Venus’s atmosphere? It’s getting bandied about again, e.g.:
From here: http://www.dailygalaxy.com/my_weblog/2014/06/-venus-and-mars-hold-priceless-climate-change-warnings-for-earth-todays-most-popular.html
Grinspoon is a real scientist, so should be taken seriously. But can “current climate models . . . reproduce [Venus’s] temperature structure well”? Why does Venus have a much denser atmosphere than Earth does?
* * * * *
That question seems to me key. Venus’s gravity is only about 90% of Earth’s, so that can’t be the explanation for the incredibly dense atmosphere. The common assumption is that Venus and Earth began similarly, but Venus suffered runaway ‘global warming’, boiling off its water, while Earth didn’t. That doesn’t account for the atmospheric density. I wonder if, instead, perhaps Earth was like Venus is today, with a CO2/nitrogen atmosphere, but being farther from the Sun was able to retain water as it rained down in the form of comets. Then perhaps the new oceans and even newer plants sucked up the CO2, leaving a much thinner atmosphere. . .
What evidence do you have that Venus is “a newcomer in the solar system”? Velikovsky of course proposed that the Greek myth of the goddess Venus springing from Jupiter’s forehead was in fact a description of what the ancients observed in the sky: a new planet ejected from the giant Jupiter. This speculation was roundly rejected by astronomers, but Velikovsky did successfully predict that Venus would be very hot, and have hydrocarbons in its atmosphere (at a time when science-fiction stories about Venus, following the astronomers, assumed its clouds were H2O and its surface a tropical jungle).
/Mr Lynn
[Mods: Post seems to have vanished into the aether. Only one link in it, and WP says “Looks like you’ve already said that!” But maybe it’s in your Spam trap. Thx. /Mr L]
Why didn’t Earth develop an atmosphere like the one on Venus? :-
1. Venus (like Mars) does not have a strong magnetic core. Therefore there aren’t any extensive magnetic fields to help protect the planet. Apparently, gases like hydrogen, helium, and oxygen ions, would have been swept away by the solar wind, leaving the higher-mass molecules like carbon dioxide. (“Venus as a more Earth-like planet”, _Nature_ 450, Nov. 2007.)
2. Venus was left with a very dense atmosphere. It is more than 96% carbon dioxide.
3. The atmosphere’s pressure at the surface is 92 times more than Earth’s pressure.
4. Venus is considerably closer to the Sun, at about 0.72 of the distance from the Sun to the Earth.
5. The equator rotates at 6.5 km/h or 4 mph. (The Earth’s is about 1,670 km/h or 1,040 mph). Therefore a Venus day is *very long! Venus takes 243 Earth days to rotate once.
6. Naturally given the above, Venus does not have biomass (or oceans) to absorb some of the CO2, and it does not have a carbon cycle to lock carbon back into the rocks.
“tty says:
June 12, 2014 at 3:46 am
MikwMCmillan says:
“The fact that the atmosphered rocky bodies in the solar system, Venus, Earth, Mars, and Titan, all fit the adiabatic temperature prediction was doubtless coincidence.”
No coincidence there. They are all convecting atmospheres which are expected to cool with altitude at the local adiabatic lapse rate (which depends on atmospheric composition). Incidentally this breaks down on Mars when there are global dust storms. Then the higher layers are warmer due to solar heating of the dust and low insolation at ground level.”
They only cool at the adiabetic lapse rate if there when greenhouse gases radiate away their heat. With NO greenhouse gases, temperatures would ultimately stabilize at a constant temperature all the way up.
Robert G Brown posted here earlier on that very subject.
http://wattsupwiththat.com/2012/01/24/refutation-of-stable-thermal-equilibrium-lapse-rates/
There’s nothing preventing temperature inversions, as in your Mars referrals. It happens all the time on Earth, too, early in the mroning, as the ground radiates away heat faster than the atmosphere radiates away heat.
It seems that skeptics and alarmists agree (97%?) that a doubling of CO2 will increase temperature. For us to insist that is not true is unsupported. Where we disagree is in feed backs ….are the positive, negative, or on the whole balance out. If we hind cast the prob .7C rise since 1850 based on estimated ppm’s, feed backs seem to show neutral to negative…. Which of course is the case in most long term systems. Runaway temp based on carbon alone would seem to be unsupportable.
So when we argue with a warmer we often are talking past each other with a different view of the problem
[This is a repeat, as the comment seems lost. If it duplicates, please delete one.]
Coincidentally, just yesterday I posted the following on the Tips and Notes page:
* * * * * *
Is it time to revisit the ‘runaway warming’ hypothesis for Venus’s atmosphere? It’s getting bandied about again, e.g.:
From here: http://www.dailygalaxy.com/my_weblog/2014/06/-venus-and-mars-hold-priceless-climate-change-warnings-for-earth-todays-most-popular.html
Grinspoon is a real scientist, so should be taken seriously. But can “current climate models . . . reproduce [Venus’s] temperature structure well”? Why does Venus have a much denser atmosphere than Earth does?
* * * * *
That question seems to me key. Venus’s gravity is only about 90% of Earth’s, so that can’t be the explanation for the incredibly dense atmosphere. The common assumption is that Venus and Earth began similarly, but Venus suffered runaway ‘global warming’, boiling off its water, while Earth didn’t. That doesn’t account for the atmospheric density. I wonder if, instead, perhaps Earth was like Venus is today, with a CO2/nitrogen atmosphere, but being farther from the Sun was able to retain water as it rained down in the form of comets. Then perhaps the new oceans and even newer plants sucked up the CO2, leaving a much thinner atmosphere. . .
What evidence do you have that Venus is “a newcomer in the solar system”? Velikovsky of course proposed that the Greek myth of the goddess Venus springing from Jupiter’s forehead was in fact a description of what the ancients observed in the sky: a new planet ejected from the giant Jupiter. This speculation was roundly rejected by astronomers, but Velikovsky did successfully predict that Venus would be very hot, and have hydrocarbons in its atmosphere (at a time when science-fiction stories about Venus, following the astronomers, assumed its clouds were H2O and its surface a tropical jungle).
/Mr Lynn
I’m speechless. “Newcomer to the solar system”? “Slowly cooling down?” “Speeding down its rotation velocity?”
No, no, no, no, no. No. And no.
Just because Velikovsky smoked crack cocaine laced with LSD and peyote before writing his science fiction novels disguised as “true fact” doesn’t mean that you have to. Oh. My. God. Next you’ll tell me that Joseph Smith (dum-dum-dum), America’s first science fiction author, really did find golden tablets buried in upstate New York that he magically translated into a True Story of white-skinned Jews battling dark-skinned descendants of Cain with steel swords after navigating to the New World with magnetic compasses, or that we are all thetans murdered with hydrogen bombs 75 million years ago by a mean old dude named Xenu, forcing our thetan consciousnesses to inhabit the bodies of nearby T. Rexes and Velociraptors (another strangely popular science fiction story from the last century).
I give up. It really is true. Isaac Newton lived in vain. George Boole too. How is it possible to grow to adulthood without ever developing even a smidgen of common sense?
Please, please, please never ever state this in public again, especially if you are trying to “represent” the scientific challenge to the hypothesis of catastrophic climate change. You’ll force me to change sides, because the hypothesis of catastrophic runaway warming, ill-supported by evidence as it is, is still far, far sounder than the notion that a planet in a comparatively circular orbit in the normal ecliptic plane around the Sun “recently” arrived there and is in any particularly meaningful sense “still slowing down”.
rgb
The plot of CO2 over the last 600My is an inverse plot of the Abundance-of-Life on Earth. It was the proliferation of life that took the atmospheric CO2 down. Extinction events allowed it to rise; but that very same rise stimulated subsequent huge surges in life bringing it back down. Today the planet is life-rich at the limit of the available CO2. And more CO2 will give rise to yet more life.
So now melting alpine glaciers is a good thing?
Prior to the advent of green algae, CO2 levels were close to 100%. And somehow life survived and we didn’t get stuck in a run away greenhouse.
OK, here is a moderately interesting screen-scraped figure I cobbled together. I took the figure above showing atmospheric CO_2 and superimposed the curve showing global average temperature as inferred from the O18 proxy here:
http://upload.wikimedia.org/wikipedia/commons/9/9c/Phanerozoic_Climate_Change.png
Note that there is no attempt to map O18 to actual global temperature, but we can get at least some idea of how the map proceeds by considering the mean temperature in the current glaciation vs temperatures when Antarctica was ice free (suggesting that the temperature range from the peaks to the troughs of O18 is between 10 and 20 C, where on geological time the Earth is as cold as it has ever been since the Ordovician-Silurian glaciation 450 million years ago.
Here is the figure, where I literally traced the Phanerozoic curves and popped them on top of the figure above, scaling them so that their time scales corresponded. The grey bars are glacial epochs, the first one to the left is the O-S glaciation.
Combined CO_2 ppm and Phanerozoic O18 concentration
The figure kinda speaks for itself. It is this blatant disregard for what should be “common knowledge” to anyone publishing in climate science that really annoys me. How can you write a whole paper even weakly asserting that CO_2 variation caused mass extinctions by changing the climate without correlating the CO_2 concentration with the actual changes in the climate inferable from a far better proxy than “mass extinctions are sometimes caused by climate change”? How is it that no referee caught this omission? I don’t know about any of you, but I don’t see the slightest degree of correlation between CO_2 concentration and global average temperature.
Indeed, I would assert that this figure is absolutely, positively incompatible with the assertions that a CO_2 of 600 ppm implies any sort of climate change at all compared to the present. The Ordovician-Silurian glaciation occurred with mean CO_2 levels of ballpark 4000 ppm, sustained. Temperatures soared in mid-Permian with atmospheric CO_2 about where it is today, sustained (all of these peaks are tens of millions of years wide or wider — the entire industrial CO_2 increase plus its “catastrophic” projection isn’t even noise on the timescales involved). The oceans evolved sea life with shells with atmospheric CO_2 five to ten times what it is today. CO_2 in the entire era of the dinosaurs was order of 2000 ppm (5x present) and yet another weaker glacial era occurred across this time frame.
The only thing one can actually say with any degree of confidence from this replotting is this: CO_2 levels have, on a very coarse grained average basis, steadily decreased over the last 600 million years. At the same time, the Earth has undergone a cycle of heating and cooling that is almost completely flat when averaged in exactly the same way. You don’t need a calculator to eyeball nearly neutral planetary climate over the last 600 million years. Yes, that climate has ice ages and hothouse ages that last tens of millions of years. No, we cannot explain it. But the hypothesis that CO_2 is even a contributing cause fails to explain even the first order gross features of the variation. CO_2 has been falling at the rate of almost 1000 ppm/100 million years for 600 million years (eyeballing a linear regression of the data). Average global temperature hasn’t changed at all, for 600 million years (eyeballing a linear regression of the data).
And that, my friends, is something that I never seem to hear climate scientists acknowledge or discuss. Surely if CO_2 is the universal climate hammer, it would explain the primary variability of the data. Instead, if one attempts to cross-correlate the two curves in this plot (via, e.g. Kolmogorov-Smirnov) to see if there is any vague possibility that one is explanatory of the other, well, most statisticians wouldn’t even bother. The effect CO_2 is supposed to have isn’t subtle, and the eye does not lie. If there is any correlation whatsoever in there, it is “subtle” to say the very least.
rgb
(p.s. — Mod, please help me embed this figure, or tell me how to do it myself, as I’ve had no luck with embedded graphics so far.)
@Peter:
I found your “life” battery thought interesting. However, not all life is dependent on CO2, just most of the “macro” life forms that we, as very large human creatures, encounter in day-to-day existence. It is unlikely that “life” on Earth will acutally become entirely extinct until our local star starts shedding its outer layers and expands nearly to Earth’s orbit. Humans will probably not exist that long, geologically speaking, on Earth. Humans are too large a creature to survive the ever changing Earth over geological time. It’s useful to remember that there are more extinct species then living species of life, and that nearly all species larger than a few inches across have become extinct throughout Earth’s existence.
Thanks for taking the time to comment.
To the best of my, admittedly deficient, knowledge all life on Earth is carbon based, dependent upon carbon, hence organic chemistry where the properties of the carbon atom, in conjunction with oxygen, hydrogen etc allow for a bewildering array of organic molecules and compounds etc., thereby allowing life.
I suspect that the carbon needs of primitive aerobic and anaerobic life are relatively meager and will probably always be met by Earth’s geologic processes, at least until such times as the Sun has other plans.
What occurs to me, and this is where I hope more knowledgable minds will contribute, is that if the reduction of CO2 continues, as it appears to have done over the deep history of Earth, we will eventually reach a point or threshold where the more complex forms of plant life will struggle to exist on land. Obviously this then affects all those organisms which rely on vegetation, in one form or another, for their continued survival.
In discussions relating to the so called Fermi Paradox, there is often mention of “the Great Filter”, something that prevents life from attaining a sufficiently advanced biological/technological state such that it can advertise its presence to the universe at large. This is where my idea of CO2 (or rather the lack of it) being one such filter comes into play, the idea being that the path to intelligent life takes so long that CO2 reserves of the planet/atmosphere system are depleted to the point where such life is untenable. Hence the “flat” battery.
It seems to me that CO2 is not the poisonous pollutant portrayed in the media etc. but rather, the”Gas of Life”. But hey, what do I know, I’m only a humble tattoo artist.
All life was in the oceans back then, Mark.
When plants colonized the above water line land, the planet’s atmosphere was already filled with goodly amounts of oxygen thanks to the single celled creatures practicing photosynthesis. Then plants grew out of control due to lack of predators back then adding to the oxygen levels and suddenly eating a lot of the CO2 which is lucky for us for we are plant predators and need this CO2 for plants to grow faster so we can eat them. 🙂
“latecommer2014 says:
June 12, 2014 at 5:30 am
It seems that skeptics and alarmists agree (97%?) that a doubling of CO2 will increase temperature. For us to insist that is not true is unsupported.”
AGAIN, those making the claim of doubling CO2 causing temperature rise need to prove and support THEIR CASE first. They could start with the RGB post above.
Bill Illis says: June 11, 2014 at 9:22 pm
They got the timing completely backwards here.
Have to agree Bill:
http://i55.tinypic.com/11awzg8.jpg
My goodness, what an emotional response! I don’t know whether Robertvd had Velikovsky in mind when he said “Venus is a newcomer in the solar system,” but that’s the only author I know who has ever suggested such a thing. Certainly Velikovsky’s attempts to reconstruct the history of the Solar System from correspondences in ancient mythologies seldom rise beyond interesting speculation, and much of it seems physically impossible, but he was prescient at times—as for example disputing the dogmatic consensus of geological uniformitarianism (not unlike the AGW ‘consensus’ today). Nor do I know that he ever indulged in drugs—that seems an unwarranted calumny.
Perhaps Robertvd will tell us where he got the “newcomer” idea, and what evidence he has for it, if any.
/Mr Lynn
Yes, this is basically the same figure as that above, but if you link it here:
http://commons.wikimedia.org/wiki/File:Phanerozoic_Carbon_Dioxide.png
it gives you the references. The (Ward) figure above is not included, but if it were it would closely correspond to geocarb, copse and the compilation. Rothman is odd man out, it is the only one that has the right shape to be a plausible link between CO_2 and the global average temperature, as it asserts that CO_2 has almost never reached 1000 ppm. It still has CO_2 over 600 ppm at the O-S glaciation, though, and has it peaking around 1000 ppm around the Permian and Jurassic glaciation IIRC the dates correctly. Indeed, it might (if correct, note that apparently everybody else from multiple data sources disagrees, which doesn’t make him wrong but might make him probably wrong pending an explanation) even count as evidence that high CO_2 causes glacial epochs, except that there is far too much confounding evidence even for that.
Unless Rothman is right and everybody else is wrong, though, there is little to no reason to think that CO_2 concentration has been well correlated with global average temperature across geological time, as it has a relative variation of concentration of perhaps 10 to 15 (maximum minus minimum divided by minimum) with a strong temporal linear trend compared to a relative variation of global average temperature of around 0.05 (maximum minus minimum divided by minimum in degrees K) and is almost trendless (if anything, it exhibits a weak positive slope, but too weak to be considered significant I think). That is, the magnitude of the strongly negatively trended variation in CO_2 is over two orders of magnitude larger than the scale of the 30+ My variations in global average temperature around a weakly positive trend.
Not exactly the story that is being told by the climate models. Indeed, I expect that if one loaded 5000 ppm CO_2 into any of the current climate models, they would produce the Ordovician-Silurian glacial epoch 0.00000000000001% of the time, and only then because somebody mis-entered data or the computer’s CPU was hit by a cosmic ray at just the wrong time that flipped a couple of bits in the CO_2 concentration register.
Which is why they are badly, badly wrong, of course. With the physics they’ve got, glaciation in over 1000 ppm CO_2 is just flat impossible no matter what confounding variables you throw in (well, maybe things like the Siberian Traps or Yellowstone could produce it if one sets aerosols but NOT particulates through the roof, but we’re well and away from having that kind of utility in our computational models and besides, we just don’t have the data to even properly explore the possibilites).
Again, climate may not be (accurately) computable. There are lots of problems that aren’t computable, and a lot of those problems “look like” climate models in terms of complexity. It isn’t really even surprising.
rgb
He continued, “We believe that it is this which led to the dramatic drop in atmospheric levels of CO2. We estimate that if it hadn’t been for the formation of the Hercynian mountains, the atmospheric CO2 levels would have reached around 25 times the pre-industrial level, meaning that CO2 levels would have reached around 7000 ppm (parts per million).
On a graph with the time scale of 600 to 0 Million Years how well can you show ‘dramatic’ or is their definition very different than everyone else’s?
Hercynian Mtns were build in late Devonian, after CO2 had already declined from 5000ppmv to about half that. So was it earlier mountain building that ate up that CO2? Also, the CO2 didn’t decline from mtn building after the late devonian, it declined because the Dev. was followed by the Carboniferous – gee what an interesting term – the period when almost all the coal on earth was formed from the massive growth of swamps with 300ft high trees that, when they died out, formed coal measures. Low humidity- bollocks- these these giant forests grew in a very humid, rainy environment. I haven’t had time to read previous posts but someone has surely pointed this out.
rgbatduke says:
June 12, 2014 at 7:21 am
IMO temperatures as cold as now occurred during the Carboniferous-Permian glaciation as well as the Ordovician-Silurian, which lasted less time than the C-P or present Icehouse. The Jurassic-Cretaceous glaciation was much less severe. Icehouses occur at about 150 million year intervals, which is one of the observations supporting Shaviv & other cosmoclimatology proponents.
Speaking of GCMs & the past, the Cretaceous is a huge problem for the models. To get a world as warm & equable as the mid-Cretaceous with its estimated level of CO2 the models need ECS of at least six to work.