From the AGU weekly highlights:
Evaluating solutions to the faint young Sun problem
During the Archean eon, between about 3.8 billion years ago and 2.5 billion years ago, the Sun was about 20 to 25 percent fainter than it is today. With less sunlight to warm the Earth, the oceans should have been frozen over, but geological evidence suggests that this was not the case.
Some proposed solutions to this problem, known as the faint young Sun problem, include an atmospheric composition with higher concentrations of greenhouse gases, higher atmospheric pressure, increased cloud droplet size, and changes in land distribution and Earth’s rotation rate.
Charnay et al. used a three-dimensional global climate model coupled to a dynamic ocean model to examine these possible solutions.
They find that an atmosphere that had 100 millibars of carbon dioxide and 2 millibars of methane 3.8 billion years ago, and 10 millibars of carbon dioxide and 2 millibars of methane 2.5 billion years ago—levels corresponding to 25 to 250 times the present level of carbon dioxide and 1000 times the present level of methane—would have made it possible for Earth to have had a temperate climate with a mean surface temperature between 10 and 20 degrees Celsius (50 and 68 degrees Fahrenheit), close to the current climate.
The authors suggest that these levels of greenhouse gases are consistent with geological data, making such an atmospheric composition a viable solution to the faint young Sun problem. Cloud feedbacks were also shown to prevent a full snowball Earth from developing during that time period. The authors find that some of the other potential solutions could have produced some warming during the Archean, but none individually produced enough warming to avoid widespread glaciation.
Source: Journal of Geophysical Research-Atmospheres, doi:10.1002/jgrd.50808, 2013 http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50808/abstract
Exploring the faint young Sun problem and the possible climates of the Archean Earth with a 3-D GCM
[1] Different solutions have been proposed to solve the “faint young Sun problem,” defined by the fact that the Earth was not fully frozen during the Archean despite the fainter Sun. Most previous studies were performed with simple 1-D radiative convective models and did not account well for the clouds and ice-albedo feedback or the atmospheric and oceanic transport of energy. We apply a global climate model (GCM) to test the different solutions to the faint young Sun problem. We explore the effect of greenhouse gases (CO2 and CH4), atmospheric pressure, cloud droplet size, land distribution, and Earth’s rotation rate. We show that neglecting organic haze, 100 mbar of CO2 with 2 mbar of CH4 at 3.8 Ga and 10 mbar of CO2 with 2 mbar of CH4 at 2.5 Ga allow a temperate climate (mean surface temperature between 10°C and 20°C). Such amounts of greenhouse gases remain consistent with the geological data. Removing continents produces a warming lower than +4°C. The effect of rotation rate is even more limited. Larger droplets (radii of 17 μm versus 12 μm) and a doubling of the atmospheric pressure produce a similar warming of around +7°C. In our model, ice-free water belts can be maintained up to 25°N/S with less than 1 mbar of CO2 and no methane. An interesting cloud feedback appears above cold oceans, stopping the glaciation. Such a resistance against full glaciation tends to strongly mitigate the faint young Sun problem.
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“Cloud feedbacks were also shown to prevent a full snowball Earth…”
What assumptions were used for the cloud feedbacks, given that there is doubt as to the magnitude and even the sign of cloud effects?
Yet another climate model study in which the conclusion of the study is one of the model inputs.
http://wattsupwiththat.com/2013/07/09/claim-faint-young-paradox-solved/
I wonder how they modeled the effect of life on the carbon cycle 3.8 Billion years ago?
Nexxxt.
More meaningless talk to try to promote their soon to be obsolete AGW theroy.
Amazing that nobody is considering planetary migration as a factor, which could greatly vary the amount of radiation receives from even an cooler sun. Gravitational forces from other planets, even ones not currently counted in our existing solar system, could migrate the earth’s orbit by a very large degree. Consider the moon, at it’s formation ~4 billion years ago, it was 80-90% closer than its current oribt. Tidal forces alone likely were the sole cause of this migration. Not a stretch to think that that Earth was much closer to the sun in its early history.
Interesting study. Sounds plausible.
In a lighter vein … um
…the study results are due to humans back then, right? Right?
Isn’t this just backcasting using a model that has already shown no ability to forecast? If the model is told CO2 drives the temperature with steady solar input, and we reduce the solar input then the model would have to react by increasing the CO2 to get the temperature wouldn’t it? Seems all this would say is the model behaves the way we told it to.
It’s like saying raindances bring rain, so by extrapolating the number of raindancers from the last rain shower we can prove the flood 100 years ago was caused by 1,000 raindancers. The rain dancing calculation is meaningless unless you have first proved raindancing causes rain. The CO2 calculation would seem the same until you can figure out what CO2 is doing to the temperature right now, which clearly nobody can.
I don’t know, maybe I’m way off. It just seems all these super hindcasting, forecasting results are nothing but mathematical masturbation. At some point you”re going to have to figure out what actually moves these temperatures, and models are not a shortcut for hardwork and patience.
Their assumptions aren’t consistent with geologic data. Archean rocks show CO2 levels at most fifty times “pre-industrial” concentration. Some banded iron formations imply that the Archean atmosphere might have contained no more than about 900 ppm, just three times the presumed pre-industrial level.
Maybe their study addresses this conundrum. In any case, models whether 3D or 1D can’t be convincing.
And then the sun grew brighter/stronger(near present levels) and in the Jurassic period some 170 million years ago when CO2 concentrations were near 2000 ppm why did the temperatures not have a run away rise to the upside and keep going? That is what AGW theory would suggest today if CO2 concentrations were to go to 2000 ppm ,let alone the 400 ppm they are making such a big deal over..
I wonder what their explanation would be for that? My answer is no explanation becaue the greenhouse gas/climate correlation does not work the way they are trying to convey.
Radioisotope decay…
The authors suggest that these levels of greenhouse gases…
I thought it was logarithmic
The orbit of the Earth was probably also different at the time.
This is something that is always neglected at the geologic timescale.
http://en.wikipedia.org/wiki/Stability_of_the_Solar_System
Fairly recent summary:
http://arxiv.org/abs/1209.5996
Is the Solar System Stable ?
Jacques Laskar
(Submitted on 26 Sep 2012)
Since the formulation of the problem by Newton, and during three centuries, astronomers and mathematicians have sought to demonstrate the stability of the Solar System. Thanks to the numerical experiments of the last two decades, we know now that the motion of the planets in the Solar System is chaotic, which prohibits any accurate prediction of their trajectories beyond a few tens of millions of years. The recent simulations even show that planetary collisions or ejections are possible on a period of less than 5 billion years, before the end of the life of the Sun.
Comments: 28 pages, 6 figures. Text of the Lecture given in the Poincar\’e S\’eminar, Paris, on June 2010, submitted
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Mathematical Physics (math-ph); Chaotic Dynamics (nlin.CD)
Cite as: arXiv:1209.5996 [astro-ph.EP]
(or arXiv:1209.5996v1 [astro-ph.EP] for this version)
Submission history
From: Jacques Laskar [view email]
[v1] Wed, 26 Sep 2012 16:34:34 GMT (1486kb,D)
Latitude,
“I thought it was logarithmic”
Yes it is, but the authors are talking about a 1 to 2 order of magnitude increase from current CO2 levels. That is going to make a noticeable difference even if the effect is logarithmic.
Salvatore Del Prete says:
September 24, 2013 at 11:41 am
The Middle & Late Jurassic & Early Cretaceous are among the epochs most destructive to the CACA hypothesis.
http://www.geocraft.com/WVFossils/Carboniferous_climate.html
Paleo proxy data suggest that during the MJ, CO2 rose rapidly without affecting temperature, but just when the gas peaked in the LJ, temperature fell precipitously (possibly promoting the proliferation of feathered dinosaurs). Carbon dioxide dropped slowly & slightly during the LJ & EK, continuing to fall while temperature was rising toward its mid-Cretaceous high.
Other mid-Mesozoic CO2 reconstructions are even worse for the CACA case, when correlated with temperature.
“… In our model, ice-free water belts can be maintained up to 25°N/S with less than 1 mbar of CO2 and no methane. An interesting cloud feedback appears above cold oceans, stopping the glaciation. Such a resistance against full glaciation tends to strongly mitigate the faint young Sun problem.”
I believe that says “less than 1000 ppm CO2 and no methane, cloud feedback stopped the glaciation at the tropics.”
In any event, a 25% less luminous Sun is entirely offset with a reduction in Albedo from today’s 30% to 5% at that period, (an unlikely number but any reduction would help).
Exactly, they are so full of it. Excellent link milodonharlani.
Reading the replies to a recent Willis Post I came to the realization how the earth maintained >273k temperature ca. 2.5 Byrs ago. Since the earth was receiving significantly less TSI, gravity was unchanged, and the atmospheric pressure had dropped to somewhere in the range of 50 – 100 bar by bleeding off into space then, any storms topped out at much lower elevations resulting in radiating significantly less energy back into space. With a higher pressure the adiabatic lapse rate had to be significantly greater than 10k/1000 M.
BTW – based on the present rate of atmosphere loss on Mars the atmospheric pressure had to be similar to Earth’s shortly after formation. That is 200 – 250 bar.
phodges says:
September 24, 2013 at 11:50 am
Same goes for climatic effects of Earth’s rotation rate & the proximity of the Moon.
There have also been studies of the effects on life forms or lack thereof on the composition of the atmosphere & cloudiness.
The causes of the paradox may be many, but IMO among them are atmospheric density & composition, even without considering CO2 & CH4. Science cannot say with any precision how long it took H2 to escape to space or be consumed by organisms. If it lingered well into the Archean to any meaningful degree, then an atmosphere with twice as much N2 as now (ie, about twice as dense as at present) could produce ammonia & other hydrogen-nitrogen compounds, however short-lived, that would act as GHGs. The recent fossil raindrop study suggests that the Archean atmosphere was no more than about twice as dense as now.
I love it when they use one faith-based theory to prove another. If the empirical evidence doesn’t support the Faint Young Sun theory, maybe the theory of stellar evolution is flawed. It’s not like anyone has ever seen one kind of star turn into a different type of star over the course of billions of years. We just observed different types of stars and imparted our own human need for order and categorization upon them.
Of course Stellar evolution may be correct and it’s the geological evidence that’s being misinterpreted. Maybe the calculation for the age of the strata is flawed. So much of what gets called science these days is nothing more than assumption stacked on assumption.
They forgot to mention that the earth was probably much more volcanic and with a hotter more radioactive core. Undersea volcanoes released enough heat to keep the seas much warmer making the atmosphere hot and humid. The atmosphere being much thicker would trap in the heat much better than the thin of atmosphere today. That is why carbon dioxide makes no difference to climate now. If you have a thick duvet on your bed in winter you will be cosy and warm but if you have a thin sheet you will be cold. Over billions of years the solar wind has stripped away some of earths atmosphere making it easier for heat to escape.
I can understand what a problem a dimmer Sun would mean. It seems that the Sun smartened up fast enough.
Of course this is a model result, and may be false:
I don’t personally view evolutionary stellar models as being particularly more robust than climate models. One of the big unknowns is the rotational profile of the interior of the Sun. If you assume a constant rotation with depth, it is true this leads to the result that the Sun was about 25% less luminous 4-billion years ago, and then to an apparent paradox between observed Earth climate and solar luminosity.
If you assume a more rapid rotation of the interior, this leads to a much “flatter” luminosity curve with time than in a standard slowly rotating star. (See Tassoul’s excellent book on stellar rotation for an overview of this.)
MattS says:
September 24, 2013 at 11:53 am
Yes it is, but the authors are talking about a 1 to 2 order of magnitude increase from current CO2 levels. That is going to make a noticeable difference even if the effect is logarithmic.
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It shouldn’t….once the bands are saturated…party’s over