From the University of Colorado at Boulder a claim that computer modeling has solved the problem, with an atmosphere that is 20,000 parts per million of CO2 and 1,000 ppm of methane.
CU study shows how early Earth kept warm enough to support life
Scientists tackle faint young sun paradox with 3-D climate models
Solving the “faint young sun paradox” — explaining how early Earth was warm and habitable for life beginning more than 3 billion years ago even though the sun was 20 percent dimmer than today — may not be as difficult as believed, says a new University of Colorado Boulder study.
In fact, two CU-Boulder researchers say all that may have been required to sustain liquid water and primitive life on Earth during the Archean eon 2.8 billion years ago were reasonable atmospheric carbon dioxide amounts believed to be present at the time and perhaps a dash of methane. The key to the solution was the use of sophisticated three-dimensional climate models that were run for thousands of hours on CU’s Janus supercomputer, rather than crude, one-dimensional models used by almost all scientists attempting to solve the paradox, said doctoral student Eric Wolf, lead study author.
“It’s really not that hard in a three-dimensional climate model to get average surface temperatures during the Archean that are in fact moderate,” said Wolf, a doctoral student in CU-Boulder’s atmospheric and oceanic sciences department. “Our models indicate the Archean climate may have been similar to our present climate, perhaps a little cooler. Even if Earth was sliding in and out of glacial periods back then, there still would have been a large amount of liquid water in equatorial regions, just like today.”
Evolutionary biologists believe life arose on Earth as simple cells roughly 3.5 billion years ago, about a billion years after the planet is thought to have formed. Scientists have speculated the first life may have evolved in shallow tide pools, freshwater ponds, freshwater or deep-sea hydrothermal vents, or even arrived on objects from space.
A cover article by Wolf and Professor Brian Toon on the topic appears in the July issue of Astrobiology. The study was funded by two NASA grants and by the National Science Foundation, which supports CU-Boulder’s Janus supercomputer used for the study.
Scientists have been trying to solve the faint young sun paradox since 1972, when Cornell University scientist Carl Sagan — Toon’s doctoral adviser at the time — and colleague George Mullen broached the subject. Since then there have been many studies using 1-D climate models to try to solve the faint young sun paradox — with results ranging from a hot, tropical Earth to a “snowball Earth” with runaway glaciation — none of which have conclusively resolved the problem.
“In our opinion, the one-dimensional models of early Earth created by scientists to solve this paradox are too simple — they are essentially taking the early Earth and reducing it to a single column atmospheric profile,” said Toon. “One-dimensional models are simply too crude to give an accurate picture.”
Wolf and Toon used a general circulation model known as the Community Atmospheric Model version 3.0 developed by the National Center for Atmospheric Research in Boulder and which contains 3-D atmosphere, ocean, land, cloud and sea ice components. The two researchers also “tuned up” the model with a sophisticated radiative transfer component that allowed for the absorption, emission and scattering of solar energy and an accurate calculation of the greenhouse effect for the unusual atmosphere of early Earth, where there was no oxygen and no ozone, but lots of CO2 and possibly methane.
The simplest solution to the faint sun paradox, which duplicates Earth’s present climate, involves maintaining roughly 20,000 parts per million of the greenhouse gas CO2 and 1,000 ppm of methane in the ancient atmosphere some 2.8 billion years ago, said Wolf. While that may seem like a lot compared to today’s 400 ppm of CO2 in the atmosphere, geological studies of ancient soil samples support the idea that CO2 likely could have been that high during that time period. Methane is considered to be at least 20 times more powerful as a greenhouse gas than CO2 and could have played a significant role in warming the early Earth as well, said the CU researchers.
There are other reasons to believe that CO2 was much higher in the Archean, said Toon, who along with Wolf is associated with CU’s Laboratory for Atmospheric and Space Physics. The continental area of Earth was smaller back then so there was less weathering of the land and a lower release of minerals to the oceans. As a result there was a smaller conversion of CO2 to limestone in the ocean. Likewise, there were no “rooted” land plants in the Archean, which could have accelerated the weathering of the soils and indirectly lowered the atmospheric abundance of CO2, Toon said.
Another solution to achieving a habitable but slightly cooler climate under the faint sun conditions is for the Archean atmosphere to have contained roughly 15,000 to 20,000 ppm of CO2 and no methane, said Wolf. “Our results indicate that a weak version of the faint young sun paradox, requiring only that some portion of the planet’s surface maintain liquid water, may be resolved with moderate greenhouse gas inventories,” the authors wrote in Astrobiology.
“Even if half of Earth’s surface was below freezing back in the Archean and half was above freezing, it still would have constituted a habitable planet since at least 50 percent of the ocean would have remained open,” said Wolf. “Most scientists have not considered that there might have been a middle ground for the climate of the Archean.
“The leap from one-dimensional to three-dimensional models is an important step,” said Wolf. “Clouds and sea ice are critical factors in determining climate, but the one-dimensional models completely ignore them.”
Has the faint young sun paradox finally been solved? “I don’t want to be presumptuous here,” said Wolf. “But we show that the paradox is definitely not as challenging as was believed over the past 40 years. While we can’t say definitively what the atmosphere looked like back then without more geological evidence, it is certainly not a stretch at all with our model to get a warm early Earth that would have been hospitable to life.”
“The Janus supercomputer has been a tremendous addition to the campus, and this early Earth climate modeling project would have impossible without it,” said Toon. The researchers estimated the project required roughly 6,000 hours of supercomputer computation time, an effort equal to about 10 years on a home computer.
h/t to Dr. Leif Svalgaard
Planet Earth has developed formidable defenses against eradicate solar variations. The planet could care less about human ants infesting the surface of the Earth. There’s nothing humans can do to the planet that will disrupt the life expectancy of the planet and its capacity to nurture life.
This is not really news.
Hart’s 1977 paper (Icarus, 33, 23-29 (1978)) on the Evolution of the atmosphere of the Earth, the one that puts the continuously habitable zone around the sun from about 0.95AU to 1.01AU, produced this result already. All this seems to do is change the emphasis from the whole sweep of atmospheric evolution on a point-model Earth to guessing an atmosphere for a more complicated temperature model.
It is not possible to use a ‘3-D model’ to model the earth’s atmosphere as there are fundamental errors in the modeling of the atmosphere related to how and why clouds form in the atmosphere. A computer modeling program cannot be written to work around incorrect knowledge of the basic science.
The 3-D modeling announcement sounds like propaganda rather than science as it has been known for at least 5 years that there are fundamental errors in atmospheric modeling.
We know there are fundamental errors in the atmospheric modeling as there has been 16 years with no warming which is impossible based on 98% of the climate models. Also we know there are fundamental errors in the modeling programs as the general circulation models predict a hot spot in the tropical troposphere which is theoretically caused by increased water vapour in the atmosphere due to CO2 forcing. There is no observed tropical troposheric warming as the peer reviewed paper linked to below notes.
The competing solution to the faint sun paradox is that a strong solar wind from the early sun blocked cosmic ray flux (CRF is also called galactic cosmic rays GCR) which is mostly high speed protons. The high speed protons create ions in the earth’s atmosphere which effects the amount and prorperties of low level clouds in the atmosphere.
Fortunately as there has been an abrupt slowdown in the solar magnetic cycle we will have a chance to resolve by observations how much of the warming in the last 70 years was due to solar cycle modulation of planetary cloud Vs C02. As noted in the paper linked to below it appears that as much as 0.47C of the warming in the last 70 years was caused by solar magnetic cycle changes rather than increases in atmospheric CO2. (The analysis in the paper is independent of the mechanism.)
A slowdown in the solar magnetic cycle temporary inhibits the GCR mechanism which explains why the planet did not cool when GCR increased in the last 12 years. As there is now the start of cooling it appears the inhibiting of the GCR mechanism is over.
http://arxiv.org/abs/astroph/0306477
Towards a Solution to the Early Faint Sun Paradox: A Lower Cosmic Ray Flux from a Stronger Solar Wind by Nir J. Shaviv
Standard solar models predict a solar luminosity that gradually increased by about 30% over the past 4.5 billion years. Under the faint sun, Earth should have been frozen solid for most of its existence. Yet, running water is observed to have been present since very early in Earth’s history. This enigma is known as the faint sun paradox. We show here that it can be partially resolved once we consider the cooling effect that cosmic rays are suspected to have on the global climate and that the younger sun must have had a stronger solar wind, such that it was more effective at stopping cosmic rays from reaching Earth. The paradox can then be completely resolved with the further contribution of modest greenhouse gas warming. When we add the cosmic ray flux modulation by a variable star formation rate in the Milky Way, we recover the long term glacial activity on Earth. As to the future, we find that the average global temperature will increase by typically 10◦K in the coming 2 Gyr.
http://www.eike-klima-energie.eu/uploads/media/Shaviv.pdf
On climate response to changes in the cosmic ray flux and radiative budget by Nir J. Shaviv
We examine the results linking cosmic ray flux (CRF) variations to global climate change. We then proceed to study various periods over which there are estimates for the radiative forcing, temperature change and CRF variations relative to today. These include the Phanerozoic as a whole, the Cretaceous, the Eocene, the Last Glacial Maximum, the 20th century, as well as the 11-yr solar cycle. This enables us to place quantitative limits on climate sensitivity to both changes in the CRF, and the radiative budget, F, under equilibrium. … …. Subject to the above caveats and those described in the text, the CRF/climate link therefore implies that the increased solar luminosity and reduced CRF over the previous century should have contributed a warming of 0.47 +/- 0.19 C, while the rest should be mainly attributed to anthropogenic causes. Without any effect of cosmic rays, the increase in solar luminosity would correspond to an increased temperature of 0.16 +/- 0.04C.
http://www.phys.huji.ac.il/~shaviv/Ice-ages/GSAToday.pdf
Celestial driver of Phanerozoic climate?
We find that at least 66% of the variance in the paleotemperature trend could be attributed to CRF variations likely due to solar system passages through the spiral arms of the galaxy. Assuming that the entire residual variance in temperature is due solely to the CO2 greenhouse effect, we propose a tentative upper limit to the long-term “equilibrium” warming effect of CO2, one which is potentially lower than that based on general circulation models.
http://icecap.us/images/uploads/DOUGLASPAPER.pdf
A comparison of tropical temperature trends with model predictions
We examine tropospheric temperature trends of 67 runs from 22 ‘Climate of the 20th Century’ model simulations and try to reconcile them with the best available updated observations (in the tropics during the satellite era). Model results and observed temperature trends are in disagreement in most of the tropical troposphere, being separated by more than twice the uncertainty of the model mean. In layers near 5 km, the modelled trend is 100 to 300% higher than observed, and, above 8 km, modelled and observed trends have opposite signs. These conclusions contrast strongly with those of recent publications based on essentially the same data.
http://www.spiegel.de/international/world/interview-hans-von-storch-on-problems-with-climate-change-models-a-906721.html
SPIEGEL: Just since the turn of the millennium, humanity has emitted another 400 billion metric tons of CO2 into the atmosphere, yet temperatures haven’t risen in nearly 15 years. What can explain this?
Storch: So far, no one has been able to provide a compelling answer to why climate change seems to be taking a break. We’re facing a puzzle. Recent CO2 emissions have actually risen even more steeply than we feared. As a result, according to most climate models, we should have seen temperatures rise by around 0.25 degrees Celsius (0.45 degrees Fahrenheit) over the past 10 years. That hasn’t happened. In fact, the increase over the last 15 years was just 0.06 degrees Celsius (0.11 degrees Fahrenheit) — a value very close to zero. This is a serious scientific problem that the Intergovernmental Panel on Climate Change (IPCC) will have to confront when it presents its next Assessment Report late next year.
Earth’s first atmosphere was 20%+ CO2 later converted by those cyanobacteria to oxygen but the primal atmosphere would have been denser so adiabatic compression would add extra heat.
Gunga Din says:
July 9, 2013 at 7:16 pm
A question. Is there anything to indicate (i.e. “evidence”) that the atmosphere really was as they say other than the assumption it was so their model would work?
====================
I’m not an expert, but there is SOME stuff. There’s evidence that single celled life has been around for at least 3.5 billion years, possibly a bit longer. That probably rules out very hot (Venus-like) or very cold (Pluto-like) conditions. And there’s evidence that oceans formed early on, that they contained considerable dissolved iron, and that the early atmosphere had essentially no free Oxygen. There are very extensive Banded Iron Formations in very old marine rocks which are thought to have been formed as Oxygen was freed by weathering(?) and/or biological action (photosynthesis presumably) and pretty much immediately combined with the iron to form layers of iron oxide. (There are, surprise, problems with that e.g. some comparatively young BIFs from 750 million years ago that aren’t all that easy to explain).
But anyway, it’s unlikely that the early Earth atmosphere contained much free Oxygen — or any other gas that would react with dissolved iron to form an insoluble compound. Presumably an Oxygen free atmosphere would allow Methane to last a lot longer than it does today.
Other than that, I don’t think there’s much evidence. But there’s lots of room for me to be wrong.
tallbloke says: July 9, 2013 at 11:47 pm
lsvalgaard says:July 9, 2013 at 9:48 pm
Gary Hladik says:July 9, 2013 at 8:45 pm
“Methane is considered to be at least 20 times more powerful as a greenhouse gas than CO2…”. I’ve seen this claim before, but I see the IR absorption spectrum of methane partially overlaps water vapor’s spectrum. Can anyone explain to me why methane is so much more of a so-called “greenhouse gas” than carbon dioxide?”
Here’s a computer generated chart on the ghg’s, water in green, co2 in red, and methane CH4 in lighter yellow. Methane is pretty well covered by water, and co2 is too, except at 4 microns. Lower chart is a blow up of part of the IR spectrum.
http://www.rockyhigh66.org/stuff/atmospheric_ghg_absorption3.png
Keith Minto says: July 9, 2013 at 10:53 pm
Mike McMillan says: July 9, 2013 at 9:03 pm
Much denser atmosphere. Adiabatic lapse rate rules.
Quite agree, now do we know with reasonable certainty the thickness/density/pressure of the atmosphere back then ?
Best I have seen elsewhere is comparable to Venus, but given the different insolation, orbital distance, rotation, atmospheric composition, – that’s way out of my league to pin down.
Conjecture from Boulder.
Steve mosher says:
July 9, 2013 at 7:20 pm
“If you want to solve the faint sun paradox you have one tool to “prove” that your hypothesis is consistent with known physics and consistent with extant data. That tool is a GCM. of course it leaves things out and gets other things wrong. But if you are a scientist interested in the question, this is all you have.”
That means it is junk science; as we already know that GCM’s are faulty even for time periods as short as 17 years.
We already know The Great Oxygenation Event (GOE), also called the Oxygen Catastrophe or Oxygen Crisis or Great Oxidation where the Earth literally rusted at about this time, ~3bya.
The simplest solution is that the global air circulation was different with different amounts of cloud as compared to today.
The differences would have been driven by the effect of the weaker sun on atmospheric temperatures above the tropopause involving ozone quantities..
As we see today with the solar/climate link that I have proposed the weaker solar effect on ozone amounts and distribution back then would have resulted in a slower throughput of energy through the Earth system such that the temperature then was not a lot different from that of today despite the sun having been weaker.
tallbloke says:
July 9, 2013 at 11:47 pm
“Can anyone explain to me why methane is so much more of a so-called “greenhouse gas” than carbon dioxide?”
——————————————————————————————————————-
Rog,
of course not, methane and carbon dioxide are not “greenhouse gases”. The only significant “greenhouse gases” in our atmosphere are N2 and O2 due to their poor IR radiative properties. Water vapour, CO2 and methane are radiative gases. Radiative gases both absorb and emit IR radiation. Radiative gases act to cool our moving atmosphere at all concentrations above 0.0ppm.
The most logical explanation for the faint sun paradox is higher atmospheric pressure. The N & Z hypothesis has flaws, but it can be easily adjusted. N & Z failed to understand the role of radiative gases in strong vertical convective circulation and atmospheric cooling. However, because all planets and moons in our solar system that have managed to retain an atmosphere have sufficient radiative gases to drive their lower atmospheric lapse rate close to the adiabatic ideal, the N & Z hypothesis works.
Occam’s razor favours negative feedback and climate regulation as the reason for stable life-supporting climate over an earth history with 30% change in TSI.
Other explanations, whether CO2 (may Allah’s blessings and peace be on this molecule), or atmospheric pressure, or volcanism, or cosmic rays, or any other agent, require the fortuitous and improbable scenario of a level of action declining linearly over all of earths history in such a way as to exactly counter-balance the increasing insolation.
This is tortuous, improbable and wishful thinking, and contradicts Occam’s razor, which in 99% of cases means its plain wrong.
So we are left with climate regulation by the biosphere and the Daisyworld scenario.
Think of all the Iron which was around before Oxygen rose and turned it into red rust.
How hot do metallic surfaces get in the sun versus crystaline rocks.
How much energy was held in the ocean when it is had all that dissolved Iron in it.
Okay, just musing. But the first real evidence of wide-spread glaciation occured at 2.4 billion years ago just as the level of Oxygen began accumulating in the atmosphere signaling that Iron and other elements with an affinity for being oxydized were being reduced.
Otherwise, I don’t think we will ever have solid answer for the Faint Young Sun paradox. It could have been any number of 100 different explanations.
Rhoda R says:
July 9, 2013 at 8:21 pm
Why are they assuming that life began in upper oceanic levels? There is a lot of life around submarine vents and the temperature around those vents is pretty high. Young sun doesn’t need to come into it. Nor does CO2 or oxygen for that matter.
——-
Agreed. There were far more tectonic plates back then, thus more spreading ridges, thus more vents. The surface could have been all ice. It’s all speculation at this point.
The Hart paper I cited above can be found here
http://www.physics.uc.edu/~sitko/AdvancedAstro2011/21-CHZs/Hart78.pdf
The contrast between this model and what was being trumpeted about the effects of a doubling of CO2 due to anthropogenic sources was what made me first say “wait, what?” about the CAGW propaganda.
johnmarshall says:
July 10, 2013 at 2:16 am
Earth’s first atmosphere was 20%+ CO2 later converted by those cyanobacteria to oxygen but the primal atmosphere would have been denser so adiabatic compression would add extra heat.
Photosynthesis converts H2O to O2.
Mike McMillan says:
July 9, 2013 at 9:03 pm
“Much denser atmosphere. Adiabatic lapse rate rules.”
+1
Surface temperature is a function of the mass of the atmosphere and solar flux at earth’s orbit. If the earth has remained in the life zone, then the mass of the atmosphere must have decreased.
“….explaining how early Earth was warm and habitable for life beginning more than 3 billion years ago even though the sun was 20 percent dimmer than today — may not be as difficult as believed, …..”
This is clearly a left-handed support for the “settled science” of the CO2 (as the only) temperature control knob. A little trip down the hall to the geology department and they would have learned that climate scientists, physicists and astronomers were the only ones who hadn’t yet solved the so-called paradox (indeed in geology there was no paradox). A number of excellent “warm” possibilities have already been discussed above by nimble contributors to WUWT. Two in particular are all that is needed, the rest is gravy. The thinner crust and stage of cooling of the “new” earth are no-brainer explanations of why there was no paradox to start with. A feature of the Archean globally are the presence of a type of basalt lava and intrusive equivalents known as komatiites. Wiki is okay on this one, although some stoat may alter it if it seems to disagree with the Boulder carbon follies.
http://en.wikipedia.org/wiki/Komatiite
“Magmas of komatiitic compositions have a very high melting point, with calculated eruption temperatures in excess of 1600 °C. Basaltic lavas normally have eruption temperatures of about 1100 to 1250 °C. The higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradients in the Archean Earth.”
The higher geothermal gradients were due to thinner crusts and a higher temperature mantle (highly magnesian hot layer that underlies the crust. These lavas were very low viscosity and spread rapidly, some as thin as a centimetre or two. The ponded into lakes and flowed in streams before they solidified. Komatiites do not occur in rocks since the Archean, which coincided nicely with the “paradox”. At this stage of cooling of the earth, it would seem that molten magmas occurred below large areas in the upper mantle. Add considerably more atmosphere that has thinned over time, and let’s not forget negative feedbacks (yeah, I know this isn’t in the scriptures). If a cooler world is still postulated then H2O in the atmosphere was lower, cloulds lower, albedo lower and you have a condition of a higher percentage of whatever sunlight there was reaching the earths surface.
Ya know, hubris among the apriori thinkers (the kind of thought that an intelligent teenager with no experience uses to argue with his parents) in physics and astronomy is one of the biggest barriers to resolution of climate science problems.
William Astley says:
July 10, 2013 at 2:04 am
The high speed protons create ions in the earth’s atmosphere which effects the amount and properties of low level clouds in the atmosphere.
This peer-reviewed paper http://www.leif.org/EOS/swsc120049-GCR-Climate.pdf shos that
“there is no robust evidence of a widespread link between the cosmic ray flux and clouds”
Let me guess … It was CO2. Was it CO2 that done it??
Leif, as far as cosmic rays, the few papers that have looked at it have
not found a strong link. But, it is still possible that certain types of clouds
or even certain energies of cosmic rays may have a bigger effect. It’s still
a young field. It may turn out to no play a role or only to play a role in a few
cases or to have only a small effect. The same with CO2 diffusion in ice. I don’t think there have been that many studies done on it and showing something over a few months in a lab or testing it in situ a few times does not prove once and for
all that CO2 does not diffuse over millions of years. I still think these questions are worth studying in more detail. Of course one should not argue for something when there are a few papers that say this something does not seem to be important, but it is also not definitive, everlasting proof either. Not really arguing with you as much as making a larger point that some things are more “settled” than others.
Phil. says: @ur momisugly July 9, 2013 at 9:20 pm
…..Photosynthesis converts H2O into O2 not CO2!
>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Is that what they are teaching in school these days?
I would not be surprised – No teacher, but every textbook, left behind
The equation for photosynthesis is
6CO2 + 12H2O + light → C6H12O6 + 6O2 + 6H2O
So all of the CO2 and half the H2O is converted into glucose and O2.
Uranium-238 has a half-life of 4.468 x 10^9 years. If you believe that this is a fixed decay rate, which is questionable under the wide range of conditions, then 2.8 x 10^9 YBP there was almost twice as much Uranium….and twice as much mantle decay heat.
“The decay of Uranium, Thorium and Potasium-40 in the Earth’s mantle is thought to be the main source of heat that keeps the outer core liquid and drives mantle convection, which in turn drives plate tectonics….Uranium’s average concentration in the Earth’s crust is (depending on the reference) 2 to 4 parts per million” ~ Wiki/Uranium
We have recently increased the core temperature estimates from 5000C to 6000C.
http://bbc.co.uk/news/science-environment-22297915
The core is a 900 mile diameter extremely dense Iron cubic crystal that is inherently a solid magnet and is rotating faster than the crust, creating an additional magnetic field. Every proxy is based on approximations that compound errors over time. Everything about this discussion is hypothesis on conditions that we cannot even currently quantify.
Steve mosher says:
July 9, 2013 at 7:20 pm
////////////////////
Steve
What a silly, and may I say childish, response to a couple of very good points raised by anticlimatic.
I know that you like to defend models and their use, and i don’t doubt that 3D are better than 1D. But the real insight would have been to clarify whether the model actually took account of the 4 hour day (I am not sure whether it was quite that short or whether it had by then extended to nearer 7 hours) and the additional gravitational pull of the moon (and the different orbital distance between Earth and Sun and different axial tilt).
Don’t forget that if the Earth is spinning not once a day but 6 times a day, there is far less time for land (or water) that has been warmed by the sun during sunlit hours to cool. The speed of rotation is a very material factor.
One only has to look at Io to see the effect of gravity, and heat generation via gravitational forces. Admittedly, that may be an extreme example because the Earth/Moon relationship is nothing like the Jovian relationship which is particularly stark due to the presence of the other Galilean moons , but nonetheless it gives a visual example of the potential strength of this force.
Now I do not know precisely what effect the points that anticlimatic raised would have, but one thing that I am certain abouit is that they are material, and the issue is therefore did the 3D model take these factors into account and what assumptions were made with respect to them.? if you could clarify that then you would be adding to the debate and general understanding of the issue.
Gail Combs says:
July 10, 2013 at 6:56 am
So all of the CO2 and half the H2O is converted into glucose and O2.
What is the glucose eventually converted into?
Stephen Wilde says:
July 10, 2013 at 4:10 am
The simplest solution is that the global air circulation was different with different amounts of cloud as compared to today.
The differences would have been driven by the effect of the weaker sun on atmospheric temperatures above the tropopause involving ozone quantities…..
>>>>>>>>>>>>>>>>>>>>>
Sorry Stephen you did not have free atmospheric O2 and O3 until after you had photosynthesis.
Like other people have said above, GHGs need a thick atmosphere to operate.
Also, once the adiabatic lapse rate is reach, the idea is that radiation to space happens at a higher altitude due to GHGs. Since GHGs are colder at a higher altitude, there is a warming. But, this is based on the idea that emissions from GHGs are due to temperature. In reality, when a CO2 molecule absorbs a IR photon, it could re-emit it instantly. Since the CO2 molecules at the top of the atmosphere are receiving a lot of IR photons from the CO2 at a lower altitude, there is a chance that some of the IR emitted by those molecules happen in addition to emissions due to the temperature. So a GHG that can absorb IR and re-emit before its temperature has raised would be that much weaker as a GHG. I wonder if this effect has been calculated correctly.