CO2 Thermagedon ?

What is the worst damage that increased Carbon Dioxide could possibly cause on earth?The  answer is  surprisingly little  (ignoring hypothetical ‘feedbacks’) !

CO2 greenhouse effect for concentrations up to 0.1 C. Shown are the direct surface temperature responses under business as usual.

CO2 greenhouse effect for concentrations up to 0.1 %. Shown are the direct surface temperature responses under ‘business as usual’ policies  untileventually  fossil fuels are exhauted.

So now let’s imagine the most extreme case possible. What   if CO2 levels were somehow to rise 300 times higher than current levels reaching crazy levels like 10%? Just how hot would the earth then get ?

Saturation of the narrow CO2 15 micron lines into the Stratosphere ensures that total greenhouse warming is limited to 13C.

Saturation of the narrow CO2 15 micron lines into the Stratosphere ensures that total greenhouse warming is limited to 13C.


So really not so bad after all! The maximum possible CO2 greenhouse effect on earth is about 13 deg. C.

These calculations are based on a line by line ‘radiative transfer’ code covering the  dominant 15 micron absorption band described here.

So what is the problem of anthropogenic global warming – if any?

For 99.9% of earth’s 4 billion year climate history CO2  never has been a problem. On the contrary CO2 has helped to keep the earth’s temperature just right for life to flourish. In reality CO2 is a wonderful stabilising feedback that counteracts  external  ‘dangerous’ forcings on climate, and will allways to do so as long as life continues to flourish.

CO2 levels in the earth’s atmosphere normally react to changes in climate. They naturally regulate atmospheric CO2 by  responding to changes in ocean temperature. It is basically only now  that CO2 levels have increased before temperature, with the possible exception of the Paleocene–Eocene Thermal Maximum (PETM) event 50 million years ago. Anthropogenic CO2 ‘climate change’ is less than a blink in the eye.

Geological  evidence shows that during the PETM, CO2 levels rose by about 3 times more than the most pessimistic levels imaginable today, even  if humans were to burn all available fossil fuels on earth. Yet during PETM  temperatures only rose by just 5C. Furthermore it is entirely possible that the PETM excursion in CO2 levels was not due to some volcanic belch of CO2,  but instead was also the result of some external astronomical forcing such as a supernova, which CO2 levels then reacted to as a response.

So we need to keep things in perspective regarding (catastrophic) anthropogenic climate change. Yes human activity will most likely result in some small warming but its effect will naturally be  rather limited.

It may even turn out to be a blessing in disguise because increased CO2 levels now may likely delay the onset of the next ice age which otherwise is due to start around now. Another ice age would be orders of magnitude more catastrophic.


About Clive Best

PhD High Energy Physics Worked at CERN, Rutherford Lab, JET, JRC, OSVision
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15 Responses to CO2 Thermagedon ?

  1. DrO says:

    Dear Clive

    By coincidence, my current drafting of my “Note 6” on the new “lows” in the AR5 includes a discussion of the IPCC’s prediction of as much as 12C rise in 300 years (due to 1,100 ppm CO2).

    … if pressed, I will release parts of the draft to the usual location here ( … let me know.

    It is, of course, ludicrous. Have at look at any temp and CO2 reconstruction of the last 500 million years. The absolute total temp range over 500 million years was at most 10C … and that for the entire 500 million years.

    In general, it takes hundreds of thousands of years for the planet to change by even 4 – 6C.

    Even when CO2 levels were 8,000 – 14,000 ppm (i.e. 8 – 14%), being hundreds of times the amount of CO2 currently (c.f. 300 million years ago), and tens of times the IPCC 300 year forecast of 1,100 ppm, temperature effects of the planet NEVER, EVER, saw a 13C change over that 500 million years.

    All that is occurring with massively greater forces at work (planetary, solar, etc etc). Moreover, 500 ma ago, the planet was much warmer simply since it had 500 ma less to cool the core.

    As such, any suggestion that the planet will undergo a +12 C change in 300 years seems so complete out of line with reality that my first question was … are they crazy?

    I hope to have Note 6 ready soon enough, it has the charts etc, but those are things you can Google.

    To be clear, it seems completely insane to speak of changes of this magnitude at all, never mind in 300 years.

    Incidental, the reason they are now moving to 300 year forecasts (1,000 year forecasts) is an interesting point in itself, but that’s for another day.

    I do have concerns with the rest of your comments:

    1) you may wish to check your sums … e.g. I may have missed something, but moving from 400 ppm (0.004 = 0.4%) to 1,000 ppm (0.01 = 1%) is a “3” time factor, and moving to 10,000 ppm (.1 = 10%) is a 30 times factor, not sure where the 300 times comes in.

    2) Please show your equations for the two charts. I am desperately hoping/praying it is NOT based on some of that

    dT = a Ln(CO2/CO2orig)

    type nonsense. If they are, I plead with you to abandon that approach as that would very much undermines your credibility, for reasons already demonstrated in the past.

    3) The link to the calculations via the “described here” url show a page that has so many problems it is hard to know where to begin.

    If you have not derived a proper heat/energy balance (and if you have please show your work), simple integrating HighTran can in NO WAY lead you to anything that results in a proper statement of what temperature might be.

    Even if you get the RF right, which I highly doubt, ignoring coupled effects in the energy balance means you couldn’t possibly get the temp forecast right.

    For example, suppose you could show an RF = 5 W/m^2 … so what? If the planet is retaining that amount of net differential energy, then the accumulation of energy will, in part, be seen as a rise in temp. However, the planet radiated energy proportional to T^4 or thereabouts. That means, that some/much of the that RF would still leave the planet, since the planet will be shedding energy at a much higher rate/flux … please show where that sort of force is accounted for.

    … and of course the planet can retain heat/energy without any temp change at all … so there is lots missing if there is not a proper energy balance.

    I am also still working on my Note 5, which will provide some modelling, some equations, and some solutions demonstrating some of the important points … but that is a ways off yet. Still, if your equations do not have a proper

    in – out +/- sink/sources = d/dt contents

    basis, then you have nothing. I cannot emphasise this enough.

    If you know what I am talking about, then please do it correctly. If you do not understand what this means, then start learning about “transport phenomenon” and especially modelling heat transfer dynamics. There is NO OTHER WAY to do this.

    If necessary, I can release Note 5 piece-meal, at least to provide some maths to illustrate the issues, again let me know …

    BTW, what makes you think 10% CO2 is saturation? Since WV spectra overlaps with CO2’s, increasing WV will also saturate the (same) spectra. As the planet warms, WV increases. So spectral saturation, almost surely, will occur long before 10% CO2, and indeed, may even occur long before 1% CO2. This is evidenced by satellite and atmospheric data.

    Also, if you are going to insist on throwing out the First Law of Thermodynamics, would you mind explaining how that might be justified (or perhaps I should say, rationalised)?

    • Michael McPhillips says:

      Are you not overlooking the temperature that our bodies evolved to be able to function? if the example of people dying in heatwaves because they can’t cool themselves tells us anything it is that at high temperatures our lives are in danger and I think that another 5 degrees C for any length of time will kill most of us. Furthermore, when any global temperature increase means double it for those living in the tropics, which means even 2C increase is life-threatening there, and where I think over 70% of the planet’s population lives, that I think will be where human extinction begins when animal extinction from lack of food and water is already in process.
      You also seem to be dismissing the effect that cloud cover and polar melted ice water into the oceans can have in starting an ice age in Europe, Alaska, Canada, and Russia.

  2. Clive Best says:

    Dr O,

    I agree that the trend of IPCC to now predict large rises in temperature 300 years ahead looks suspicious. It seems more self serving than science. In fact it isn’t science since it can’t be tested. Predicting the future beyond your lifetime is more like Nostradamus.

    Your comments

    1) 400 ppm = 4*10^2 times 10^-6 or 4*10^-4 or 4*10^-2% = 0.04%

    so 300 times larger is 12% OK it really should hab=ve be 250 times larger.

    2) There are no equations. The only way to do this calculation is to use the cross-sections for all the measured quatum absorption lines ( ) and calculate for the current atmospheric profile ( pressure, temperature, content) the efefctive height where photons of a given wavelength escape to space. Then you increase the CO2 content and leave everything else the same and recalculate the effective heights. These are slightly colder.

    The basic assumption of all radiative transfer codes is that CO2 emits radiation as if it were a black body of temperature T at each layer in the atmosphere. An average lapse rate in the troposphere and a stratosphere profile is assumed such as that given by US Standard atmosphere.

    Of course this is still an approximation as the profile responds in synch with any changes especially H2O profiles etc. but this is ignored to first order.

    Finally we get out for a given CO2 increase how much smaller the outgoing radiation becomes eg. 2 W/m2. This is called ‘radiative forcing’ and it is assumed that the surface temperaure increases to rebalance this ‘forcing’ by warming by DT. DS = 4.epsilon.sigma^T^3.DT

    The logarithmic formula is simply a fit to the resultant DS versus CO2.

    3) see 2)

    It is essentially exactly that in – out +/- sink/sources = d/dt contents

    However it indeed ignores H2O and any overlap with 15 micron band. It ignore changes in clouds or ice albedo or lapse rate etc.

    These are hard and IPCC models do not really know either. They are mostly parameterisations based on assumptions. The bias to exaggerate feedbacks is blatant since if net feedbacks from H2O turn out to be negative then the whole show is over.

    I wanted to avoid all this complication and assume a planet with just N2 and CO2 even though that is impossible.

  3. DrO says:

    Dear Clive

    1) Re “300 time”: oops, I misread your chart … “just lost my mind for a moment” 🙂 we’ll have the jury disregard my comment on that.

    2) As for the rest of it, I am afraid you are digging yourself deeper. There is no way that your approach even vaguely attempts any

    in – out +/-sink/source = d/dt content.

    For example, nowhere in the expressions is there a d/dt content … surely that is significant, since it is the d/dt of the contents that is actually the “global warming” bit.

    HOWEVER, the real insight is that your approach relies on “curve fitting” to get a T = f(CO2). That immediately guaranties, in the context as presented, that you cannot possibly have arrived at a model that is based in “proper” physics as such.

    The only thing your HighTran calc’s produce is a per molecule absorption. It says nothing about an energy balance for the planet, where the energy then goes etc etc

    While the concept of RF is useful in conceptual sense, and sometime to use as a summary measure to compare certain types of the “things”, it is a massive MISTAKE to attempt any sort of T function solely in terms of CO2’s RF as an “explanation” of the planet’s climate.

    Separate from having omitted the requirements for the First Law of Thermodynamics, the fitting process makes the results meaningless.

    You can FIT ANYTHING, and claim it to be “correct”.

    And that is exactly what has been done.

    Your fit not only ignores the (by far) most important GHG (WV), but also ignores all the other massive forces in the process. For example, I don’t see any sink/source terms in your expression, I don’t see any ocean warming, I don’t see any heat required to create/maintain life, and about a million other things.

    Also, over the past 200 years, the Sun’s flux as easily varied 6 or so W/m^2, where is that in your equation (i.e that the “In” is not a constant, etc), what about the “In” from core of the planet”, etc etc. Put differently, if you ignore CO2 completely, just the variance in solar flux could produce exactly the same “fit” … would that then prove that CO2 is irrelevant? … and so on.

    Even worse, to perform a fit, you have choose a sample data set. How do you decide on that? What if I take the 19th century as my data set, or the 300 years between 1,200 and 1,500, or the last 18,000 years starting from just before the last ice age to present …. or what about the last 18 years (nice decoupling between CO2 & T in that period) …. and so on, and so on.

    Curve fitting, in this sense, creates utterly meaningless results.

    If this was just science for the sake of science, well it would be a “technical problem”. HOWEVER, as this subject has been hijacked for ideological purposes, posting results of this sort will allow some to “believe” (falsely) that this is proper science … IT IS NOT!

    I will try my best to move my Note 5 along a bit faster, and perhaps release just portions of the early draft that allow some illustration of exactly why/how a proper heat/energy balance is required, and how that produces a very different result.

    • Clive Best says:

      There is no curve fitting. The curves are the result of 100 runs of the radiative transfer calculation changing CO2 levels.

      Incoming Solar – Outgoing IR = 0 from space

      Now increase CO2 levels by an infinitessimal amount.

      The atmosphere radiates slightly less energy to space – DS

      There is now a negative energy imbalance of -DS

      Surface warms to a new temperature DT to rebalance energy with +DS

      S = eps.sigma.T^4

      DS = 4.eps.sigma.T^3. DT

      So ‘forced’ temperature rise of surface to rebalance energy is

      DT = DS/(4.eps.sigma.t^3)


      That is all I have done. The only tricky bit is to calculate DS from the absorption lines of CO2. There is a simplification in that the US standard atmosphere is assumed constant during the whole process.

    • Clive Best says: ”The atmosphere radiates slightly less energy to space”

      Clive, you are brilliantly articulate in English, can bring the truth to the public, BUT: ”atmosphere doesn’t radiate any heat / energy to space!!!”

      TRUTH: almost ALL the heat is canceled / neutralized in the first 100km above the ground; by the cold vacuum that penetrates constantly in the thinner air – as the planet orbits around the sun as a Frisbee!!! No heat can be detected above 10km, unless is super-heated air from volcano or nuclear explosion = you are barking up the wrong tree, as the propaganda prefers…
      To get the real truth and, with your brilliant English, YOU can make a big impact – please read the proven facts and discard the pagan beliefs:

      Merry Christmas!

      • Clive Best says:

        Hi Stefan,

        OK let’s not call it ‘heat’ but IR photons instead that escape from the atmosphere to space. That is what satellites measure when they scan the earth’s IR spectrum from space. You’re right that the cold vacuum of space has a temperarure of 3K but heat can’t conduct into a vacuum so the atmosphere loses heat by radiating. In that sense the cold of the vaccum does seep into the atmosphjere.

        Happy Christmas !

      • roberto says:

        Sorry… looked at the website you’ve linked… but things like…

        “into that cold vacuum which constantly penetrates into the troposphere”

        … is absolutely nonsense!… if it’d penetrate the atmosphere it would have diluted it eons ago.

        Are you a lawyer or some accountant with an interest in science or what?


      • roberto says: ”… if it’d penetrate the atmosphere it would have diluted it eons ago”l

        Roberto, roberto, happy new year!

        1] if you read the whole post, you would have found the answer to your question, there it says: -” because the cold vacuum doesn’t have friction, OR gravity, stays where it is; the earth cannot take it with her spinning around the sun as a Frisbee”

        Same as: air goes trough your car radiator, but doesn’t ”DILUTE IT” The way air goes trough your radiator = cold vacuum goes trough the air – air has ”gravity” and travels with the earth = same as your radiator bolted to the car, travels BUT doesn’t accumulate extra air to ”dilute” itself.

        the difference with the atmosphere is: when gets warmer than normal -> the space between gas molecules increases and lets extra cold vacuum trough b] troposphere increases in ”volume” that encompasses more cold vacuum = same as if your radiator can ”expand / get larger” when hotter and to shrink when cooler!

        You shouldn’t be scared from real proofs, should read the lot, twice – that post will win on the end against the misleading propaganda. P.s you shouldn’t call me a solicitor; I hate solicitors – because: my ex wife, the bitch is a solicitor…

  4. DrO says:

    Dear Clive

    1) In your original response, you had

    “The logarithmic formula is simply a fit to the resultant DS versus CO2.”

    But now you say “There is no curve fitting.” … it may be help to be consistent about this.

    2) Why not just show the exact formula you used for plotting the charts above? Somewhere you must have something to the effect T=f(CO2), what is that f()?

    3) Your explanation of your “balance” clearly demonstrates you have NOT performed a proper balance. One easy way to see this is to notice that you appear to have only “flows” in your expression. While heat transfer itself is a “flow thing”, to get temperature response you must have a “content thing”. Indeed, even then it appears that you only allow for changes in the outflow, and not in the inflow., and of course no sinks/sources.

    Be that as it may, even to keep to the ridiculously over simplified version as presented, a balance would have to have at least the form:

    SolarFlux – a T^3 dT/dr = d/dt(M cp T)

    which is a crude in – out = accumulation. The RHS should really be a Sum of many things, but let us assume the terms imply that.

    Your argument is then to use an altered form that separates out the “flow impact” of CO2 as

    SolarFlux – aT^3 dT/dr – RF(CO2) = d/dt(M cp T)

    … which would otherwise be buried in the dT/dr term.

    Then, apparently, you alter the differential of out flow to allow some form TOA argument, and immediately do away with all the many things that happen at the surface (and indeed seem to completely ignore that the surface is a “volume”, etc), and through the atmosphere.

    Incidentally doing a HighTran run at 25km, where there is total of about 3 molecules, seems curious to me.

    Then, apparently, knowingly or not, you assume that the planet comes to thermal equilibrium instantaneously … which then would allow dropping the RHS.entirely … though of course making a dog’s breakfast of the T forecast, since then there is no “time” component … so even if the equations were correct in some sense, there would be no way to tell if all this happens in a day or over 10,000 years etc. This is further complicated by the day/night cycle, and given that your outflow is f(T^3), and given that daily temp fluctuations are, in many place 10C, that will have a significant impact, and so on, and so on.

    I presume you will say that time is not considered here, since you were looking to establish only the “worst case scenario” … though clearly, if the worst case scenario happens in 1 hour, it has very different “worst case” meaning compared to “worst case” that occurs in 100,000 years.

    … so by the wave of a magic wand, we ignore any flow effects radially, we ignore any accumulation effects …. which is the actual bit where the planet warming T comes from, and of course all the sinks sources etc.

    … have I got it essentially correct, that this is what you have done?

    Then, since you calculate RF based on HighTran, which is where you introduce CO2 concentration, you end up with something like

    SolarFlux – a T^3 – RF(CO2) = 0

    … so is your plot above something to the effect T = [(-SolarFlux + RF(CO2))/a]^(1/3) ?

    … though you say it is logarithmic, so clearly I am missing something in your derivation.

    PS, just for completeness, of the many things missing from your approach, and as indicated previously, Solar flux can easily vary 6 W/m^2, which alone could “explain” the CO2 RF effect without any CO2 and so on, and so on.

    PSS. your model also implicitly assumes “causality”, and that can be questioned based on all of the real world data showing CO2 always lags T, and so on, and so on.

    BTW, you can do away with much of the absorption lines integration problems quite easily if you are to ignore those many other effects anyway. Instead of worrying about complex spectral issues, just take the distribution of the planet’s radiance at the surface as a given curve, perhaps arrived at by some curve fitting. Since the total flux is the area under the curve, it is a simple matter to use quadrature to integrate the “fit” curve for scenarios where increasing bigger “bites” are taken at 14 – 16 um. That will massively reduce the complexity of your code, and massively reduce CPU time etc. Since increasing “bites” can be reasonably approximated as “taller/deeper” and “taller/deeper” trapezoids, your RF(CO2) calculation becomes trivially simple.

    Anyway, I’ll put a push on parts of my Note 5 to show a (more) proper heat balance, and ways to solve it. I’ll need at least a week or two for that. So look for “something” Re Note 5 sometime in the new year here (

    BUT MOST IMPORTANT … Happy Holidays and all the best in the New Year 🙂

    • Clive Best says:

      Dr O,

      I only mentioned the logarithmic formula to try and explain its origin. There is no fundamental physics behind it. It was simply a fit that Mehr et al. made to a selection of radiative tansfer results.

      The method I use is to essentially to calculate the optical depth downward from space for each wavelength line in the 15 micro band of CO2. This gives the heights above the surface where photons can escape directly to space. The flux of such photons is proportional to the temperature and density of CO2 molecules at that height. There is an assumption of local termodynamic equilibrium. Then the density is given by barometric pressure times CO2 concentration. The tremperature is defined by the US sttandard atmosphere which has a lapse rate of 6.5C/km a tropopause at 1km and a stratosphere above 20 km increasing in temperature.
      The software is written in PERL reading the HITRAN absorption cross-sections from a file. A write a Fortran program to extract the CO2 cross-section data. I can make the code available if any one wants it.

      Happy Christmas !

      • DrO says:

        It looks like the problems are even worse compared to earlier discussions:

        1) Ok, so we are back to fitting “guesses”, and we accept that there is no fundamental physics behind it … that rather reduces the (scientific) credibility … and surely we must NOT accept any UN/IPCC “planetary social upheaval” policies on such.

        2) But it gets MUCH worse. As a scientist one of our key obligations is not only to obtain proper data, but also to check the data’s integrity.

        To this end I have started researching satellite data, particularly as relating to In and Out bound radiation so that I can parametrise my models. I may well get around to writing a note on this, but here are a few facts/results that UTTERLY CRUSH any notion of UN/IPCC “results”:

        a) I have not found all the satellite data that I would like, but something I found recently here ( is at least a small attempt at assessing the “value/reliability” of in/out energy/radiation from a large number of satellites (not all) between approx 1980 – 2005. I will provide just a few of the important results therein:

        (i) Satellite data disagree amongst themselves. The differences are typically in the 4 – 10 W/m^2 range … that is a huge difference/variability in the “actual/real” data.

        (ii) The differences between the real satellite data and (IPCC) model results are very much greater, on the order of 40 W/m^2 in some cases, and the “wrong sign” in other cases (see below).

        (iii) Crucial intermediate results in the models, such as the fundamental impact of clouds are profoundly contradicted by the satellite data. For example, all the real satellite data (e.g. CERES) shows CRE as -8 to -10 W/m^2, while the IPCC models use +6 to +7 W/m^2.

        … get it, they have the wrong sign in the models, and absolute differences are massive.

        (iv) The primary explanations for the differences/errors/unreliability seem to relate to the use of “ancillary” inputs/data (e.g. databases and data models such a HiTran/ModTran), and of course the near complete inability to handle water vapour correctly, etc.

        The ancillary data problem is huge outright, but has other rather “sneaky” elements to it, see below.

        In short, these massive uncertainties COMPLETELY swamp the sort of “hysteria” over 2 – 5 W/m^2 “forcing” claimed by the IPCC/UN et al.

        … note: these fluxes are in “insolation” terms, which are about 1/4 of the actual fluxes, so the actual differences are generally much larger.

        3) In your charts above you will notice that there are two temperature “minima” (of sorts) with altitude. Many of the satellites use “glancing” reading of sun light etc reflected off the atmosphere (c.f. looking straight down). The instrumentation used to obtain spectral profiles (such as the type in your Nimbus II chart used in another of your threads) tends to report results for a narrow altitude range, and in particular lower and mid altitudes. As such, the “CO2 bite” in the spectra may very well be from 10-20k altitude, NOT 30-50k altitude. This has profound implications for the “meaning” of those spectra, and of course makes a complete dog’s breakfast of the GHG speculation … is it really TOA? Do the Boltzman profiles have the meaning as advertised? … apparently not.

        There are many other problems with the instrumentation and which make a huge impact on the meaning/interpretation/usage of those results. Not to mention questions like night time vs. day time biases, and data as it varies with land/sea/ice and latitude (I have finally found at least a few satellite etc results comparing tropics to poles … what a difference).

        4) As the assessment cited above emphasises, the ancillary data is highly suspect, and the results are highly sensitive to changes in those inputs … e.g. HiTran etc.

        However, even worse, the satellites themselves often convert the electrical signals from their detectors to “results” (like spectra) by using exactly those (dodgy) ancillary inputs (e.g. HiTran/ModTran). That is, the so-called “satellite data/results” have been pre-processed with known to be unreliable “ancillary” data/inputs.

        This means not only wanting reliability in the reported results, but also means that there will appear to be an “excellent” agreement between satellite spectra and models … NOT because the models are good, BUT because they both use the same models …

        5) Solar irradiance can also vary 4 – 6 W/m^2, we know very little about historical water vapour records (at the moment WV accounts for 80% of GHG effects according to the IPCC), they completely ignore/scrub volcanoes from their calibrations and forecasts, etc etc

        BTW, NASA has started to publish its OCO-2 satellite data. The data format for their files has changed, and unfortunately, there is not a file smaller than a GIG, and you need hundreds of them to get a comprehensive assessment. Still, look at some of their results. One particularly interesting observations is that, by far, the highest CO2 concentrations are in Africa and India … not NA or Europe … hmmm, I wonder what that will mean for the UN’s policies (I expect denial, or silence … along with some “slience” 🙂 )

        The list goes on and on ….

        Previously, I had proven that (see here the mathematical prediction of the climate a la IPCC/UN is categorically prohibited by the properties/rules of the cosmos.

        Now, NASA et al confirm that the most basic and crucial data required to establish any sort of energy balance is so unreliable as to make a mockery of the IPCC/UN et al “science”, and in many cases profoundly contradict the IPCC et al.

        • clivebest says:

          It is certainly true that satellites are unable to measure any energy imbalance at TOA. CERES admit that their errors are > ± 10W/m2, and hidden away on their site you will find that the data have been ‘normalised’ so as to agree with model predictions of an imbalance of ~3 W/m2.

          Many people believe that satellites have confirmed an energy imbalance but that is not true. Indeed as you point out the CERES measured value for CRE ~ -20 W/m2. That means that any small change in cloud cover could completely offset CO2 forcing.

          The IPCC argument as to why cloud feedback could be positive is IMHO not very rational since more water vapor = more clouds. They admit that this is the largest uncertainty and that cloud feedback could be negative. I am sure it is negative ! – see

  5. Grant says:

    Don’t CO2 levels above 1,500ppm or so tend to start to depress plant growth? The (little) data I’ve seen from CO2 enrichment in greenhouses suggests so.

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