New Study: Human Contribution To Enhancement Of Earth’s Greenhouse Effect A Negligible 0.2 Percent

“[T]he contribution of CO2 to the greenhouse effect is 4% – 5%. Human CO2 emissions represent 4% of the total, which means that the total human contribution to the enhancement of the greenhouse effect is 0.16% to 0.20% – a negligible effect.” – Dr. Demetris Koutsoyiannis (2024)

New research exposes the vacuousness of the “imaginary world” models proclaiming CO2 the dominant regulator of the Earth’s climate.

A CO2-less or CO2-only atmosphere…an imaginary-world thought experiment

An oft-heard claim is that, due to the prominence of CO2 as the Earth’s climate “control knob” (see Lacis et al., 2010), the greenhouse effect could not exist – indeed, it would collapse – if there was no CO2 in the atmosphere.

Image Source: Lacis et al., 2010 and Schmidt et al., 2006

However, it should go without saying that this CO2-less atmospheric condition itself is an imaginary-world conceptualization. Thus, fantasizing about what would happen if the atmosphere was comprised 0 ppm CO2, 1,000,000 ppm CO2, 0 ppm water vapor…are all just untestable, never-observable thought experiments. They cannot be subjected to the scientific method. Thus, they are unfalsifiable.

CO2’s climate effects are undetectable

Of course, this very unfalsifiable thought experiment is what believers in the CO2-is-the-climate-control-knob narrative rest their case on. But even if we do use this imaginary-world premise, the existing models (MODTRAN, HITRAN) that allegedly support the CO2-controls-climate orthodoxy actually undermine it.

For example, as Dr. Koutsoyiannis points out in his extensively-referenced paper, the MODTRAN data show that the Earth’s temperature remains at the default greenhouse-effect value if the water vapor scale is adjusted upwards slightly, by just 30%. The greenhouse effect does not “collapse” as claimed by Lacis et al. disciples – the control-knob believers.

The HITRAN database also indicates the imaginary-world condition of doubling CO2 from 400 to 800 ppm would only alter the radiation flux at the top of the atmosphere by -1.1%, a hypothetical realization that could not even be detected in future macroscopic measurements (if the atmosphere ever were to reach a CO2 concentration of 800 ppm).

MODTRAN models further affirm that (1) there is only a 1% temperature difference between either doubling (800 ppm) or halving (200 ppm) the atmospheric CO2 concentration, and (2) the change in the downwelling radiation resulting from an increase from 300 ppm (1900) to 420 ppm (2023) is only 0.5%. These tiny changes “could not be discerned by observations.”

Image Source: Koutsoyiannis, 2024

CO2 has not been detectably reducing the outgoing longwave radiation

As a “control knob” for the climate, CO2 is believed to be the principal reason why the Earth’s outgoing longwave radiation (OLR) should be reducing (Dewitte and Clerbaux, 2018).

“…the increase of Greenhouse Gasses (GHG) primarily CO2 reduces the OLR”

However, despite the increase in CO2 concentration in recent decades, OLR has been increasing. Any reduction in OLR from the CO2 effect is not detectable.

Image Source: Dewitte and Clerbaux, 2018

Likewise, the MODTRAN clear-sky results (i.e., an atmosphere where no clouds exist and CO2 and water vapor are the main greenhouse effect agents) show OLR has increased by +0.38 to +0.60 W/m² from 2001 to 2022, consistent with the increase in temperature.

According to the data reviewed by Dr. Koutsoyiannis, any record of decrease in OLR “can hardly be attributed to increased CO2, but it can be related to water vapor and cloud profiles,” as the “effect of CO2 is trumped by the effect of clouds, which is consistent with the major role of water on climate and the minor one of CO2.”

95% of the greenhouse effect (downwelling radiation) is from water vapor, clouds

Per the MODTRAN calculations, CO2’s contribution to the planetary greenhouse effect is only 4% to 5%, and the contribution from water vapor and clouds is 87% (outgoing radiation) to 95% (downwelling radiation). The CO2 contribution to greenhouse effect changes over the last century, as CO2 increased from 300 ppm to 420 ppm, is only about 0.5%. This quantified percentage is “below any threshold to make it observable.”

Worse, when we consider that human CO2 emissions are only 4% of Earth’s total CO2 emissions, and that the CO2 contribution to the greenhouse effect is just 4% to 5%, “the total human contribution to the enhancement of the greenhouse effect is 0.16% to 0.20%.”

Image Source: Koutsoyiannis, 2024

Supporting evidence for CO2’s negligible role

Another set of sources supporting the contention that CO2’s greenhouse effect contribution is only 4% to 5% comes from the notorious Trenberth radiation budget charts. First, notice the 333 W/m² value identified for downwelling radiation from greenhouse gases (lower right).

Image Source: Trenberth and Fasullo, 2011

Now consider the estimated greenhouse effect (downwelling radiation) contribution from CO2 alone as shown in  Schmithüsen et al., 2015.

Notice it ranges from about 0 W/m² (or less) near the poles, about 10-15 W/m² at mid-high latitudes, and about 25 W/m² around the tropics. Averaged over the globe, it would appear the total mean CO2 greenhouse effect contribution is about 13 to 15 W/m². If CO2 indeed accounts for ~14 W/m² of the 333 W/m² downwelling radiation from greenhouse gases, its contribution is 4.2%. The other ~95%, or ~320 W/m², is necessarily from water vapor and cloud.

Image Source: Schmithüsen et al., 2015

As shown in the Koutsoyiannis review of results from HITRAN database, a doubling of CO2 from 400 to 800 ppm only produces a ~1.1% perturbation to the radiative flux at the top of the atmosphere (3 W/m²), which is not discernible. This is consistent with Chen et al. (2024), who assess that a doubling of CO2 produces a negative top-of-atmosphere (TOA) forcing (-1 W/m²), and a positive TOA forcing of just +2-3 W/m² in the mid-high latitudes and tropics.

These papers further establish the negligible role of CO2 in the Earth’s greenhouse effect.

Image Source: Chen et al., 2024

15 responses to “New Study: Human Contribution To Enhancement Of Earth’s Greenhouse Effect A Negligible 0.2 Percent”

  1. oebele bruinsma

    “95% of the greenhouse effect (downwelling radiation) is from water vapor, clouds”.

    The irrelevance of COP 19 and its predecessors in full view. History will treat it harshly.

  2. Andy May

    Great post! Thanks.

  3. New Study: Human Contribution To Enhancement Of Earth's Greenhouse Effect A Negligible 0.2 Percent | Un hobby...

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  4. The_Rationalist

    Kenneth Richard, I have a lot of respect towards you, you might not be always 100% objective but you definitely are the most prolific science communicator in climatology, in the world, and you have an admirable free thinking ability.

    Indeed both water vapor and clouds long term alterations are the best contenders to CO2 and sadly quite underresearched (albeit it seems to improve recently).

    There are two main topics that I believe you have not yet completely addressed and that are the absolute keys to solving the question of the root causes of climate change.

    If you are the most prolific science communicator, I consider myself as the most prolific science lurker, meaning that I generally don’t publish my results but I have derived unique and absolutely essential insights in climatology.

    The first topic and major issues of “alternative” climatologists is that they do not have a proper end to end explanatory model of climate change.
    Of course I could write a lot about it but concisely:
    Even if water vapour and or clouds alterations could explain the observed warming, and that those augmentations were to be reliably empirically observed (still an open question, iirc observations are potent but do not fully explain warming)
    One still has to answer why there would be a long term increase, despite water vapour having a half life in air of 10 days (iirc)
    While warming increase relative humidity capacitance, it is not a root cause.
    Even though mankind emits water in air (via agriculture, land use and biomass changes, via nuclear reactors, many industries, etc), I am skeptical those quantities are sufficent to durably increase the quantities of something with such a short half life.

    A question that has to be asked regarding climate warming is: why now?
    Why is the signal such a historical anomaly and so tightly correlated to the industrial revolution. I am aware of milankovitch cycles, of the natural drivers (solar minimum, etc) and of the issues that co2 spikes geologically lag with warming.
    While some natural drivers (especially orbitals) do matter, they mostly matter over too long periods (or too short periods) or are too regional.
    As such natural explanations as a concommitant coincidence with mankind economic revolution are ad hoc and weak explanations of current climate change.
    It is why the most defendable thesis of water and cloud changes gains popularity, however there is no decent explanation as to what could be the cause of those changes.
    My polymathic knowledge in biology has allowed me to find a unique explanation to climate change that is potent, directly empirically backed and this explanation has never been mentioned before, making it in effect, the most original and promising idea in climatology:
    Climatologists don’t appreciate the fact that altering the levels of chemicals in air, especially CO2 (but not only) alters the biochemistry of living beings, and of them, most importantly of plants (and phytoplanktons).
    CO2 is the main cause behind the worlwide global greening effect, it has been reliably proven (and is commercially used in agriculture) that a CO2 doubling leads to a ~40-50% increase in the speed of plant growth. It can also alter the size of the plants. This is because co2 is the rate limiting bioenergetic substrate for photosynthesis. (and synergetic with nitric oxide, water and temperature concommitants increases).
    Much less appreciated is that a CO2 doubling, leads to a considerable increase in stomata density (used e.g. for dating) and various metabolic alterations, including an insane 2.8X increase in mitochondria!!!
    Most importantly, CO2 doubling leads to plants needing 40% less water!! via considerably reduced evapotranspiration.
    This means that a CO2 increase should lead to less water evaporation, therefore to less water in the air, therefore showing the opposite effect of the thesis, a global cooling induced by CO2 increase.
    While the fact that the effect goes in the “wrong” direction should alert the mind of the reader, what should even more alert the mind of the reader is that a 40% reduction in evapotranspiration is a fact nobody knows yet it potentially trumps the potency of the classical greenhouse effect of CO2 which is remarkably ironic.
    The effect of plants on humidity is actually extremely potent, in the amazon for instance, iirc, 50% of the humidity is caused by plants.
    Moreover, it actually goes into the right direction, CO2 increase is shown to very potently increase humidity via decreased raining and not via decreased evaporation.
    https://bg.copernicus.org/articles/18/2511/2021/

    So one has to wonder, if CO2 is the root cause of the global increase in water vapor and or a decrease in cloud albedo, despite reduced evapotranspiration of 40%, why is that?
    To understand this question, one has to understand why it rains at all, AKA the topic of cloud seeding.
    50% of raining is caused by aerosols. Mankind has learned how to create clouds on demand via liberating very specific aerosols, such as iodine. The issue with the classical theory of aerosols is that the specific aerosols identified as inducing raining, were not found naturally in sufficent quantity, meaning that most of the 50% of raining were literally scientifically unexplained!
    It was obvious that life, especially plants should be the main driver of flux of rain, in cosmology because of the gaia hypothesis, in the theory of evolution because stimulating (or downregulating) the rate of raining is one of the most major evolutionnary advantage for plants to maximize their prosperity. And indeed research in cloud seeding has shown that cloud nucleation is best catalyzed by specific molecules that life could engineer and life is well known to emits molecules in air (pheromones, etc).
    While this should have been obvious that life is the major cause of regulation of clouds on earth, it has only been recently proven once and for all.
    > https://www.nature.com/articles/nature.2016.19971

    This discovery, that molecules emitted by plants, especially terpenoids are the major cause of raining on earth, has a record high number of citations in meteorology and yet is absolutely unused in climatology which is inept and peak mediocrity.
    Not only has it been shown that terpenoids are the cause but it has also serendipitously been shown by anterior research that terpenoid synthesis and emission in air is dynamically regulated.
    Since those are carbon molecules that compete with sugar synthesis, increased CO2 theoretically allows plants to secrete more terpenoids and therefore ask for more rain. However, in practice, at least in many species, it is found that terpenoid emission considerably increase during perceived water deficiency stress.
    This means that plants have evolved to dynamically ask for more rain especially in periods of micro drought. But since a CO2 doubling also concomittantly makes plants need considerably less water, in practice it makes sense (and is empirically testable) that a CO2 doubling would lead to a downregulation of terpenoid emission, especially during periods of micro droughts, and that this would be a direct causative and the most potent mechanism on earth to explain the empirical deficit of raining observed worlwide and e.g. in amazonia.

    As such, not only is this empirically backed and the only alternative root cause explanation to climate change, and a very potent mechanism, but it also is of striking irony, since those facts shows that CO2, even if indirectly, are the cause of the cloud albedo decrease, and therefore are, accidentally, the right target to fight climate change.

    The second major topic not addressed enough on this blog, is the debate of OLR vs ASR, as there are some papers that try to explain the counterintuitive effect of CO2 on OLR.
    Moreover, since CO2 and h2o greenhouse effect target distinct spectral bands, a space based spectrograph should, be able to directly measure the degree of warming caused by co2 vs h2o molecules, it is insane that such direct measurement has never been attempted.
    There was in fact a direct experiment (via a telescope looking at a reflective effect on the moon surface) for CO2, it claimed a null result but there might have been systematics.
    More recently has been claimed the first space based spectral test and it seems to corroborate CO2 greenhouse as being causative, it would be nice if you would review the study as this is probably the best empirical evidence for the CO2 greenhouse effect theory.
    here: https://acp.copernicus.org/articles/24/6375/2024/

    1. Posa

      Extremely interesting research Rationalist… but probably irrelevant. Even within the recorded history of the past two millennia, climate has been, by turns, warmer and colder than current global temperatures . Examples: the Roman and the Medieval Period on one end; and the Little Ice on the other. Yet all indications are that until the late 20th Century CO2 levels were relatively constant at around 285 ppm.

      Conclusion: CO2 levels have little or no impact on global temperatures

  5. John Hultquist

    I think as this idea has started to be recognized, the ClimateCult™ started using “carbon” and pollution (and various other tactics) in their narrative.
    A new “crisis” will soon be needed.

    1. John Brown

      Or as I say, in order to avert a crisis we have to have a new one!

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  7. soundos

    Thank you for sharing such an informative blog

  8. DS

    Climate Science is missing both. Like virology science. These fields have been corrupted by small, fearful thinkers who cling to consensus instead of seeking challenges.

    These pfake scientists reject the possibility of alternative levers causing the observed effects. They need to spend some quality time with astrophysicists who readily admit they don’t know 80-90% of the reasons why our universe is expanding so quickly – they call it Dark matter/energy. And they still get funding.

    Hubris & Consensus do not good science make.

    #fightpfake #fightfraud #stayhuman

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  13. Thomas Schinkel

    Brilliant article. The so-called climate change consensus is mostly formed by scientists that are directly or indirectly on the payroll of governments and supra-national governments and non-government organizations NGO’S.
    It has become a self-perpetuating force of terror that needs to be eradicated from our lives root and branch. The earth’s Climate has been changing “up and down and up again” from day one – so to speak. Let’s learn to live with it already.

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