Cassandra has moved. Ugo Bardi publishes now on a new site called "The Seneca Effect."

Monday, February 26, 2018

Where is the proof that CO2 warms the Earth?

A persistent element of the climate debate is the claim that "there is no proof" that CO2 and other greenhouse gases warm the atmosphere. This has generated a number of amateurish demonstrations of how the greenhouse effect works  A good example of how NOT to carry out such a demonstration is shown above. Nobody told this poor kid how to perform a scientific measurement. If he had switched his jars he would have discovered that the effects he observes are only the result of one of the two jars being closer than the other to the light source. And they didn't even explain to him how the greenhouse effect actually works: you cannot see any warming in this set-up unless you place a light adsorber (e.g. a piece of black cloth) in the jar discuss this and other disasters in a post of mine (in Italian), see also here.

Imagine that someone asks you to prove that the Moon orbits around the Earth because it is pulled by the force of gravity. Your first reaction would be to say something like "huh?" But - assuming you are in a good mood - you might try to explain how Newton's law of universal gravitation works and how it can be used to describe the moon's trajectory.

"So," your opponent could say, "is it correct to say that nobody ever measured the gravity pull of the Earth at the Earth-Moon distance?"

"Aw... No. What for? It would be terribly expensive. And useless, too."

"Then, you have no proof that the Moon goes around the Earth because of gravity. So, can you prove that the Moon is not being pushed by invisible angels, instead?"

That would end the civil conversation, but there is some logic in this kind of questions. You can't reproduce the Moon's motion in a lab, here on the Earth. Instead, to prove that Newton's law is valid you create a model based on the law and then use it to describe the movement of moons, planets, and stars. The model works, hence the law behind it is correct. No need of measuring the Earth's gravity pull at the Earth-Moon distance (and no need of invisible angels pushing).

Now, let's translate all this to a question often asked in the climate debate. What proof do we have that greenhouse gases, and CO2 in particular, warm the Earth's atmosphere? As a question, it is similar to the one about the Moon orbiting the Earth, in the sense that we can't reproduce the properties of a whole planetary atmosphere in the lab.

To answer the question, we can start from laboratory experiments showing that CO2 absorbs infrared radiation - they were done already by Tyndall in the 19th century. We don't need amateurs today to remake those experiments, doing the job poorly. Then, we create models that describe the Earth's atmosphere and we use them to fine-tune the parameters of the warming effect. The models follow reasonably well the warming trends of the past so that we confirm that CO2 warms the Earth.

In addition, we even have direct experiments showing that, as the atmosphere warms, more infrared radiation is radiated to space, while at the same time less infrared radiation escapes at the wavelengths where CO2 absorbs radiation. It is what we expect a greenhouse gas should do.

Case closed, then? Not really. The Moon-Earth system is relatively simple and, unless you really want to believe in invisible angels, there is no doubt that the Moon is kept in its orbit by gravity, and by gravity only. Instead, the Earth's ecosystem system is a tangle of subsystems interacting with each other in ways that - in many cases - we have troubles in quantifying exactly. Newton could never have described the Earth's atmosphere by means of a single universal equation. So, how to disentangle the various contributions to the Earth's temperature: albedo, atmospheric particulate, vegetation cover, and more?

This is the task of models, coupled with various kinds of measurements. For what we can say nowadays, the rising CO2 concentration is the main factor in the observed warming, but that's subjected to changes and refinements as we have new data. Among other examples, a very recent paper appeared in Nature quantified the effects of the vegetation cover. This is mainly a local effect and changes little to the overall picture, but it shows how dangerous it can be to say that "the science is settled." Of course, that doesn't mean jumping to the conclusion that angels are warming the Earth with their breath. And it doesn't mean to engage in silly games of data torturing. It just means recognizing the complexity of the problem.

Then, there is an even deeper problem: complex systems such as the Earth's ecosystem are just that: complex. They may react to perturbations in a strongly non-linear way, amplifying or dampening the perturbation. In a complex system, it is always difficult to say what causes what. You can say that in a complex system there are no causes and no effects, only forcings and feedbacks. So, when people say that the increase in CO2 concentration is not a cause but an effect of global warming, are they wrong? Yes, they are basically wrong, but it is also true that increasing concentrations of greenhouse gases may be both a cause and an effect of global warming. Complex systems are dominated by feedbacks. And that means they can amplify the effect of a small forcing, turning it into a disaster. This is, by the way, the origin of the "Seneca Effect"

In the end, it all means that we have to recognize that the Earth's climate could react to perturbations in ways we can't even imagine. And more than seven billion humans on the planet have been a huge perturbation, no matter how we want to see the relative importance of what we have been doing. We ignore that at our risk.


  1. Demanding "proof" was a very smart move by the climate sceptic propagandists to befuddle the public. They knew very well that the there is no proof in natural science as Popper formulated it, only falsifications. For grandpa Simpson the phrase "there is no proof" makes perfect sense though.

    Any honest scientest who is asked "do you have prrof for the man made climate change" would say no. Immediatly the whole thing sundds as if there are "two competing scientific standpoints" on climate change, wuth no "proof" for one side or the other.

    The whole thing is a failure of our educational standards. People generally don't have any clue about science. All over the world, it is totally socially accepted to say "I dont get math and science", even in "educated" middle class circles.

    Especially in the USA, the general public knowledge about "what science is" and what it does, is pretty depressing.

    When technology and human actions can today destroy the earth or all human life in countless ways and nobody gives a shit about science, things are destined to blow up in our face.

  2. You are basically arguing that a cold gas is heating it's heat source. Which is a ridiculous claim.
    To make it even more obvious how crazy this "theory" is, you are claiming that water and dry ice in -18C air, transfers heat to the hot surface. The exact opposite of what physics say is possible.

    1. There is something like a virus affecting human brains. I think it is becoming clearer and clearer that it is spreading everywhere.

    2. LOL! Please Ugo do not look into the growing zombie mob of flat earthers! They are now consistently infecting the comments section of SpaceX videos on Youtube among others. It is most startling!

    3. Ah, well, but they are growing!

    4. Flat earthers are so yesterday. I have learned from a enlightened Facebook group, that what we have is an expanding earth. No more worries about peak oil or population explosions. The expanding earth solved it. Trust me I've seen hard to understand reports, with graphs and number things.

    5. The thing with the flat earthers is batshit crazy, but its also a great allegory. In all our day to day experience the theory of a flat earth is actualy what we very successfully work with. When building a normal house i.e. the earths curvature does not play a role in our designs.

      In a small enough radius from where I am standing, the assumption that the earth indeed is flat is a valid one. Only if I widen my perspective, the theory breaks down.

      Same thing with Newton. The theories of Newton are in fact as valid as the flat earth theory as they only work with specific marginal conditions. Obviously if go beyond those boundaries It breaks down. Newtons theories are disproven since we have been able to measure relativistic effects of speed and mass.

      Widening our perspective has been the means to enhance our understanding of the universe. We had collectively to grow out of our own heads to get to where we are now.

      It seems us shrinking back into our own little bubbles of perception and understanding is what our time suffers from. In this regard I see hardly a difference between fascists, nationalists, xenophobes, flat earthers, fundamentalists or esoterics.

      Fake news,alternative facts and flat earthers can only exist in a society where we collectively forgot how to grow beyond our individual flat earth perspective. I wonder where this regression comes from.

    6. Alien, good points. I'm reminded of the pro-ana phenomenon. Basically some years ago (mostly) young women at risk of anorexia started finding each other via the internet and formed groups where they encourage each other to diet and even recruit new members. Critical mass and feedback loops became possible in this case.

      We also seem to be seeing a flattening of the scientific education hierarchy. Access to scientific knowledge is now much less restricted to anyone and everyone, but the rational analytical mental faculties required to develop, maintaining and simply grasp it has not changed much. We still have the same normal distribution or bell curve among the human population, whether it is politically correct or not.

      I think we are seeing the emergence of a new phenomena, some type of pseudo-scientific techno-voodoo? Hard earned facts seem to be drowning in a flood of easy opinions, feelings, subjectivity and alternative truth. Choice over proof, à l'improviste.

  3. the ''no proof'' problem perhaps what will tip us over the edge

    as wlie e coyote might have said---I demand proof that there is no road under my feet (while refusing to look down)

  4. I once had this discussion with a persistently ignorant distant family member. He said "I don't believe in climate change" and I said "hows that working for ya. how about gravity?"they don't even know how gravity, you believe in that" Him " well all I know is that they say that the earth spinning keeps people from flying off the planet and I call BS" so I says" try this. fill a pot half way with water, bring to simmer, put a woodspoon in and swirl it around until you have a whirlpool then crack an egg into the middle. you might get a little white spinning off to the edge (that represents the bad people) but the majority stays in the center".

    That kept him thinking for a while until his head started hurting then he grabbed a beer and flicked on the game.

    1. we must be distantly related

      i recall talking to him too

  5. May it be that we are , as a race, very smart, but just not smart enough, lacking the last bit of smartness necessary to not shoot ourselves into the foot?

  6. You might want to agree with that 'someone' and tell them that they are correct and the Moon does not orbit the Earth.

    Rather they both orbit a common centre of gravity which is located, on average 4,671 km from the Earth's centre, but still within the Earth. :-)

  7. Ugo, you have misunderstood the growing movement against the catastrophic warming scenario. The scientists that argue against this don’t argue against CO2 having some greenhouse effect properties. They are just showing how tiny this effect is compared to all other things that effect the climate, not at least the sun for example. Remember that CO2 is measured in parts per millions.
    All temperature models 10-20 years old, from IPC and others, have failed miserably, do you still believe in them?
    Here in Sweden the alarmists said that around 2020 we would not be able to go skiing any more.
    Yesterday they discussed if the Vasalopp (traditional skiing event in Sweden) should be shut down today because of too cold weather…

    1. The beauty of comments like this is that they are supposed to be serious. Isn't it amazing?

    2. no one can pinpoint the exact effects of global warming in specific areas---thus the deniers jump up and down at confirmation of their ''facts''

      but right now the north pole is at or just around freezing---it should be around -30 or so, does that frighten you?--it should, considering the methane bomb sitting under the tundra

      right across the world, glaciers are clearly in retreat---they are the water reserves for millions of people---maybe that might scare you?

  8. Most of the relevant knowledge we have is based on indirect proofs and the science is not exception. For instance, nobody can give the proof that the love exists. We can not show some substance or some measurement as the proof that our parents love us. We know that indirectly by looking at all their effort and trouble they invested in us during many years of our youth. They certainly can not show something tangible, some stuff that the love is made of. Does that mean that there is no love?

  9. Ivan - Are you saying we gotta love climate change?

    1. No. My comment is about method, not about anything in particular. Abstract notion (love) was just an example.

    2. But, in a sense, there is an experimental proof of, let say, love. In an experimental setting you have your sepcimen, or observed fact, to be obseved AND a measuremenet device. The measuremnet device translates some signal from the specimen or observed fact to an information suitable for our senses (a gauge on a quadrant, a number on a dipaly, a color, a sound etc.) and from these signals your brain is able to extract some regularities that can be mapped in a model of what is happening "outside there". In case of love you have the experimental signals coming to your sensorial apparatus and these signals trigger an information elaboration inside your brain: a configuration made of electrical signals, hormones, neurotransmitters. This configuration of yours can be compared with the configuration of other people (by means of literature, or movie, or intimacy and so on) and you can discover some regularities between your experience of "love" and what is felt by the others. And then you got an experimental proof of "something", with some regularities with the experience of other people, that we collectively agreed to name "love".
      So, in some sense, "love" is as tangible as a rock (or, if you want, a rock is as intangible as love)

  10. All of us should read this article carefully:

  11. Climate science has come a long way since the excellent early work and the acknowledgement of the physics of atmospheric gases. Think of decades of satellite data and detailed time series recorded in the ice and sediments. But science from the beginning said change was going to be slow, by political standards very slow. It was predicted that we would not be sure, that is closing on 100% sure of the signal(s)emerging from climate variability, until into the 21st Century. But an early prediction from models was that the arctic would warm faster than the rest.

    My understanding is that the trace gases contribute about 25% of the total greenhouse effect. Without the GH effect the earth/ocean would be frozen as the water vapour condensed out. Critically it is those non-condensing trace gases that modulate the major GH effect of atmospheric water. Atmospheric CO2 is still increasing. It would be very surprising if it does not reach double the concentration of pre-industrial times. The results of the accumulating heat pulse will persist over the many centuries.

    Ugo knows all this stuff better than me of course. As he said above of one comment: "The beauty of comments like this is that they are supposed to be serious. Isn't it amazing?" Perhaps we should treasure our amazement?

    But we will be barely a memory by the time climate change comes of age. I had an insight some decades ago while travelling in the London Underground. The tunnels would fill with the whisper of salt water. That is a kind of memorial I suppose.


  12. Thanks for this post. You talk about invisible angles the people beleave in to explain gravity. The problem to accept climate change is, that the people really want to believe at invisible angles and not on man made, rapid climate change, because this would allow them them to keep there livestyle with big houses, cars and holliday trips by plane... .

    So a school experiment to explain climate change would be in my eyes really helpful. After an chemical school experiment with acid and base nobody denies that this is an intensive exotherm reaction. So I hope it would be the same with an small scale cliimate change experiment for each kid.

    1. Alas, karly, these amateurish experiments do more harm than good. The can convince the believer, but leave unimpressed the disbeliever. And they are bad experiments anyway



Ugo Bardi is a member of the Club of Rome, faculty member of the University of Florence, and the author of "Extracted" (Chelsea Green 2014), "The Seneca Effect" (Springer 2017), and Before the Collapse (Springer 2019)