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SkS Analogy 6 - Speakers, tuning forks, and global warming

Posted on 29 May 2017 by Evan, jg

Tag Line

The physics of global warming by greenhouse gases is well understood and can be illustrated by items we use every day.

Elevator Statement

Simple, well-understood physics indicate the following:

  • Sound waves vibrate speakers (think microphone1) and vibrating speakers make sound waves
  • Sound waves vibrate tuning forks and vibrating tuning forks make sound waves (with a narrow range of frequencies)
  • Infrared waves vibrate CO2 molecules (increased vibration means more energy, which means warmer) and vibrating CO2 molecules make infrared waves (think CO2 lasers, which make waves with a narrow range of frequencies)

Almost everybody is familiar with microphones, speakers, and tuning forks. These are items you can see, touch, and feel, so they are familiar. Even though we cannot see greenhouse gases like CO2, they operate the same as speakers and tuning forks: they absorb and reemit waves, just on a very small scale. When they absorb waves they trap heat, warming the atmosphere.

Tuning fork and CO2 molecule

Excitation of tuning fork by sound and CO2 molecule by infrared radiation.

Climate Science

The physics of how CO2 molecules interact with infrared waves was first discovered in the 1850’s. Einstein had not even been born by the time that we knew that CO2 combined with infrared radiation caused warming in the atmosphere. By the 1890’s the first calculation was made of how much the atmosphere would warm up if we doubled CO2 concentrations (i.e., equilibrium climate sensitivity, ECS). This work was published by Svante Arrhenius, a Nobel prize winner, and was titled “On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground” (read here). Since Arrhenius’ original calculations, estimates of the climate sensitivity have been refined, and the current average estimate from the IPCC is about 3°C of warming for doubling CO2.

Study of the interaction between infrared radiation and atmospheric gases was significantly ramped up in the 1950’s when the US Air Force developed heat-seeking missiles. The Air Force wanted their sensors to “see” the hot exhaust of airplane engines, and so they had to learn which wavelengths were least affected by atmospheric gases such as CO2. The physics of how CO2 molecules and infrared radiation interact has also been used to develop CO2 lasers. Therefore, from many types of research, we have learned about the detailed interactions between infrared radiation and atmospheric gases. This is well-understood science.

For a more in-depth look, see the "The History of Climate Science" by John Mason.

By now the physics that tells us that increasing atmospheric CO2 levels increases atmospheric warming is well understood by all major academies of science, the Vatican, the insurance industry (they see the rising financial losses from increasing weather-related disasters), the US military (they refer to Climate Change as a threat multiplier), and many others. More than 97% of climate scientists agree that increasing greenhouse gas concentrations in the atmosphere are causing the Earth to warm up. What does it say when an organization like the United Nations, which acts cautiously by consensus of most of the world’s leaders, states the following regarding the link between CO2 and global warming (read herel)?

“There are some basic well-established scientific links:

  • The concentration of GHGs in the earth’s atmosphere is directly linked to the average global temperature on Earth;
  • The concentration has been rising steadily, and mean global temperatures along with it, since the time of the Industrial Revolution;
  • The most abundant GHG, carbon dioxide (CO2), is the product of burning fossil fuels.”

Put more CO2 into the atmosphere, and there are more CO2 molecules absorbing infrared radiation. CO2 molecules share their energy with the surrounding air molecules, the atmosphere heats up, and so do we.

It is basic physics. The same physics known for over 150 years and illustrated by a common, musical, tuning fork.

1. A microphone is really just a small speaker used in reverse.

For a more in-depth look at the detailed physics that governs the interaction between GHGs, infrared radiation, and ultimate heating, see the following SkS articles.

Is the CO2 effect saturated?

Rob Honeycutt's chapter on "Radiative Gases".


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Comments 1 to 17:

  1. Explaination needed here"     "...When they absorb waves they trap heat, warming the atmosphere."

    I thought that rather than absorb and retain heat, the CO2 more accurately, quickly reradiated it, some downward, which warmed the surface and the ocean. The warming surface/ocean then warms the lower to middle atmosphere.

    Is that correct?

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  2. sailingfree @1, actually nearly all absorbed radiation is given up as kinetic energy in collisions with other molecules in the atmosphere, most of which are to nitrogen and oxygen (N2 and O2).  On the other hand, the CO2 molecules are continously being excited by those same collisions.  As a result a near constant proportion of the CO2 molecules will be in an excited state, and able to radiate IR radiation at any given time.  As a result, the radiation is governed by the local atmospheric temperature, not the rate of absorption of IR radiation. 

    The radiated IR photons can, however, go in any direction with equal probability.  Because those radiated with a side ways component are matched by radiation from neighbouring  parcels of gass, the energy tranfer from which effectively cancels out, the lateral components can be ignored, and the radiation treated as being radiated in equal amounts upwards and downwards.

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  3. The main point is that with increasing CO2 concentrations, that more energy is trapped. The details of how much is retained, reradiated, etc. is another story. When you sit next to a fire, you absorb infrared radiation. This causes you to heat up, so that your surface temperature increases. Because your surface temperature increases, the amount of infrared radiation you radiate also increases. But air molecules next to your skin will heat up, because your skin is warmer. So for CO2 molecules, whatever the detailed mechanism of the fraction that is retained vs reradiated, there is some local heating in addition to the heating that occurs due to reradiation.

    Another SkS article explains what I think you are getting at, that the actual mechanism of global warming is that the layer where CO2 is are saturated moves to higher altitudes as their concentration increases. By trapping an increasing fraction at higher altitudes, more energy is added to the higher altitudes, where the greenhouse effect is not yet saturated.

    This is a lot of detail, an in the spirit of how Fourier looked at the problem in the early 1800's from an overall balance of the energy into and out of Earth's atmosphere, all that I am saying is that from a simple energy balance, when we put more CO2 into the atmosphere it traps more energy. The details of how that happen are slightly more complicated.

    As an interesting note, there is a similar phenomenon with the sun. We all know that light coming from the surface of the sun only takes about 8.5 minutes to reach Earth, but for light to get from the center of the sun, where nuclear fushion creates the photons, to the surface, takes about 100,000 years. The atmosphere is so dense in the core of the sun that the photons bounce around from atom to atom (or whatever state the matter is in) for many millenia before making it to the surface.

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  4. This article below is a simple, clear, animated version of the whole process.

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  5. Thanks Nigel for the link. Very effective and educational.

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  6. I'm not at all sure that these analogies are helpful in convincing anyone. They insert an extra layer of "debate" and offer yet another opportunity for deniers to fabricate "arguments".

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  7. One of the beauties of online publication is that we can continually improve the publications. They are not stagnant. So with the help of useful criticism, we will continue to improve the effectiveness of these analogies.

    There are many deniers who simply will not change their position, yet there are others who are truly confused and trying to understand. It is to this latter group that we expend great effort to help them, and it is our hope that these analogies will help those "seekers" understand. I really don't know what formula will convert the deniers, but I am open to criticism about what will improve these analogies. Do you have a specific suggestion?

    Is it by chance that nearly all Republicans oppose action on climate change and nearly all Democrates support it? Could there be something larger at play here? Should it be our goal to write analogies that will convert even the most stubborn Republican, or simply try to clarify the truth?

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  8. Wol@6. Another point about the useful of analogies. I have often heard it said that the best learning occurs when 80% is familiar and 20% is new. The goal of analogies is to relate things that are new to things that are familiar, thereby facilitating learning. I can accept that I may be missing the mark in crafting analogies, and that these can be improved, but analogies are commonly used by most every speaker, writer, and teacher I've encountered. They therefore seem, to me anyway, to be extremely powerful tools for conveying information about subjects that are new to people.

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  9. I can relate to Wol's comment that analogies create another target for denialists. I have noticed that when I use analogies in recent years, they come under a lot of attack, much of it dumb and cynical, and very annoying.

    But if anything this suggests the climate denialists have come to see analogies as a big threat to their junk science, so it suggests analogies have value. Analogies have also helped me understand things. I think on balance analogies are useful.

    Reading the comments, I  was wondering about the history of whether analogies worked, and came across  this persons personal blog which so perfectly describes the issues.  

    But it means analogies have to be pretty good, and carefully considered, or they will be torn apart. This creates a challenge, as the value of analogies is simplicity, but this very simplicity makes them an easy target for criticism sometimes. 

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  10. Thanks Nigel@9 for the comments and the article. It is an interesting perspective. I would add the following in defense of analogies, accepting that they might invite increased criticism from deniers.

    The analogies are not intended to be a better form of communication, just a different form. The hope is that the analogies will resonate with people, for whom some of the other material in SkS does not. We write to help people who are honestly searching and trying to understand. We are not trying to convert the deniers.

    It is absolutely monumental what a 1% shift in voters in the last US presidential election would have made to the very direction of our efforts to combat climate change and to the direction of global politics. Look at what is happening because 1% voted for one candidate versus the other. All we needed to do was to reach 1% of the voters and sensitize them to the issue of climate change, and the outcome might have been very different. Things might have been very different. So we don't necessarily want to measure our success by 10's of percentage points, but by much more modest gains, with can have a magnified effect at the voting booth. The hope is that an increased variety of messaging methods will increase the penetration of our message.

    Of course, if you feel that the analogies are hurting our messaging of the need for urgent action on climate change, then that gives me reason for being much more careful in crafting these. I am trying to create understanding that will help those honestly searching to see through the denier arguments.

    Thanks again for your input Nigel@9.

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  11. Another possible way of understanding the green house effect

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  12. Evan @10

    "We write to help people who are honestly searching and trying to understand. We are not trying to convert the deniers."

    Yes this seems the best approach to me. There is a good sized group of people in the middle on scientific debates, and politics, the rational moderates, and they should generally be your target. I have thought the same for some time. There are others, the deniers that are so intransigent they wont ever change. You see the same with the tocacco issue and other issues, but what I find positive is over time, most people accepted the science on tobacco, or at least more and more did over time. In reality even if you target people want to learn, you will reach at least some of the deniers anyway.

    Also regarding the American election. In todays world you have a smallish group of swing voters, and they need to be the target, and so you need to understand how they think. Clinton was probably on the right track with these people, but got broadsided by certain other events.

    I think there are several reasons for climate denialism to do with politics and world views, vested interests, personal reliance on oil (and its almost a type of addiction or at least a habit), poor quality thinking, and human psychology. I went through a brief sceptical phase myself, and it took a careful look at the detail to persuade me otherwise. The devil is in the detail on the climate debates to some extent. I think you have to just chip away at the climate denial theories.

    Maybe the best way to handle analogies is don't get carried away with them, or regularly make them the centre piece, or leading element of discussion. Dont go crazy with them or use silly analogies. Use them when really needed, and generally keep them simple because complex analogies will go over most peoples heads, and your target audience on climate science tends to have an average education in the main. This is all the traditional way analogies have been used anyway, and I would be loathe to change this.

    But I do strongly think analogies can certainly sometimes be very powerful. I think the rational moderates in the middle would respond to analogies, but I admit this is just based on my personal observations, and I'm not sure how deep it would go.

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  13. Nigel@12. Great thoughts. Thanks.

    William@11. Great article comparing the Sun's greenhouse effect to the Earth's. Thanks for sharing.

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  14. Perfect analogy. "The History of Climate Science" link address is incorrent. 

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  15. AmericanIdle@14. Thanks. I fixed the link.

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  16.  I think the laser analogy is very bad.

     If I think about a laser, I think about molecules absorbing energy to emit energy as infrared waves. In this case, I don't think that the amount of total energy in the system is lost; if anything, I think that the system will emit more infrared waves from excited CO2 molecules, and thus will cool down (or at least stay the same) - as the Earth loses heat to space only through radiation.

     At the very least, the laser analogy is very counterintuitive.

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  17. DeCadillac@16. Tuning forks produce sound waves in a very narrow frequency range. CO2 lasers produce infrared waves in a very narrow frequency range. That is the similarity, and I expect that for many people that in itself is something they did not consider. The problem with analogies is that technical people can easily pick them apart. Non-technical people are the ones that tend to learn the most, because they don't necessarily think beyond the intended scope of the analogy.

    You point is otherwise well taken, because good analogies require framing so that the intended scope is well defined.

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