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Carbon Dioxide's invisibility is what causes global warming

Posted on 16 July 2013 by John Cook

Australia's leader of the opposition Tony Abbott recently derided an emission trading scheme as "so-called market in the non-delivery of an invisible substance to no one". This echoes an earlier statement where Abbott dismissed carbon dioxide as an "invisible, odourless, weightless, tasteless substance". In this modern age, most people are aware of how something that is invisible to the eye can nevertheless have a significant impact. Examples include radiation from radioactive material, germs and well, gravity. In the case of carbon dioxide, it is actually its invisibility that is the key factor in how it causes global warming.

When sunlight reaches the Earth, it passes through our atmosphere. Greenhouse gases such as carbon dioxide are invisible to sunlight, also known as shortwave radiation because of its short wavelength. This allows the sunlight to pass through the atmosphere unhindered by greenhouse gases, and warm the Earth's surface.

The warm surface of the Earth radiates infrared heat, also known as longwave radiation because of its long wavelength. Greenhouse gases absorb longwave radiation. This results in the atmosphere trapping some of the Earth's heat as it tries to escape out to space. Heat-trapping gases such as carbon dioxide make the atmosphere warmer than it would be without any greenhouse gases.

Currently, we are adding greenhouse gases to the atmosphere through the burning of fossil fuels. As more greenhouse gases accumulate in the atmosphere, more heat is being trapped. This causes global warming. Consequently, the fact that carbon dioxide lets sunlight pass freely through the atmosphere is an integral aspect of the greenhouse effect. Carbon dioxide's invisibility is a key part of what causes global warming.

Greenhouse warming has distinct fingerprints that have been observed throughout our climate. As greenhouse gases trap more heat, satellites should measure less heat escaping out to space. This has been observed by a number of different satellites. Surface measurements observe more heat returning back to Earth.

Over 150 years ago, John Tyndall predicted the specific patterns of greenhouse warming - nights warming faster than days and winters warming faster than summers. Both these patterns have been observed. Another distinctive pattern of human-caused global warming is a cooling upper atmosphere at the same time that the lower atmosphere warms. This has also been observed.

Our confidence that humans are causing global warming is based on many, independent lines of evidence. Human fingerprints are being observed all over our climate.

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Comments 1 to 28:

  1. Abbot: "invisible, odourless, weightless, tasteless substance".

    Invisible: So is the oxygen in our atmosphere which would only burn us down if it were to double in proportion to the other gases.

    Odourless: So is Methane.

    Weightless: Take some physics. A Carbon Dioxide molecule has more "weight" - mass than an oxygen molecule.

    Tasteless: It makes for a great flavor in phizzy drinks.



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  2. Hey, I think I saw this coming!


    There are no limits for denialism. Barton Paul Levenson recently quoted something that applies here:


    Gegen Dummheit kämpfen Götter selbst vergebens.*
    --Friedrich Schiller


    *against stupidity even gods fight in vain.

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  3. As a non-chemist, I would appreciate an 'intermediate' version which explains the actual mechanism that CO2 uses to trap the infra-red photons and then release them in all directions, only some of which are spacebound.

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  4. Yeah, except that I object to the use of the term "trapped" with respect to energy and greenhouse gases, for the same reason Professor Fraser does here ...  It's misleading.  It assumes the energy radiating from Earth remains intact somehow.

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  5. In public discussion of science there will always be a compromise between using language that will be understood and remaining completely accurate to finest of detail.  Saying that the energy is "trapped" is reasonable as a place to start.  If one were to be really pedantic, we could take Fraser's statement

    "No, the atmosphere absorbs radiation emitted by the Earth. But, upon being absorbed, the radiation has ceased to exist by having been transformed into the kinetic and potential energy of the molecules. The atmosphere cannot be said to have succeeded in trapping something that has ceased to exist."

    and say that matter and energy can't be created or destroyed, only transformed.  Therefore Fraser's statement is innacurate as the radiation emitted by the surface has not ceased to exist, but has merely been transformed into kinetic and potential energy of the molecules, exchanged a bit and then re-transformed to come back to us as "backradiation".  However there comes a point where attention to detail becomes pedantry and obstructs communication of the central point, rather than assisting it, the point at which this happens is not fixed, but depends on the audience.

    The "intactness" is irrelevant to the issue, essentially energy is energy is energy - the thing that matters is the rate at which it enters the system and the rate at which it leaves the system.

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  6. Carbon dioxide is just the by-product of human blunder.  Global warming is caused by humans who ignore, deny or permit carbon emissions. CO2 is just part of the chemical mechanism we discovered.  

    When a plane crashes, we don't blame gravity.

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  7. Finally some scientific clarity.  It's CO2 not carbon that causes global warming. Please inform the politicians and mainstream media.

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  8. Muzz @7, well actually its carbon dioxide and carbon monoxide, and Methane (CH4), and flourocarbons.  Are we noticing a common theme here?  Of course, there is also ozone and nitrous oxide, but in general the most potent well mixed greenhouse gases are carbon based, and most are produced by the use of carbon based fuels.  Further, the greenhouse potential of all well mixed greenhouse gases is measured in terms of "carbon dioxide equivalents".  I wonder what a convenient short hand reference for a tax on "carbon dioxide equivalents" of emissions would be?

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  9. Tom Curtis @8, all correct points I'm sure. Thankyou. "Carbon" no doubt is a convenient short hand reference for "carbon dioxide equivalents", but IMO is very misleading and I would suggest is one that scientists would or should shy away from using. A name for a tax? How about a greenhouse gas tax (GGT)? Its hard to beat a TLA

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  10. Muzz, you still have this wrong.

    "Carbon" is NOT a short hand for "carbon dioxide equivalent". Carbon is simply the substance which, when burned, produces carbon dioxide. Carbon based fuels come in many forms. But it is the carbon content of what is burned that counts, because this is the major factor that determines how much carbon dioxide is produced.

    The carbon tax, or price, applies for carbon based fuels. It is a tax on carbon. Not on equivalents; on carbon specifically.

    Carbon dioxide equivalence is actually a (fairly crude) unit of measure for the impact of other greenhouse gases. I am not entirely sure why Tom mentions this; it is not, as far as I am aware, used as a basis for taxes on other gases. (Is it?) This might be a reasonable basis for fixing appropriate prices on other substances as a proprotion of the carbon price; though I not heard of such a thing.

    In the meantime, we put a price on carbon because it is the burning of carbon based fuels which are by far the largest driver of the enhanced greenhouse effect though the emissions of carbon dioxide, and the consequence global warming.

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  11. Sylas @10, from the law for Australia's Carbon Tax:

    "The following is a simplified outline of this Act:
    • This Act sets up a mechanism to deal with climate change by encouraging the use of clean energy.
    • The mechanism begins on 1 July 2012, and operates on a financial year basis.
    • The mechanism is administered by the Clean Energy Regulator.
    • If a person is responsible for covered emissions of greenhouse gas from the operation of a facility, the facility’s annual emissions are above a threshold, and the person does not surrender one eligible emissions unit for each tonne of carbon dioxide equivalence of the gas, the person is liable to pay unit shortfall charge.
    • If a natural gas supplier supplies natural gas, and does not surrender one eligible emissions unit for each tonne of carbon dioxide equivalence of the potential greenhouse gas emissions embodied in the natural gas, the supplier is liable to pay unit shortfall charge.
    • If a person opts in to the mechanism, the person acquires, manufactures or imports taxable fuel in specified circumstances, and does not surrender one eligible emissions unit for each tonne of carbon dioxide equivalence of the potential greenhouse gas emissions embodied in the fuel, the person is liable to pay unit shortfall charge."

    "14 Carbon pollution cap
    Carbon pollution cap
    (1) The regulations may declare that:
    (a) a quantity of greenhouse gas that has a carbon dioxide equivalence of a specified number of tonnes is the carbon pollution cap for a specified flexible charge year; and
    (b) that number is the carbon pollution cap number for that flexible charge year."

    (My emphasis)

    Such laws must be in terms of carbon dioxide equivalents (or some similar unit) or else they will not effect emissions of any controlled substance under the Kyoto protocols other than CO2. 

    Carbon dioxide equivalents is the standard unit for measuring global warming potential, defined by the IPCC as follows:

    "Global Warming Potential (GWP) An index, based upon radiative properties of well-mixed greenhouse gases, measuring the radiative forcing of a unit mass of a given well-mixed greenhouse gas in the present-day atmosphere integrated over a chosen time horizon, relative to that of carbon dioxide. The GWP represents the combined effect of the differing times these gases remain in the atmosphere and their relative effectiveness in absorbing outgoing thermal infrared radiation. The Kyoto Protocol is based on GWPs from pulse emissions over a 100-year time frame."

    The idea is that a substance with a strong greenhouse effect measured in forcing, but a very short life time before decomposing is not as dangerous as a substance with a weaker forcing but which endures (effectively) forever.  Necessarilly the approach is crude, but duration in the atmosphere is a factor in how dangerous the emissions are, so some such measure is required.  I am all for anybody who can proposing and defending a better unit than CO2 eq, but absent such a proposal we must use the units we have or, for example, not tax fugitive emissions of methane from garbage dumps, or the production of halo-carbons etc.

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  12. Muzz @10, you missed my main point.  Of course, I framed that point as a rhetorical question so I must accept blame for that.

    The fact is that "carbon tax" as a short hand for "a tax on carbon dioxide equivalents" is perfectly reasonable nomenclature.  That does not mean there are not other reasonable names for the same thing.  Nor does it mean people cannot, for rhetorical purposes, deliberately misunderstand the name.  Australia's Fringe Benifits Tax, for example, is not a tax on the length of peoples hair hanging over their forehead, but could be so misconstrued if somebody wanted to make a political point from it.

    These defects will aflict almost any name chosen.

    Given that, arguing about mere naming is rather silly.

    (As an aside, why would I want to take a cane to a TLA, and what is a TLA in the first place?)

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  13. Dikan Marsupial@5

    Thanks for the detailed explanation. I notice no mention of something called dipoles, which I thought had something to do with how CO2 traps, sorry, 'absorbs' (or whatever) the longwave (re)radiation. I suppose it is around that dipole - whatever it is - where my ignorance about how global warming happens actually resides. (Perhaps it is the engineer in me that feeds my desire to know the nuts and bolts of the issue. I doubt I am alone.)

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  14. funglestrumpet - my post wasn't a detailed explanation, just an appeal for the discussion not to be distracted by quibbles over terminology that obstruct the discussion.  The mere fact that molecules such as CO2 can absorb outbound IR radiation is only one element of the explanation of the greenhouse effect, it is the way this affects the radiation of IR into space from the upper atmosphere that is the key to understanding the mechanism.

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  15. Tom, thanks very much. I've learned something. Muzz, sorry for introducing confusion to the thread.

    Given your lead I've looked further and indeed (for example) the Australian carbon pricing system does include emissions of Nitrous Oxide (NO2); this is also an important secondary greenhouse gas emission from conventional fuels, and has no carbon involved.

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  16. @villabolo

    In fairness, the sourness of carbonated water is H2CO3 in aqueous solution, not gaseous CO2.

    Otherwise though I'm right there with you. :P

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  17. funglestrumpet@13

    If you are interested in the intricacies of the physics, it is taught in undergraduate and graduate classes on physical chemistry, atmospheric physics or radiation, or specifically spectroscopy or quantum mechanics in higher education institutions; thus you will find it described explained in the respective textbooks or online classes. It would be beyond the scope of this website to educate to this detail.

    But yes, you need a permanent or inducible dipole moment to observe an infrared absorption spectrum in a molecule. The dominant atmospheric gases N2, O2, and Ar do not have that, thus their apparent IR transparancy.

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  18. funglestrumpet, here is an explanation of CO2, dipole moment, and infrared absorption from Illinois State U; see pages 4 and 5.

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  19. @14,@17 and @18

    Thanks! I did ask for an 'intermediate' level version in my original comment! Your links are way over my head, I am afraid, but thanks all the same. I was just trying to grasp how the infra-red radiation is absorbed by the CO2 molecule and re-radiated in random directions. I did read somewhere that it had something to do with a dipole feature of the CO2 molecule. I now wish I hadn't read it because I have been trying to find a better description of what actually happens without all the math ever since. I have now stopped the search.

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  20. funglestrumpet, pages 4 and 5 of the doc I linked for you have diagrams and short text explanations of those diagrams.  Skimming those might give you what you want; skip all the other parts of the doc.  And here is a great animation; note the wiggling of the oxygen atom "ears" around the carbon atom "head."

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  21. There is also an ear-wiggling animation in the Greenhouse Gases section of a UCAR page.

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  22. @20 & 21 Tom Dayton

    Thanks, the two animations plus the accompanying UCAR page are very clear. I guess it was worth hanging in there for a clear explanation, thanks again.

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  23. funglestrumpet @22

    Just to be clear:

    The change in dipole-moment during a molecular vibration is a requirement for IR radiation to be absorbed. It has nothing to do with the random direction of the subsequently emitted radiation.

    The fact that a gas will emit radiation in all directions is, I think, intuitively obvious; in that the molecules of a gas are freely and randomly oriented with respect to each other.

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  24. funglestrumpet, try this description.

    • Atoms have a property called Electronegativity. This essentially describes how strongly an atopm holds its electrons to itself. Oxygen is strongly electronegative, Hydrogen much less so for example
    • When aroms are combined to form molecules, differences in the electronegativity of the component atoms can mean that the electrons from all the atoms in the molecule may tend to cluster  bit closer to the more electronegative atoms. As a result some molecules can have what is known as a charge separation across the molecule. One side of the molecule is somewhat negative and the other side is somewhat positive. This can't happen for symetrical molecules such as O2 or N2 - this is why they aren't GH molecules.
    • The bonds that link the atoms in a molecule together aren't rigid, they are flexible. So the atoms can jiggle around on the ends of their bonds like balls on springs.
    • So with a charge separation and 'jiggling', we end up with electric charges that are in motion. In particular, charges that are accelerating. Maxwells Equations that describe all electrical activity tell us that acelerating electric charges can generate Electro-Magnetic Radiation. A transmitter for example works because electrons are sent charging backwards and forwards along a wire, 'launching' EM radiation into space. The movement of the charges on the end of the molecular bonds are doing the same thing. When a GH molecule radiates some EM Radiation, it is acting just like a transmitter.
    • Conversely, when EM radiation passes over an electric charge it can set that charge into motion. This is how a receiving antenna works - the EM radiation passing by sets the electrons racing in the antenna. So to for those charges on the molecular bonds; some EM RAdiation can set them jiggling faster. So when a GH molecule absorbs some EM radiation, it is acting just like a receiver.
    • So when a GH molecule absorbs some energy from a photon of EM Radiation, the energy of that photon gets converted into Kinetic energy of motion for the atoms in the molecule.


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  25. Glenn Tamblyn @ 24

    Thank you for taking the trouble to assist me in understanding the phenomenon of global warming in more detail. I imagine that others will have puzzled over the exact mechanism that greenhouse gasses employ in relation to IR radiation; I hope that they have been following the comments section of this post.

    Thanks again to all who have commented in reply to my original request!

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  26. You miss the point of this little Abbott dog-whistle, it's a cleverly coded message to his lunatic support base:

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  27. gingcckgo, re Abbott's Dog Whistle.

    Absolutely. The problem for Abbott is that a majority of the rest of the population don't agree with him on this and the dog whistle isn't silent for them, it is a horrible screeching in their ear. If he appeals to his rabid base, he alienates his broader or swinging base.

    Something to do with petards and hoisting...

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  28. Thanks for taking the time to illustrate this very important point, so I don't have to!

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