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Bushfires and extreme heat in south-east Australia

Filed under: — group @ 16 February 2009 - (Deutsch) (Español) (Italian)

Guest commentary by David Karoly, Professor of Meteorology at the University of Melbourne in Australia

On Saturday 7 February 2009, Australia experienced its worst natural disaster in more than 100 years, when catastrophic bushfires killed more than 200 people and destroyed more than 1800 homes in Victoria, Australia. These fires occurred on a day of unprecedented high temperatures in south-east Australia, part of a heat wave that started 10 days earlier, and a record dry spell.

This has been written from Melbourne, Australia, exactly one week after the fires, just enough time to pause and reflect on this tragedy and the extraordinary weather that led to it. First, I want to express my sincere sympathy to all who have lost family members or friends and all who have suffered through this disaster.

There has been very high global media coverage of this natural disaster and, of course, speculation on the possible role of climate change in these fires. So, did climate change cause these fires? The simple answer is “No!” Climate change did not start the fires. Unfortunately, it appears that one or more of the fires may have been lit by arsonists, others may have started by accident and some may have been started by fallen power lines, lightning or other natural causes.

Maybe there is a different way to phrase that question: In what way, if any, is climate change likely to have affected these bush fires?

To answer that question, we need to look at the history of fires and fire weather over the last hundred years or so. Bushfires are a regular occurrence in south-east Australia, with previous disastrous fires on Ash Wednesday, 16 February 1983, and Black Friday, 13 January 1939, both of which led to significant loss of life and property. Fortunately, a recent report “Bushfire Weather in Southeast Australia: Recent Trends and Projected Climate Change Impacts”(ref. 1) in 2007 provides a comprehensive assessment on this topic. In addition, a Special Climate Statement(ref 2) from the Australian Bureau of Meteorology describes the extraordinary heat wave and drought conditions at the time of the fires.

Following the Black Friday fires, the MacArthur Forest Fire Danger Index (FFDI) was developed in the 1960s as an empirical indicator of weather conditions associated with high and extreme fire danger and the difficulty of fire suppression. The FFDI is the product of terms related to exponentials of maximum temperature, relative humidity, wind speed, and dryness of fuel (measured using a drought factor). Each of these terms is related to environmental factors affecting the severity of bushfire conditions. The formula for FFDI is given in the report on Bushfire Weather in Southeast Australia. The FFDI scale is used for the rating of fire danger and the declaration of total fire ban days in Victoria.

Fire Danger Rating           FFDI range
High                          12 to 25
Very High                     25 to 50
Extreme                         >50

The FFDI scale was developed so that the disastrous Black Friday fires in 1939 had an FFDI of 100.

To understand the environmental conditions associated with the catastrophic bushfires on 7 February 2009, we need to consider each of the factors and the possible role of climate change in them.

Maximum temperature: This is the easiest factor to consider. Melbourne and much of Victoria had record high maximum temperatures on 7 February (2). Melbourne set a new record maximum of 46.4°C, 0.8°C hotter than the previous all-time record on Black Friday 1939 and 3°C higher than the previous February record set on 8 February 1983 (the day of a dramatic dust storm in Melbourne), based on more than 100 years of observations. But maybe the urban heat island in Melbourne has influenced these new records. That may be true for Melbourne, but many other stations in Victoria set new all-time record maximum temperatures on 7 February, including the high-quality rural site of Laverton, near Melbourne, with a new record maximum temperature of 47.5°C, 2.5°C higher than its previous record in 1983. The extreme heat wave on 7 February came after another record-setting heat wave 10 days earlier, with Melbourne experiencing three days in a row with maximum temperatures higher than 43°C during 28-30 January, unprecedented in 154 years of Melbourne observations. A remarkable image of the surface temperature anomalies associated with this heat wave is available from the NASA Earth Observatory.

Increases of mean temperature and mean maximum temperature in Australia have been attributed to anthropogenic climate change, as reported in the IPCC Fourth Assessment, with a best estimate of the anthropogenic contribution to mean maximum temperature increases of about 0.6°C from 1950 to 1999 (Karoly and Braganza, 2005). A recent analysis of observed and modelled extremes in Australia finds a trend to warming of temperature extremes and a significant increase in the duration of heat waves from 1957 to 1999 (Alexander and Arblaster, 2009). Hence, anthropogenic climate change is likely an important contributing factor in the unprecedented maximum temperatures on 7 February 2009.

Relative humidity: Record low values of relative humidity were set in Melbourne and other sites in Victoria on 7 February, with values as low as 5% in the late afternoon. While very long-term high quality records of humidity are not available for Australia, the very low humidity is likely associated with the unprecedented low rainfall since the start of the year in Melbourne and the protracted heat wave. No specific studies have attributed reduced relative humidity in Australia to anthropogenic climate change, but it is consistent with increased temperatures and reduced rainfall, expected due to climate change in southern Australia.

Wind speed: Extreme fire danger events in south-east Australia are associated with very strong northerly winds bringing hot dry air from central Australia. The weather pattern and northerly winds on 7 February were similar to those on Ash Wednesday and Black Friday, and the very high winds do not appear to be exceptional nor related to climate change.

Drought factor: As mentioned above, Melbourne and much of Victoria had received record low rainfall for the start of the year. Melbourne had 35 days with no measurable rain up to 7 February, the second longest period ever with no rain, and the period up to 8 February, with a total of only 2.2 mm was the driest start to the year for Melbourne in more than 150 years (2). This was preceded by 12 years of very much below average rainfall over much of south-east Australia, with record low 12-year rainfall over southern Victoria (2). This contributed to extremely low fuel moisture (3-5%) on 7 February 2009. While south-east Australia is expected to have reduced rainfall and more droughts due to anthropogenic climate change, it is difficult to quantify the relative contributions of natural variability and climate change to the low rainfall at the start of 2009.

Although formal attribution studies quantifying the influence of climate change on the increased likelihood of extreme fire danger in south-east Australia have not yet been undertaken, it is very likely that there has been such an influence. Long-term increases in maximum temperature have been attributed to anthropogenic climate change. In addition, reduced rainfall and low relative humidity are expected in
southern Australia due to anthropogenic climate change. The FFDI for a number of sites in Victoria on 7 February reached unprecedented levels, ranging from 120 to 190, much higher than the fire weather conditions on Black Friday or Ash Wednesday, and well above the “catastrophic” fire danger rating (1).

Of course, the impacts of anthropogenic climate change on bushfires in southeast Australia or elsewhere in the world are not new or unexpected. In 2007, the IPCC Fourth Assessment Report WGII chapter “Australia and New Zealand” concluded

An increase in fire danger in Australia is likely to be associated with a reduced interval between fires, increased fire intensity, a decrease in fire extinguishments and faster fire spread. In south-east Australia, the frequency of very high and extreme fire danger days is likely to rise 4-25% by 2020 and 15-70% by 2050.

Similarly, observed and expected increases in forest fire activity have been linked to climate change in the western US, in Canada and in Spain (Westerling et al, 2006; Gillett et al, 2004; Pausas, 2004). While it is difficult to separate the influences of climate variability, climate change, and changes in fire management strategies on the observed increases in fire activity, it is clear that climate change is increasing the likelihood of environmental conditions associated with extreme fire danger in south-east Australia and a number of other parts of the world.

References and further reading:

(1) Bushfire Weather in Southeast Australia: Recent Trends and Projected Climate Change Impacts, C. Lucas et al, Consultancy Report prepared for the Climate Institute of Australia by the Bushfire CRC and CSIRO, 2007.

(2) Special Climate Statement from the Australian Bureau of Meteorology “The exceptional January-February 2009 heatwave in south-eastern Australia”

Karoly, D. J., and K. Braganza, 2005: Attribution of recent temperature changes in the Australian region. J. Climate, 18, 457-464.

Alexander, L.V., and J. M. Arblaster, 2009: Assessing trends in observed and modelled climate extremes over Australia in relation to future projections. Int. J Climatol., available online.

Hennessy, K., et al., 2007: Australia and New Zealand. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, M.L. Parry, et al., Eds., Cambridge University Press, Cambridge, UK, 507-540.

Westerling, A. L., et al., 2006: Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity. Science, 313, 940.

Gillett, N. P., et al., 2004: Detecting the effect of climate change on Canadian forest fires. Geophys. Res. Lett., 31, L18211, doi:10.1029/2004GL020876.

Pausas, J. G., 2004: Changes In Fire And Climate In The Eastern Iberian Peninsula (Mediterranean Basin). Climatic Change, 63, 337–350.

399 Responses to “Bushfires and extreme heat in south-east Australia”

  1. 351
    Mark says:

    And if people want to read about what equipartition of energy means, google the phrase. My five top links:

    http://www.mathpages.com/HOME/kmath606/kmath606.htm
    http://webpages.marshall.edu/~larson/c357/equi.htm
    http://en.wikipedia.org/wiki/Equipartition_theorem
    http://hyperphysics.phy-astr.gsu.edu/Hbase/kinetic/eqpar.html
    http://www.practicalphysics.org/go/print/Guidance_45.html?topic_id=4&guidance_id=1
    (excluding pay-for links)

    and for how this can be seen, see a google search on

    equipartition of energy rotation of a solid object
    http://books.google.co.uk/books?id=tSJGiq4xUP8C&pg=PA100&lpg=PA100&dq=equipartition+of+energy+rotation+of+a+solid+object&source=bl&ots=P9HZC2O6Hp&sig=3oYr2oDbi3U28ZioQnTOP2aUCVs&hl=en&ei=By6tScGsAeDDjAeMr8ibBg&sa=X&oi=book_result&resnum=4&ct=result
    http://www.phy.duke.edu/~lee/P53/therm2.pdf

    Or even try this:

    Take an ordinary pencil.
    Lie it on a flat surface
    Spin it horizontally so that the two furthest points of the pencil are moving and the centre point is not.
    Try and do it without the pencil spinning along its longitudinal axis.

    Can’t be done because the energy needed to spin the pencil horizontally is less than the energy needed to spin it along its length. So energy will syphon off from that more energetic motion into the lesser one until the energies are equalised.

    Much the same happens with excited molecules in a gas: they will exchange energy with other molecules until the energy amongst all the degrees of freedom to place energy are equally full.

    Three of those degrees of freedom being kinetic in nature.

    And kinetic energy in a gas in bulk is called temperature.

    So more kinetic energy, higher temperature.

    Higher temperature? More black-body radiation commensurate with that temperature, same as any other material object of sufficient size.

  2. 352
    Ray Ladbury says:

    Rod, put up or shut up. You keep contending that blackbody radiation is distinct from the absorption/emission between quantized energy states in matter. Find just one physicist who agrees with you. Or alternatively, show me how an material absorbs at an energy other than its quantized energy levels.

    I have directed you to numerous references–Kittel is another one with a good treatment. I have done the math. You haven’t. This is elementary, Rod. For your own benefit, you need to do the math or you’ll never understand how the greenhouse effect works.

  3. 353
    Rod B says:

    Mark (349), you might have read my post before shooting. As I said, microwave energy is absorbed by a H2O molecule into a higher state of its molecular rotation energy. That molecule then collides with another (of any type) molecule, transfers the high rotation energy to translation energy of the collidee. That translation energy increase manifests as higher temperature. There are of course other paths of absorption and relaxation, but this is the predominate basic one.

    And BTW, this process does in fact convert the equivalent of quantized energy (the rotation) to continuous spectrum type energy. Why you think that can not happen is beyond me. It is the basic process behind global warming.

  4. 354
    Mark says:

    Ray, 352, you’re incorrect, to all intents and purposes, the energy levels absorbed by a solid are not discrete absorption spectra, since the intra-molecular energy is so loosely quantised, there is no effective quantisation level.

    Where RodB has the stick well and truly stuck up his nethers is that whilst a solid has the energy states of the lattice construction to hold this energy continua, it has no significant ability to use kinetic energy as a sink for this energy. Meanwhile, the solid or liquid phases do not have a lattice to store energy in but it DOES have a great deal of freedom to store such energy kinetically. In addiction the vibrational states are in many cases so spread in energy and so numerous within a band, it is effectively not quantised either.

    So there IS NO DIFFERENCE between the ability of a solid to partition or absorb continua and the ability of other phases of matter to do so. The mechanism, NOT THE RESULT changes on the state of matter.

  5. 355
    Mark says:

    Rod B Says: “As I said, microwave energy is absorbed by a H2O molecule into a higher state of its molecular rotation energy. That molecule then collides with another (of any type) molecule, transfers the high rotation energy to translation energy of the collidee.”

    And that collidee could be one excited CO2 molecule colliding with another CO2 molecule. This will then result in thermalisation of the IR radiation. Which you seem to insist cannot happen.

    Or is it only when it’s CO2 it can’t happen?

    You also have the loss of that IR can be shifter by the motion of the emitter either to a longer or shorter wavelengh. You also have the equipartition of energy meaning that the energy absorbed in the IR photon doesn’t have to come out as a photon of the same wavelength (misapplication of Kirchoff’s law: it doesn’t say it must be the same energy photon, just that emissivity is the same as absorptivity). It could be changed into a different rovibrational state, which is likely to result in emission of a less energetic photon or by absorption of extra energy of the right magnitude (inelastic collision again, or a photon impinging on the excited molecule before it can release the energy in a sympathetic photon emission.

    This is how thermalisation happens even in the absence of significant inelastic collision events.

  6. 356
    Mark says:

    Rod B asks:

    “And BTW, this process does in fact convert the equivalent of quantized energy (the rotation) to continuous spectrum type energy. Why you think that can not happen is beyond me. It is the basic process behind global warming.”

    So when you say:

    “While there is emission and absorption with changes in intramolecular electronic energy levels, the overwhelming generation of blackbody type radiation is intermolecular (interparticle) collision of charges of one sort or another. The former has a role but it is insignificant for basic blackbody radiation.”

    You meant what?

    Interception of energy in a resonant system such as CO2 and IR radiation is how energy is intercepted. Like with your microwave, this radiation is held on to and then passed on to other constituents and thermalised by that exchange.

    So how does line spectra absorption not have anything to do with the black body radiation of the atmosphere or earth surface?

    WHAT EXACTLY are you trying to ask/claim?

  7. 357
    Ray Ladbury says:

    Mark, I realize that the situation is somewhat different for solids, liquids, etc. However, you still have absorption bands and forbidden energies. I’m trying not to get Rod to confused, and since absorption/emission by gasses is what is needed to understand the greenhouse effect, that is what I am concentrating on. The point I am trying to make is that the absorption/emission in blackbody radiation is exactly the same quantum process. It is not a distinct physical process, and most important, for a real material, you do not really have a continuum of absorption/radiation but a continuum convoluted with an emissivity.

    Rod, No. What happens with greenhouse warming is that you have a source of IR photons that is warm radiating into a layer that is cooler. Because the upper layer is cooler, the predominant mode of excitation is photo-absorption. The predominant mode of relaxation is collision with a cooler atom. If the upper and lower layer were equally warm, you’d be as likely to have excitation by collision, and so the net radiation absorption would be zero.

  8. 358
    Rod B says:

    Mark (351), I disagree with just a few minor points and one major point.

    All of the energy in any and all systems is quantized. Electronic, vibration, and rotation energy is quantized in relatively limited levels with comparatively massive granularity. Things like translation molecular energy, Planck emission from a heated body, and baseballs have humongous number of levels with near infinitesimal granularity — so much so that it is accurately portrayed as continuous. Electromagnetic energy is quantized but gets a little funny to picture unless you use photons as a construct.

    One can read that you are implying (though possibly not…) that the vibration and rotation energy levels are very numerous when in fact they are limited, and for all practical purposes to two or three each. If a 15um photon is absorbed into a vibration energy state and that vibration relaxes in any way, it must (in 99+% of the time) discharge exactly 100% of the energy in joules that it absorbed. You can not get a relaxation with a lot of different energy levels, let alone anything near a blackbody spectrumexcept when it relaxes through a collision and the energy is transferred to translation energy in the collidee. Jillions of these and secondary collisions will spread the energy around ala Boltzmann, as you say. There are other ways the energy can get transferred around, as you say, and this can result in a little more heterogeneous mix — it’s just not predominate.

    Other than these clarifications and your silly closing rant, I pretty much agree with what you say.

  9. 359
    llewelly says:

    Ray:

    It is not a distinct physical process, and most important, for a real material, you do not really have a continuum of absorption/radiation but a continuum convoluted with an emissivity.

    Convoluted or convolved?

  10. 360
    Rod B says:

    Ray, I’m not sure when you lost your Freshmen physics forest in the trees of post doctoral work. Planck-type black body radiation results from (gee I’m getting tire of this… as are others, probably) the acceleration of charges, predominately as a result of collisions (which include crystal vibrations for these purposes) among electrons and ions. The amount of blackbody energy emitted is strictly and solely a function of the thermal temperature of the substance, mitigated by the characteristic of the substance called emissivity (which can, as you say, by frequency dependent). The emission/absorption of vibration and rotation radiative energy is strictly a function of the physical connective intramolecular properties and the distinctly quantized energy states. Acceleration of charges have nothing to do with it other than as a very minor factor in the teeny physical movement of the molecule’s bonds and rotation. Temperature has nothing to do with it, other than as a background factor in the probability of filling one of those states.

    Not the same. (Even though one can utilize the construct of one to analyze the other. Planck blackbody radiation theory is heavily used in analyzing greenhouse gas warming, though it plays a very minor physical part itself.)

    Believe what you will. I’m done. (Hold the applause everyone!)

  11. 361
    Rod B says:

    Mark (355), you say, “…that collidee could be one excited CO2 molecule colliding with another CO2 molecule. This will then result in thermalisation of the IR radiation…”

    Sure. So? Where did you get I disagreed with that? Especially when I have explicitly said that here a number of times — though the collidee is not limited to CO2: it can be CO2, or much more likely N2 or O2.

    Your follow-on description is also true, though the process you discuss is a small percentage of the thermalizing process — not exactly “…how thermalisation happens…”

    356: I mean clearly and simply (and NOTHING else) that the physical/physics processes of the two radiation types are not the same, ergo they are not the same thing. See my next post to Ray (assuming it gets in…).

  12. 362
    Hank Roberts says:

    Mark, I am sure you meant, above, to write “gas”:

    “… whilst a solid has the energy states of the lattice …. Meanwhile, the [gas] or liquid phases do not have a lattice ….”

  13. 363

    Mark wrote in 354:

    Ray, 352, you’re incorrect, to all intents and purposes, the energy levels absorbed by a solid are not discrete absorption spectra, since the intra-molecular energy is so loosely quantised, there is no effective quantisation level.

    What I would emphasize is that the difference between the thermal radiation of solids, liquids and gases is a matter of degree, not kind. Solids can approximate blackbody radiation, but blackbody radiation itself is an idealization. Individual gasses at low pressures and temperatures have well-defined lines and bands, but at higher pressures and temperatures both broaden with lines bleeding into lines and bands bleeding into bands. Dusts, crystals and alloys have relatively discrete spectra. However, impurities, clustering, ions and pressure broaden these spectra. And atmospheres are composed of multiple gasses where each gas is at the same temperature. Individually, the spectra of any one gas in the atmosphere is a poor approximation for a blackbody emitter, but taken together, the atmosphere does much better.

  14. 364
    Rod B says:

    Ray (357), a belated question. I understood your description of the radiation going into cooler atmosphere. But it occurred to me: isn’t the probability of a, say, vibration energy level being filled by absorbing IR radiation proportional to e–E/kT, with T being the background temperature and E being the vibration energy level? meaning would it not be more likely to fill a vibration level the higher the background temperature is, regardless of the source of the IR? Or, what am I missing?

  15. 365
    Mark says:

    364 nope, the higher the temperature the more likely the energy level is to REMAIN filled.

    Ordinary relaxation would mean it is out of equilibrium with the surrounding medium and it is more likely that it will regain the lost energy through another source (such as a collision between it and a relatively faster moving object).

    You have the cart firmly before the horse, Rod.

    And probably deliberately too.

  16. 366
    Mark says:

    re: 363, yup, the RESULT is the same: energy spread amongst elements that are used to define what temperature *means*.

    Solids: the energy unbinding the solid structure (hence get a solid hot enough and it melts).

    Liquids: the random motion randomising the energy undoing the bonds between weaker bound elements not in a structured lattice (hence when it boils, you see bits boiling first: bubbles)

    Vapours: the random motion in the gaseous media constituents and for asymetric constituents (e.g. diatom and bigger), the energy that can be stored in the rotational and vibrational states.

    ALL merely ways of putting that energy somewhere else that maintains the maximum amount of entropy.

  17. 367
    Mark says:

    Re: 361. Nope, not in any meaningful sense: they are degrees of freedom for energy deposition and dispersal.

    And even if it weren’t, the result is still the same: energy partitioned out into measures that are statistically distributed in a manner that obeys the Boltzman law, which is the derivation (along with the quantisation of photons that stops the UV catastrophe) of the black body radiation.

    And there is no meaning to your assertion that there is a difference. There is none in the phenomenology of this system either solid or gaseous.

    If all you had to say was that, it means nothing. Merely different ways of doing the same thing (cf a monatomic gas ideal law being 2/3RT energy per molecule, and adding two more degrees of freedom changes that to 4/3RT, because where the energy goes doesn’t matter to the energy).

    PS Hank, you’re right, it should have been gas.

  18. 368
    Ray Ladbury says:

    Rod B., Gee, given the choice between your view of blackbody radiation and that of the physics community–from Planck through Landau, Kittel…–I’m afraid I’ll have to stick with the physicists. YOU have yet to cite even one text to support your viewpoint. You have steadfastly refused to consult the references I’ve given–all standard stat mech texts.

    Re 364: The higher the temperature, the more molecules will be in higher energy states–whether that energy is kinetic, electrical, vibrational, rotational, whatever. If the molecules are in equilibrium with the radiation field, you will have proportionity between the photon number and the number of excited states.

  19. 369
    Hank Roberts says:

    Radiation physics without math is hard.
    Or do I mean almost impossible (grin).
    Visualizing it might be possible.

    I’d like to see something done with visualizing it, like I tried above, along the lines of this:

    http://javaboutique.internet.com/BallDrop/

    That does in Java what the Exploratorium and other science museums built as wall-size hardware:

    dropping balls through a grid — produces a random distribution (and how many iterations it takes to get that nice smooth line from discrete chunky reality).

    I keep trying to imagine a way to visualize the process of high energy photons zinging through the atmosphere, hitting the ground, infrared photons radiating from the ground and then the complicated bounce-and-wiggle-and-randomization in the atmosphere (as per the attempt above).

    If I could _see_ it clearly enough, I could convince one of my Javascript-competent friends to build a picture of it, along the same lines as that one.

  20. 370
    Rod B says:

    Ray (368 – part 2): I’m still having trouble grasping this. Why then does the vast majority of absorption by CO2 occur very close to the surface, where the temperature is about equal to source of the IR? It just sounds illogical and I can’t seem to grasp it. (Though your basic description, which generated my query, of the “hot” radiation getting absorbed by the higher altitude “cold” gases is logical.)

    (part 1): One last thing (against my better judgment): Can you describe precisely what the particles (molecules, atoms, ions, electrons) do to generate Planck style blackbody radiation? Then precisely what the particles do to emit/absorb radiation at, say, 15um?

  21. 371
    Mark says:

    Because you’re making it sound awkward, Rodb (370). The vast majority of the abosbtion OF THE EARTH’S IR OUTPUT is absorbed very close to the surface. And that is then passed around back to the earth (making it warmer) and around the rest of the atmosphere (making that warmer).

    Why does that sound illogical?

    Here’s an equivalent query: blue light is only prevalent in thermal bodies around the 12,000K level. So why is our ***blue*** planet not at 12,000K?

    Why does that sound illogical?

    And your part 1 request is illogical: they are random stochastic events with multiple avenues of progression. Such a work would take dozens of pages just to STATE, never mind prove.

  22. 372
    Ray Ladbury says:

    Rod B., OK, bear with me. Consider a bunch of photons passing through a material–start with a gas to keep the interactions simple. Either the photons can be absorbed by the gas or they cannot. Those that cannot be absorbed will pass through the gas, leaving the energy distributions for the gas and for the photons–IN THE NON-INTERACTING PORTION OF THE SPECTRUM–unchanged. With me so far?
    Now in the interacting portion of the spectrum, the photons will be absorbed, changing the energy distribution of the gas. But the energy distribution of the gas also depends on its temperature, and depending on that temperature, a certain proportion of the molecules will be in the same excited state (e.g. by collisions with other energetic molecules) corresponding to the energy of the absorbed photons. OK?
    Once the gas molecule is excited–regardless of the cause–it can relax in a number of ways. It can emit a photon with the same energy as the absorbed light. It can relax collisionally, imparting the excess energy to another atom. Which of these dominates depends on a variety of things–the dynamics of the reaction mechanism, the density of the gas, density of the photons, gas temperature… If collisional decay is more probable, you’ll have a net conversion of photons into gas thermal energy. If the gas is hot, and there are lots of collisionally excited molecules, you’ll get a net production of photons. Eventually, the interacting photons and the gas will come into thermal equilibrium–that is, they’ll have the same temperature. We’ve taken the case of a simple gas with a single excitation level and a single photon energy. However, if we have a more complicated gas, a liquid or solid, all that changes is that we have more energy levels–even energy bands, so we can take more slices out of the initial photon spectrum, and these slices can then come into thermal equilibrium (both with the gas and with themselves). If we extend this process to the IDEALIZED case where the medium is a perfect absorber (and so a perfect emitter), we cause the entire initial photon distribution to be absorbed. The energy then gets redistributed over several interactions so that photons and matter are in equilibrium at the same temperature. Do you follow?

    As to the reason why most of the IR absorption takes place close to the ground–remember, there will always be far more CO2 molecules in the ground state than the excited state–plenty of targets close to the ground, so plenty of absorption. Now if the air is the same temperature as the ground, you’ll get the same number of photons emitted as absorbed, because even though you well be relaxing via collision, you’ll also be exciting CO2 via collision, and this will be the case until you get to a cooler layer of the atmosphere. Still plenty of targets for absorbing photons. But now, there are fewer thermally excited molecules, so you’ll get fewer radiative decays and proportionally more energy going into heating the atmosphere at this layer. And so on, as long as the atmosphere continues to cool with altitude.

  23. 373
    Hank Roberts says:

    > Planck style blackbody radiation
    Line dance, square dance, holding hands

    > specific wavelength
    Mosh pit

  24. 374
    Hank Roberts says:

    Or, Rod, try this:

    http://www2.jpl.nasa.gov/radioastronomy/Chapter3.pdf

    BASICS OF RADIO ASTRONOMY
    Chapter 3
    The Mechanisms of Electromagnetic Emissions

    Objectives:
    Upon completion of this chapter, you will be able to describe the difference between thermal and non-thermal radiation and give some examples of each. You will be able to distinguish between thermal and non-thermal radiation curves. You will be able to describe the significance of the 21-cm hydrogen line in radio astronomy.
    If the material in this chapter is unfamiliar to you, do not be discouraged if you don’t understand everything the first time through. Some of these concepts are a little complicated and few non-
    scientists have much awareness of them. ….

    __ReCaptcha__
    ex- annoyance

  25. 375
    Rod B says:

    Mark (371), that has a ring of sense to it; I’ll have to think about it.

    So, we don’t have a clue what is happening physically? Like 1) we heat something 2) a little HPFM, 3) it radiates…??? That’s nowhere near what any text describes (though the texts are more precise with molecular emission/absorption than Planck blackbody radiation).

  26. 376
    Ray Ladbury says:

    Rod B. says “That’s nowhere near what any text describes (though the texts are more precise with molecular emission/absorption than Planck blackbody radiation).”

    What texts, Rod? Be specific. We can’t help you unless we know where you are getting your (mis)information.

  27. 377
    Mark says:

    RodB, 375. No, YOU don’t have a clue as to why it happens.

    Explaining it to you is futile and a waste of time. doesn’t mean there isn’t an explanation, just that this isn’t the place to put such a long piece of first-year undergraduate work and you have shown an unwillingness to educate yourself.

    Pay me £25 an hour and I’ll be a tutor for you. Should get a couple of grand out of you no worries.

  28. 378
    Hank Roberts says:

    Rod:
    Work through that NASA chapter (link above).
    Open yourself a blog page somewhere (else).
    Invite people to help you with it (there).
    Profit!

  29. 379
    Rod B says:

    Ray (372), that (too) sounds logical. I’ll have to let it soak.

  30. 380
    Hank Roberts says:

    Australia?
    Bushfires-and-Climate?

    How’s it going there?

  31. 381
    Ray Ladbury says:

    Rod B., Don’t get discouraged. Stat mech is not easy stuff. I do heartily recommend Landau and Lifshitz on the subject. Kittel is also not bad. There are lots of little subtleties at a very deep philosophical level here. Hell, even statistics and probability are not quite where mathematicians would like it to be. However, rest assured that the subject is sufficiently well understood that it is not in danger of overturning those disciplines built upon it–e.g. climate science.

  32. 382
    David Horton says:

    Hank #308
    I dropped out after the discussion shifted to the physics of greenhouse gases.
    Four fires are still burning, but cooler weather in the last week and a very little rain has helped. Containment lines weren’t broken during high winds earlier in the week, and no more houses have been lost. So that seems, touch wood, to be the worst over for now.

    But in the men time those who want to burn the bush all the time to prevent it being burnt are growing in loudness, and I fear for the Australian environment when populist politicians make demands for simplistic solutions (http://www.blognow.com.au/mrpickwick/128862/The_worst_of_times.html).

    I’m about to publish a stinging rejoinder to the burn the bush brigade. Will keep you advised. But they, with the help of conservative politicians, and big business, have succeeded in pretending that climate change induced high temperatures, strong winds, extended drought, trees dying or shedding leaves and branches under stress, are nothing to do with climate change. And demanding that the government delay even its derisory 5% CO2 reduction ETS scheme until next year, or the year after, or perhaps the year after that.

  33. 383
    Hank Roberts says:

    Global concern but with special relevance for Australia:

    One of Climate Change’s Most Important Equations
    By John Fleck
    Wednesday, 04 March 2009 09:33

    In understanding the implications of climate change, a lot of attention is paid to the question of whether precipitation will rise or fall in any given region. It seems a critical question. Will it rain more here? But a more important factor tends to get short shrift – the interplay between precipitation and evaporation.

    http://www.abqjournal.com/abqnews/index.php?view=article&catid=18%3Anm-science&id=11143%3Aone-of-climate-changes-most-important-equations&option=com_content&Itemid=31

  34. 384
    Steven Chamberlain says:

    As a student of ecology for the last 15 years and of the rudiments of bushfire for 6 years, it pains me to see how much spin and polemic is being generated in Oz at the moment. Like My sincere thanks to David Karoly for posting the original article, and to all those who debated the issues of conservation, appropriate fire regimes, planning and the costs/ benefits of fuel reduction with such diplomacy and aplomb. I’ve learnt more than I could have contributed (though I have to say much of the physics also discussed by others went way over my head). Would that the current “debate” (I use the term in its loosest sense) here in Oz was half as sober and informed as that which has gone on here. On that note (apologies for being a little O/T) I’ve sent complaints to both the Sydney Morning Herald and the Oz Press Council about Devine’s polemic, which is currently in progress, as they say. Like Alan (#187) I refuse point blank to link to Ms Devine’s article, as she and the editors of the SMH know full well that divisive articles like hers are designed to sell papers and generate website hits. She and her ilk (Andrew Bolt of The Australian for example) positively revel in the attention, be it good bad or indifferent. The pity of it is that much of the commentary is designed to stir people up, not inform or encourage debate based on facts, but ’twas ever thus.

  35. 385
    Ray Ladbury says:

    Rod B.,Over at Tamino’s Open Mind blog, Lazar has a couple of posts on the Open Thread #10 (beginning @12:19 on 2 March) on first-principles calculations of warming. You might find them interesting.

  36. 386
    Steven Chamberlain says:

    For those not fully up on the science, below is a link to a research project commissioned by the Climate Institute of Australia that looked at projected increases in FFDI under two CSIRO climate scenarios, hosted by the Australasian Fire and Emergency Service Authorities Council (AFAC).

    http://tinyurl.com/atvhml

    The page gives a summary of findings – if you click on the link at “title” a new window opens up:

    http://ams.confex.com/ams/7firenortheast/techprogram/paper_126843.htm

    Clicking on “Recorded presentation” brings up a web-based presentation. I realise much of what Chris Lucas is saying here will seem overly simplistic to many on this site, but for those not deeply involved in climate modelling, it’s as good an overview or background briefing as one could wish for. Particularly scary are the constant upward trends in FFDI at decadal scales, much earlier starts to the fire season and much earlier first high fire danger days. He also reinforces the point that while much of the public debate here focuses on fuel loads, what’s generally forgotten about are the weather patterns that contribute to high fire danger periods. Though this was written almost 2 years ago, some of the forecasts for future fire weather in SE Australia seem to have been borne out in the last couple of months.

  37. 387

    Ray Ladbury wrote in 385:

    Rod B.,Over at Tamino’s Open Mind blog, Lazar has a couple of posts on the Open Thread #10 (beginning @12:19 on 2 March) on first-principles calculations of warming. You might find them interesting.

    Lazar’s “A first principles derivation of the enhanced GHG effect…” entry is at:
    http://tamino.wordpress.com/2009/01/31/open-thread-10/#comment-29240.

    Actually I believe the entire discussion as it relates to Svante Arrhenius and the history of thought regarding greenhouse gases (complete with a link to the original paper on carbonic acid) is well worth a look.

  38. 388
    GregE says:

    Apart from the climate physics there is a psychological issue. There are about 6 billion people in the world. 5 billion of them have an IQ of 115 or less. That means that most of this article and discussion is incomprehensible to 5 out of every 6 people on planet earth. I am being generous it is probably more like 98% cannot understand the science and maths. The physics and statistical analysis is too hard. Just look at the comments from those that think a bit of northern hemisphere snow disproves AGW. The 5 will always out vote the 1.

    I despair for the future because nothing will be done until the taps run dry and the supermarkets run out of food and then it will be too late. If you think I am wrong just look at the crap that our politicians spout everyday. Penny Wong talks of delaying the Carbon Trading scheme to save jobs. The best Rudd can do is a non target of 5% reduction. The state of Victoria could massively reduce emissions just by switching electricity generation from brown coal to natural gas. The gas is sitting under the ocean right next to the current coal stations. Will this happen? No, too many vested interests and short sighted politicians. Nothing is done except endless talk and debate about useless carbon trading.

    The only future now is Geo-Engineering, it is too late for reductions when the politicians, and those who vote for them, have so far achieved nothing but a steadily increasing CO2 level.

    As for the fires, they came to within 15km of my house, then the wind changed. My family was lucky. It does not matter what caused the fires, this fire was very different because of the conditions on the day. These same conditions will recur at much more frequent intervals. Climate change is not in the future, it is outside the window, in front of those willing to look.

  39. 389
    Bruce Tabor says:

    When temperatures exceed previous maximums by 2.5 to 3 C over a large area – as occurred in Victoria on Feb 7 – I struggle to believe that an “anthropogenic contribution to mean maximum temperature increases of about 0.6°C” is the explanation.

    One would expect that the temperature distribution would be shifted upward by 0.6C, which is probably the reasoning underlting the IPCC Fourth Assessment Report estimates of the increase in extreme fire danger days. For a 100 year event the maximum would be 0.5 to 1 C above previous records (given the 150 year history).

    I suspect that something non-linear is happening in the tails of the temperature distribution that we don’t fully understand.

  40. 390
    Mark says:

    Bruce says “When temperatures exceed previous maximums by 2.5 to 3 C over a large area – as occurred in Victoria on Feb 7 – I struggle to believe that an “anthropogenic contribution to mean maximum temperature increases of about 0.6°C” is the explanation.”

    Why?

    One standard deviation or more from the mean in a normal distribution is about 33% of the time going to happen. Two standard deviations about 6% of the time. Three would be 0.1%. (IIRC). If the mean has moved 0.6C higher, what was three SD away from the mean has increased in its chances by maybe as much as 60x.

    So why do you believe that explanation is not sufficient?

  41. 391
    Ray Ladbury says:

    Greg E. says, “The only future now is Geo-Engineering…”

    Great, so what do you propose. I don’t know of a single geoengineering technique that is ready for prime time. Iron fertilization–shown not to be effective. CCS–not ready. Sulfate aerosols–not only no, but hell no.

    You are presuming that 5/6 of the population is not only incapable of understanding climate change, but is also incapable of acting in their own interest or caring whether their children survive. You presume democracy cannot work…and yet it does, better than any other system of government.

  42. 392
    Bruce Tabor says:

    Hi Mark (#390),
    A full treatment of this problem belongs to the statistics of extreme value theory. To avoid this complication I’ll keep it simple.

    Assume that the maximum temperature of a predefined region in a year follows a normal distribution, or indeed any distribution with a known mean and variance. In any one year the chance of getting a one in one hundred year maximum (about 2.3 standard deviations above the mean maximum for a normal distribution) is 1%. As temperature records exist for 150 years or so, the existing maximum recorded temperature in that region will be a reasonable approximation to that “100 year event”.

    Now assume the effect of global warming is to shift the temperature distribution up by 0.6 C. If the effect is linear, one would expect the distribution of maximum temperatures to also be shifted upward by 0.6 C. For our predefined region our new 100 year event will be 0.6 C above the old one, as the whole distribution has shifted up 0.6 C.

    There are several problems with this reasoning. Most importantly our region is not predefined. A large part of Victoria was drawn to our attention simply because of the extreme weather. (And adjacent regions are of course correlated.) Here in Sydney only 800 km away no records were set, although it was very hot on one day when the Victorian weather finally moved north. Climate change is not required to produce new records somewhere in the world quite frequently, especially if that “somewhere” is geographically constrained.

    Other problems relate to the distinctly non-normal behaviour of extreme value distributions.

    However it is my intuitive feel that to produce huge jumps over previous records over a large area suggests an altered weather regime, not just a linear contribution from AGW to the existing climate. The fact that the extreme heat was preceded by a record breaking dry period seems to support this (but this could also be correlated with the extreme heat). The effect of this may be to broaden the “extreme value distribution” making such events more likely. Or it may be the “extreme value distribution” has been shifted by more than 0.6 C.

    I may be wrong. There is no rigorous analysis underpinning my intuition.

  43. 393
    GregE says:

    Ray Ladbury Says:
    You are presuming that 5/6 of the population is not only incapable of understanding climate change

    I did not say that they could not understand climate change, I said they cannot understand the Physics and Mathematics – the proof. Perhaps I was a little extreme in my grammar. Eventually even the most ardent naysayer will be able to see it.

    I hope your assessment of democracy is true and the people demand action from recalcitrant politicians. I will believe it when Bob Brown is PM with a majority in both houses.

    As for Geo-Engineering I still think it is the only answer. What form that Geo-Engineering will take no one yet knows, but at least there are plenty of people willing to work on it. We need a carbon neutral world in the long term, but first the future has to be secured. With China and India rapidly expanding, and the rest of the world dithering, CO2 keeps going up, not down, not even a slowing increase. In a recent article in New Scientist the author postulated a real danger is a single nation or even wealthy individual deciding to go it alone with unforeseen consequences. But then getting the whole world to agree to anything is almost impossible.

    Unfortunately we are living in interesting times.

    To the other discussion on the distribution assessment of “anthropogenic contribution to mean maximum temperature increases of about 0.6°C”. The 0.6 degrees is an average, there is no assumption that it is globally uniform, in fact my reading of the models is quite the opposite. Some places get hotter, some may even get colder in the short term. Weather patterns are altered, changing climate in many ways in many places. The whole world distribution may be moved up a small amount of 0.6 so far, but that does not mean individual areas will not be much greater (eg Victoria), and others barely changed.

  44. 394
    Mark says:

    “However it is my intuitive feel that to produce huge jumps over previous records over a large area suggests an altered weather regime”

    Is quite a bit different from

    “I struggle to believe that an “anthropogenic contribution to mean maximum temperature increases of about 0.6°C” is the explanation.”

    And you still have “gut feeling” which, along with 50p, will get you a mars bar at most shops. You admit that at the end, but you should be starting off with that, not ending with it. It is, after all, central to your explanation.

  45. 395
    Ray Ladbury says:

    Bruce Tabor, While Extreme temperatures clearly follow an extreme value distribution, the physics tells us that the temperature cannot be unlimited, so the particular EV distribution is the Weibull. We know that for the Weibull, standard deviation is proportional to mean, so as the mean rises, the distribution becomes broader. The problem with extreme value distributions is that samples are necessarily sparse–you only get one yearly maximum and there is by definition only one all-time maximum. Kind of hard to do statistics. Also, keep in mind that 0.6°C is only a global mean. Local increases can be quite a bit higher. I’d say we don’t have much evidence to support our being in a “new regime” just yet.

  46. 396
    Ray Ladbury says:

    Greg E., I think we’ll have no choice but to rely on geo-engineering. I also think it will be quite awhile before geoengineering will be ready for prime time. Conservation and mitigations like forestry and terra preta sequestration are the only games in town for the present.

  47. 397
    Bruce Tabor says:

    Hi Ray (395),
    Usually Weibull distributions are used to model minima rather than maxima (eg time to failure, where failure time is the minimum of a number of components each modeled by normally distributed failure times).

    For the example I gave (a normal parent distribution) the relevant EVD is the Gumbel, the variance of which is not affected by translation of the underlying parent distribution.

    The “new regime” I was speculating on is one local to this region of Australia. My argument is not rigorous, it’s just a gut feeling based on my experience as a statistician (which doesn’t include work in extreme value theory). Records weren’t just broken, they were smashed.

  48. 398
    Karmakaze says:

    I know I’m very late but I just HAD to vent my spleen at one of the most annoying assertions the deniers like “Truth” (Ha!) make:

    “Since the measures called for by the AGW proponents have the potential for enormous damage to economies and standards of living around the world”

    This is a massive lie. Standards of living do seem to be correlated to CO2 emissions but negatively! For example, if you look at The Economist Intelligence Unit’s Quality of Life index for 2005, you find that the US is 13th on the list, but only ONE of the first 12 countries has higher per capita CO2 emissions as of 2004 and that is Luxembourg! Of course total output from Luxembourg is orders of magnitude smaller than the US.

    The truth is, the countries with the HIGHEST Quality of Life have some of the LOWEST CO2 emissions of the industrialised world.

    Funny that!

    http://en.wikipedia.org/wiki/List_of_countries_by_carbon_dioxide_emissions_per_capita
    http://en.wikipedia.org/wiki/Quality-of-life_index

  49. 399
    Jim Galasyn says:

    Global warming 37 percent to blame for droughts: scientist

    SINGAPORE (Reuters) – Global warming is more than a third to blame for a major drop in rainfall that includes a decade-long drought in Australia and a lengthy dry spell in the United States, a scientist said on Wednesday.

    Peter Baines of Melbourne University in Australia analyzed global rainfall observations, sea surface temperature data as well as a reconstruction of how the atmosphere has behaved over the past 50 years to reveal rainfall winners and losers.

    What he found was an underlying trend where rainfall over the past 15 years or so has been steadily decreasing, with global warming 37 percent responsible for the drop. …