There is a new paper in Science this week on changes to atmospheric visibility. In clear sky conditions (no clouds), this is related mainly to the amount of aerosols (particulate matter) in the air (but is slightly dependent on the amount of water vapour as well, which is corrected for in this study). The authors report that the clear-sky visibility has decreased almost everywhere (particularly in Asia) from 1973 to 2007, with the exception of Europe where visibility has increased (consistent with the ‘brightening trend’ reported recently). Trends in North American stations seem relatively flat.
There is another story that didn’t get as much press when it came out late last year but that is highly relevant to this issue – whether any of the efforts that the Chinese authorities to reduce air pollution ahead of the Olympics last year had any impact. To the extent that they did, they might point the way to reducing aerosols and other pollutants across Asia, but it might also reveal how hard it is to do so.
The press release and abstract for the Science paper link their results to the ‘global dimming’ trends we have reported on in the past, but it’s worth perhaps pointing out that previous studies (and the term ‘global dimming” itself) have referred to all-sky conditions. So that includes changes in clouds – which are obviously a big factor in how much sunlight gets to the surface. Looking at the clear sky conditions (i.e. only when there are no clouds) can help attribute changes to aerosols or atmospheric dynamics say, but since aerosols affect clouds (the ‘indirect effect’) as well as circulation too, it is only a partial estimate of the true impact of aerosols.
But getting back to the Olympics…. Monitoring of pollutants near the surface has improved enormously in recent years with the various satellite instruments now in orbit (MOPITT, GOME, OMI and TES for instance (sounds like a comedy revue team, no?)). These instruments detect specific frequencies where pollutants are known to absorb and so can give a birds eye view of where the pollutants are and how they are changing. Among other things, the satellites can detect ozone, NOx, SO2, the total amount of aerosols and carbon monoxide. Each of these have different atmospheric lifetimes and so can be used either to detect point sources (from pollutants that only last a short time) or long range transports of pollution (from the longer lived pollutants). NO2 (a big component of NOx – which lumps together NO and NO2all of the reactive nitrogen oxides), is very short-lived and so tells you a lot about local sources. Carbon monoxide has a longer lifetime (a couple of months) and so can show the long-range impacts. Many of these pollutants have related industrial sources (car exhausts, coal burning, industrial production etc) and so can be used as proxies for many other pollutants (such as specific aerosols) which can’t (yet) be directly measured.
What do the results show? The team at GSFC have released preliminary images from the NO2 analysis showing the before and during the pollution controls. In both images, Beijing shows up as a huge hotspot of pollution, but relatively, the levels during the Olympics were significantly smaller:
August 2008 levels were therefore about 50% less than a similar period the year before. Meanwhile values at other hotspots in China were steady or got even worse. So there was a significant effect, but the scale of the task was indeed Olympian.
“Forgive a brief (I hope!) digression into geopolitics, but I fail to see why proliferation should be an issue, since it’s been amply demonstrated that countries which want nuclear weapons can develop them without first developing nuclear power generation. So why should the rest of the world refuse to use nuclear power in order to prevent proliferation that has happened anyway?” – James
Because the materials, skills and technologies for the two are so intimately connected, that the more there is of civil nuclear power, the easier it will be to develop nuclear weapons programmes: more plutonium and enriched uranium around, wider distribution of enrichment and other relevant materials-handling technologies, more people with the skills needed in weapons programmes. It’s actually quite remarkable how little proliferation there has been so far – take a look at predictions from a couple of decades or more ago of how many nuclear-weapons states there would be by now. The NPT is clearly part of the explanation, but the failure of the civil nuclear industry to expand as expected may have been more important.
James, you mean like Korea and Iran? Israel? Pakistan? S. Africa? All used civilian nuclear power as a cover for weapons activities. Using Th cycle ameliorates the issue somewhat (e.g. for Korea). It does nothing for the waste issue.
Ray #252, you mean ***accused*** of using the civilian operations as a cover.
The capability for weapons-grade purification wasn’t there for Iran. The “explanation” of “why do they need nuclear when they have all that oil” ignores that the US has one of the largest reserves in the world now. Yet they use nuclear.
Rod –
Agreeing with Ray, Mark, et al, my understanding is that, not only does thermally-emitted radiation (radiation emitted by energy transitions with average power according to their likelihood for that temperature; availability of transitions also being a material property depending on atoms, molecules, and their interactions – at very high temperatures, nuclear interactions) obey some descriptions of blackbody radiation (within an isothermal material of sufficient optical thickness, fluxes and intensities at any given wavelength approach the blackbody values), it can be called blackbody radiation.
But it may also be true (if I recall correctly) that Planck’s original proposed mechanism for emission of blackbody radiation, though it produced the correct temperature and wavelength dependencies (he was trying to solve the “ultraviolet catastrophe” issue), was not quite correct itself.
—- Additional tidbits of information about radiation, of importance to solar cells.
PS Ia. (In the absence of scattering, emission, and/or absorption, radiant flux away from a spherical source decreases with an inverse square law, but the intensity (flux per unit solid angle – how bright it appears within it’s fraction of one’s field of view) is conserved, except upon refraction. Refraction changes the solid angle envelope of any set of rays, so that intensity is proportional to the square of real component of the index of refraction when there is no emission,absorption,or scattering. Assuming the second law of thermodynamics still applies, blackbody radiation intensity and fluxes must also be proportional to the square of the real component of the index of refraction. Within a blackbody material with real index of refraction n, with an isothermal region of infinite optical thickness, or an infinite isothermal expanse of blackbodies embeded within some material with index of refraction n, the blackbody fluxes and intensities within the material will be proportional to n^2. If there is an antireflective interface with a vacuum (n=1) or air (n ~= 1), Total internal reflection keeps the flux and intensity of blackbody radiation escaping the material across the interface equal to (or very nearly so for air) the standard blackbody values if the isothermal material is thick enough to block any radiation from behind it. If the interface does have some reflection (at any direction on the outside, or within the cone of acceptance on the inside – I think the reflectivity must be equal in both directions for any pair of directions corresponding to refracted rays, or else second law violations occur, although there is some complexity regarding polarizations), then the material doesn’t act like a blackbody in terms of emission from it’s surface even if it does inside of itself. Anyway, the interesting point here, is that total internal reflection (which can be used to reduce necessary thickness of photovoltaic layers to absorb most of the radiation they are using – by having a diffuse (lambertian, preferably) back reflecting interface to scatter rays out of the cone of acceptance) can be related to the second law of thermodynamics.)
PS Ib. Geometric (ray-tracing) concentration by reflection (parabolic and/or ellipsoidal, etc, dish or trough mirrors) concentrate flux but conserve intensity.
PS Ic. Luminescent concentrators work by absorbing some wavelengths with fluorescent material, which emits some portion of incident photon energy as photons of lower energy (longer wavelengths) (PS an example of non-blackbody emission – the electron energy is temporarily distributed in a way that could not be achieved by spontaneous redistributions of thermal energy in a body at local thermodynamic equilibrium). The emitted radiation is at least partly trapped within a plate by total internal reflection, and thus is focussed onto a small area on the edges of the plate. Plates working with different wavelengths can be stacked, analogous to multijunction solar cells. Radiation emitted by fluorescence is monochromatic (or nearly so) and so solar cells can be matched to fluorescent materials to improve conversion efficiency. (Geometric concentrators could also be combined with prisms/etc to direct different wavelengths to different solar cells). Unlike geometric concentrators, luminescent concentrators can use diffuse light (blue sky, clouds, snow) and do not need to be aimed with much precisions (don’t need tracking). Diffuse light at any one wavelenght could be assigned a temperature based on the blackbody that would emit at that wavelength with the same intensity (direct solar radiation reaching the surface is generally not as hot as it is in space because of absorption and scattering removing some intensity out of the beam of light, while scattered radiation will be cooler still (but still quite hot relative to the Earth’s surface and atmosphere)); the potential for luminescent concentration can be analysed by applying the second law of thermodynamics, factoring in the change in wavelength during fluorescence and the index of refraction.
PS II (reflection is due to sharp (relative to wavelength)discontinuities in index of refraction n. Approximating a gradual change in n with an infinite number of infinetisimal interfaces, the relatively weak reflections from multiple interfaces are out of phase with each other and thus sum to near zero, resulting in nearly zero reflection. Antireflective coatings for specific sets of wavelength-direction combinations work with some finite number of steps in the value of n with some spacing. Large scale texturization also reduces reflection by giving reflected rays multiple intersections with the surface; if the reflectivity of the surface is not perfect, there will be some loss from the reflected ray after each reflection. Texturization works best for normal rays (perpendicular to the average surface) – it works better and over a larger range of angles for steeper texturization. It is possible to conclude that total internal reflection works with texturization based on the previous paragraph. Texturization on scales smaller than a wavelength can simulate gradual transitions).
Speaking of Olympian efforts to control pollution, here’s a dispatch from the trenches.
Lead paragraphs:
“OSLO, March 23 (Reuters) – Governments broadly support tough 2050 goals for cuts in greenhouse gas emissions but are split on how to share out the reductions, according to a new guide to negotiators of a new U.N. climate pact.
A document to be presented to U.N. climate talks in Bonn from March 29-April 8 narrows down a list of ideas for fighting global warming in a new treaty due to be agreed in December to about 30 pages from 120 in a text late last year.”
veritas36 (250) — My hazy understanding is that ABC results in global cooling via global dimming.
We neither need nuclear power nor is it an effective solution for reducing carbon pollution — especially in the time frame within which major reductions are needed.
Wind, solar, geothermal, hydro, and biomass — and of course efficiency and conservation — can do the job faster, better and cheaper.
So there is really no need to deal with the very real dangers and risks of nuclear power.
Sec, it’d help to cite to someone who’s actually doing the math on these issues. Try Fields, as cited by John Massey in the ‘Young Climate Blogger’ thread just recently. He’s seriously assessing this stuff.
Without the numbers, it’s a profession of faith.
With the numbers, it’s an investment plan.
Patrick 027 (210)
The flaw in your logic about the coat analogy to IR emission and absorption its purpose is not to prevent IR emission. Coats work by preventing convective and conductive loss of body heat to the surrounding air. A coat is analogous to a glass walled enclosure, e.g. a greenhouse. It confines warm air to a specific volume.
Patrick 027 (210) and Barton Paul Levenson (218)
You both make the point that net heat flux must be from a warm body to a cold body does not mean that IR absorption by the atmosphere cannot mitigate temperature swings at the surface of the earth. The atmosphere, mostly the water vapor, does that. In effect, the atmosphere introduces hysteresis into the surface temperature. Compare the temperature on the surface of Earth to the temperature on the surface of the moon. The surface temperature of the moon is about 110 degrees C on the lighted side and about 250 degrees below zero on the dark side. That is a swing of about 360 degrees C day to night, which is quite a bit more than the temperature swing on the surface of Earth.
Patrick 027 (232)
The chamber that you describe is what Gerlich & Tscheuschner call a cavity radiator. That is the classic thought experiment and is the basis for the T4 radiant heat transfer model. Gerlich & Tscheuschner discuss this model in detail and discuss why that model is not applicable to radiant heat transfer among molecules. Their primary point is that molecular radiant heat transfer is far more complex than is the transfer of radiant heat from a cavity to a flat surface. They further aver that no simple bulk model, such as those you propose can approximate the exchange of radiant heat among molecules.
If I understand Gerlich & Tscheuschner correctly (a big IF, I admit) their reasoning is that the existing models describe radiation of heat from hot surfaces to cold surfaces. Molecules do not have surface temperatures.
James, I’m not sure how we ended up talking about “flat-panel TVs, cell phones, and so on”
Most of the world lives in poverty, and millions die every year from ridiculous causes that are a thing of the past for us in the developed countries. I use the word ‘developed’ on purpose. It is a word that represents industry that brings such things as nutrition, employment, security, hospitals, antibiotics, emergency services, etc. The rest of the world is poised to join us, and will, if given access to the cheap readily available energy that brought us to this point.
The world needs our help, not our restrictions. This can be in direct conflict with the ‘end coal now’ movement.
http://rabett.blogspot.com/2009/03/burrow-project-gerlich-and-t-have.html
Hank Roberts wrote: “Sec, it’d help to cite to someone who’s actually doing the math on these issues.”
I have done so numerous times in previous comments posted to this site. I don’t have my references available this afternoon. What I need to do, I guess, is put up a site of my own with links to all the relevant studies and then link to that from my comments.
Hank Roberts wrote: “Without the numbers, it’s a profession of faith. With the numbers, it’s an investment plan.”
There is a reason that wind and solar are growing at record-breaking double-digit rates and attracting billions of dollars in private venture capital every year (Nanosolar was the top recipient of venture capital investment in the USA in 2008), while nuclear power is barely holding its share of electricity generation and nuclear corporations are lobbying to make the taxpayers and ratepayers pay all the costs of any new plants up front.
Barton Paul Levenson writes:
“You’d prefer a billion people to be without fresh water when the glaciers they depend on for it are gone? You’d prefer 100 million climate refugees when countries like Bangladesh are under water? You’d prefer massive starvation because of vastly increased droughts in continental interiors?
Because that’s what you’re going to get if you DON’T restrict fossil fuels. Period.”
I’m interested in what thought process brought you to that ‘period’.
What source of information convinces you that restricting fossil fuels will save these people from death and starvation?
Is there a way to know if these 100 million would-be climate refugees might be better prepared for flood and famine if they had jobs, transportation/roads, education/expertise, emergency services, healthcare, etc.?
In #257, secularanimist writes: “We neither need nuclear power nor is it an effective solution for reducing carbon pollution — especially in the time frame within which major reductions are needed.
Wind, solar, geothermal, hydro, and biomass — and of course efficiency and conservation — can do the job faster, better and cheaper.
So there is really no need to deal with the very real dangers and risks of nuclear power.”
I just sent off an article to my paper which implicitly argues the same thing. (see http://www.burgy.50megs.com/what.htm).
I’ve been reading some arguments, however, which assert that renewables cannot be brought on stream fast enough, or cheap enough, and so some kind of nuclear plants must necessarily be built. The latest book I’ve read on this is by Joseph Schuster BEYOND FOSSIL FOOLS. Joe argues for fast neutron reactors, which apparently solve the “not enough uranium in the earth” problem.
Joe writes in a “conversational tone,” which I find annoying; perhaps because of this I tend not to take the book seriously. But perhaps I should?
Burgy
> jobs, transportation/roads, education/expertise,
> emergency services, healthcare, etc.?
King Canute
http://www.cartoonstock.com/lowres/jpo0006l.jpg
Back to the topic for a moment if I may, and a question for any astronomers watching sunspots — does the change in clear sky visibility documented in the Science article require any adjustment for those trying to emulate the original sunspot counters’ methods and using contemporaneous tools?
I know there’s question about even those because they weren’t aware of some major volcanic eruptions, so their sunspot numbers were way low after the volcanos and they attributed the cooling to the change they observed — thinking it was the sun rather than Earth’s upper atmosphere that had changed.
Lots of factors hard to sort out.
Re 259
PART I:
The analogy works in so far as pointing out that while spontaneous net heat flow must always be from warmer to cooler, the heat flow depends on – in one case, thermal conductivity and convection; in another case, radiation. Each is a greenhouse in the idea that heat can be trapped, forced to build up to a higher concentration in order to drive a heat flux to balance heat production or inflow by other forms (solar energy).
The individual photons that travel from emission to absorption from cooler to warmer are what slows the net radiant flux from warmer to cooler. Although it also depends on the opacity of the warmer and cooler layers themselves, not just that of the intervening layers (see my other comments above).
At any given wavelength, the net radiative flux at any level depends on what is visible. If the air is very opaque, one cannot see very far, and thus, larger temperature variations are hidden; the radiation tends to be more isotropic (invariant over direction) and tends to have the intensity of blackbody radiation for temperature near or at the viewing location. At more moderate opacity, relative to distances across which temperature variations are significant, greater temperature variation is ‘visible’, so there will be a difference between radiant fluxes in different directions, and so there will be a net radiative energy flux. If opacity is very low, the net flux decreases because there are not sources of radiation. However, the surface of the Earth is generally quite opaque and has a rather low (not zero) albedo in LW wavelengths – hence high emissivity and absorptivity. Aside from the sun, space can be considered a perfect blackbody with very very low temperature (essentially zero) for climatological purposes.
PART II:
Yes, the downward LW (longwave, terrestrial – as opposed to SW – shortwave, solar visible, solar IR, and UV) radiation at the surface, by making the SW radiation smaller in proportion to the total downward flux (that upward LW and convective fluxes tend to balance, on average), reduce the diurnal variation in temperature near the surface. Direct solar heating is concentrated at the surface, which does not have a high effective heat capacity on land (it takes time for heating/cooling variations to penetrated downward), hence the temperature variation over short time periods; above the boundary layer (lowest layer of air that interacts more closely with the surface convectively and mechanically), diurnal temperature variations are small in the troposphere and at least most of the stratosphere because direct solar heating per unit mass is relatively small. Where the surface can emit more radiation directly to space or exchange radiation directly across a larger vertical distance within the atmosphere, the diurnal temperature range will be larger. It will also be larger if the air above is colder relative to the diurnal range of solar heating.
What has much greater control over the average surface temperature (globally, and averaged over at least short term cycles) is the radiative forcing at the top of the troposphere. This is because the surface and layers of tropospheric air are, globally and over time, convectively coupled – pure radiative equilibrium would make the lower atmosphere convectively unstable; moist convection tends to maintain vertical temperature variation close to a ‘moist adiabatic lapse rate’ (with regional variations from that). Thus, the greenhouse effect warms the surface and troposphere by reducing the net upward LW flux at the tropopause level for a given temperature distribution; the surface and troposphere tend to warm together (connected by convection) to increase net upward LW flux until it nearly balances the incoming SW flux, or in terms of climate change, until it balances the initial LW forcing plus any feedbacks.
PART III:
In practice, any cavity has walls that are made out of molecules.
Gas molecule spectrums can be different than solids, but the basic idea is the same; there are energy transitions that can occur with some average power depending on temperature. (Solids’ thermal energy can be quantized – phonons are quanta of crystal lattice vibrations, which can be either thermal or acoustic. At sufficiently high temperatures, semiconductors would spontaneously emit photons according to electronic energy levels as thermal energy excites electrons across band-gaps (although the band gap will change a bit with large changes in temperature and also with phase transitions, etc.), whereas at lower temperature, some electrical work is required to produce such luminosity as in an LED.
The surface of the Earth is opaque because it is not a sufficiently thin shell (with low enough refractive index, etc.) to be otherwise. At sufficiently small scales, the surface is not a surface, it is a field of atoms. At wavelengths where there is just sufficient opacity, the atmosphere looks like a surface on a large scale, although it will not radiate as a perfect blackbody because it is not isothermal across the visible depth – but at sufficiently high opacity, individual nearly-isothermal layers of air will act, radiatively, like surfaces. Individual molecules and particles can be assigned emmission and absorption cross sections according to the size of an idealized perfect blackbody they simulate – of course atoms and molecules do not actually have surfaces; nothing can on that spatial scale, but averaged over time and over molecules, they radiatively act, in terms of emission and absorption amounts, as the mathematical equivalent of little spherical blackbodies (assuming random distribution of orientations, as is ordinarily the case in a gas – otherwise they might be oblong).
“as the mathematical equivalent of little spherical blackbodies”
The size being a function of wavelength, among other things. More generally, when scattering is important, they would act like little spherical ‘greybodies’ of size and darkness being wavelength dependent. You will usually see the term ‘greybody’ in a somewhat different context, describing bulk materials with optical properties that are invarient with respect to wavelength, as opposed to redbody, bluebody, etc. Atmospheric scattering is important for SW radiation but is not of much importance to LW radiation under Earthly conditions.
… And greybody in the more usual context would not automatically imply that there is any reflection; I’ve seen it used to describe the hypothetical case of an atmosphere that absorbs the same fraction of radiation over a given distance at any wavelength within the LW portion of the spectrum. This is opposed to a blackbody in the sense that the atmosphere might not be perfectly opaque, but the emitted radiation would still be called blackbody radiation and it would obey the rules of blackbody radiation.
Patrick, I wish you’d put that in some topic where people could find it later and maybe use it. In this topic on China’s atmospheric efforts, it’s like crosstalk from the lecture across the hall. Are you writing this stuff off the cuff or pasting it in from something you’ve got all together in a page somewhere? I’ve seen chunks of it on other blogs too.
Patrick 027 wrote:
I believe that normally one would distinguish between the reflection, scattering, absorption and transmission, at least with bodies. And even with the atmosphere scattering would be an issue with clouds and other aerosols.
Patrick 027 wrote:
As I understand it, sometimes we refer to this as grey body radiation, indicating that the spectral emissivity is constant at all wavelengths, in which case one may simply speak of “the emissivity.” However, when the spectral emissivity is not constant, one can still apply Planck’s law to describe it by calculating its intensity at a given frequency as a function of temperature, but one multiplies that intensity by the spectral emissivity, where the spectral emissivity is the emissivity at the corresponding wavelength.
Of course one could argue that this is tautological if one defines spectral emissivity as the ratio of the intensity of thermal radiation emitted at a given frequency and temperature over the intensity of thermal radiation from a blackbody at the same frequency and temperature. And it should be noted that for a given material the spectral emissivity may change substantially as a function of the temperature.
But in any case, one may refer to a body which has a spectral emissivity that varies with respect to wavelength as a “realistic body,” and then refer to its thermal radiation as “realistic body radiation” or more simply as “thermal radiation.” This last is perhaps most appropriate as both blackbody radiation and line radiation (with zero width) are somewhat unrealistic, idealized cases, and to one degree or another all thermal radiation is “realistic.”
Speaking for the moment of China’s efforts to control atmospheric pollution, one recycling effort appears to have gone cattywampus — making artificial gypsum board out of the residue from capturing sulfate from coal plant smoke (a method used worldwide that, if the result is cleaned up, makes chemical gypsum; if not, it makes gypsum “plus”)
http://www.bizjournals.com/southflorida/stories/2009/03/09/daily63.html
More, generally, on air pollution in Asia with mention of China, here:
http://www.env.go.jp/earth/coop/coop/materials/01-apctme/01-apctme-013.pdf
excerpt:
“Page 1
1.3 Air Pollution and the Issue of Resources
1.3.1 Energy and Air Pollution
Air pollution is brought about by substances like sulfur oxides, nitrogen oxides, soot and dust, hazardous substance, dust, carbon monoxide, and hydrocarbon species emitted from stationary source like factories and mobile sources like motor vehicles. Most air pollution is accounted for by combustion reactions to fossil fuels, but much air pollution caused by improvements made in combustion has been eliminated. Air pollution problems are closely related to problems with energy resources, and those material industries which dircctlyemploy these resources have become a major issue.
Energy consumption in developing nations, as shown in Fig. 1.3.1, has been increasing rapidly in recent years. Energy consumption levels in 1993 were nearly three times those in 1973. Emissions of air pollutants like sulfur oxides and nitrogen oxides have also increased along with the increases in energy consumption levels. To be more specific, there are countries which do not have flue-gas desulfurization equipment and flue-gas denitrification equipment, countries like China which are generating grave air pollution problems, and countries which, if left alone, may develop problems in the future….
Re 271 – okay – agreed, although I tend to think of any thermally emitted radiation as being blackbody radiation, in the sense that this is the name of the ‘substance’ being deal with, regardless of the amount (relative to a perfect blackbody’s emission). Am I wrong to do that?
My introduction of ‘greybody’ was a bit clumsy – although different from its normal usage, I thought it a nice visual for what a particle with some scattering as well as absorption/emission cross section would ‘look like’.
Re 270 – pretty much off the cuff, except I did look up a few figures as I found myself wanting to discuss them. Some Te info came from USGS websites and an economics blog which I mean to identify, although I’ll have to get back to that.
I don’t have my own blog and I’m not sure that I am ready to have one, so…
David B. Benson wrote in 256:
True. However, locally the Asian Brown Cloud contributes substantially to warming trends.
Please see:
However, they note that globally at the surface it still appears to produce cooling. The warming is important, particularly around the Himalayas as it appears to be speeding up the melting process with regard to the glaciers.
They note that the Asian Brown Cloud appears to be largely responsible for the recent decline of glaciers in the Himalalyas.
Please see:
It has been projected elsewhere (by the IPCC) that the Himalayas may be 80% free of glaciers relative to the present) by 2030.
I also remember some time ago that Gavin noted it is a bit more complex thana given aerosol being warming or cooling as warming may be taking place at higher altitudes even when cooling is taking place at lower altitudes due to dimming. This is perhaps easiest to see in the case of aerosols which contain some carbon: reflective sulfate and nitrate aerosols which contain as little as five percent carbon will accelerate the melting process when they lower the albedo of snow, and as such, at higher altitudes and latitudes they may contribute to warming when elsewhere they are cooling due to their reflective properties.
Correction
I wrote in 275:
Actually Gavin was specifically referring to cooling near the surface due to dimming and warming in the mid to upper troposphere due to the absorption of radiation if I remember correctly, whereas I go on to discuss the effects reflective aerosols with some black carbon content (5% or above) upon ice and snow.
Re #266,
Hank, I’m a bit of a stargazer but too lazy to count stuff. However I don’t think haze, dust, etc makes much difference to traditional sun-spot counting. The reason I say this is that sun-spots are ‘backlit’ for want of a better term. If you can see the sun then you should be able to count the spots because the brightest source of light that would overwhelm them is the sun itself. Light pollution reflected off dust is really only a problem because it overwhelms the weak signals in the night sky.
I don’t know if they still use traditional counts from ground based observatories but regardless of how the count is done I’d imagine they just compare old observations with new using a ratio based on the two resolutions. Anyway, the people who collate all the sun-spot stuff for NOAA, etc go by the acronym SIDC
Michael writes:
Actually reading the relevant climatology literature. Start with the IPCC AR4 if you’re interested.
Because global warming will melt glaciers (is already doing so), cause more droughts in continental interiors (ask the Australians), more violent weather along coastlines (ask in New Orleans), and increase sea level (ask in Tuvalu). Were you unaware of all of this?
Hank,
Your cartoonist is illiterate. There is no ‘S’ in ‘Canute.’
Alan is correct in #277.
Though it’s not quite “backlit”. Optical depth=1 for visible light is higher up the atmosphere and because it’s a stratified atmosphere getting cooler as it goes up (until you get to the corona where temperature doesn’t really have any meaning any more since the gass is so diffuse) this means it is colder and so compared to the sun, darker.
It would still burn your fingers if you touched it.
But yes, the dust doesn’t stop you seeing sunspots until it’s thick enough to stop incandescence from the sun at 6000K getting through. A bigger problem is that seeing in sunlight is pretty bad: 5 seconds of arc seeing error is darn good in daytime anywhere. cf 1 second which is darn good at night anywhere.
Patrick: “I tend to think of any thermally emitted radiation as being blackbody radiation”
Actually, as you allude to later, thermal radiation can cause emission at a very high energy. Blackbody means that this energy is bounced around, shaken, split, added and subtracted to until it has been formed into a photon gas that has a generally black-body-curve distribution of energy.
The corona of the sun is given a “temperature” of millions of degrees. This (IIRC) is done by saying “well, what temperature would give the same intensity of emission as the peak emission of the corona”. So a very high “temperature” is given for thin emission media but the overall energy doesn’t obey Stephan-Boltzman law and, despite being millions of degrees (and E~T^4), the corona isn’t the source of most of the sun’s energy output.
(why and what is “spam in this message????? [edit – re-cipro-city])
But a gas at a per-particle energy of 1/40th eV can still have some particles at an energy of 1/10 eV or higher. And this can be the same as the excitation energy of a quantum state. If the temperature of the gas goes up, more of the gas is at the excited state. This excitation is not because of absorption of an IR photon (necessarily) but could be from an inelastic collision. Likewise, a loss of energy from a gas molec ule in this excited state can be lost not as an IR photon lost, but as an inelastic collision. The reciprocity principle demands it (which is where Kirchoff’s law comes from too: so you can’t just ignore it RodB).
And that doesn’t have to be from external or internal absorption of a line spectra, merely from the gas being warm.
Patrick 027
The ideal black body radiator, a cavity, is a theoretical construct. It does not exist. Its surface does not consist of molecules or anything else that is real.
re “(why and what is “spam in this message????? [edit – re-ci pro-city])”
Sheesh. I hope the spammers don’t start selling ecstasy..!
Alan and Mark write their opinions that atmospheric dust cannot have influenced sunspot counts. I’d suggest you guys publish. Here are links to a couple of the papers I was recalling. You’ll find others.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19980233233_1998361054.pdf
http://linkinghub.elsevier.com/retrieve/pii/S1364682699000553
Here’s a good general writeup on the methods of observation generally:
http://www.agu.org/pubs/crossref/2002/2002JD002105.shtml
snorbert #283:
How philosophical… reality doesn’t exist either, only our imperfect perception of it ;-)
Hey, you can build a decent approximation of a black body radiator by building a big cavity with a small hole in it. Not happy? Make the cavity bigger and the hole smaller. It will converge to the ideal BBR, irrespective of what material it was made of — that’s the whole point! Even an optically thick cloud of CO2 will do.
This gets the abstract for the first cite (Wilson) at the NASA technical server. (The abstract was abysmally OCR’d and not proofread but is readable.)
And this may be futile on a blog but I’ll try:
Please, guys, read the paper, it’s 36 pages, and don’t essay to debate me. Publish; it’s the author whose idea you disagree with.
http://ntrs.nasa.gov/search.jsp?R=992589&id=1&qs=Ntt%3DVolcanism%2C+%252BCold%252BTemperature%2C+%252Band%252BPaucity%252Bof%252BSunspot%252BObserving%252BDays%26Ntk%3Dall%26Ntx%3Dmode%2520matchall%26N%3D123%26Ns%3DHarvestDate%257c1
You’ll need the title if you search on the server:
Volcanism, Cold Temperature, and Paucity of Sunspot Observing Days (1818-1858): A Connection
Martin, 286, you’re right but that isn’t undoing what snorbert said. You even acknowledged it. You can get *arbitrarily close* to the ideal black body by making the cavity as close to completely enclosed as will make it work. But you can’t *get* perfect blackbody radiation from a cavity, since you still have to let the photons out at some point and that means there’s a chance that a photon will escape before thermalisation has happened.
Black body radiation from a cavity is an asymptotic extreme.
Your point that even if you make it of CO2 is a good one. RodB doesn’t seem to think you can make the cavity out of *anything* and as long as the photons spend long enough bouncing around in there, it WILL BECOME black body in form. The cavity walls don’t even have to be black. They can be mirrored. As long as the photon bounces around enough, it will be a black body cavity.
Martin Vermeer (286)
Gerlich & Tscheuschner disagree with you. They state that a cloud of carbon dioxide molecules at 300 ppm consists of just 8 million carbon dioxide atoms per volume contained by a 10-micrometer cube (10x10x10 micrometers). They go on to state, “In this context an application of the formulas of cavity radiation is sheer nonsense.” You may not agree, however you should explain the basis for your disagreement.
Snorbert, absolute horse puckey. Martin specified that the CO2 cloud must be optically thick. Why restrict it to 10 microns on a side. As long as the medium is optically thick in the wavelength band of interest, you will reach equilibrium and the photon gas will approach thermal equilibrium–for that band. Voila, blackbody radiation (or at least grey-body).
The fact that you even give G&T any consideration is proof that you don’t understand the relevant physics. G&T may well be the worst science paper ever written–and that includes the ouvre of Energy and Environment! It is so bad they should make it required reading in the 5th circle of hell! G&T is a joke and you are the punchline.
Ray Ladbury (290)
Gerlich & Tscheuschner calculated the molecules inside of a 10-micrometer box, which is approximately the length of an IR wave of interest in these radiation studies, merely to demonstrate the extreme dilution of carbon dioxide in the atmosphere at 300 ppm. I know the present day concentration is closer to 400 ppm, but that is not significant is it. I am referring to text on page 12 of the Gerlich & Tscheuschner article. Perhaps you should read it.
I have, from the beginning of my posts on this site, admitted that I am not an expert in the area of absorption and emission of IR radiation. You imply that you understand the relevant physics. If that is true, would you please read the Gerlich & Tscheuschner article and provide some specific and detailed analyses of what they have written? Name-calling and cutsie references to Hell and fifth grade reading do nothing to help me.
“Snorbert, absolute horse puckey. Martin specified that the CO2 cloud must be optically thick. Why restrict it to 10 microns on a side.”
Misreading Ray.
I read it as “at 10 microns the solid isn’t all that solid after all, so why is the solidity needed?” the answer being, of course “it isn’t”. A solid becomes optically thick at, say 30 microns. The earth’s atmosphere at 15um wavelengths becomes optically thick at, say 10m. The difference is the same: none.
Therefore “black body” applies just as well to an atmosphere with enough CO2 to be ~1000 optical depths (10km) as it does with a solid 3cm thick (1000 optical depths).
“Alan and Mark write their opinions that atmospheric dust cannot have influenced sunspot counts.”
Hank, a wee bit of advice to “the Link Man”: you can find a link that has someone telling you that there was a Tyrannosaur in the Garden Of Eden.
OK, a link doesn’t cut it.
The headline of the PDF:
VOLCANISM, COLD TEMPERATURE, AND PAUCITY OF SUNSPOT OBSERVING DAYS (1818-1858): A CONNECTION?
Which doesn’t mean there are days unable to see sunspots because the spots themselves are gone. Just that the sunspots can’t be seen (as you can’t see them if there’s a sodding big Cumulonimbus cloud in the way).
It’s talking about how many observing days there are.
Not how many sunspots can be seen.
Snorbert, why have you chosen to believe these two crank physicists (G&T), when it’s obvious that there’s absolutely no support for their trash in the physics community?
Physicists are making it obvious that G&T’s paper is dumber than cold fusion. I see no reason to disbelieve them.
I wonder what G&T’s explanation for a hot Venus is? Apparently its very existence violates the 2nd law of thermodynamics …
Mark, please read the article. Seriously, logic will only take you so far in refuting published work. Actually reading the article _will_ help you here.
And, look, Snorbert, the physicists writing here *have* provided some specific and detailed analyses as to why G&T’s article is crap, in particular the 10-micron cube not containing enough CO2 bit.
Mark (292)
Gerlich & Tscheuschner calculated the number of molecules inside of a box, whose dimensions approximate the length of the IR photon of interest. They then gave some reasons why they believe that the rules of radiation exchange between solid planes do not apply to volumes of such dilute mass. Martin said that he thinks that equations that describe the exchange of IR between solid planes do describe IR exchange among molecules of a dilute gas. I did not even disagree with Martin; I merely asked him to explain why he thinks what he said that he thinks.
dhogza (294)
I have not even said that I agree with Gerlich & Tscheuschner. I said that I find the article interesting.
Let me ask you a question that is similar to what I asked Ray Ladbury. Which physicists? Where can I find the articles?
[Response: Try here. – gavin]
dhogza (296)
I also am not convinced that Gerlich & Tscheuschner would disagree with the statement that IR absorption and re-emission by atmospheric gases can delay the emission of IR and thereby cause a temperature increase. I need to re-read some of the paper.
I am certain that they did say that the model of planar radiators and absorbers cannot describe IR exchange among molecules. They also have described some of the complexities of intermolecular IR exchange and have said that it the problem may be intractable.
They also have said that the IPCC methods overestimate the warming effect of carbon dioxide. Others have said the same thing; Gerlich & Tscheuschner attempted an explanation based on physical theory. Are they correct? I don’t know. Are they incorrect? I don’t know that either. I do know that no one has described any reasons why Gerlich & Tscheuschner are wrong.
Now I am going to concentrate on reading Arthur P. Smith’s proof of the greenhouse effect, one of the articles that Gavin offered as demonstration of the nonsensical nature of the Gerlich & Tscheuschner paper.
For starters, Ray Ladbury has a PhD in physics.
Snorbert:
Then why would the abstract claim:
?