Contrails and Climate – follow up

Water vapor contrails left by high-altitude je...

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Dr. Roger Pielke Senior writes:

Ben Herman of the University of Arizona has responded to the post…

News Article “Aircraft Condensation Trails Criss-Crossing The Sky May Be Warming The Planet On A Normal Day More Than The Carbon Dioxide Emitted By All Planes Since The Wright Brothers’ First Flight In 1903, A Study Said On Tuesday”

…with the following insightful information.

“I read your recent post concerning the possible effects of contrails on global warming. While the effect of contrails in low humidity atmosphere may be something to think about, such is not the case. The water vapor trails only occur  in a saturated, or near saturated environment, as witnessed by their presence being almost entirely limited to regions where cirrus clouds are present, or to regions in close proximity to cirrus clouds. The point here is, in such an environment, the water vapor and/or ice crystals already present are most likely absorbing a good deal of the IR radiation that would be absorbed by contrails in a dry environment. Therefore the increase of absorption is certainly quite limited. Of course a more thorough investigation of this is required for an accurate estimate of the actual effect of contrails, but this was apparently not considered, or at least not mentioned in the Reuter’s article you referred to in your blog.”

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The original WUWT version of the article can be seen here

Note: this thread will not discuss theories on “chemtrails”. Moderators, as in that previous article. please delete any comments that reference them even obliquely.

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45 thoughts on “Contrails and Climate – follow up

  1. The length and duration of contrails has long been one of my predictors for an approaching “warm” front, or higher humidity air mass, one that is a low rather than a high pressure mass. The source of the contrail is water, produced largely by the hydrogen content of the kerosene jet fuel in combination with the oxygen in air, at the rate of about 1.1 gallons of water per gallon of kerosene burned.

  2. The point of contrails is that they spread outwards over the sky from the initial jet-trails, thus clouding over a sky which otherwise would have remained clear. This both reflects sunlight away (via albedo), and keeps surface heat from radiating directly back into space. Not sure how the energy balance is affected in toto.

    Whilst true that the high-altitude sky must be near saturation for the contrails to spread, it is also true that the air is thin enough at that altitude that the water content is not great. So we are indeed talking about big effects from a small water budget.

  3. So the contrails are much more prevalent now than a decade ago (and the general population is very much aware of a marked change). This is a testament to the increased water vapor in the atmosphere. Is this increase in water vapor due to increased GCRs making more aerosols?

  4. “keeps surface heat from radiating directly back into space.”….Exactly how would contrails up at 30,000 or so ft with an outside temperature of say -50 degrees radiate heat back to earth???

  5. I never got why high clouds are supposed to increase warming whilst low clouds are said to cool. Surely any cloud reflects incoming solar energy back out into space. I see that clouds reflect energy back towards earth and thus delay some cooling, but if the clouds weren’t there then there would be more energy in the system.

  6. OK, reality check time. I took a look at the actual study, which is in Nature Climate Change. In 2005, they estimate the total forcing from all types of contrails to be about 31 mW/m2.

    Now, in the terms we are used to, that would be about 0.03 W/m2, or on the order of the contribution from geothermal heat.

    Have we really sunk this far, that Nature Climate Science and the mainstream media are hyperventilating about three hundredths of a watt per square metre?

    w.

  7. I thought after the 9-11 attacks, when air traffic was suspended for a few days the effects of less contrails was studied, and a net cooling was observed.

    Meaning contrails cool the day temps, and warm the night temps, like other clouds.

    My memory is fading of the details, so a Google refresh is in order for discussions of the 9-11 findings.
    -Jay

  8. Willis Eschenbach says:
    April 7, 2011 at 1:23 pm

    There are nations which have told the hyperventilators to mind thier own climate change business.
    India comes to mind as the most recent case.

  9. We might be wrong to assume that the contrail once it is produced stays where it is. I would think that the water from the combustion gases coming out of the reactors quickly condenses in a zone that is saturated already with water. I suppose that this saturation concentration is easily attained since at those sort of temperature water will easily freeze also. Those ice crystals will most likely fall down to lower altitude saturation zone and in the process seed the lower zones to form clouds. The seeding process is exothermic. It will warm up the atmosphere at that altitude. Would that heat escape to space more easily though?

  10. @Willis Eschenbach

    “Now, in the terms we are used to, that would be about 0.03 W/m2, or on the order of the contribution from geothermal heat.”

    Is that really all the heat there is from geothermal heat? I wonder though, how did they calculate as to how much geothermal heat is released beneath the deep deep sea, or did they as per usual not include that?

  11. But what about the heat from the jet engines? Maybe that’s the real source of all the warming?

    ;-)

  12. I have observed planes at altitude leaving long persistent contrails and everything in between down to contrails that last a few seconds to none at all. There are also plenty of photos showing contrails being produced by a planes wings passing through the air. This last phenomena is possible considering that a wing will lower the atmospheric pressure over it’s upper surface. As all flights at altitude will be conducted with much the same throttle settings from day to day, then, as stated by others here, it is the varying amount of moisture already in the air that determines whether contrail persist or not. If the burning of Kerosene at altitude is the main source of contrails then why are there days when none appear?

  13. “”””” Kevin B says:
    April 7, 2011 at 1:09 pm
    I never got why high clouds are supposed to increase warming whilst low clouds are said to cool. Surely any cloud reflects incoming solar energy back out into space. I see that clouds reflect energy back towards earth and thus delay some cooling, but if the clouds weren’t there then there would be more energy in the system. “””””

    It seems as if some climatists need to take a course in remedial geometrical optics.

    The sun from the point of view as a radiant energy souce, is a near point source. Well specifically it has an apparent angular diameter of about 30 minutes of arc, as seen from earth.

    If you put a cloud with some optical density, having an area of say one square Km, up at some normal cloud altitude, you will get a shadow on the ground of also about one square km area. If we make a simplifying assumption that any cloud height is small compared to the earth radius, and we are dealing with a one square km crossection area which is essentially parallel to the earth surface, then it is apparent, to anyone who can spell Euclidean geometry, that the shadow cast on the ground is also largely independent of sun angle. And for the leagal disclaimer, we are excepting fringe cases, like the sun on the horizon; shall we say a 10 AM to 2 pm sun.

    Now a tall billowy cloud of course will have a varying section with sun angle; but we are thinking here of a thin layer cloud; well something of contrail thickness.

    The actual ground shadow will have a penumbral edge dictated by the sun 30 min divergence angle. Otherwise the shadow is a replica of the cloud crossection; and within that shadow the sunlight reacvhing the ground will have been diminished because of scattering by the cloud. Well some would call it reflection; but it really is more of a refractive scattering; but seen from above the cloud it appears as a highly diffuse, perhaps 80% reflectance over the solar spectral range where say 98% of the energy resides. A thermometer reading the near ground air temperature in the shadow would report a lower temperature than one situated just outside the shadow.

    Now consider the LWIR thermal emission from the surface in that one square km shadow zone. If that surface were optically flat, say a quiet water pond or lake, the LWIR emission from the surface will be radiated in a Lambertian (constant radiance) angular distribution pattern whose radiant intensity would vary as cosine of the angle off normal to the suface. The total emitted power (Watts ) is just pi times the normal radiant intensity (Watts per steradian).

    A more realistic sample earth surface will have a randow oriented surface texture, each facet of which would be a separate Lambertian emitter, and the overall result, is an essentially isotropic emission pattern rather than a Lambertian one. The constant intensity should be half of the normal intensity for the Lambertian case. So the surface LWIR emission is extremely diffuse; and only a small fraction of that emission is going to get intercepted by that cloud. The higher the cloud is, the less interception of LWIR emitted from the shadow zone will be. There will be an inverse square of cloud altitude fall off in interception, as well as an obliquity factor (cosine^n). It would be cosine^4 for a Lambertian emission patetrn, but only a cosine^3 for the isotropic emission; which in any case starts off at half the maximum intensity.

    The lost sunlight due to that cloud is essentially independent of cloud height. The angular extent of the cloud as seen from the sun’s surface is near zero and it isn’t going to change with cloud height; but the interception of outgoing LWIR will and dramatically so, with change in cloud height.

    But we shouldn’t let a little geometrical optics get in the way of a good model.

    So if you think that high clouds warm the surface, and the higher the cloud, the more the warming; then I have a bridge I would like to sell to you.

  14. 1DandyTroll says:
    April 7, 2011 at 2:10 pm

    @Willis Eschenbach

    “Now, in the terms we are used to, that would be about 0.03 W/m2, or on the order of the contribution from geothermal heat.”

    Is that really all the heat there is from geothermal heat? I wonder though, how did they calculate as to how much geothermal heat is released beneath the deep deep sea, or did they as per usual not include that?

    That’s what the estimates are. You have to remember that for each geothermal “hot spot”, whether in Yellowstone Park or under the ocean, there are thousands of square kilometers of desert and prairie and ocean floor with almost no heat coming out at all.

    So the average is quite small. For example, think about the huge number of natural springs, and the tiny number of natural hot springs. The average temperature of all spring water is going to be only a few hundredths of a degree warmer than the average of just the unheated springs …

    They do include ocean-rift heat. However, as you indicate, the estimates of ocean-bottom heat are just that … estimates.

    w.

  15. This from NOAA and there ‘puzzlement’ as to why the 2002 Arctic melt was late even though there was evidence of ‘down-welling’ radiation.

    http://www.arctic.noaa.gov/essay_untersteiner2.html

    Observations from the North Pole in summer 2002
    The recently recorded data from automatic buoys and web cams represent a large, and very inexpensively obtained, increment of information about summer conditions in the central Arctic.
    The onset of melting usually occurs in early June, when the temperature reaches 0°C and the surface layer turns into a constant-temperature ice bath. In 2002, the temperature record shows an abrupt warming to about 0°C, on 24 May, suggesting an early arrival of the melt season. The warming event coincides with about a week of low short-wave (250 Wm-2) and high long-wave (300 Wm-2) down-welling radiation, which are typical of low overcast conditions. The web cam pictures of that period confirm the overcast. Both radiation and temperature values remained in the normal range for the rest of the summer, and freeze-up occurred as usual in the last week of August. Based on the early warming event in May, one may have expected an early onset of surface melting. Contrary to that expectation, the web cams show that it was not until late July 2002 when the snow cover took on a soggy appearance and isolated melt ponds appeared on the surface (Fig.2).

    For the rest of the summer, the web cam pictures show only insignificant melt pond coverage until the deposition of new snow in late August. The pictures clearly show that snow from the preceding winter survived the entire summer, and we must assume that there was no, or very little, ice ablation at the surface.

    Soviet (Russian) records suggest a small probability of an all-summer snow cover. But none of the U.S. ice camps experienced a persistent summer snow. In light of recent news about global warming and polar amplification, the all-summer snow cover of 2002 is clearly unexpected.

  16. Some question why the trails appear sometimes and not others. It would seem obvious that the trails are not caused by the release of water alone, but are caused by that AND the existing amount of vapour. If there is a lot already, a little more will cause a trail. If there is little, then it won’t.

    I think the statement:

    The water vapor trails only occur in a saturated, or near saturated environment, as witnessed by their presence being almost entirely limited to regions where cirrus clouds are present, or to regions in close proximity to cirrus clouds.

    explains that fully.

  17. @Willis Eschenbach

    “They do include ocean-rift heat. However, as you indicate, the estimates of ocean-bottom heat are just that … estimates.”

    Thanks.

    How do they, or you, rate the quality of those estimates?

    I wonder because I got astound the other week (looking up submarine volcanos) at the ignorance, as in lack of knowledge but ignorance no less, of the amount of active, as in venting pressure, submarine volcanos per year. There’s about 70 surface volcanos going cranky each year but, apparently, thousands to tens of thousands submarine volcanos blows a fuse each year. Nobody seem to know, which, appear to, indicate that nobody really knows wether an earth quake out to sea is really an earth quake or a volcano who vents its pressure. However, though, if there’s tens of thousands of active submarine volcanos (as in like “active” surface volcanos) then there could exist millions of submarine hot vents, hot springs, and them critter crawling chimneys. And, apparently, even in the arctic and antarctic regions volcanos have been highly volatile active without people being the wiser, so if they haven’t been able to account for what has been under their own shoes how much quality is their assumptions of whats out beneath the deep blue, I truly wonder.

    An old submariner use to say that it is mandatory to know the onion layers that is the temperature of the oceans, now I wonder where does all the heat that constitute those layers really come from for surface temperature can’t seem to include the necessary ingredient to form layers.

    And, of course, heat goes up and eventually escapes to the freezing freedom of the outer space. Heat rarely travels the other way. :p

  18. If contrails are like clouds they will have a negative forcing. This was demonstrated after analyzing the temperature increases around various cities after grounding of aircraft due to 9/11. This article from ..ugh.. CNN in 2002. http://articles.cnn.com/2002-08-07/tech/contrails.climate_1_contrails-cirrus-clouds-david-travis?_s=PM:TECH
    >> During the three-day commercial flight hiatus, when the artificial clouds known as contrails all but disappeared, the variations in high and low temperatures increased by 1.1 degrees Celsius (2 degrees Fahrenheit) each day, said meteorological researchers.<<

    Whether they cause the globe to warm is a net energy gain issue. Good luck with that.

  19. Jay says:
    April 7, 2011 at 1:33 pm
    I thought after the 9-11 attacks, when air traffic was suspended for a few days the effects of less contrails was studied, and a net cooling was observed.

    Meaning contrails cool the day temps, and warm the night temps, like other clouds.

    My memory is fading of the details, so a Google refresh is in order for discussions of the 9-11 findings.
    -Jay

    This was some measurements done by some NASA researchers who didn’t bother to check the weather. As people will remember 9/11 and the subsequent days were bright clear days as there was a large dome of high pressure settled over the Eastern US with very dry air. The effect of this type of weather is to significantly lower temperatures at night and early mornings as there is no water vapor acting as the ‘green house gas’ (sic). The presence or absence of the aircraft would not affect the forecast temperatures with this type of weather system.

  20. Ok, so if the contrails are causing so much warming … how come it isn’t warming? If you would consider that the US probably has more contrails than anywhere else on the planet, why has the continental US temperature been dropping like a rock since 1998?

    Nice hypothesis but for the “it isn’t warming” part.

  21. Ok. Why don’t we just put this contrail thing to rest with a few very simple experiments?? There’s got to be a hungry atmospheric physicist out there with a good grant proposal talent, and a funding agency, like NSF, NASA, DOE, or even the EPA just dying to fund a project to prove contrails create warming.

    You contract a jet and instrument it to fly at altitude, in the right conditions, and make a contrail. While it’s on it’s initial pass, you’re measuring broad-spectrum radiation hitting the top and bottom of the aircraft and simultaneously creating the contrails. You turn the plane around, fly just under the brand new contrail you’ve created, and measure the radiation hitting the top of the aircraft that’s below and shaded by the contrail, then compare the two values. Just for fun, fly back over the top of it and measure the upward reflected radiation and integrate that into the mix.
    Let’s quantify this.

    $300,000 grant anyone???

  22. Have I missed something?

    Since when do contrails make clouds that spread out over the entire sky?

    “The fact that we can not account for what is happening in the climate system makes any consideration of geoengineering quite hopeless as we will never be able to tell if it is successful or not! It is a travesty!”
    – Kevin Trenberth

    This famous quote tells us they are, at the very least, considering geoengineering.

    ..but, what if, they have already started geoengineering.

    Would it really be that big of a shock?

    It also changes the calculations on the effects of these contrails because, we are not just dealing with water vapour, there will be other particles in these geoengineering clouds that will need to be considered.

    Would it make a difference if there was aluminium particles those clouds?

    For most of us we can use an extract of Kevin’s quote and say:

    “We cannot account for what is happening in the climate system” full stop

  23. Jer0me says:
    April 7, 2011 at 4:00 pm

    If you have the chance to observe contrails in an unstable atmosphere (with globs of dry and wet air) you will see broken lines as the jet enters/leaves the moist air.

  24. Isn’t the major contrail effect going to be to the albedo? If so, then satellite image analysis ought to give the answer.

    It could also give evidence in the case of clouds being part of the feedback loop. With increasing contrails should we see a compensating decrease in natural cloud formation?

  25. “””The water vapor trails only occur  in a saturated, or near saturated environment, as witnessed by their presence being almost entirely limited to regions where cirrus clouds are present, or to regions in close proximity to cirrus clouds. “”””

    Utter tripe.

    I fly through contrailing regions every day, and they are most certainly not all associated with natural cirrus cloud. Most of the cirrus, is actually spread out contrails from previous aircraft. This is doubly so when one considers that most aircraft fly above the natural cirrus levels. At 38 – 42,000 ft, we are very rarely in any natural cloud formations, apart from spreading CBs – but they do not last too long.

    Contrailing occurs where there is a saturated atmosphere that will sustain the vapour from the engine for a reasonable period of time. So most contrails are entirely man-made and are an additional factor on the weather/climate.

    Since most flights are scheduled in daylight hours, it would seem axiomatic to me that the net effect of contrails should be a cooling of the earth.

    .

  26. Since we are hyperventilating about atmospheric events lets consider lightning. Commercial aircraft are struck on average once in every 5,000 to 10,000 hours of flying time.
    France has an electronic lightning detection network, Meteorage, that records some 800,000 lightning bolts that strike the ground each year. That is just in France!
    A short description of lightning that occurs in thunder clouds:
    “The electric current that flows, astronomically high and virtually instantaneous, heats the air in the leader channel to a temperature greater than 30,000 degrees C (55,000F), four or five times the temperature of the surface of the Sun. The initial expansion of the air produces a pressure 100 times normal atmospheric pressure and a shock wave heard as thunder.”
    Bear in mind that all that energy was TRANSPORTED UPWARDS from the surface by molecules of water vapour.

  27. Ralph says: April 8, 2011 at 12:23 am
    Utter tripe (about contrails at cirrus cloud levels).

    Yeah, have a look at the images of the contrails given above by
    Stephen Skinner April 7, 2011 at 3:13 pm

    Notice how much is coming from the engines and how much from the wings and bodies of the aircraft. Is it not simplistic to say the kero done it, gallon for gallon, when there is ample visual evidence of pressure changes causing nucleation? So, what nucleates cirrus clouds lower down? I do not know, but I do know an incomplete explanation when I see one.

    Remember, until recent camera on tail devices, most pilots could not see where the contrails from their own aircraft originated, engines or wings. Sometimes you can see shadows way down below you and sometimes you can see 2 lines from a twin and 4 lines from a Jumbo. But this does not prove that the engines did it with their kero.

    Seems to me that a contrail arises from the temporary pressure disturbance of a tiny amount of energy deposited by a passing aircraft and that its effect on global temperature is about nil. Try looking up at the sky in Central Australia and buying yourself a Fosters if you see a contrail. MAAN! (Much Ado About Nothing).

  28. Today over southern England vapour trails are short and completely dissipating between 5 and 10 secs. This must mean all the airliners are cruising with engines throttled right back?

  29. Willis Eschenbach says:
    They do include ocean-rift heat. However, as you indicate, the estimates of ocean-bottom heat are just that … estimates.

    Estimates….perhaps UNKNOWN is more appropriate…
    Like so many other parameters in the real work energy budget.

    This is a short series of two posts that discusses Three-Valued Logic (3VL) and uses it to demonstrate how irreproducible results corrupt not only the scientific work in which they appear, but also spread that corruption to any related work. In short, this series of posts demonstrates that irreproducible results are viral.

    http://magicjava.blogspot.com/2010/04/three-valued-logic-and-irreproducible.html

  30. From my layman’s POV, this is the way I understand contrails, and please correct me if I’m wrong because I’m here to learn :):

    Below freezing temperature + Supercooled Water (metastable water below the freezing point) + Relative Humidity Over Ice (RHI) > 100% + Seed Particles (Nucleus) = Ice.

    Reference: http://www.rhsystems.net/papers/RH_WMO.pdf

    All of the above + engines from an aircraft generating the seed particles and the water that is then quickly supercooled = contrails.

    Low air pressure at high altitudes, although related to water vapor, is not a prerequisite for contrails, as they can form at very low altitudes given the above requirements. It is well documented that in the 1940’s piston powered aircraft routinely generated contrails over Europe, and their flight levels were generally between FL180 and FL250 feet.

    It seems counter-intuitive to me that ice crystals at high altitudes should create warming. The opposite should be true but I don’t have enough knowledge on the subject to make that determination.

    Best,

    Jose

  31. Jose Suro says:
    April 8, 2011 at 6:28 am
    “…It seems counter-intuitive to me that ice crystals at high altitudes should create warming. The opposite should be true but I don’t have enough knowledge on the subject to make that determination”

    Indeed
    I remember an earlier IPCC report on aviation that actually used the words “clouds heating the surface”. The report admitted it could find no affect to the environment caused by aviation. However by putting various projections together they were able o show that aviation was going to be serious threat to the enviornment by 2050. The only thing that could be pinned on aviation were the contrails and thus the idea that clouds heat the ground, and the word used was ‘heat’.

    I found this in Wikipedia on Cirrus clouds and their effect on climate:
    “When cirrus clouds are only 0.1 km (0.062 mi) thick, they reflect only around 9% of the incoming sunlight, and yet they prevent almost 50% of the Earth’s emitted infrared radiation from escaping. This raises the temperature of the lower atmosphere beneath the cirrus clouds by an average of 10 Kelvin (18 Rankine).”
    This is a very careless comparison as the heat coming in is much more than that going out, so this is an apples and oranges comparison. In addition does reality confirm this?

  32. I just pulled up a google satellite view of my area. There’s a huge military base and very busy international airport. Not a contrail in the sky in the sat photo. Going outside just now with the base 50 miles north and international airport 22 miles south it’s maybe 50% cloudy. Good contrail conditions. The contrails not occluded by clouds above can’t possibly occupy more than a percent of my view of the sky and this is prime time for them.

    Nothing convinces me that on a global basis contrails occlude any more than a tiny fraction of otherwise clear sky. Nothing convinces me that contrails have a warming vs. a cooling effect in the first place. Contrails are generally considered aerosols and ostensibly have a cooling effect:

    http://en.wikipedia.org/wiki/Global_dimming#Causes_and_effects

    I’m gonna have to call bullshit on any notion that contrails have any significant effect on global climate and in some restricted locales with frequent good conditions and plenty of air traffic to generate contrails they actually have a measurable cooling effect which was noted in a few places over the US when all air traffic was shut down for 3 days following 9/11/2001.

  33. >>Geof
    >>Yeah, have a look at the images of the contrails given above by
    >>Stephen Skinner April 7, 2011 at 3:13 pm
    >>Notice how much is coming from the engines and how much from the
    >>wings and bodies of the aircraft. Is it not simplistic to say the kero done it,

    Those images are very rare, and I suspect are low level images in humid climates.

    In the upper atmosphere the air is very dry, and I have never seen condensation from the back of a wing from an aircraft passing over or under us, when at cruise altitude. The only contrails are from the engine exhaust.

    .

  34. This is the link into the wikipedia article which specifically mentions contrails.

    http://en.wikipedia.org/wiki/Global_dimming#Probable_causes

    I think it was already mentioned but commercial jet contrails are ice crystals. Nowhere on the planet is 30,000 feet (10 kilometers ASL) not somewhere south of fifty degrees C below zero.

    What’s having more of an effect is Mexico’s slash & burn agriculture hundreds of miles to the south dimming the sky here quite noticeably for the past several days. Once in a while under the right conditions it can turn the whole sky a light brown.

  35. The photo of an airplane trailing dark squiggly lines off of its wingtips, in the Print view of the Reuters article, looks more like what is often seen on approach. (Note the landing lights are on, and the flaps are well extended.)

    Those are from the wingtip vortices, whereas contrails are from engine exhausts!

    (That airplane’s engines are on the fuselage, visible just above the landing lights – nothing visible from the engines.)

    Reuter’s blows it again.

  36. “”””” Stephen Skinner says:
    April 8, 2011 at 8:23 am
    Jose Suro says:
    April 8, 2011 at 6:28 am
    …………………………………
    ………………………………..
    I found this in Wikipedia on Cirrus clouds and their effect on climate:
    “When cirrus clouds are only 0.1 km (0.062 mi) thick, they reflect only around 9% of the incoming sunlight, and yet they prevent almost 50% of the Earth’s emitted infrared radiation from escaping. “””””

    “”””” “When cirrus clouds are only 0.1 km (0.062 mi) thick, they reflect only around 9% of the incoming sunlight, (THAT HITS THEM) and yet they prevent almost 50% of the Earth’s emitted infrared radiation (THAT HITS THEM) from escaping. “””””

    So let’s do the math again. Wiki says the thin cirrus prevents the escape of “nearly” 50% of the outgoing LWIR. Well of the radiant energy that is absorbed by the cloud, about half escapes, and half returns, since the cloud re-emission is isotropic; so either wiki is saying the thin cloud absorbs “almost” 100% of the earth emitted LWIR, or else they are saying the cloud captures “almost” 50%; of which half returns, and half escapes, so only 25% of the total emission is prevented from escaping.

    NOTE !! for the incoming sunlight, that 9% is REFLECTED , not ABSORBED, so ALL of that is a loss to the earth.

    So now we have 9% incoming loss to 25% outgoing retained (2.8 to one) unless they mean 9% incoming loss to 50% outgoing retained, and 100% cloud absorption of outgoing (which is about as likely as the sun rising in the west tomorrow morning).

    BUT !! that 9% is the REFLECTION LOSS. What about the direct absorption loss of incoming sunlight by the cloud between 700 nm and 4.0 microns wavelength; that can be as much as 20% of the solar spectrum energy (absorbed by water). Well by the same argument as above, only halfg of that energy is a net loss, since the re-emission in the LWIR spectrum is also isotropic, so half escapes, and half reaches the ground; NOT AS PENETRATING SUNLIGHT, BUT AS SHALLOW ABSORBED LWIR. But still the cloud attenuation of incoming sunlight is clearly greater than 9%, because of the absorbed fraction.

    So that 2.8 ratio is a max for out/in cloud interference.

    Remember Trenberth’s cartoon global energy budget. It starts out with a 4:1 ratio between WHAT REALLY IS COMING IN, and the number in Trenberth’s picture; so the incoming sunlight that hits the cloud and is reflected, is really four times higher than Wiki’s number; so that 2.8:1 max ratio, now looks more like a 0.7 :1 out/in ratio.

    Ooops !!! I almost forgot; the sun only shines on one half of the earth surface at a time; whereas the surface radiates 24-7, so the incoming sunlight blockage is only active half the time, so the 0.7:1 ratio should be moved back up to 1.4 :1, out/in. since the incoming is blocked only half the time of the outgoing.

    Well there is another problem for that outgoing blockage. The outgoing emission is essentially isotropic, so it is spread over 2 .pi steradians of solid angle, whereas the incoming sunbeam is 0.5 degrees total divergence. The cloud shadow on the ground is essentially the same as the area of the thin cloud layer, and blocks its percentage of the incoming sunlight over that same cloud shadow area on the ground. The outgoing emission from that shadow zone nearly all completely misses the cloud; and the higher the cloud layer is the smaller the fraction of the outgoing energy, that hits the cloud; and remember that the cloud only interracts with the radiation that hits it.

    So there’s a big attenuation factor now in favor of blocking incoming over outgoing; and you can clalculate that yourselves for whatever cloud height you want.

    Now the cloud will also block some oblique LWIR emissions from the rest of the surface outside the shadow zone; but there’s a cosine^4 th obliquity attenuation, and of course the inverse square of cloud altitude fall-off as well. For a Lambertian emitted radiation pattern (from an optically flat surface) the total flux is pi times the axial (normal) intensity; but for an isotropically 4emitting surface, the axial intensity drops by another factor of two because of that 2 pi steradian solid angle.

    So don’t believe that 5.5 to one factor of outgoing LWIR interception to incoming sunlight reflection; the cloud can only absorb what hits it, and most of the energy going out down’t hit the cloud. For a complete cloud layer over the entire surface, you still get that factor of 2 pi lower diffuse absorption verus direct beam absorption for the incoming sunlight; and of course the sunlight absorption would now be 24 hours per day as well, instead of 12.

  37. It is simple. We pilots have a control knob specifically set up to adjust the size and duration of a contrail. Bigger engines, bigger contrails. More engines, more contrails. Bigger plus more is directly proportional to contrail exaggeration. Thus, the contrail exaggeration controller, or CEC. How else could the poor schmuck behind you find their way? And at night or instrument meteorological conditions (IMC) , we use special color coded injections that glow, but only can be seen through the specialized eye wear device (SEWD) that only pilots can acquire.

    I hope this “clears the air” regarding contrails. (I waive my usual fee)

  38. My memory of digging into contrails a couple of years ago to counter an idiot conspiracy theorist is that they are caused by soot particles in the exhaust, and newer engines are cleaner so not nearly as likely to generate contrails.

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