From the American Geophysical Union weekly highlights:
Estimating climate effects of contrails
In a new study, Voigt et al. directly measured ice particle sizes and numbers in 14 contrails from 9 different aircraft of the present-day commercial fleet, including the largest operating passenger aircraft. They obtained an extensive data set of contrails from which they determined the contrail optical depth, a measure of how much light is attenuated by these man-made clouds.
They use their measurements to estimate that the radiative forcing of line-shaped contrails is about 15.9 milliwatts per square meter, which represents a small positive contribution to the anthropogenic global warming. Yet an expected doubling of aircraft passenger transport within the coming two decades will enhance contrail effects on the atmosphere. The detailed contrail measurements will help modelers working to assess the actual and future impact of aviation on climate.
Source: Geophysical Research Letters, doi:10.1029/2011GL047189, 2011
http://dx.doi.org/10.1029/2011GL047189
Title: Extinction and optical depth of contrails
Authors: C. Voigt: Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt, Oberpfaffenhofen, Germany; and Institut für Physik der Atmosphäre, Johannes-Gutenberg University, Mainz, Germany;
U. Schumann, P. Jessberger, T. Jurkat, and A. Petzold: Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt, Oberpfaffenhofen, Germany;
J.-F. Gayet: LaMP, University Blaise Pascal, Clermont-Ferrand, France;
M. Krämer: IEK-7, Institute for Energy and Climate Research, Forschungszentrum Jülich, Jülich, Germany; T. Thornberry and D. W. Fahey; Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA.
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Some basic science behind contrails from http://cimss.ssec.wisc.edu/wxwise/class/contrail.html:
The condensation trail left behind jet aircrafts are called contrails. Contrails form when hot humid air from jet exhaust mixes with environmental air of low vapor pressure and low temperature. The mixing is a result of turbulence generated by the engine exhaust. Cloud formation by a mixing process is similar to the cloud you see when you exhale and “see your breath”. The figure below represents how saturation vapor pressure varies as a function of temperature. The blue line is the saturation vapor pressure for ice as a function of temperature (in degrees Kelvin). Air parcels in the region labeled saturated will form a cloud. Imagine two parcels of air, A and B as located on the diagram. Both parcels are unsaturated. If B represents the engine exhaust, then as it mixes with the environment (parcel A) its temperature and corresponding vapor pressure will follow the dotted line. Where this dotted line intersects the blue line is were the parcel becomes saturated.
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NOTE: Any commenters that discuss or link to “chemtrail” discussions will have the comment automatically deleted. No exceptions, and no, I don’t care if it upsets you – Anthony
Wow, I had to look up what Chemtrails was. That was good for a laugh. Thanks.
Otherwise, a good step in the right direction for actual science.
Oh come on. Aren’t there more important problems to deal with?
I guess it’s nice to know even if I never use the information again, I’m interested though in how they measured particle size, etc. Also interested that they studied contrails for the effect on light, but what about regular H2O emissions from jet aircraft? The moisture is still put into the atmosphere whether contrails are formed or not.
I’m skeptical about contrails having much effect. I don’t remember ever feeling cooler from a contrail passing in front of the sun. I usually feel cooler as a cloud passes in front of the sun.
Also, did this paper take into account that most flights are during daylight hours? In the case of cirrus clouds the warmist claim is that the surface heat relected is more than the sunlight lost because clouds reflect heat 24 hours, but only reflect sunlight for 12 hours. That wouldn’t apply to contrails.
Chemtrail, chemtrail, chemtrai….this is a test.”
[Thin ice ahead. ~dbs]
Would a giant tinfoil hat protect the planet from contrails?
Look up in the sky anywhere on earth and you don’t see a lot of contrails at any time. Are contrails another butterfly effect?
air of low vapor pressure…..
No, not really. They should have written “low pressure”. The “vapor pressure” isn’t relevant until the jet exhaust mixes with the cold, low pressure air. In fact, the lower the vapor pressure of the air, the more water must be in the jet exhaust to make a mixture that will condense the vapor from the jet exhaust.
“but also by preventing terrestrial radiation from escaping the Earth’s atmosphere. ”
WHEN I see some empirical evidence of this ?crap? then I will agree with the corrupt and unsubstantiated false “consensus.” This simplistic idea simply does not hold water, as shown by the last 10-15 years’ data. And logic!
Just to be more pedantic, I should have written, “vapor pressure of the water in the air”.
“NOTE: Any commenters that discuss or link to “chemtrail” discussions will have the comment automatically deleted. No exceptions, and no, I don’t care if it upsets you – Anthony”
Why not?
What happened to open scientific debate?
I am old enough to know for a fact that jets did not always leave lines in the sky.
I do not know for sure but it feels like this has climate related implications (geoengineering).. why not discuss it?
[Reply: As guests on Anthony’s site we should respect his wishes. Also, chemtrails discussions tend to get completely out of hand. ~dbs, mod.]
wow geoengineering for free!
Ok so if we don’t use the aviation fuel (it’s part of the oil), we’ll have to burn it off, so is it better to use it and fly around or just get a smoke stack and burn it in the air.
The Note at the top made me laugh, about the Chem trails LOL!! This thread would become Chem Trail city ROFL
I’ve yet to be persuaded that the “downward reflection” exceeds the upward. Selective albedo is a pretty tricky characteristic to prove and quantify, IMO.
I think some wise person said a little knowledge is dangerous. I guess that is true if one acts on the little knowledge on the assumption it is some how greater then reality. I guess a little is just that a little ice.
Dammit, I have been asking this same question for about 5 years now, and still don’t have a decent answer: WHY is it hotter in Phoenix than in Atlanta in the summer, when Atlanta has more than three times as much greenhouse gases as Phoenix? Day AND NIGHT!. Same latitude and elevation. Where can we actually have some empirical evidence about that mythical? damn “greenhouse effect?”
Those things cause Global Dimming. Haven’t ever of GD? It’s the next big thing to destroy the Earth! Watch this BBC documentary and then go promptly into hysterical mode!
What does that warning about comments mean? I understand moderators hate seeing the same thing over and over again, but since I’ve never heard of the term and probably many others haven’t, maybe a slightly more thorough explanation makes sense.
“I am old enough to know for a fact that jets did not always leave lines in the sky.” (ShaneCMuir, June 23, 2011 at 7:31 pm)
Careful, Mr Muir, you might be dating yourself here. Actually, even fast prop planes, going back to WW I, will leave distinct and long con trails under the right temperature and air humidity conditions. Dirigibles won’t, though 🙂
ShaneCMui doesn’t think contrails were generated in the past…
The fact is that even piston powered aircraft generate them. B17 bombers generated contrails over Germany. That, or the USA was violating the Geneva convention. You must be old enough to remember that!
Jae:
I would guess it is hotter in Phoenix because it is surrounded by the desert, and air there isn’t exchanging much, whereas Atlanta is near the ocean, and there is always a breeze. In short, Phoenix has a ventilation problem.
@Mark: Try Google.
You do know that all those small fighter/bomber military type jets don’t have on board latrines, right? They add a tiny bit more moisture to the atmosphere occasionally.
ShaneCMuir says:
June 23, 2011 at 7:31 pm
I am old enough to know for a fact that jets did not always leave lines in the sky.
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Thats right, because prior to the late 1960’s commercial jets didn’t have enough power to fly above about 27,000 feet (if I remember correctly from my time at a jet engine manufacturer). Therefore, the atmospheric pressure was generally too high to form contrails. Now almost all flights of any length have a cruising altitude above 35,000 feet.
Correct Wilky. Contrails were a big issue for the USAAF in WWII. The were a dead giveaway for German air defence.
Moving on, in Europe last spring there was about a month of clear skies and zero aircraft/zero contrails. The data must exist for a nice study in min/max temperatures.
Why is this not a zero-sum game? If the same contrail blocks incoming (reflects back into space) and blocks LWIR outgoing, then the result should be a NULL. If it is not, and something needs to be done about it, reformulation for a NULL effect should be pursued. Seems to me that is what research is for.
I’m not so sure about Jet traffic doubling, what with a global economic downturn and high prices for fuel. People are getting fed up with all the fees and extra charges that have no end in sight. Then you toss in all the inspections, and the Friendly Skies are not so pleasant anymore.
Thanks for the lovely video, Gee Willikers. The carbon tax isn’t working out as planned, and the UN has been hinting about a global air transport tax. This must be the intro to the next revenue harvest. Con Trail Credits, coloquially to be called con jobs. This is becoming banal, I’m almost wishing they’d cut these expensive and no longer interesting melodramas, jpointed a gun at our heads and just helped themselves to our wallets.
“Any commenters that discuss or link to “chemtrail” discussions will have the comment automatically deleted. No exceptions, and no, I don’t care if it upsets you – Anthony”
Good for you. Don’t apologize for having comment policy standards that differ from those which others might wish for or find appropriate for other venues.
As for the contrails, it is cool that there will be opportunities to observe specific changes in the trails over time and compare them with effects over the same period. Of course, it sounds like it will be challenging to separate different causes and effects from the mix. But then, if research into more efficient engines causes the water to stay in gas form until it is too disperse to form as many droplets the opportunity might be short-lived.
I believe that right after 9/11 while all flights were grounded, some enterprising scientists did a series of measurements to test the effect of contrails. It was their one opportunity to measure the before and after effects in a short time frame. I thought they decided that the contrails cooled off the day and warmed the night by a small amount. Bing search time ….. after my root beer float.
@Dennis Nikols:
The wise person was Alexander Pope and he actually wrote:
” A little learning is a dangerous thing”.
“The detailed contrail measurements will help modelers working to assess the actual and future impact of aviation on climate.”
[sigh] The purpose of this press release is revealed…
Ahhh, that was nice. Well, my quick search revealed that there was a temperature check after 9/11 and a temperature change. The questioned remained, however, was it the contrails or just a weather pattern? Unfortunately, the experiment cannot be run again until the next national emergency.
In regard to contrail formation, I would like to take a guess as to the dynamics as follows. Please correct me if I am mistaken.
The warm engine exhaust (think a long string) absorbs moisture from the immediate surrounding air (think long tube) and quickly cools forming condensation or ice. Turbulence from wing lift/tips causes some mixing and assists in condensation formation.
Just change in properies of existing moisture. Nothing added but heat and pressure change.
A CLOUDY night sky vs a CLOUDLESS night sky and the effect on GROUND TEMPERATURE? (demonstrating cloud IR reflectivity)
But, you reject this form of evidence … no?
.
Speaking of water droplets/ice crystals in clouds or contrails…
I recently read that a plant’s total photosynthesis was more efficient on cloudy days because, while there is less light falling on plant surfaces directly in line with the sun, more light hits surfaces that are obstructed by other leaves and branches and such. Why do heat waves not do the same as the visible spectrum so that, while sun-facing surfaces don’t get as hot, surfaces that would have been in shadow get more heat waves? If this happened, wouldn’t cloudy days (not thick rain clouds–just overcast) be nearly as warm as sunny ones, at least near ground level?
Contrails probably have more effect when they trigger the formation of a cirrus deck. I saw this once at Douglas County Airport, Minden, Nevada. Clear blue sky, a couple of jets flew over making contrails which then spread out and we had 8/8 cirrus after that.
Has aviation fuel changed over recent years in such a way that the contrails are being formed differently in atmospheric conditions that in the past would not have lead to their formation?
Any increase in the size or lasting duration of present day contrails might be a result of changes in the newer engines or fuel now being used. Is it possible that both improvements would cause better utilization of less fuel and therefore maybe increase the amount of water vapor leaving the engines?
Global dimming is not a problem. It’s global dumbing that we should be concerned about. And the BBC is the hot spot of global dumbing.
Corr: @Wilky, not “Shane”. It’s conspiracy theory stuff, about spraying poisons and bioagents, etc.
Hmmm … not everyone growing up necessarily saw contrails – until later in life it turns out.
From: Contrail Confusion is Nothing New we have this account and reasoning:
…
Back in the 50′s in America, contrails were a fairly rare sight in many parts of the country. Air travel was a fraction of what it is now, commercial jet travel did not start until 1958, and military operations were generally limited to particular areas. So it was not surprising that when someone noticed a contrail for the first time, they might think it to be unusual.
This account from 1951 reads almost exactly like the misunderstanding of current contrails:
Galveston, Texas, Sunday, October 28, 1951, in The Galveston Daily News:
– – – – – – – – – – – – – – – – – – – – – – – – – – – –
See also a photo of B-36 contrails at 37,000 feet, from the Operation Teapot nuclear tests on 6th April 1955 at the link above.
.
Jea, it might be:
A) Atlanta has a lot of trees, clouds and rain while Phoenix has more sunshine, brown dessert and very little rain.
B) Phoenix sits in a valley that blocks W/E winds while Atlanta sits on a Plateau at the foothills to the Smokey Mountains.
Or both.
Any comments?
Bill
Higher ‘bypass’ (bigger fanjet) engines perhaps in the newer engines – leading to larger volumes of ‘air’ in which the vapor trail may form? Just looking for a working hypothesis …
http://en.wikipedia.org/wiki/Turbofan#High-bypass_turbofan
Partial excerpt:
High-bypass turbofan
The low specific thrust/high bypass ratio turbofans used in today’s civil jetliners (and some military transport aircraft) evolved from the high specific thrust/low bypass ratio turbofans used in such [production] aircraft back in the 1960s.
Low specific thrust is achieved by replacing the multi-stage fan with a single stage unit. Unlike some military engines, modern civil turbofans do not have any stationary inlet guide vanes in front of the fan rotor. The fan is scaled to achieve the desired net thrust.
The core (or gas generator) of the engine must generate sufficient core power to at least drive the fan at its design flow and pressure ratio. Through improvements in turbine cooling/material technology, a higher (HP) turbine rotor inlet temperature can be used, thus facilitating a smaller (and lighter) core and (potentially) improving the core thermal efficiency. Reducing the core mass flow tends to increase the load on the LP turbine, so this unit may require additional stages to reduce the average stage loading and to maintain LP turbine efficiency. Reducing core flow also increases bypass ratio (5:1, or more, is now common).
.
@eyesonu:
The burning of jet fuel results in CO2 and H20 as significant combustion products. Jets add water to the stratosphere. Roughly for every CO2 molecule created, there is an H2O molecule.
Jeff (of Colorado) : Two of our favourite sources of information here on WUWT – Wikipedia and Nature – report temperature changes in the aircraft-grounded days after 9/11:
http://en.wikipedia.org/wiki/Contrail
“on the 3 days after the 11th …Travis’ research documented an “anomalous increase in the average diurnal temperature change””
http://www.ldeo.columbia.edu/edu/eesj/gradpubs/sciencemag/Sept%202006%20Sciam%20Hot%20Trails.pdf
“after the events of 9/11 grounded all commercial U.S. flights for three days, daytime temperatures across the country rose slightly, whereas nighttime temperatures dropped.”
So, contrails cool by day and warm by night. As you thought.
Very interesting study. Other earlier studies certainly support these findings and add other interesting details, such as the role of contrails in the formation of cirrus clouds:
http://www.nerc-essc.ac.uk/~rpa/PAPERS/Haywood09JGR.pdf
There might well be a radiative forcing but how does it compare to the release of radiant energy as the low temperature ice is formed from the water vapor produced by the jet engine at much higher temperature and pressure.
Mike Borgelt says:
Contrails probably have more effect when they trigger the formation of a cirrus deck. I saw this once at Douglas County Airport, Minden, Nevada. Clear blue sky, a couple of jets flew over making contrails which then spread out and we had 8/8 cirrus after that.
I’ve seen that happen in Beaverton, OR, more than once. Nice clear blue sky. I start planning stargazing. Then a jet or two pass overhead and before sunset there’s a haze of cirrus across most of the sky.
Hey guys! don’t you remember that one of the effects of the global no-fly zone immediately after 9/11 was that the amount of light reaching the earth’s surface increased, and that this phenomenom was put down to the absence of contrails? I seem to remember a post to that effect on this blog. When I was in the RAF, the daily met briefing contained the heights between which contrails could be expected, and this layer was dependent upon the atmospheric conditions. Sometimes there would be several layers . Generally, it went up in the Summer and down in the Winter. Contrails are not only the product of engines, but also can result from wing-tip vortices. I remember an aircraft taking off early one bright sunny Spring morning in north Yorkshire. The air was so finely balanced that the wing-tip vortices were enough to act as a tipping point and we trainee jocks watched spell-bound as the mist slowly rolled across the airfield. The airfield was fog-bound until early afternoon.
Anthony,
I thought Jim Hansen and Mike Mann waived off contrails as a possible factor
in the cloud formation process several years ago during a public presentation.
I’m pretty sure increased air traffic and subsequent contrails acting as a seeding
mechanism for clouds or as a blocking agent for incoming sunlight and outgoing
radiative heat isn’t a dimension factored into any of the current climate models.
It’s nice when a bit of reality slips through once in a while.
This from a layman which probably is now evident – it’s been my understanding that vapor trails are created not by jet engine exhausts (hence contrails from piston engined planes) but by pressure difference between the top and bottom of a wing created by slip stream spilling (spiraling) around the wing tip. When the atmosphere has the right combination of moisture and temperature, the contrail is formed by the sudden drop in air pressure. Can anyone put me right?
In the immediate aftermath of the 911 tragedy, most commercial flights in the US were grounded for a few days. And weather buffs noticed a small effect on temperatures. The relative dearth of contrails during those few days kicked off the research on Global Dimming. Until I see good evidence to the contrary, I’m assuming that that effect is real albeit small.
Meanwhile, I have a stoopid question. Ice is considerably denser than air. How do contrails and cirrus clouds stay aloft? I’d expect them to slowly settle down to the ground, and leave a thin layer of dew on everything.
WWII B17s with contrails.
[IMG]http://img101.imageshack.us/img101/3130/b17contrail.jpg[/IMG]
http://img190.imageshack.us/img190/4333/largeformationofboeingb.jpg
[Note: No need for the IMG tags. I’ve deleted the ones in the second link so you can see the result. ~dbs, mod.]
My memory, from 20 years of jet fighter flying, is that contrails form only in a layer of air a few thousand feet thick. That layer over the U.S. tended to be over 30,000 ft and below 50,000 ft altitude. (Yes, some military jets could fly above 50,000 ft). In some clear air conditions there would be no contrail level,
We certainly did avoid the contrail level in tactical situations.
By the way, if someone is going to study the effects of aircraft flying in clear air, how about the effects of aircraft flying through various kinds of clouds. Maybe they could be disrupting something.
@eyesonu
The warm engine exhaust (think a long string) absorbs moisture from the immediate surrounding air (think long tube) and quickly cools forming condensation or ice. Turbulence from wing lift/tips causes some mixing and assists in condensation formation.
The moisture for the contrail comes from the burning of the hydrocarbon fuel (which is mostly kerosene). Jet exhaust is somewhere in the neighborhood of 10% water. By comparison hot, humid air in Miami is something like 2.5% water vapor (I forget off the top of my head). The condensed liquid forms as the jet exhaust mixes with the surrounding air and the temperature of the water vapor in the jet cools and becomes liquid or solid water. The jet will quickly mix with the surrounding air regardless of the wing tip vortexes (it’s movin!).
I live under Green 1. Many times I have started using my solar cooker and then a contrail gets between the sun and my cooker. You can’t see any shadow yourself but the thermometer inside the cooker soon shows a drop. Being as the trails run mostly east – west they track the sun nicely. If it happens too many times then its off indoors to finish cooking on the stove. 🙁
[Reply: As guests on Anthony’s site we should respect his wishes. Also, chemtrails discussions tend to get completely out of hand. ~dbs, mod.]
As I don’t understand the difference (I skimmed the article and went straight to the comments), I for one would quite appreciate a proper discussion.
Also, how am I going to get high and might with alarmists who don’t allow free and open discussion, if the so called “sceptics” begin doing the same?
REPLY: Use Google, visit a website, watch a video or two, then you tell me – Anthony
JAE – AGWScience excludes the water cycle proper as a greenhouse gas from its energy budget, so a good question to ask them.
As Alexander Feht notes Atlanta is by the sea. The water vapour in the cycle, lighter than air anyway, takes up the heat which rises bringing in cooler air underneath – the convection cycle continues to the water vapour condensing higher up and coming down as rain and the heat taken up dissipated away from the surface.
The idea that ‘greenhouse gases only add warmth’ is an AGWScience ‘meme’, of misinformation. Without the greenhouse gas water vapour the Earth would be around 67°C, it wouldn’t be colder as they claim, but hotter. The difference as between hot coastal areas and inland deserts in the two cities Atlanta and Phoenix you mention a good example of the cooling power of water in our atmosphere and of how heat really gets moved around by convection.
I don’t know on what figures the 67°C has been calculated, but the principle is there. The Earth with the real greenhouse which is our total atmosphere of gases around it including water vapour, when taking out water would give us desert type conditions. The main greenhouse gas water vapour cools the Earth rather than warms it.
eyesonu says:
June 23, 2011 at 8:45 pm
In regard to contrail formation, I would like to take a guess as to the dynamics as follows. Please correct me if I am mistaken.
I seem to remember years ago we used to have a ‘Mintra level’ calculated for our flights, which was the flight level at which contrails would start to appear. I had forgotten most of the details now but I found this on pprune which might be of use (or not:-)….
“To aid the forecasting of condensation trails emitted (or not) from high-flying aircraft, a line marking the critical temperatures (altitude dependent), above which trails are not possible, is marked on a tephigram. The values are approximately -24degC at 1000 hPa (i.e. roughly sea-level), -39degC at 250 hPa (34000ft / 10.4 km) and about -45degC at 130 hPa (50000feet/15km). Using the MINTRA line (as it has come to be called – based on experiments by JK Bannon during World War II with the piston-engined Spitfire), a forecaster will mark two further lines on a tephigram: MINTRA minus 11degC (A) and MINTRA minus 14degC (B). If the ambient temperature (from the tephigram air temperature plot) lies between (A) and (B), then short, non-persistent trails are possible. If colder than (B), then long, persistent trails should be expected. However, some note should be paid to the relative humidity – high values will tip the balance to trailing (or longer/persistent trails.), even with air temperatures warmer than (A); ultra-low rh% will reduce the risk of condensation trails – the design of engines will have an effect as well. In broad terms, warm Tropical Maritime airmasses with a high but cold tropopause will result in a good deal of trailing, whilst cold, polar air-masses with a low, relatively warm tropopause will seldom give rise to significant aircraft trails.”
[Sorry, no chemtrails. ~dbs, mod.]
Is the air different in USA/Uk since never seem to see the trails much in Australia?
And i firmly believed that freedom of speech was à great good om WUWT.. After reading the note at the bottom of this article i can set aside my believe..
Interesting research. But if these contrails prevent 15mw of energy leaving earth as radiation then they will prevent 15mw of energy incoming from the sun for the same reasons. So nil effect.
When flying with the RAF we were told at which level to fly to prevent the formation of contrails. Not for any supposed environmental reason but it made finding a high flying aircraft more difficult to see by some sharp eyed guy with a missile like a Sam7.
Dennis Nikols says:
June 23, 2011 at 7:50 pm
I think some wise person said a little knowledge is dangerous.
A little Learning is a dang’rous Thing;
Drink deep, or taste not the Pierian Spring:
There shallow Draughts intoxicate the Brain,
And drinking largely sobers us again.
Alexander Pope: Essay on Criticism
For real? The paper gives a contrail forcing of 15mw/m2 +- 47mw.
I have an investment I’d like to offer these guys. It carries a 15% annual return, plus or minus 47%.
Good grief. They don’t even know the polarity of the forcing. At least we can rest assured it’s miniscule either way and nothing to be concerned about if they got the margin of error right. I wasn’t worried in the first place but this offers some justification for my lack of concern.
That used to puzzle me, as the temp drop under a cloud seemed too high and too sudden to be explained by the sun being obscured.
Then I heard a TV weatherman asked the same question, and he said the reason was that the mass of air under the cloud was often drifting along at the same speed, so remained under the cloud for prolonged periods, and it was this cold air you were feeling, not just the lack of sunshine.
Myrrh says:
June 24, 2011 at 12:24 am
“The idea that ‘greenhouse gases only add warmth’ is an AGWScience ‘meme’, of misinformation. Without the greenhouse gas water vapour the Earth would be around 67°C, it wouldn’t be colder as they claim, but hotter.”
No, it would be like the moon which is -23C. It’s not water vapor, per se, that does the job. It’s a 4000 meter deep liquid ocean covering 70% of the surface that does it. Liquid water is like water vapor on steroids as far as greenhouse warming. Sunlight, with very little reflected, penetrates to a depth of up to 100 meters warming the water all the way down. Water is opaque to infrared radiation and can only escape from the top few microns at the water surface and likewise downwelling infrared from greenhouse gases can’t penetrate beyond the first few microns at the surface and largely does nothing more than raise the evaporation rate which very effectively transports the energy in the downwelling infrared as latent heat of vaporization back up to the cloud deck where it becomes sensible heat upon condensation.
The ocean (google ocean heat budget) actually stores a lot of solar energy in the summer and releases it in the winter when the atmosphere is dryer. This greatly moderates the temperature difference between winter and summer. The effect, which has been known for 200 years, is called “continentality” and explains why continental interiors have far colder winters and far warmer summers than those seasons over the ocean at the same latitude.
Absent the liquid ocean but presuming water vapor was still somehow present in the atmosphere the first winter in each hemisphere would blanket most of the hemisphere in snow which reflects north of 90% of incoming sunlight. So instead of an ocean absorbing almost all incident sunlight we get snowcover reflecting almost all of it instead. The earth would become a frozen wasteland in the blink of an eye.
In reality there’s no way to remove the global ocean and still leave the atmosphere charged with water vapor so what you’d actually end up with is cold barren rock pretty much like the moon with a similar average surface temperature of -23C.
Having lived in Europe and the clear skies of Australia, I definitely know that contrails have a local temperature effect. Even the brightest clear day in any European city will end up completely dull and overcast by the afternoon as the contrails separate into high-level cloud cover. I’ve no idea what size effect it has on the atmosphere as a whole, but for those missing out on clear sunny afternoons it definitely has an effect.
Here in Australia the conditions seems to be rarely right for contrails, and there just plain isn’t enough air traffic for it to be an issue. I probably see 5 contrails a year. And the clear sunny winter afternoons are a beauty to behold.
Oh, and as for the guy with the ‘jets didn’t use to leave contrails’. Massive FAIL Any aircraft will leave them if the conditions are correct. Go Google some WW2 footage as others have said.
Just a minute, just a minute, not so fast.
Clouds cool the planet by reflecting sunlight.
Hence numerous posts and discussions on WUWT on the cloud thermostat of climate, the ITCZ tropical cloud bands, etc., etc..
Aircraft contrails are clouds. No more, no less.
And yet – somehow magically they WARM the planet???
No – they also cool the planet, just like all other clouds. Nice try, but FAIL.
So all the class war dressed up as environmentalist envy-driven attack on aviation is, unsurprisingly, totally wrong and opposite of reality.
The CO2 released by aircraft is irrelevant since the CO2 effect on radiation balance is already saturated.
Aviation cools, not warms, the earth’s climate.
Larry Fields says:
June 23, 2011 at 11:58 pm
http://epod.usra.edu/blog/2011/05/hole-punch-and-fall-streak-over-grimsby-uk.html
Atlanta is over 100 miles from the ocean and doesn’t get any sea breeze. Atlanta is also about 1000 feet in elevation.
Contrails are very high up in the atmosphere and very cold, made of ice crystals, rather than from the water droplets found in lower altitude clouds. One has only to look at an IR satellite image to see the differences between low and high clouds. The IR satellite image is a “negative” – the image is an inverse of what the detector sees. This way the colder clouds (and cloud tops) can be represented in a lighter shade. Higher clouds show almost as pure white (which is really almost pure black). This tells us that they are really cold with little or no IR radiation signature. Some of the lower clouds, especially ones close to the ground are almost invisible in IR images, meaning that they radiate almost as much IR as the surface.
A nice experiment would be to point on IR detector at clouds, but from the ground. Then read the IR signature for different heights. My bet is that contrails would show very little if any IR radiation signature from below as well.
Best,
J.
I know I’m probably too late to this party but…
1) Most airline flights are in relatively narrow corridors, so the contrail effect is limited in scope.
2) There was a study done after 9/11/2001 (US Date format) comparing the amount of sunshine reaching the ground during the brief grounding of all flights to the same days in the previous year, and concluded that the average temperature rose 1.1° C during the three no-fly days in the U.S.
3) If you are a warmists, then you want more flights, not fewer.
Here in north central Texas, I’m underneath a set of regularly-traveled air routes. Contrails are often visible, and almost as often they serve as seeds for formation of cirrus clouds, which may cover the sky. I’ve even seen a “negative contrail”, in which a jet traveling through a high cloud formation disturbed the air enough to dissipate the clouds, leaving a clear trail behind. I would post the photo but it’s on a computer that doesn’t work at the moment.
Despite subsequent obfuscation in the service of Warmism, the post-9/11 data indicates a clear net cooling influence for contrails. This suggests a geoengineering tactic that is also an economic stimulus: every citizen of a developed country should get a ticket to some faraway place at regular intervals. The resulting contrails would cool the Earth as needed — the schedule for subsidized tickets could be adjusted according to results and necessity — and the boost to the aircraft and airline industries would provide employment to millions. Alas, it doesn’t fit with Warmist dogma.
Clouds are cooling during the day and warming at night. You do not need a model for this. Just spend a few hours outside. Most flights are during the day so the net effect of contrails must be cooling.
I wonder how hard they had to work to make sure that their estimate of the net effect was warming? Their grant money is safe.
I live in Winnipeg Manitoba Canada, and it is a rare thing that we do not have a multiplicity of contrails in our air space. We are on the “great polar route” for all airlines, and can observe aircraft 24 hours a day flying from Europe and Asia to California and the American Midwest and even East Coast, nevermind our own domestic traffic. I have often thought that there must be some small effect, and it is nice to note the there are those who agree, and are looking at the situation. Thanks Again Anthony, you keep my mind working.
Scottish Sceptic says:
June 24, 2011 at 12:21 am
[Reply: As guests on Anthony’s site we should respect his wishes. Also, chemtrails discussions tend to get completely out of hand. ~dbs, mod.]
“Also, how am I going to get high and might with alarmists who don’t allow free and open discussion, if the so called “sceptics” begin doing the same?”
Because the unmentionable is of the same scientific standard as subjects like Elvis is still alive and was abducted by aliens or Apollo never went to the moon.
On the subject of contrails I found an excellent YouTube movie of an airliner going through different air masses so that contrails were being produced intermittently and by the wings. Unfortunately the accompanying comments were just juvenile and the usual conspiracy science fiction type.
My memory may be deceiving me, but I seem to recall reading in New Scientist in the 70s or so, about a study around Chicago airport. It seemed that the increase of contrails in the previous decade over a very busy airfield had detectable effects on local temperatures: daytime temperatures a fraction lower in summer, nighttime temperatures a fraction higher in winter (where detectable=imperceptible to unassisted human senses)
Which seemed to me to make sense, but I never read of any followup
As I recall, the post 9/11 jet grounding was determined to have no effect on the median temperature, but the variability did increase.
Elsewhere, it’s believed that the altitude of a cloud determines if it has a slight net cooling or warming effect.
The IPCC says that since no cause can be found for the late 20th century warming, it must be caused by CO2.
Jet contrails only became common in the late 20th century. As such, the changes in the atmosphere that they cause could explain the warming, and CO2 simply be a coincidence.
So comments on cloud warming vs. cooling:
Clouds can reflect both sunlight and the IR from the surface. There can be differences in reflection/transmission at different wavelengths, and that was what was studied in this paper. For a thick layer this would be ~100% at all wavelengths, but contrails aren’t thick enough to make such an assumption. The phenomenon is scattering off droplets or crystals, not absorption by a gas or liquid, so there are no wavelength windows to consider.
Sunlight carries much more energy than the IR re-radiation, so all things being equal clouds should have a strong negative effect on global temperature. Even if you factor in the much larger radiating surface of the ground compared to the sun’s apparent size, and the fact that the ground radiates 24/7, the total upward radiation going through an area, long term, has to equal the downward radiation. But the average downward radiation includes energy that never reaches the surface, so clouds must still have an overall negative impact on temperature.
As far as contrails, I mentioned the day/night difference in air traffic. With clouds, there also is a day/night difference in many cases. Maybe someone here knows of a study that actually measured this.
[stopping this discussion ~ ctm]
With regard to contrails in Australia, besides having a lot less traffic than the US/Europe, the vast majority of the Australian population is situated in the east coast capital cities and see very few high altitude overflights.
Virtually all the aircraft traffic people in these places see is either on approach or departure to/from Sydney, Melbourne or Brisbane and therefore are not at altitudes conducive to the formation of contrails.
As for myself I live in the country and besides RFDS flights pretty much all I see is high altitude overflights of commercial aircraft (based on direction of travel I assume it is mostly Perth-Melbourne, Adelaide-Hobart) and quite often these aircraft have contrails.
Check out the B-17 contrails in WWII. http://www.mcmahanphoto.com/af248–boeingb-17flyingfortresswcontrailsphoto.html
I can’t remember. Did the climate warm or cool 1939-1945?
TOM_R states: Sunlight carries much more energy than the IR re-radiation, so all things being equal clouds should have a strong negative effect on global temperature.
I concur, then add that some contrail generation actually continue to grow as the seeding process of cloud formation has been increased by the exhaust of aircraft, leading to additional cooling.
I think that pretty much settles the discussion. 🙂
P.S.
..what is that green ice falling into my back yard??? Hey I did not mention the “C” word.
I am using condensation trails as mesure for Humidity of the “local” atmosphere”. If t trails are long and persistent, than atmosphere is humid and les transparent. Short trails or no trails than is good visibillity.
[see edits above. I apologize, the original poster is a conspiracy theory nut among other things, who is tolerated here somewhat, but sometimes sneaks past the other moderators. ~ ctm]
[see edits above. I apologize, the original poster is a conspiracy theory nut among other things, who is tolerated here somewhat, but sometimes sneaks past the other moderators. ~ ctm]
Al(BH4)3, for example, is a fuel, and can be diluted in hydrocarbons for civil avaiation. Borohydrides are reducing agents, and can protect fuel tanks from oxidation.
Guys, did you read the article? It said 15 mW/m2. That’s a measurable but miniscule amount. It is perfectly reasonable answer, and perfectly indicative of it being a non-issue. Y’all are agreeing with the conclusion and somehow being upset about it.
>>ShaneCMuir says: June 23, 2011 at 7:31 pm
>>What happened to open scientific debate?
Deat Shane McNutter. Older aircraft did not often leave contrails because the rarely got up into the contrailing levels. But ever since the B707 era, they have been contrailing as much as now. Only problem being, there are more aircraft now.
But I do not believe this particular paper. More aircraft fly in daylight hours than night, and so the forcing aught to be slightly negative (cooling). This is what the 7/11 survey found. I fly every other day, and on some occasions all the high stratus you see is actually spread out contrails. On these days, the forcing should be quite significant.
.
Dave Springer noted: “The paper gives a contrail forcing of 15mw/m2 +- 47mw.”
Exactly right, sir.
When your resultant margin for error is six times the size of your supposed data, you don’t actually have any data; you have a theoretical range.
When that range also crosses zero, you cannot use your result to make any statement whatsoever with regard to influence on other processes.
In other words, no matter how thin you slice this, it remains bologna.
Oh darn, shouldn’t have gotten involved it that conversation. I wish the unrelated part of my comment had been left untouched, though…
Well, anyway, what I said that was unrelated was that, with regard to all the comments about the 9/11 contrail effects study, subsequent studies have basically determined that the effect claimed by the original study was wrong:
http://www.ottokinne.de/articles/cr2004/26/c026p001.pdf
http://journals.ametsoc.org/doi/abs/10.1175/2008JCLI2255.1
http://geotest.tamu.edu/userfiles/245/2008GL036108.pdf
[sorry about that, once it spirals, I have to chop hard ~ ctm]
GaryP says:
June 24, 2011 at 6:04 am
Clouds are cooling during the day and warming at night. You do not need a model for this. Just spend a few hours outside.
After reading through the whole thread that is exactly what I was going to say…but being impolite I was going to lead it with “Any idiot knows….”
Climate effects of contrails are between negligible and zero. Those who wish to disagree are welcome to do their own measurements at their own expense – do not look for Uncle Sam to pick up the tab for your wild goose chase.
This is an old chestnut that really needs putting to bed.
First the very precise paper that is the subject of this entry did not account for the fact that contrails will NOT appear in dry air. There are aircraft flying at high level almost everywhere in the developed world – but they are not leaving continuous contrails. The contrails ONLY appear when there is a layer of water vapor such that addition of the hot water vapor in the jet eflux leads to water vapor condensing into droplets and then freezing, If the vapor pressure of water is low then the ice crystals will rapidly sublimate back to vapor and the result is a non-persistent contrail. If there is sufficient water vapor that the vapor pressure is higher then the contrails will be persistent. If the water vapor layer was ‘supercooled’ just needing something to trigger condensation there is a possibility that the contrails may trigger more ice crystals to form and lead to persistent cirrus.
NOTE The presence of contrails signals the presence of water vapor and the persistence of the trails or their changing to cirrus indicates the amount of water vapor.
Readers of this blog will be aware that water vapor is several times more powerful than CO2 as a ‘GHG’. So what is being measured is the forcing of the layer of water vapor around the contrails not the contrails themselves. I have seen NO research where such a contrailing layer was identified – measured – then a contrail formed in it and the measurement repeated. But then that would be science and may lead to an unwelcome result.
Contrails are a sign of a water vapor layer.
9/11 and no Contrails Some NASA researchers from Langley went out and measured the temperatures of the days during the flying ban and put down the fact that it was cooler than normal to the lack of contrails. This got wide publicity. Nobody asked – would there have been any contrails on 9/11 – 9/15 even with aircraft flying? An entirely reasonable question as there are days when there are no contrails but the aircraft are still flying. As it happens on 9/11 there was a large dome of very dry high pressure over the East coast (remember all those clear as day bright sunshine views of New York?) A cool clear day under an anticyclone is something that is not uncommon in early fall /late summer. But this particular cool day has to be due to lack of contrails as we cannot think of anything else? This sounds suspiciously similar to other AGW reasoning.
Ah well, not a good comparison then.. http://en.wikipedia.org/wiki/Atlanta_Georgia#Geography
..does mention maritime air though..
Having lived in the desert southwest for a lot of years, I’ve learned to estimate the tropospheric humidity level by the height of the cloud base- the lower the clouds, the higher the humidity. When the clouds run aground, it’s 100% . Many summer days in Mojave have clear blue skies overhead, even though there are some clouds over the Tehachapi mountains, upwind to the west. Google “Foehn wind” for details. This foehn heating often eliminates clouds downwind of the mountains, and makes contrails disappear when the aircraft passes from west to east.
Contrails are few here, but get noticeably thicker when the aircraft in question goes on afterburner (we get quite a few high performance planes over Mojave, go figure). One of the more eye-catching examples was when White Knight was carrying Space Ship One high overhead; WK used afterburners to generate enough thrust out of the cheap but thirsty J85 engines to haul its cargo to drop altitude. Right after the drop, the crew would throttle back, and the contrail would thin out (SS1 made a thick contrail due to the high burn rate of its hybrid motor).
Ian W-“A cool clear day under an anticyclone is something that is not uncommon in early fall /late summer. But this particular cool day has to be due to lack of contrails as we cannot think of anything else?”
If you see my post above, other explanations of the temperatures during that period have been offered, and found more plausible than contrail connect proposed. So thankfully more logical thinking seems to have prevailed, at least in the literature. Sadly the public has caught on to the meme that contrails explained it and the much less interesting finding that they didn’t never got much media attention, so few are aware of it.
DonS says:
June 24, 2011 at 8:50 am
Check out the B-17 contrails in WWII. http://www.mcmahanphoto.com/af248–boeingb-17flyingfortresswcontrailsphoto.html
Some times missions had to be rerouted to avoid the persistent contrails from the previous day.
http://www.mcmahanphoto.com/af248–boeingb-17flyingfortresswcontrailsphoto.html
Tom_R says:
June 24, 2011 at 7:23 am
So comments on cloud warming vs. cooling:
Clouds can reflect both sunlight and the IR from the surface. There can be differences in reflection/transmission at different wavelengths, and that was what was studied in this paper. For a thick layer this would be ~100% at all wavelengths, but contrails aren’t thick enough to make such an assumption. The phenomenon is scattering off droplets or crystals, not absorption by a gas or liquid, so there are no wavelength windows to consider.
Sunlight carries much more energy than the IR re-radiation, so all things being equal clouds should have a strong negative effect on global temperature.
But all things are not equal, solar irradiation will typically have wavelengths less than the particle size and give Mie scattering which will scatter in all directions whereas the IR has wavelengths significantly larger than the particle size which will give Fraunhofer scattering which will be predominantly in the forward lobe.
Haydenlee says:
June 23, 2011 at 11:20 pm
This from a layman which probably is now evident – it’s been my understanding that vapor trails are created not by jet engine exhausts (hence contrails from piston engined planes) but by pressure difference between the top and bottom of a wing created by slip stream spilling (spiraling) around the wing tip. When the atmosphere has the right combination of moisture and temperature, the contrail is formed by the sudden drop in air pressure. Can anyone put me right?
Vapor trails are caused by the combustion exhaust gases which can contain fairly high water vapor pressures, these condense under the appropriate conditions as shown above. If a plane flies through just subsaturated air then wing-tip vortices can also cause a vapor trail. In this photo you can also see condensation in the low-pressure region above the wing.
>> Phil. says:
June 24, 2011 at 6:45 pm
But all things are not equal, solar irradiation will typically have wavelengths less than the particle size and give Mie scattering which will scatter in all directions whereas the IR has wavelengths significantly larger than the particle size which will give Fraunhofer scattering which will be predominantly in the forward lobe. <<
My point was that any scattering will give the same end result if the layer is thick enough.
As far as size is concerned, are the ice crystals (or water droplets in the case of clouds) really significantly smaller than 10 microns?
I guess I should Google it myself. Answer, water droplets are 6-14 microns, cirrus ice crystals 5-40 microns.
http://www.sciencemag.org/content/295/5556/834.abstract
http://www.inscc.utah.edu/~tgarrett/Publications/Icescattering/GarrettGRL2003.pdf
How would the presence of barium and aluminium affect the radiative forcing of a contrail, perhaps as part of a weather modification programme?
Tom_R says:
June 24, 2011 at 9:13 pm
>> Phil. says:
June 24, 2011 at 6:45 pm
My point was that any scattering will give the same end result if the layer is thick enough.
As far as size is concerned, are the ice crystals (or water droplets in the case of clouds) really significantly smaller than 10 microns?
I guess I should Google it myself. Answer, water droplets are 6-14 microns, cirrus ice crystals 5-40 microns.
Or read the paper referred to in the OP which gives 2.9 microns.
>> Phil. says:
June 25, 2011 at 5:13 am
Or read the paper referred to in the OP which gives 2.9 microns. <<
That's the effective size the authors measured for contrails. But my comments in the post you originally quoted were about clouds.
As an old fighter pilot, we used to brief the contrail levels (nominally 30-35000 ft over the UK) and avoid flying in them to negate an adversary’s visual pickup. Now, as a B747 Captain, I sit happily in the trail levels as these are the fuel-based optimum levels, for up to 12 hours. If (?) things are as bad as our great thinkers (!!!!!) propose then how about going back to the fighter pilot mentality and avoid the (bad) levels – and burn more nasty jet fuel?
@ al gallacher
Now that is interesting. Nice to have a bit of practical knowledge thrown in.
Since my post from yesterday apparently didn’t make it I’ll repeat it:
Tom_R says:
June 25, 2011 at 6:30 am
>> Phil. says:
June 25, 2011 at 5:13 am
“Or read the paper referred to in the OP which gives 2.9 microns.”
That’s the effective size the authors measured for contrails. But my comments in the post you originally quoted were about clouds.
Perhaps you should have stuck to the subject.
Thanks for the video Gee Willikers. I find myself almost unable to watch BBC documentaries these days. They are so overblown and ridiculous they almost parody themselves. I find their excessively emotive propagandizing very annoying. That is a shame because there is often an interesting fact or two in them albeit buried deeply in the rest of the garbage. Indeed watching this prompted a number of interesting thoughts.
1. Remember that fleet of wind powered robot ships that were supposed to spray salt water into the air to make clouds whiter and protect us from global warming? Looks like the idea might work, but why bother with the robot ships – just catch a plane.
2. CO_2 greenhouse physics by itself absolutely cannot account for more than 1.2 degrees per doubling of CO_2 without some kind of positive feedback mechanism operating. That mechanism was supposed to be additional greenhouse warming from higher levels of water vapor resulting from increased evaporation in a warmer world. But this whole global dimming scenario seems to completely destroy that as a working hypothesis. If pan evaporation rates have declined significantly in the 20th century then there cannot have been any positive feedback from water vapor operating over this time period. Unless an alternative positive feedback mechanism can be cooked up this leaves the CO_2 greenhouse effect acting by itself, and that effect is therefore far too small to explain the observed warming in the second half of the 20th century. That warming must have been caused by something else. The dramatic doomsday predictions at the end of the documentary nicely ignore the fact that global dimming has just destroyed the only proposed physical mechanism by which it is envisaged that CO_2 could cause this level of warming.
3. This will also cause problems for the solar warming people. The global dimming caused by contrails involves and interferes with the exact same mechanism by which changes in solar activity are supposed to effect the climate. The idea is that solar activity changes the cosmic radiation flux effecting rates of cloud seeding. The good news for this theory is that rates of cloud seeding do indeed seem to have a significant impact on climate making the mechanism more plausible. The bad news is that temperature increased anyway during a period where cloud seeding rates had apparently been significantly increased due to contrails. Why? Something else must have done it. Furthermore if we are directly changing cloud seeding rates ourselves then we cannot expect this mechanism to work the same way in future as it did in the past. So the solar Maunder minimum type period we may be looking at now might not have quite the impact some people expect it to have.
So where does this leave us? Perhaps merely with an increased appreciation of how much there is about climate we don’t understand.
Cynical S;
AFAIK, the Svensmark GCR hypothesis speaks of low-level clouds, not high cirrus type. Contrails are way too high to be low-level cloud seeding, and are far less effective reflectors.