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
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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.