Contrails – itty bitty icy forcing

From the American Geophysical Union weekly highlights:

Estimating climate effects of contrails

Image: NOAA/NWS

Condensation trails, or so-called contrails, formed by freezing of ice crystals in the exhaust from aircraft jet engines could affect climate. Like natural cirrus clouds, contrails change atmospheric temperatures not only by blocking sunlight from reaching the Earth’s surface but also by preventing terrestrial radiation from escaping the Earth’s atmosphere. However, contrails’ effects on climate are not well constrained because only few studies of contrail properties exist, and hence, their microphysical properties are poorly known.

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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Martin M

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.

Steve R

Oh come on. Aren’t there more important problems to deal with?

Randy Links

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.

Tom_R

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.

Claude Harvey

Chemtrail, chemtrail, chemtrai….this is a test.”
[Thin ice ahead. ~dbs]

Lew Skannen

Would a giant tinfoil hat protect the planet from contrails?

Olen

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?

Dinostratus

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.

jae

“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!

Dinostratus

Just to be more pedantic, I should have written, “vapor pressure of the water in the air”.

ShaneCMuir

“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.]

Scarlet Pumpernickel

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.

jae

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?”

Gee Willikers

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 🙂

Wilky

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.

DCC

@Mark: Try Google.

Curiousgeorge

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.

old engineer

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.

Hector Pascal

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.

rbateman

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.

Jeff (of Colorado)

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.

Denis Purdy

@Dennis Nikols:
The wise person was Alexander Pope and he actually wrote:
” A little learning is a dangerous thing”.

Frank K.

“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…

Jeff (of Colorado)

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.

eyesonu

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.

jae says June 23, 2011 at 7:28 pm
“but also by preventing terrestrial radiation from escaping the Earth’s atmosphere. ”
WHEN I see some empirical evidence of this ?crap?

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.

Ken S

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?

jorgekafkazar

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.

ShaneCMuir says on 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.

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:

Mystery Veils Vapor Wreath in Galveston’s Sunny Skies
It wasn’t a sky-written soft-drink ad and the weatherman couldn’t offer an explanation either for the fat white streaks of vapor hanging motionless in Galveston skies around noon Saturday.
But it seems fairly certain that a six-engined B-36 left the heavy white trail in its wake as it circled over the city.
Neither municipal airport nor civil aeronautics authority official had a flight plan on the bomber. Both outfits however, believed that the jet-powered B-36 was on a training mission from Carswell Air Force Base in Fort Worth.
An Air Force spokesman at Carswell Base refused to comment on either the bomber or its “vapor trail” when contacted late Saturday by The News.
Mystery of the massive vapor streaks was their long steady persistence in breeze-stirred skies rather than their expulsion from the jet-powered plane. Airport officials commented that a vapor trail usually fades away swiftly, as in sky-writing.
They also said that planes may leave vapor trails when flying at high altitudes. But it was unlikely, they added, that the air would remain still enough to keep the vapor from fading swiftly.
Another odd thing – onlookers said the bomber engines rather than the jet exhausts were pushing out the vapor clouds.
The only thing certain about the vapor mystery seems to be that the B-36 was flying at altitudes between 10,000 and 25,000 feet when it circled Galveston.

– – – – – – – – – – – – – – – – – – – – – – – – – – – –
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.
.

Bill Yarber

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

Ken S says on June 23, 2011 at 9:03 pm
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?

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.

R. Gates

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.

Katherine

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.

Grumpy Old Man UK

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.

R.S.Brown

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.

Haydenlee

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?

Larry Fields

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.