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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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.