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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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.