Dr. Roger Pielke Senior writes:
Ben Herman of the University of Arizona has responded to the post…
…with the following insightful information.
“I read your recent post concerning the possible effects of contrails on global warming. While the effect of contrails in low humidity atmosphere may be something to think about, such is not the case. The water vapor trails only occur in a saturated, or near saturated environment, as witnessed by their presence being almost entirely limited to regions where cirrus clouds are present, or to regions in close proximity to cirrus clouds. The point here is, in such an environment, the water vapor and/or ice crystals already present are most likely absorbing a good deal of the IR radiation that would be absorbed by contrails in a dry environment. Therefore the increase of absorption is certainly quite limited. Of course a more thorough investigation of this is required for an accurate estimate of the actual effect of contrails, but this was apparently not considered, or at least not mentioned in the Reuter’s article you referred to in your blog.”
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The original WUWT version of the article can be seen here
Note: this thread will not discuss theories on “chemtrails”. Moderators, as in that previous article. please delete any comments that reference them even obliquely.
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The length and duration of contrails has long been one of my predictors for an approaching “warm” front, or higher humidity air mass, one that is a low rather than a high pressure mass. The source of the contrail is water, produced largely by the hydrogen content of the kerosene jet fuel in combination with the oxygen in air, at the rate of about 1.1 gallons of water per gallon of kerosene burned.
The point of contrails is that they spread outwards over the sky from the initial jet-trails, thus clouding over a sky which otherwise would have remained clear. This both reflects sunlight away (via albedo), and keeps surface heat from radiating directly back into space. Not sure how the energy balance is affected in toto.
Whilst true that the high-altitude sky must be near saturation for the contrails to spread, it is also true that the air is thin enough at that altitude that the water content is not great. So we are indeed talking about big effects from a small water budget.
So the contrails are much more prevalent now than a decade ago (and the general population is very much aware of a marked change). This is a testament to the increased water vapor in the atmosphere. Is this increase in water vapor due to increased GCRs making more aerosols?
“keeps surface heat from radiating directly back into space.”….Exactly how would contrails up at 30,000 or so ft with an outside temperature of say -50 degrees radiate heat back to earth???
I never got why high clouds are supposed to increase warming whilst low clouds are said to cool. Surely any cloud reflects incoming solar energy back out into space. I see that clouds reflect energy back towards earth and thus delay some cooling, but if the clouds weren’t there then there would be more energy in the system.
OK, reality check time. I took a look at the actual study, which is in Nature Climate Change. In 2005, they estimate the total forcing from all types of contrails to be about 31 mW/m2.
Now, in the terms we are used to, that would be about 0.03 W/m2, or on the order of the contribution from geothermal heat.
Have we really sunk this far, that Nature Climate Science and the mainstream media are hyperventilating about three hundredths of a watt per square metre?
w.
Well it hyperventilates about decimals of a degree that they can’t measure reliably…
I thought after the 9-11 attacks, when air traffic was suspended for a few days the effects of less contrails was studied, and a net cooling was observed.
Meaning contrails cool the day temps, and warm the night temps, like other clouds.
My memory is fading of the details, so a Google refresh is in order for discussions of the 9-11 findings.
-Jay
Whatever floats your govt. grant…..even though it passed absurd a long time ago.
Willis Eschenbach says:
April 7, 2011 at 1:23 pm
There are nations which have told the hyperventilators to mind thier own climate change business.
India comes to mind as the most recent case.
We might be wrong to assume that the contrail once it is produced stays where it is. I would think that the water from the combustion gases coming out of the reactors quickly condenses in a zone that is saturated already with water. I suppose that this saturation concentration is easily attained since at those sort of temperature water will easily freeze also. Those ice crystals will most likely fall down to lower altitude saturation zone and in the process seed the lower zones to form clouds. The seeding process is exothermic. It will warm up the atmosphere at that altitude. Would that heat escape to space more easily though?
For contrail study and forecasts, see:
http://contrail.gi.alaska.edu/
@Willis Eschenbach
“Now, in the terms we are used to, that would be about 0.03 W/m2, or on the order of the contribution from geothermal heat.”
Is that really all the heat there is from geothermal heat? I wonder though, how did they calculate as to how much geothermal heat is released beneath the deep deep sea, or did they as per usual not include that?
But what about the heat from the jet engines? Maybe that’s the real source of all the warming?
😉
I have observed planes at altitude leaving long persistent contrails and everything in between down to contrails that last a few seconds to none at all. There are also plenty of photos showing contrails being produced by a planes wings passing through the air. This last phenomena is possible considering that a wing will lower the atmospheric pressure over it’s upper surface. As all flights at altitude will be conducted with much the same throttle settings from day to day, then, as stated by others here, it is the varying amount of moisture already in the air that determines whether contrail persist or not. If the burning of Kerosene at altitude is the main source of contrails then why are there days when none appear?
There is no evidence that contrails persist.
Here is a contrail at ground level and -39
http://www.airliners.net/photo/Canadian-North/Boeing-737-232-Adv/1865339/L/
Here is contrail with a large contribution from the wings:
http://www.airliners.net/photo/Cathay-Pacific-Airways/Boeing-747-412(BCF)/1776362/L/
And others:
http://www.airliners.net/photo/Skynet-Asia-Airways/Boeing-737-4M0/1551174/L/
http://www.airliners.net/open.file/0606470/L/
http://www.airliners.net/open.file/0870588/L/
http://www.airliners.net/photo/Shanghai-Airlines/Boeing-767-36D/0907833/L/
http://www.airliners.net/open.file/0980583/L/
http://www.airliners.net/open.file/0632268/L/
And these at low altitude
http://www.airliners.net/open.file/0464227/L/
http://www.airliners.net/open.file/0981791/L/
“”””” Kevin B says:
April 7, 2011 at 1:09 pm
I never got why high clouds are supposed to increase warming whilst low clouds are said to cool. Surely any cloud reflects incoming solar energy back out into space. I see that clouds reflect energy back towards earth and thus delay some cooling, but if the clouds weren’t there then there would be more energy in the system. “””””
It seems as if some climatists need to take a course in remedial geometrical optics.
The sun from the point of view as a radiant energy souce, is a near point source. Well specifically it has an apparent angular diameter of about 30 minutes of arc, as seen from earth.
If you put a cloud with some optical density, having an area of say one square Km, up at some normal cloud altitude, you will get a shadow on the ground of also about one square km area. If we make a simplifying assumption that any cloud height is small compared to the earth radius, and we are dealing with a one square km crossection area which is essentially parallel to the earth surface, then it is apparent, to anyone who can spell Euclidean geometry, that the shadow cast on the ground is also largely independent of sun angle. And for the leagal disclaimer, we are excepting fringe cases, like the sun on the horizon; shall we say a 10 AM to 2 pm sun.
Now a tall billowy cloud of course will have a varying section with sun angle; but we are thinking here of a thin layer cloud; well something of contrail thickness.
The actual ground shadow will have a penumbral edge dictated by the sun 30 min divergence angle. Otherwise the shadow is a replica of the cloud crossection; and within that shadow the sunlight reacvhing the ground will have been diminished because of scattering by the cloud. Well some would call it reflection; but it really is more of a refractive scattering; but seen from above the cloud it appears as a highly diffuse, perhaps 80% reflectance over the solar spectral range where say 98% of the energy resides. A thermometer reading the near ground air temperature in the shadow would report a lower temperature than one situated just outside the shadow.
Now consider the LWIR thermal emission from the surface in that one square km shadow zone. If that surface were optically flat, say a quiet water pond or lake, the LWIR emission from the surface will be radiated in a Lambertian (constant radiance) angular distribution pattern whose radiant intensity would vary as cosine of the angle off normal to the suface. The total emitted power (Watts ) is just pi times the normal radiant intensity (Watts per steradian).
A more realistic sample earth surface will have a randow oriented surface texture, each facet of which would be a separate Lambertian emitter, and the overall result, is an essentially isotropic emission pattern rather than a Lambertian one. The constant intensity should be half of the normal intensity for the Lambertian case. So the surface LWIR emission is extremely diffuse; and only a small fraction of that emission is going to get intercepted by that cloud. The higher the cloud is, the less interception of LWIR emitted from the shadow zone will be. There will be an inverse square of cloud altitude fall off in interception, as well as an obliquity factor (cosine^n). It would be cosine^4 for a Lambertian emission patetrn, but only a cosine^3 for the isotropic emission; which in any case starts off at half the maximum intensity.
The lost sunlight due to that cloud is essentially independent of cloud height. The angular extent of the cloud as seen from the sun’s surface is near zero and it isn’t going to change with cloud height; but the interception of outgoing LWIR will and dramatically so, with change in cloud height.
But we shouldn’t let a little geometrical optics get in the way of a good model.
So if you think that high clouds warm the surface, and the higher the cloud, the more the warming; then I have a bridge I would like to sell to you.
1DandyTroll says:
April 7, 2011 at 2:10 pm
That’s what the estimates are. You have to remember that for each geothermal “hot spot”, whether in Yellowstone Park or under the ocean, there are thousands of square kilometers of desert and prairie and ocean floor with almost no heat coming out at all.
So the average is quite small. For example, think about the huge number of natural springs, and the tiny number of natural hot springs. The average temperature of all spring water is going to be only a few hundredths of a degree warmer than the average of just the unheated springs …
They do include ocean-rift heat. However, as you indicate, the estimates of ocean-bottom heat are just that … estimates.
w.
This from NOAA and there ‘puzzlement’ as to why the 2002 Arctic melt was late even though there was evidence of ‘down-welling’ radiation.
http://www.arctic.noaa.gov/essay_untersteiner2.html
Observations from the North Pole in summer 2002
The recently recorded data from automatic buoys and web cams represent a large, and very inexpensively obtained, increment of information about summer conditions in the central Arctic.
The onset of melting usually occurs in early June, when the temperature reaches 0°C and the surface layer turns into a constant-temperature ice bath. In 2002, the temperature record shows an abrupt warming to about 0°C, on 24 May, suggesting an early arrival of the melt season. The warming event coincides with about a week of low short-wave (250 Wm-2) and high long-wave (300 Wm-2) down-welling radiation, which are typical of low overcast conditions. The web cam pictures of that period confirm the overcast. Both radiation and temperature values remained in the normal range for the rest of the summer, and freeze-up occurred as usual in the last week of August. Based on the early warming event in May, one may have expected an early onset of surface melting. Contrary to that expectation, the web cams show that it was not until late July 2002 when the snow cover took on a soggy appearance and isolated melt ponds appeared on the surface (Fig.2).
For the rest of the summer, the web cam pictures show only insignificant melt pond coverage until the deposition of new snow in late August. The pictures clearly show that snow from the preceding winter survived the entire summer, and we must assume that there was no, or very little, ice ablation at the surface.
Soviet (Russian) records suggest a small probability of an all-summer snow cover. But none of the U.S. ice camps experienced a persistent summer snow. In light of recent news about global warming and polar amplification, the all-summer snow cover of 2002 is clearly unexpected.
Some question why the trails appear sometimes and not others. It would seem obvious that the trails are not caused by the release of water alone, but are caused by that AND the existing amount of vapour. If there is a lot already, a little more will cause a trail. If there is little, then it won’t.
I think the statement:
explains that fully.
Is this a cause of warmists ‘getting the vapours’?
[Sorry, couldn’t resist]
@Willis Eschenbach
“They do include ocean-rift heat. However, as you indicate, the estimates of ocean-bottom heat are just that … estimates.”
Thanks.
How do they, or you, rate the quality of those estimates?
I wonder because I got astound the other week (looking up submarine volcanos) at the ignorance, as in lack of knowledge but ignorance no less, of the amount of active, as in venting pressure, submarine volcanos per year. There’s about 70 surface volcanos going cranky each year but, apparently, thousands to tens of thousands submarine volcanos blows a fuse each year. Nobody seem to know, which, appear to, indicate that nobody really knows wether an earth quake out to sea is really an earth quake or a volcano who vents its pressure. However, though, if there’s tens of thousands of active submarine volcanos (as in like “active” surface volcanos) then there could exist millions of submarine hot vents, hot springs, and them critter crawling chimneys. And, apparently, even in the arctic and antarctic regions volcanos have been highly volatile active without people being the wiser, so if they haven’t been able to account for what has been under their own shoes how much quality is their assumptions of whats out beneath the deep blue, I truly wonder.
An old submariner use to say that it is mandatory to know the onion layers that is the temperature of the oceans, now I wonder where does all the heat that constitute those layers really come from for surface temperature can’t seem to include the necessary ingredient to form layers.
And, of course, heat goes up and eventually escapes to the freezing freedom of the outer space. Heat rarely travels the other way. :p
If contrails are like clouds they will have a negative forcing. This was demonstrated after analyzing the temperature increases around various cities after grounding of aircraft due to 9/11. This article from ..ugh.. CNN in 2002. http://articles.cnn.com/2002-08-07/tech/contrails.climate_1_contrails-cirrus-clouds-david-travis?_s=PM:TECH
>> During the three-day commercial flight hiatus, when the artificial clouds known as contrails all but disappeared, the variations in high and low temperatures increased by 1.1 degrees Celsius (2 degrees Fahrenheit) each day, said meteorological researchers.<<
Whether they cause the globe to warm is a net energy gain issue. Good luck with that.
Jay says:
April 7, 2011 at 1:33 pm
I thought after the 9-11 attacks, when air traffic was suspended for a few days the effects of less contrails was studied, and a net cooling was observed.
Meaning contrails cool the day temps, and warm the night temps, like other clouds.
My memory is fading of the details, so a Google refresh is in order for discussions of the 9-11 findings.
-Jay
This was some measurements done by some NASA researchers who didn’t bother to check the weather. As people will remember 9/11 and the subsequent days were bright clear days as there was a large dome of high pressure settled over the Eastern US with very dry air. The effect of this type of weather is to significantly lower temperatures at night and early mornings as there is no water vapor acting as the ‘green house gas’ (sic). The presence or absence of the aircraft would not affect the forecast temperatures with this type of weather system.