The planes! The planes!

From Dr. Roger Pielke Senior: (with apologies to Tattoo)

Aircraft Contrails

Contrails southeast lrg.gif MODIS tracking of contrails generated by air traffic over the southeastern United States on January 29, 2004. Source: NASA Earth Observatory, click the image for details

There is a news article on March 29 2011 from Rueters titled

Aircraft condensation trails criss-crossing the sky may be warming the planet on a normal day more than the carbon dioxide emitted by all planes since the Wright Brothers’ first flight in 1903, a study said on Tuesday.

The text begins with [highlight added]

Aircraft condensation trails criss-crossing the sky may be warming the planet on a normal day more than the carbon dioxide emitted by all planes since the Wright Brothers’ first flight in 1903, a study said on Tuesday.”

Another excerpt reads

“The study, by experts at the DLR German Aerospace Center, estimated that the net warming effect for the Earth of contrails and related cirrus clouds at any one time was 31 milliwatts per square meter, more than the warming effect of accumulated CO2 from aviation of 28 milliwatts.”

If correct, this is a remarkable finding with respect to contrails as a climate forcing. It also shows that as we study the climate system, we find it is affected by a wider diversity of human climate forcings than concluded by the IPCC. The human effect on the climate system is not dominated by CO2 and a few other greenhouse gases.


Just a firm reminder, any comment mentioning, referring to, or paraphrasing anything to do with “chemtrails” will be automatically sent to the bit bucket. – Anthony


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I should think at night and in winter – where we’re seeing the greatest increase in temperatures – would be the critical times to investigate in detail.

R. de Haan

This will end the era of air travel.
As in the UK the roll out of the 11.5 billion pound smart grid is underway all we need is a personal carbon budget and our traveling days are over.
Any opposition to the green totalitarians will be punished immediately by a power cut off. That will teach the skeptic bastards.

R. Gates

This effect from contrails is quite interesting and something I’ve often wondered about as I’ve watched the many contrails over my home state of Colorado. It certainly does seem to be a strong rebuttal to those who say humans can’t affect something as “large as the earth”, when in fact, the atmosphere is just a relatively thin layer and something as seemingly insignificant as contrail, when multiplied by the tens of thousands generated everyday, and then expanded in the way described in the study, you’d expect an impact. I am surprised it was this large however…

Martin C

I thought that the clouds in general provided a cooling effect, and that the effect of clouds higher in the atmosphere (such as cirrus clouds) was greater due to reflecting the sunlight. Also, wasn’t there some evaluation of temperatures just after 9/11, where for three days there were NO aircraft in the sky (though I don’t remember what the finding of this were . . . ) , and how it compared to days before, or after ?

Chris D.

Doesn’t this fly in the face of what NOAA (I believe) was saying about the 3 days of no flights over the US right after 9/11/01, specifically that temps spiked during that period?

R. Shearer

Sounds like a world wide no fly zone could be proposed. I’d begin with private jets.


Wait just a minute….I thought all those contrails were COOLING the planet by increasing reflectivity? My understanding is that the water is mostly already there but the planes exhaust just causes it to precipitate?
More “science” to confuse people….confused people are more easily deceived.


I had heard previously that the effect was exactly the opposite. Didn’t someone use the post-9/11 shutdown of air traffic to evaluate the climate forcing of contrails? I seem to recall seeing this on a Nova episode (“Dimming the Sun”, Apr 18, 2006; ). Perhaps this is all “TV science”, but it’s interesting to have the Hansen set essentially contradicting the finding of this study. I have often wondered after seeing this if the Clean Air Act was not itself a climate forcing that impacted some of the trends of US temperatures in the second half of the 20th century.

The timing of this is suspect…just when Britain proposes a “masterplan” regarding transportation and rationing holiday flights. Hmmm
But you’re right – if true it reveals lots of gaps in IPCC knowledge.

TFN Johnson

Ch**tr***s —-Why? Some Americanism I haven’t hitherto come acoss?

homo sapiens

“This is a breakthrough in modeling and understanding of contrails,” Olivier Boucher, of the Met Office Hadley Center in England who wrote a related article in Nature, told Reuters.
Those models again!
So the temperature rise (unadjusted upwards) of the past 100 years due to CO2 emissions is even less than 0.3degC!


Well then let me be the first to propose hydrogen-free jet fuel. Just imagine the cooling that could be achieved if we were to stop dumping water vapor into the stratosphere!
…yet another danger posed by our insatiable need to dump DHMO residue wherever we see fit, I’m afraid.

F. Ross

Wouldn’t the contrails also have an effect on albedo and cool the earth a bit?

If clouds are a negative feedback, then wouldn’t con trails be as well? Mind you, I wouldn’t have guessed that global warming causes snow and cold weather either. Does anything cause cooling any more?

Dear Anthony,
The little red warning clause at the end certainly cooled my jets. Think of the humor foregone!!!
How about Contrailians? Can we mention those folks? UFO’s? Tinfoil hats?

Roger Knights

I presume this is based on the theory that high-altitude clouds have a warming effect and low-altitude clouds have a cooling one (?)


Anthony, if you’re not going to read the Tips & Notes thread then just get rid of it so people don’t waste time posting. This story was noted there at least six times before the Pielke post.
REPLY: Apologies, given what transpired today, and what I had to do yesterday to defend my work, I’ve been a little busy. – Anthony

Jeff W

Wouldn’t the albedo increase caused by the predominately daytime contrails have to block more incoming solar radiation than outgoing re-radiation. I don’t get it.


I see subsidized solar airplanes in our future.


Now I will have to go and read this thoroughly – as it sounds like a contradiction of the cloud providing cooling (-ve feedback) theory if contrails are going to contribute warming? Or is it just related to the height of contrails compared to real clouds?


This might very well be true for it’s probable, however everyone seem to (dis)miss proportions.
If CO2 affect climate like a woman fart in the universe does, and them planes affect the climate like a couple of Al Bundy farts in the universe. It’s still just three farts in the universe and will take a few billion years until they really starts to smell the place up.
So how big is its effect?
Oh, sorry, essentially they just need tons of more of the tax payers money to figure that one out.


My first gut reaction is that on the scale of that photograph, actual jet contrails would be far far thinner in width than they appear on the photo. I wonder if there is a way for the public to have access the original photo just to verify its authenticity?


Wait a minute – I remember a documentary a few years ago going on about “global cooling” which blamed contrails on cooling the planet, rather than warming.
There was a study done on the effect of 9/11 (all planes were grounded for 3 days) and the surface temperature, which apparently “proved” the effect.
This hasn’t been turned into warmcool has it?

Jeroen B.

I seem to recall but I’m not sure that this effect was first seen just after 9/11 where the absence of contrails led to more intense temperature differences between day and night ?? (It might be I’m remembering wrong, dredging up an old memory! I’ll be happy to be corrected!)

Didn’t the temperature go up a little bit after 9/11 when there weren’t any contrails when all the planes over the US were grounded?

How is it possible to isolate the effect of contrails from all the other effects on climate? There are two opposite effects from contrails; first they can reflect some of the sun’s radiation away from the surface, and second they can prevent some radiation from leaving the Earth by reflecting it back down. But which is the greater? I would have thought it was impossible to find out practically, so I assume it was done using a computer programme, in which case it all depends on what data was fed into the programme in the first place.


Further to the comment above IIRC the documentary was called “Global Dimming” and was by the BBC’s Horizon.


No refection of sunlight back out to space then?


I meant reflection…sorry.
One of our grandsons calls them ‘Aeroplane Tails’!

Con-trail = Cloud
Albedo vs GH gas ?
Would the Earth totally covered with cloud be warmer than the Earth with no cloud at all ?

Bob Diaz

If they waited a few days, it would have been April1.

Paul Deacon

Anthony – I seem to remember a paper (?) soon after 9/11 which attempted to calculate the effect of vapour trails from aircraft based on observation (taking advantage of the fact that for a couple of days the skies in the US were free of aircraft). I recall the conclusion was that vapour trails had the effect of cooling the atmosphere (by reflecting sunlight).


So that is where the “UnitRoot” has been hiding !!

Papa Bear

homo sapiens says:
March 31, 2011 at 12:54 pm
You beat me to it – it is all models.
The same models that say that clouds are positive feedback …


As pointed out by others. This was covered post-9/11. Look up global dimming on wikipedia for a synopsis.

Self-flagellation masquerading as science.


Chemtrails?? I thought that is what came through a straw from a mirror??? Nothing to do with climate or aircraft really.


And here I thought clouds cooled the earth! (I notice a distinct cooling when a cloud drifts by on a hot day.) Are you sure these “researchers” haven’t got their mathematical sign backwards??

This has been busted, or at least there is a peer-reviewed paper that disputes this totally.
The Hong paper made mincemeat out of the whole argument around 9/11 and this paper is just that same issue, but recycled. I didn’t tackle the issue directly, but I do cite the original papers when I was discussing the climate response time.

Vince Causey

Have they taken the contrail densities from the USA and extrapolated that to the entire planet? The USA and Western Europe have the densist air corridors, and there are corridors connecting Europe, Asia and the USA. But I would imagine that covers only a few percent of the Earth’s surface. I bet under most of the globe, you would be lucky to catch sight of a single contrail all day.


Simple observations…
Usually, on a nice clear summer morning, the sky is all blue without a trace of vapour or whatever. You can feel the warmth of the sun and you can see your garden being all happy to grow. Then you can see one trail, then another, and another and before noon comes the sky is always covered with a white veil of condensed vapour. Then it gets cooler but more importantly, the amount of photons reaching the surface and exciting the chlorophyll of my tomato plants is significantly reduced. Should they make a study on the effect of contrails on crop yield instead? I bet there should be a significant reduction, much more than a few tenth a degree of warming.
Now, since contrails are mainly found above continents and that the sun can still warm up the oceans, how a somewhat permanent cloud cover above land only should affect the global temperature?


This will never work…
…at least until they figure out a way to tax it


Funny how RAF jets contrails are absolutely… fine.


I think it is disingenious to use merged photos/elapsed time photography to “illustrate” and thus “overstate” the potential impact of contrails that is suggested by yet again another model. And I am with several other commenters, even if this extremely thin layer within the thin layer of the atomosphere does have an effect, I think the albedo effect from a contrail is of greater importance that their ability to hold in heat.
Sorry R. Gates, I don’t see this report in any way being a “strong rebuttal” of my thinking on human impacts on the “earth” – which are at best regional and to which regional actions are perfectly sufficient to address. (Beijing needs to get its pollution under control for its own residents or China’s, and eventually it will, just as LA has/is doing)

Tom in Florida

Whether it has a warming or cooling effect, file this under HIVES (Human Influenced Variations of Ecological Systems)


[snip – links to a chemtrails website]

David L

It’s worse than we thought! ( humans are having a wider impact on the climate than previously thought)

Stephen Skinner

I have never ever ever been on any holiday or beach or both where any sort of cloud made it warmer. Ever. Whenever the sun comes out from behind any sort of cloud it has always felt warmer and perceivably more than temperatures like 0.92C
My first cross country attempt in a glider ended in a field very near Aldermaston in the UK. What ended it was a very high and thin layer of cloud that came between the sun and the bit of the Earth I was flying over. I was at about 4,000 ft and it took about 5 minutes for the last thermals to come up and then I couldn’t find any lift. The cloud cover was continuous and 6 other gliders landed out at the same time across 2 counties.


If contrails are such a strong positive forcing, and the world hasn’t been warming since 1998, and we also had a growing CO2 positive forcing, this means that without human activities we would be… in an ice age already?
Phew. So let’s book some cheap holiday flights; keep up the good work, fellow humans!


Clouds, including from aircraft, cool the climate. They dont warm it.
O but I forgot – cooling is the new warming, or “disruption”.
Aircraft harm the climate by angering the evil spirits that live in the upper troposphere, who are also responsible for malicious global warming unless offerings of money and human blood are made to appease them.