Long before there were commercial jet flights, observers on the ground were curious – and sometimes concerned – about the vapour trails that materialized behind planes. They are still being studied today. In this post, we’ll look at some of the most frequently-asked questions about contrails. Why do some contrails persist while others rapidly fade? Can contrails form over deserts? Don’t contrails look a lot different than they did a few years ago? What are those weird clouds?
What Contrails Are Not
Among chemtrail-watchers, there exists some confusion as to what contrails actually are. For instance, the website The Truth Denied, which purports to tell us all about chemtrails and chemtrail-related issues, identifies contrails as “smoke” from jets. But contrails are not smoke, and they are not just jet exhaust.
|Not a contrail.|
What Contrails (Condensation Trails) Are
Contrails, originally known as vapour trails, are essentially artificial clouds formed behind high-flying aircraft. As mentioned in the last post, the high-temperature combustion of jet fuel during flight causes jet engines to emit water vapour, gases, and particles. The hydrocarbons in jet fuel produce water vapor as a by-product of combustion. Sometimes only water vapour is required for contrail formation, since aerosols (tiny particles) suitable for water droplet formation are already in the air. In the sub-zero temperatures found at high altitudes, this water vapour can raise the relative humidity of the air behind the plane past saturation point. The vapour then condenses and freezes around aerosols in the air, and these millions of tiny water droplets or ice crystals are what you’re looking at when you see a contrail.
Contrails typically become visible about a wingspan distance behind the plane, as it takes some time for the vapour to cool down enough to condense. (1)
Contrails most commonly form behind jets flying at high altitude (over 26,000 feet), but they can occur at lower altitudes under certain conditions. And other aircraft can produce them as well. In fact, the first known contrail sighting occurred during WWI, over 20 years before the first jet was in the air.
In 1918, Captain Ward Wells of the U.S. Army Medical Corps, who was serving in France during the Meuse-Argonne campaign, wrote of seeing “several strange and startling clouds” in the air. When he and his fellow ground observers looked at these “long, looping, graceful ribbons of white” more closely, they found “some distance ahead of each cloud point the tiny speck of a chasse [sic] plane.” (2)
These contrails developed on a cloudless day, giving lie to claims that contrails don’t appear when the sky is clear and blue. (Above Top Secret forum member “cutbothways“: “So, what it boils down to, is that on a clear day, it’s very, very unlikely that a contrail would form, let alone persist.”)
Captain Wells’s brother, Everett Wells, was so fascinated by the phenomena that he reported it to Scientific American magazine. (“Clouds formed by Airplanes“, June 7, 1919)
The term “contrail” is also attached to the short vapour trails that sometimes appear for a brief time over aircraft wings or engine propellers, made up of atmospheric water that has condensed due to air pressure reductions caused by the movement of the wing or propeller. We’ll go into more detail about that later. (1)
As contrails became increasingly common over the U.S. in the ’50s, confusion and worry set in among people on the ground. A retired aerospace engineer told me he first learned of this in 1964, when a man of his acquaintance expressed concern that vapour trails might actually be Soviet chemical-spraying operations, intended to harm U.S. citizens. Once the man learned what the trails were and viewed them being laid down by ordinary American planes, he calmed down.
Numerous newspaper articles from the ’40s and ’50s attest to the bafflement people felt when viewing contrails for the first time, and to the nascent state of our knowledge about contrails.
– Weird Signals In Skies As 1950 Dawns (December 29, 1949 Los Angeles Evening Herald and Express). This article describes pilots actually chasing an unseen plane because it was leaving a smoke-like “mystery vapor in strange designs”. The author notes, “Observers at the U.S. Weather Bureau spotted the trails spreading across the sky at an estimated 20,000-or-25,000 feet.”
You can see a few more of these at Contrail Science. The headlines alone indicate how people were feeling about vapour trails:
– Vapor Trails Get Many Excited (January 12, 1950 San Mateo Times)
– Mystery Veils Vapor Wreath in Galveston’s Sunny Skies (October 28, 1951 Galveston Daily News). This article notes that even the local weatherman was stumped.
These reactions were not as extreme as that of Brazil’s Yanomami Indians, who huddled by their fires and waited for death when they first saw smoke spewing from the “asses” of airplanes in the early 1940s. As Helena Valero described it, they feared their creator had returned to end their civilization by releasing some awful sickness in the form of smoke.
Americans of the ’50s didn’t view contrails as the exhalations of a vengeful god, but they were quite spooked by the “mystery trails” (and as we’ll see in later posts, chemtrail-watchers are some of the gloomiest Cassandras in the world; like the Yanomami of the ’40s, they see death and cataclysm in each and every airplane that crosses the sky).
On the other hand, pilots were already very familiar with vapour trails by 1950. In several reports of UFO sightings made by pilots in that year, the men specifically mentioned vapour trails.
– “We know all about jets and vapor trails and optical illusions,” airline captain Sam Wiper told the Marysville-Yuba City Appeal Democrat. (“Veteran Pilots Glimpse Strange Object”, June 28, 1950)
– A Feburary 27, 1950 report archived by NICAP describes a sighting made over Illinois by a man piloting a PT19. “He did not notice any flames or smoke and could see no vapor trails.”
– In the July 1950 issue of FLYING magazine, airline pilot G.W. Anderson said of the strange object he and the captain saw, “There was no reflection, no exhaust, and no vapor trail.”
Lack of knowledge, perhaps more than anything else, nourishes fear and allows it to grow. By the mid-90s, Yanomami in even the remotest highland villages were accustomed to seeing planes, understood they contained valuable trade goods, and often welcomed their arrivals.
Back in 1953, National Weather Service scientist Herbert Appleman came up with a chart to determine when a jet would or would not produce a contrail. For years, the U.S. Air Force Weather Agency used variations of this chart to make contrail forecasts. In 1954, Appleman used similar calculations to help determine when icing would occur (as described in the last post, the problem of fuel icing was identified that year, after a tragic B-52 crash). These calculations are also still used today, in updated forms.
Because weather data is never perfect, contrail predictions made by modified Appleman charts are never perfect, either. What the results indicate is that when it comes to contrail formation, the words “never” and “always” don’t come into play at all. Contrails can and have been produced under less-than-optimal conditions. Ideal contrail conditions are generalities, in other words.
Numerous variables determine contrail formation: The efficiency of the plane engine, air temperature, air pressure/altitude and relative humidity with respect to ice are a few of them. (3)
Very generally speaking, when a contrail forms, the temperature is below -40º (4), and the humidity level most frequently mentioned is 70% or higher (the warmer the air, the more humidity will be needed to produce a contrail). Necessary altitude varies. Contrails can form as low as 16,500 feet under the right conditions. (5) Various types of jet engines require different conditions to leave contrails. Some produce more water vapour than others, some are less efficient and have hotter exhaust. Humidity, too, is flexible; results from NASA experiments show contrails persisting in humidity as low as 10%.
Some chemtrail-watchers, like “cutbothways”, contend that long-lasting contrails have formed and spread even when the humidity was too low for contrails to form at all. Ergo, these must be chemtrails. The problem with this reasoning is that weather data is never completely up-to-the-minute and accurate. For instance, as explained at Contrail Science, it is basically impossible to measure humidity in a specific part of the sky at a specific altitude at a specific time. Estimates must be drawn from measurements taken by weather balloons that are launched from weather stations an average of 235 miles apart every 12 hours. Humidity can vary up to 80% during a 12-hour period. Also, the balloons can drift as far as 100 miles from their launch sites, so we never know precisely where the measurements are being taken.
So when someone tells you that contrails never form at -37ºC, or that humidity is always above 70% when a contrail forms, or that we know the exact humidity in the vicinity of a certain plane, take that with a grain of salt the size of your arm. If NASA can’t nail this stuff down, I don’t think some guy with an old-school Appleman chart is going to be able to do it.
Yes, Contrails Do Persist
Nearly every source of chemtrail information will tell you that jet contrails shouldn’t last more than a couple of minutes. That’s the core of the entire chemtrail theory. Here are a few examples of that claim:
“Chemtrails are said to vary from contrails in their length of persistence.” – FAQ page of Chemtrail Central.com
“Chemtrails (CTs) look like contrails initially, but are much thicker, extend across the sky and are often laid down in varying patterns of Xs, tick-tack-toe grids, cross-hatched and parallel lines. Instead of quickly dissipating, chemtrails expand and drip feathers and mare’s tails.” – Toni Thayer of Blue Skies International (now defunct), reposted @ rense.com
“For some reason, after 1998, there were SO MANY jets leaving white trails in the sky that lasted all day, making THE WHOLE SKY OVERCAST, that NASA decided we now had a phenomenon called ‘persistent jet contrails.’ But they cannot explain why they are persistent …” – “Basic Facts – About the Sky” @ 911WeKnow.com
“These ‘tracks’ in the skies…are unlike regular high-flying aircraft’s vapor trails. Instead of dissipating rapidly, these so-called ‘chemtrails’ mesh together for hours and are often mistaken for natural clouds.” – “Military Said Behind Up to Four Different Chemtrail Progams” by Mike Blair, The Spotlight (now defunct)
But persistent contrails are nothing new, and there’s nothing strange or mysterious about how and why they form. The first known persistent contrail was spotted in 1921.
Here’s how it works: If the humidity is high (higher than that needed for ice condensation), the ice particles of a contrail will continue to grow in size by attracting water from the surrounding atmosphere, and you have a persistent contrail. As the abstract for a 1998 paper by Eric J. Jensen et al puts it, “At temperatures above about −50°C, contrails can only form if the ambient air is supersaturated with respect to ice, so these contrails should persist and grow.” When you think about it, contrails have to spread in high humidity. What else could they do? (6)
Contrails spread, also, because of air turbulence created by the passage of aircraft and differences in wind speed, as we’ll get into later. Persistent contrails can last for hours while growing to several miles in width and over 1000 feet in height. (1)
The first known sighting of a persistent contrail was made in 1921, 18 years prior to the first jet flight. A La Pere plane flown by Lt. J. A. Macready left what was described as “long feathery white streamers” at an altitude of 26,000-27,000 feet. This was a discontinous contrail, with a gap between the first and second “streamers”. The contrail lingered for about 20 minutes before spreading and merging with existing cirrus clouds. (2)
One question frequently asked by chemtrail-watchers is, “How can a ‘normal’ contrail and a persistent contrail exist in the sky at the same time?” Seeing this, they conclude there must be something unusual about the persistent contrail – it has to contain some special ingredient the other contrail doesn’t. In other words, it must be a chemtrail.
|This photo, taken in British Columbia, appears to show a contrail and a chemtrail|
Here’s the thing: Atmospheric conditions are not uniform throughout the visible sky. Even on a clear, blue day, the wind, temperature and humidity in one part of the sky can differ dramatically from conditions in another part of the sky (as little as half a mile can make the difference when it comes to contrail formation). So one jet flying at 30,000 feet may leave a contrail that fades rapidly, while another jet flying 10,000 feet higher at around the same time leaves a contrail that lingers and spreads because the humidity is different in that part of the sky. Areas of uneven temperature and humidity also account for discontinuous contrails, vapour trails that thin out or halt completely in places (chemtrail-watchers point to these as evidence that the plane’s chemtrail sprayers have been briefly shut off). Recall, though, that in 1921 we already had a contrail that exhibited three of the characteristics most frequently cited as impossible by chemtrail-watchers; it was discontinuous, it persisted for more than a few minutes, and it became indistinguishable from cirrus cloud cover.
Standing on the ground, you might think you can accurately gauge the altitudes of two airplanes, and estimate how far apart they are, but that’s actually almost impossible to do. Two planes, clouds or contrails in the sky can look like they’re within a few hundred feet of one another, when in reality they’re thousands of feet apart and at different altitudes.
The shapes and “behaviour” of certain contrails also baffle chemtrail-watchers. Why are some contrails swirly or corkscrew-shaped? Why do some of them zig-zag, curve or squiggle after forming in a straight line? Why do some of them “drip”?
Once again, I turned to Captain Bruce Sinclair for an explanation. He’s a pilot with nearly 46 years of flight experience, and knows more about contrails than anyone I know. Here’s what he had to say about some of the unusual contrail shapes:
In a presentation given last year, chemtrail researcher Sofia Smallstorm showed a photo of a “wine-opener style” contrail and said, “Nowadays, we have an effect coming out of the environment that can’t possibly be natural.” (7)
Contrails that appear to be corkscrew-shaped, or have corkscrew formations at their edges, have been shaped by the wake turbulence behind the plane. These contrails, which aren’t particularly rare, have been seen in the skies for decades, and wake vortex studies have supplied us with the knowledge of why and how they form.
Wake turbulence can be broken down into two main phenomena, wingtip vortices and jet wash. Jet wash refers to the rapid movement of gases expelled from a jet engine. It is extremely turbulent, but lasts only a short time. (8) Wingtip vortices occur when a wing is generating lift. Air from below the wing is drawn around the wingtip into the area above the wing by the lower pressure above the wing, creating long tubes of circulating air. Wingtip vortices are more stable than jet wash. They can remain in the air for up to 3 minutes after the passage of an aircraft, creating turbulence for any aircraft flying near it. (9)
If no contrail forms behind a plane, the wingtip vortex is completely invisible. If a contrail does form, that contrail can take on the swirly shape of the vortex. A NASA study of wake turbulence used coloured smoke to make wingtip vortices visible, resulting in some amazing film footage.
In the video clip below, Captain Sinclair and a friend describe wingtip vortices while examining the photo seen above.
These contrails start out straight, then spread out into squiggly formations. The reason for this is quite simple; the ice crystals have been dispersed by wind, specifically by vertical and horizontal wind shear. In this clip, Captain Sinclair talks about how wind affects contrails.
Rarely, you’ll see a dramatically loopy, squiggly trail in the sky that isn’t a contrail at all, but a rocket trail made up of smoke. Photos of rocket trails have also been presented as evidence of chemtrails.
There are many photos said to show mysteriously “dripping” chemtrails. Some of these are misidentified cirrus clouds. Others are “corkscrews” seen from an angle that makes them appear to be drips instead of swirls. But most of the dripping chemtrails are contrails that have formed pendules, like the one in the picture below (often called “doughnuts on a rope”). This particular contrail photo, found on the Contrail Science website, is from the 1991 edition of the Peterson First Guide to Clouds and Weather. Like the caption indicates, parts of this contrail are sinking at a faster rate than other parts, and it’s not because they’re saturated with extra chemicals. Rather, this involves wake vortices. The long tubes of air left by wingtip vortices usually sink more slowly than the “core” of the wake.
Pendules can also form from skywriting and skytyping trails, which consist only of smoke. In short, it’s about the air, not what’s in the trails.
Many of the “dripping” chemtrail photos I’ve seen show fall streaks from cirrus clouds.
Other unusual contrails are formed by military jets, which can perform maneuvers that commercial jets seldom or never do. If you see a “doughnut” contrail, or a contrail with a right angle in it, chances are good it was left by a military plane or a plane performing aerobatics. It formed the same way as any other contrail, but the movements of the plane gave it a distinctive appearance.
Contrails over desert areas
This fellow and many other chemtrail-watchers find it extremely peculiar that persistent contrails can appear over desert areas.
But they can. It’s not unusual, and it’s nothing new.
Jets are flying in the upper troposphere, the tropopause, and the lower stratosphere. It’s cold up there. There can be humidity sufficient for contrail formation even when it’s hot and dry on the ground. You probably won’t see as many persistent contrails over desert regions as you will over moist regions, but you will see them. Contrails have been spotted over the Gobi and every other desert on the planet. George Marrett, a test pilot who flew experimental aircraft in the ’60s, even titled his memoirs Contrails Over the Mojave.
Do contrails look different today?
Quite simply, yes, contrails do look somewhat different than contrails of previous decades. We’ve always had persistent contrails and weirdly-shaped contrails, but contrails tend to be larger than ever due to the increased size of jet engines, and innovations in jet engine technology have resulted in fuel being burned more efficiently. This creates cooler water vapour in the exhaust, which is more likely to condense.
Perhaps most significantly, as discussed in the last post, the amount of air traffic has increased dramatically, producing more contrails than ever. For this reason alone, your odds of seeing persistent contrails today are far better than they were in the ’60s, ’70s, ’80s, or even the ’90s. And it is no longer unusual to see crosshatched contrails in the sky, left by some of the thousands of planes that fly in the east-west, north-south grids of the National Airspace System (NAS).
We Really Don’t Know Clouds At All
Chemtrails are usually defined as contrails that don’t dissipate quickly, and/or spread out into cloudlike or mistlike formations. “Contrails don’t form clouds, but chemtrails do,” is the refrain. Chemtrail-watchers tell me that contrails (chemtrails) began to form clouds beginning in the late ’90s or early ’00s. Prior to that, they say, contrails disappeared within minutes. A 2010 article at Infowars.com, “Scientists Admit Chemtrails are Creating Artificial Clouds“, states that scientists only recently began saying that contrails can create cloud cover, and insists this is not a natural occurrence. Ten years ago, the author writes, contrails dissipated within minutes. He contends that contrails – which are essentially clouds – can only form cloud cover if they’re not contrails at all, but chemtrails.
Some chemtrail-watchers even point to animated contrails and clouds in children’s cartoons as evidence that someone is trying to brainwash children into believing that chemtrails are normal, and/or that jet contrails can create clouds:
- “Chemtrails in Disney Movie Cars” @ rense.com
- A video by YouTube user “ChemtrailsEire” shows us stills from movies, cartoons and TV programs that supposedly feature “chemtrails” (an effort to “dumb down the children”). However, these are all ordinary-looking contrails – and in one case, simulated skywriting.
- At the blog Runnymede Institute, “rmiglobal” urges us to boycott LEGO toys because a TV commercial with “chemtrails” in it is “being used to condition children that Geo-Engineering our atmosphere is normal.”
- As I mentioned in a 2008 post, a commenter on the Rigourous Intuition blog forum was alarmed by the Disney cartoon series Little Einsteins, partly because a jet leaves a chemtrail behind it in one episode. Another commenter chimed in, “Chemtrails are being normaled into some media despite some disinfo around this topic to create disbelief.” Another added, “What it is is a pictogram for ‘Jets create clouds.'”
But what if contrails forming cloud cover isn’t a recent phenomena? What if this has been going on over our heads for years, and we just weren’t paying attention?
That, I’m sorry to say, is exactly the case. The phenomenon of artificial cloud cover created by contrails has been observed and studied for decades. In the last post, I mentioned two scientific papers on the subject, written in 1971 and 1981. Now let’s look at more examples. Keep in mind that these are only a few of the papers related to contrail clouds; the more you look, the more you’ll find. My purpose here is not to exhaustively detail the issue (let’s face it, that would be boring), nor to vouch for the scientific value of these papers, but to provide evidence that we have known for many years that contrails can (and do) contribute to cloud cover, and that this was amply documented prior to the chemtrail sightings of the late ’90s.
- A 1970 scientific article by Peter M. Kuhn, “Airborne Observations of Contrail Effects on the Thermal Radiation Budget“, has this to say: “The spreading of jet contrails into extensive cirrus sheets is a familiar sight. Often, when persistent contrails exist from 25,000 to 40,000 ft, several long contrails increase in number and gradually merge into an almost solid interlaced sheet.”
- The 1971 paper by Machta and Carpenter, “Trends in High Cloudiness at Denver and Salt Lake City”, published In Man’s Impact on the Climate [Study of Critical Environmental Problems (SCEP) Report], edited by William H. Matthews et al. (MIT Press)
- A Field Guide to the Atmosphere (1981) on contrails: “Sometimes they are ephemeral and dissipate as quickly as they form; other times they persist and grow wide enough to cover a substantial portion of the sky with a sheet of cirrostratus.”
- Stanley Changnon’s 1981 paper. An earlier draft of this paper inspired an NBC news segment on contrail cloud cover in 1980.
- James K. Angell’s 1990 paper “Variation in United States cloudiness and sunshine duration between 1950 and the drought year of 1988” suggested that contrails were responsible for a 2% increase in cloudiness over the U.S. between 1950 and 1988. (Journal of Climate, vol. 3)
- In 1991, similar “contrail cloudiness” findings for Salt Lake City were reported by K.N. Liou and S.C. Ou in their paper “An Investigation on the Climatic Effect of Contrail Cirrus”. (PDF)
- and for Europe, as laid out in a 1994 paper, “Contrail frequency over Europe from NOAA-satellite images“, by S. Bakan, M. Betancor, V. Gayler, and H. Graßl.
- The title of K. Sassen’s 1997 paper, “Contrail-cirrus and their potential for regional climate change“, is pretty self-explanatory.
And a few post-1997 studies bear mentioning as well, because they show that interest in contrail clouds remains high.
- In a 1998 paper, Patrick Minnis et. al. reported that the growth of contrails into extensive cirrus clouds was documented by satellite observations made during NASA’s SUCCESS mission (more on that later).
- The 1999 paper “Radiative forcing by contrails
- A 2001 paper by D.P. Duda, Patrick Minnis and L. Nguyen, “Estimates of cloud radiative forcing in contrail clusters using GOES imagery” (abstract)
- The 2002 paper “US Jet contrail frequency changes: influences of jet aircraft flight activity and atmospheric conditions” by David J. Travis, Andrew M. Carleton, Jeffrey S. Johnson and James Q. DeGrandd reported results of the study of satellite images of contrails left by military jets during the three days when U.S. civilian air traffic was grounded in the wake of the 9/11 attacks. They found that the cirrus clouds formed from these contrails lasted an average of 6-8 hours, and that just 6-8 contrails could expand to create cloud cover the size of Massachusetts. (PDF)
If you’re deeply interested in chemtrails and really want to get to the truth about what they are, you will probably benefit more from perusing some of these papers than from watching Disney cartoons.
For reasons that I don’t entirely understand, chemtrail-watchers sometimes refer to various types of clouds as “new” clouds, clouds that didn’t exist until just the other day. The one mentioned most often is cirrus uncinus. Sofia Smallstorm: “And here we have this new form, they tell us, new form of cloud, a hooked cloud called cirrus uncinus.” (7)
This is the kind of cirrus cloud that develops curving, hook-like “mare’s tails”, which you have probably seen at some point. They’re not new. Perhaps the name is new, but the cloud type itself is not. The only reason mare’s tail clouds may seem to be new is that they’re somewhat rare. As I was writing this, however, I noticed cirrus clouds that had formed slight hooks and snapped a picture (the dark smudge near them is just a camera defect).
Cirrus fibratus clouds can sometimes look like vertically pulled cotton candy, and are occasionally mistaken for persistent spreading contrails. At other times they have a patchy appearance, similar to altocumulus clouds, and are considered to be HAARP-related clouds.
Of the two photos below, can you guess which one appears on a chemtrail website with the caption “Pulsating frequencies create ripples in the layers of ‘clouds’. Google ‘HAARP’, located in Alaska”, and which one is captioned “Altocumulus are shown over the campus of North Dakota State University”?
I don’t know the original source of the second photo, but the first photo was taken by Prof. Donald Schwert in South Dakota in 1986, six years before work on the HAARP installation began.
Clouds will come up again in later posts, as some chemtrail researchers like to show us vintage paintings and photos as evidence that the fat, puffy clouds of the past have been almost entirely supplanted by streaky, chemtrail-created haze. As you can see in my photo, fat puffy clouds and blue sky aren’t quite dead yet.
Because the ice crystals in cirrus clouds can refract sunlight to produce dazzling iridescent effects like glories and circumhorizontal arcs, chemtrail-watchers have been known to think they’re really looking at a chemtrail that shimmers like an oil slick. There are many gorgeous photos of these effects at KaleidoscopeSky.net, the website of meterologist/naturalist Tim Herd. Herd’s book of the same title, by the way, includes a photo of a spreading contrail and a contrail that is still being laid down by a jet, much like the one already shown here. The caption reads, “Two jet condensation trails spread into lengthy new cirrus clouds in the sky over Estonia on August 20, 2005, revealing ripe conditions for ice crystal growth and halo appearances.” (p. 137)
It isn’t uncommon for contrails to appear iridescent, since they’re made up of ice crystals. It would only be weird if they never exhibited the rainbow effects of sunlight refraction.
Contrail Research and Forecasting
The sheer number of scientific studies involving contrails and contrail clouds indicates that meteorologists, atmospheric physicists and other weather-related scientists are paying close attention to what’s in the sky, and are willing to draw attention to contrail-related problems.
Satellite imagery is being used to routinely monitor and measure contrails, as you can see at this page about NASA’s Office of Earth Science Pathfinder program. Using this data, NASA maintains a contrail forecast page.
NASA has also undertaken the Subsonic Aircraft Contrail and Clouds Effects Special Study (SUCCESS) mentioned above, which employs a combination of ground-based equipment and aircraft equipped with scientific instruments to study the effects of subsonic aircraft on contrails, cirrus clouds and atmospheric chemistry.
Another program called Atmospheric Effects of Aviation Project (AEAP) was launched to assess the effects of aircraft emissions on the atmosphere.
And it’s not just NASA. A Google Scholar search for recent contrail papers returns hundreds of results, and a search for papers written after 1998 gives you thousands. People are looking up.
1. EPA factsheet on contrails
2. “Wakes of war: contrails and the rise of air power, 1918-1945, Part I: early sightings and preliminary explanations, 1918-1938” by Donald R. Baucom. Air Power History. Summer 2007.
3. NASA Contrail Forecast page
4. “The Contrail Effect” by Peter Tyson @ the PBS NOVA website (posted April 18, 2006)
5. Wikipedia entry for contrails (accessed June 26, 2012)
7. Sofia Smallstorm presentation, “From Chemtrails to Pseudo-life: Dark Agenda of Synthetic Biology”, given at Conspiracy Con 2011 (available on YouTube)