We all see trails growing in clear blue skies, and we know the importance of the saturation point.
We know highly supersaturated, 125% – 140%, air allows for clouds to form, and subsaturation results in clear blue skies.
We have learned that jet engines are flying water-making machines.
We know that the word “chemtrails” has been socially stigmatised with conspiracies that make it an impossible subject to investigate or talk about.
We have learned that “trace” amounts are actually astronomically large numbers. We know the metallic elements and the high sulfur content of the fuel make the trails grow logarithmically, directly behind the engines. The hygroscopic ice nuclei are able to scavenge the water in the supersaturated exhaust and hold it to resist dissipation in subsaturated areas, and also accelerate trail growth in saturated areas.
Trails not only cause local changes in climate by making a sunny day cloudy, but the black carbon aerosols travel in the stratosphere to have a vast influence over global weather patterns. This is not considered geoengineering because trails are not made for the express purpose of changing the climate; they are a by-product of ordinary airline flights moving passengers and freight. If the same planes flew the same routes without passengers or freight as their purpose, they would be called geoengineering.
This section will discuss mitigation strategies and what can be done to limit the number of trails.
“Avoidance of contrail cirrus cloud” is a well-studied subject. One of the simplest methods is to fly the planes around the humid areas in which trails can be made.
A 2013 study by Wei showed that up to 70% of trails could be avoided by flying planes around humid areas. His “grid shifting” system adjusted the altitude and flight path of individual planes likely to form contrails, rather than changing the routing of the whole fleet.
This approach was more precise and targeted, with minimal disruption to existing flight plans, making it a more efficient and environmentally friendly solution.
The red areas of the map show the relatively small areas of the sky that can make trails, the graph shows the expected savings in trail numbers.
This world map highlights the areas of the sky in light blue, which are saturated and traditionally humid enough to support trail growth.
The dark blue areas are slightly subsaturated and would not traditionally have beeen humid enough to support trail growth. However, it is now possilbe for trails to grow in these subsaturated areas too.
The areas to avoid has got larger, but they can still be avoided using the grid shifting system. They still only represent about 20% of the sky.
The brown areas are far below saturation and can’t support any trails, not even chemtrails.
This 2013 study by Campbell investigated the extra fuel used to make changes to flight paths and found 48% of persistent trails are eliminated with a 0.5% increase in fuel consumption.
Additionally, it was found that for absolute contrail avoidance, fuel consumption increased by only 6.2%.
A 2018 study by Yin investigated transatlantic flights and found changes in route returned a reduction of up to 80% in exhaust trail formation.
Routing flights around the humid areas is a much studied concept.
A 1998 study by Sausen found that a dramatic reduction in contrails would be made if flights were routed either 1 km higher or 1 km lower than the preferred cruising altitude adopted by air traffic.
A 2005 study by Fichter found that lowering flights by 6,000 ft reduced exhaust trails by 60%.
A 2020 study by Teoh identified trails as climate forcing. Teoh’s strategy for mitigation involved rerouting only 15.3% of flights and says their “results show that small changes in flight altitudes are an opportunity for aviation to significantly and rapidly reduce its effect on the climate.”
A 2023 research article by Li found that most trails were produced not in the most saturated areas as expected, but more often in slightly less ice-saturated areas. Leading them to conclude the possibility that larger areas of sky exist in which trails could form.
This explains why we see many trails forming adjacent to naturally occurring cirrus clouds. Thus, extending the natural cloud to encompass vast areas of the sky.
This also confirms the effect of modern jet fuel composition on trail enhancement into subsaturated areas.
A 2020 study by Gierens found that areas predisposed to trail formation could be accurately identified using weather data readily published.
It confirmed the instrumentation was correct and the weather conditions were correctly measured, but they failed to reliably predict trail formation because they were not considering the ability of trails to form in subsaturated areas.
Similarly, the 2022 study by Moldanova called the OP-FLYKLIM project, and funded by the Swedish Transport Administration’s research and innovation portfolio for aviation, also failed for the same reason.
Both the Gierens and Moldanova studies were commissioned by high-profile institutions and should not have failed, but no study will be able to predict trails accurately if they use the traditional understanding of trail formation. This traditional view of trails has long been established and successful; there is no reason for it to be questioned or altered by science unless the role of small particles and sulfur-rich fuel is acknowledged.
The understanding of why contrail predictions are failing can only be gained if scientists consider studies like Wang (2022) and Li (2023), which recorded trail growth in subsaturated areas. If scientists do not understand that this change is because of the influence of hygroscopic particles in modern jet fuel, and do not make the appropriate changes to the traditional prediction models, they will always fail.
Li (2023) noted that mitigation of trails has become more difficult because they now form in subsaturated areas of the sky. This will affect any mitigation strategies using a re-routing flights system, but it has not made it impossible.
Routing planes around the humid areas is still the best option, and if these changes in routes are supported by changes in fuel composition, then trails can truly be stopped completely.
Jet A1 fuel has these chemicals that produce small ice nuclei: aluminium, iron, chromium, titanium and silicon. It has these elements that stick to the small nuclei and make them grow to the optimum size: calcium, magnesium, sodium, manganese, and zirconium.
We have 2 sets of chemicals, and by altering the ratio of one set to the other, we can control the size of the ice nuclei produced by the engine.
Fuel sulfur content provides the activation coating; therefore, removing aluminium, iron, chromium, titanium, and silicon will reduce the small ice nuclei, and removing the sulfur will prevent their enhanced hygroscopicity.