Who hasn’t spotted a plane and those wispy white trails and thought, “I wonder where they’re headed? Wherever it is, I wish I were jetting off too”. However, those wispy white clouds are a huge cost to the environment and now subject to conspiracy theorists. Here we will debunk the theories, explain why contrails are such a problem, and how geoengineering could be here to help.
We’ve all seen the white cloud trails left behind an aeroplane, these are called contrails. Firstly, imagine a very cold day and you can see your breath. When the moisture in our breath is hotter than the air, the air we breathe out condenses into tiny droplets of water which appear as a small, misty cloud. Contrails are formed under the same principle. When the hot, humid exhaust from a jet engine mixes with the cold atmosphere, the water vapour condenses or even freezes around soot from the exhaust to leave a contrail (or condensation trail). Dependent on a plane’s altitude, and the temperature and humidity of the atmosphere, contrails can vary in their thickness, extent and duration. In fact, we can use contrails to predict the weather. A thin, short contrail indicates low-humidity air at high altitude, a sign of good weather. Whereas a much thicker, long contrail suggests more humid air at high altitudes, which can be an early indicator of a storm.
However, unlike our breath on a cold day, jet exhaust fumes contain a whole host of chemicals such as: carbon dioxide, oxides of sulfur and nitrogen, unburned fuel, soot and metal particles, alongside the water vapour. IN ADDITION to the already huge environmental impact caused by the carbon emissions from the aviation industry, studies have now shown that contrails are a even more potent contributor to global warming. Unlike thicker, naturally occurring low-level clouds which reflect 20-90% of sunlight and can subsequently cool the Earth, contrails are too thin to reflect much sunlight. Instead, contrails are much higher in the atmosphere, and the ice-crystals within them can trap heat from the Earth, warming the climate. Contrails can stretch for tens of miles, with the wind spreading them further and can last for hours.
When commercial air traffic was halted over September 11th-12th in the U.S in 2001, researchers could look at a “control sky” without any contrails to quantify the environmental effects of contrails. Since then, there have been many more studies into the environmental effects of contrails. In 2011, one study suggested the net effect of contrails has contributed more to atmospheric warming than all the carbon dioxide produced by planes EVER, and this is only getting worse as air traffic increases across the Globe. An initial proposed solution involved rerouting planes or the level at which they fly (by 2,000ft up or down), as contrails are impacted by weather and atmosphere. However, rerouting could lead to planes burning more fuel and thus releasing more CO2. The use of more efficient fuels which release less soot is another suggestion to reduce contrails, but if air traffic continues to increase the effect may be minimal. Cloud physicist, Andrew Gettelman argues in the 2019 Science article that contrails are a small part of the planet’s global warming problem but that the aviation industry still needs to consider the science and act accordingly to reduce their impact.
What about geoengineering? The concept of solar geoengineering is to remove CO2 from the atmosphere or reflect more sunlight from the planet. To do the latter, scientists propose launching tiny reflective particles into the stratosphere (forming a barrier around 20km up) which could reflect sunlight and thus cool the planet, counteracting global warming. However, to achieve this, millions of tonnes would be required and getting that volume of material 20 km up is a difficult task. Both China and the UAE have trialled “cloud seeding“ whereby silver ions are dropped into the atmosphere to make it rain, but solar geoengineering is a much bigger task. The idea originates from volcanoes; when a volcano erupts, a lot of sulfur is released which in turn reflects sunlight from the planet. The process is highly contentious with opponents arguing that even outdoor experiments could be politically dangerous and may eventually lead to military use of weather-controlling technology.
Due to the above concerns, current research is conducted in lab environments, with a leading group at Harvard, headed by David Keith. The group aims to send a steerable balloon into the lower stratosphere to release a small cloud of particles (firstly a harmless cloud of ice crystals, after which they would try other chemicals such as sulfur). The balloon would then fly back and forth through the cloud to analyse how it behaves. However, sulfate particles could damage the ozone layer, so many chemicals are under investigation to see which may reflect solar radiation but have the fewest side effects.
Whilst there are still many controversial points to solar geoengineering which need to be further researched, “chemtrails” conspiracy theories threaten geoengineering efforts before they quite literally get off the ground. Chemtrails theorists refer to the suggestion that governments etc. are secretly adding toxic chemicals to the atmosphere from aircraft (with a similar appearance to contrails) with various speculated motivations including sterilisation, reduction of life expectancy, mind control or weather control… There is no credible evidence that chemtrails exist. So, whilst many scientists argue that solar geoengineering would not reverse global warming, or be the answer to all our problems, many agree that the technology could slow effects from getting worse in the meantime.