Non-carbon emissions from aviation and their impact on our environment
When discussing the environmental impact of aviation, much of the focus falls on carbon dioxide (CO₂) emissions. However, aviation’s contribution to climate change extends far beyond CO₂. Planes release a range of other emissions and byproducts that have complex effects on our atmosphere, some of which may contribute to warming even more than CO₂ itself.
Recently, these non-CO₂ emissions have started gaining the attention they deserve. At COP29, the UN Climate Change Conference hosted a dedicated discussion on contrails for the first time, marking a growing awareness of aviation’s broader environmental footprint. To fully address the environmental challenges of air travel, we must look beyond CO₂ and find ways to mitigate aviation’s full range of emissions.
Water vapour and contrails
Carbon dioxide is not the only greenhouse gas emitted by aircraft. At high altitudes, water vapour acts as a greenhouse gas, and when jet engines burn fuel, they release large amounts of water vapour as a byproduct — approximately 1.25 kg of water per 1 kg of fuel — considerably increasing the warming effects of air travel. Another phenomenon that occurs at high altitudes is the condensation of water vapour in the cold, dry air, forming cloudy streaks of condensation trails, or contrails for short.
Although they may seem harmless, these cirrus-like clouds trap heat in the Earth’s atmosphere, further amplifying the greenhouse effect. Unlike natural clouds, these artificial formations are directly linked to flight activity and can persist for hours under the right conditions. Studies suggest that contrails and induced cloud formation could have a climate impact comparable to or even greater than CO₂ emissions from aviation.
Particulate Matter
Jet engines also emit particulate matter, namely soot or black carbon, from incomplete combustion. These tiny particles play a role in cloud formation, acting as nuclei around which water vapour condenses and altering rainfall and weather patterns as a result.
Black carbon is particularly concerning because it absorbs sunlight very effectively, directly warming the atmosphere with greater potency than CO2. When it settles on snow or ice, it reduces reflectivity of light, accelerating melting and further contributing to climate change.
Sulphur oxides and nitrogen oxides
Fossil-based aviation fuels contain small amounts of sulphur, which, when burned, produces sulphur oxides (SOx). Similarly, the high-temperature combustion of fuels in jet engines creates nitrogen oxides (NOx). Both substances contribute to air pollution and cause harm to the human respiratory system when in the atmosphere as a hazy smog. They are also the precursors to acid rain, which has damaging effects on wildlife and ecosystems by altering soil and water chemistry.
Furthermore, NOx emissions react with atmospheric gases to form ground-level ozone, a greenhouse gas more powerful than CO₂. Meanwhile, SOx emissions actually have a temporary positive effect on global warming. Sulphur oxides lead to the formation of sulphate aerosols, which reflect sunlight and cool the atmosphere — as observed when Mount Pinatubo’s volcanic eruption in the Philippines in 1991 released massive amounts of aerosols, causing a global temperature drop of about 0.5°C over the next 15 months. However, these aerosols also act as seeds for cloud formation, the climate effects of which are not yet fully understood.
Addressing the environmental challenge
When taking contrails, sulphur oxides, nitrogen oxides, and black carbon into account, aviation’s total climate impact is estimated to be two to four times greater than CO₂ emissions alone. Despite this, many climate policies and emissions reduction strategies focus only on CO₂, overlooking aviation’s full environmental footprint.
With contrails and non-CO₂ emissions now on the global climate agenda, discussions like those at COP29 mark an important step toward addressing these overlooked contributors to climate change.
Addressing aviation’s full climate impact requires a combination of technological advancements, operational strategies, and policy shifts. For example, optimising flight paths and altitudes could minimise contrail formation by avoiding atmospheric conditions that favour their persistence.
Another solution that can easily be implemented is switching to sustainable aviation fuels (SAFs), particularly synthetic fuels such as those we are developing at Avioxx. SAFs not only have the potential to substantially reduce the lifecycle carbon emissions of air travel, but they also produce fewer soot and sulphur emissions when burned. This is because typical SAF production processes require clean, high-purity inputs, unlike fossil-based jet fuel, which is derived from crude oil containing vast amounts of impurities.
A more sustainable future for aviation
The conversation around aviation and climate change is evolving. While CO₂ reduction remains essential, ignoring non-CO₂ emissions leaves a significant gap in the fight against global warming.
With growing attention on contrails, particulate matter, and sulphur and nitrogen oxides, the aviation industry and global policymakers are beginning to recognise and that the environmental impact of aviation is far more complex than carbon emissions alone. By implementing science-driven solutions and prioritising sustainable aviation technologies, we can work toward a cleaner, more sustainable future for air travel.
To learn more about how Avioxx is contributing to a greener aviation future, please get in touch at info@avioxx.com.