3 November 2022

Preconceived ideas on aviation and climate

From its beginning, aviation has been an object of dreams and fears, raising strong interest in society. It is now caught up in the storm of climate transition. On one side, the green aircraft will be the solution to every issue, on the other side “flygskam”, the “shame of flying”, emerged for a mean of transport to be banned. In this context, Carbone 4 aims to lighten up the debate by answering a series of questions & answers with a scientific and quantified approach. This first part aims at carrying out the state of affairs between climate change and aviation.

Links between aviation and climate change

1. Isn’t the impact of aviation on climate change minor?

Commercial aviation represented 2.6% of greenhouse gases emissions worldwide in 2018, and 5.1% of anthropic global warming between 2000 and 2018 taking into account non-CO2 effect. That corresponds to approximately 1 billion tons of CO2, equivalent in order of magnitude to the emissions of Japan (3rd global power and 5th emitting country). It is far from being insignificant.

Even more so when zooming on the individual scale: as an example, a round trip flight from Paris to New-York (1.7 tCO2e considering non-CO2 effects) represents 20% of the annual emissions of an average French person. Definitively significant. In view of the high awaited growth of the sector (approximately at least +3%/year according to estimates of the sector), its share in global emissions can easily explode and therefore weigh even more in climate change.

2. The non-CO2 effects of aviation are too uncertain to be considered…

 Certain human activities can influence climate differently than by emitting greenhouse gases (GHG). Aviation is one of these activities: beyond GHG emissions from the combustion of fossil fuel, it has an impact through physical and chemical atmospheric processes. The main non-CO2 impact of aviation is the effect of the contrails (condensation trails) appearing in an aircraft’s wake. They are the well-known white trails one can spot in clear skies. These trails can persist in a sufficiently wet and cold air and evolve into cirrus clouds (ice clouds) when the meteorological conditions are met. These kinds of clouds have an overall warming effect on climate. They reflect towards earth the radiation it emits without no equivalent albedo effect (reflecting sun’s radiation towards space). But these clouds are too small and unstable to be considered in climate models. Therefore, the magnitude of their effect remains uncertain, but this uncertainty is evaluated, as in every scientific work. Latest studies show that their effect is equivalent to double or even triple the radiative impact due to GHG emitted by aircrafts. Evaluation of non-CO2 effects is yet to improve, but their significance is demonstrated. By counting them to zero, one is sure to be mistaken!

Climate effect of contrails

3. And air cargo?

In 2020, air cargo represented less that 0.5% of transported goods in Europe but 10% of overall freight emissions. Indeed, on the distances for which it flies, a plane  is 2 to 5 times more emissive than a truck and 200 to 400 times more emissive than a train or a cargo ship! With a stable share until the beginning of the Covid crises, goods air transportation has greatly risen since, especially with the development of online shopping. It has progressed by 19% between 2020 and 2021, and it’s a trend that should continue according to the international air transport association (IATA), an increase of emissions will follow. 

Today, 70% of payload is transported in the cargo compartment of passenger aircraft. Cargos can be seen as a co-product of commercial flights, but it is a share that could decrease. Big transport companies and integrators plan to acquire more cargo planes (in average 2 times more emissive per ton) to remedy to the explosion of online retail responsible of the increase of the share of air cargo

However, to put the subject back into perspective, freight accounts for 15% of aviation emissions, whereas the 85% remaining correspond to passenger transportation.

4. Should aviation fear the physical effects of climate change? 

In comparison to other means of transport, aeronautics facilities has a relatively small infrastructure footprint: no railway, road, bridge nor tunnels. It would be easy to wrongfully conclude that aviation isn’t exposed to climate change’s physical impacts. 

Most airports are located on coastal, low altitude zones, making them sensible to sea level rise. It is probably the first risk factor for the sector: submersion. 269 airports are already subject to this risk. In a 2°C scenario, respecting the Paris agreement, the number already rises by 30% in 2100. In a more pessimist scenario, this number could rise by 50% and affect 13% of global air traffic. The annual number of disruptions due to submersions would be multiplied by 18. These impressive numbers don’t even consider possible interactions between sea level rise and other climate hazards such as river floods or the increasing intensity of hurricanes and tropical storms. 

Other climate hazards can also disrupt air traffic from running smoothly. The heat wave that stuck 50 planes to the ground in Phoenix (Arizona, USA) in 2017 was an illustration of the vulnerability of aviation to heat. No taking off on too short runways or with some types of regional aircrafts (hot air is less dense, reducing lift), and accelerated wearing of the tarmac with time. It raises the question of the future of some hubs, such as Dubaï, fourth global airport in frequentation in 2019…