Why is there so much talk about CO2? 8 points to decipher


1. Why is there so much talk about CO₂?
We often hear about CO₂, but what is it really? In a nutshell, carbon dioxide (CO₂) is a natural gas that plays a crucial role in the carbon cycle, a vital element for sustaining life on Earth. It's part of the air we breathe, and without it, life as we know it would not be possible. However, since the industrial era, we have enormously increased the amount of CO₂ in the atmosphere, mainly by burning fossil fuels such as coal, oil and gas, as well as by modifying our natural environment, for example through deforestation.
Although the Earth has natural and highly ingenious mechanisms for absorbing some of this CO₂, such as with forests and oceans, known as "carbon sinks", today these sinks are no longer sufficient to compensate for the massive quantities we are emitting. Excess CO₂ intensifies the greenhouse effect, a process that keeps the Earth warm. Now, in excess, this greenhouse effect causes climatic imbalances, including global warming, which manifests itself in melting glaciers, the disruption of terrestrial and marine ecosystems and the disappearance of certain species. (1)
2. CO₂ emissions by type of transport

For a 1'000 km journey, the choice of means of transport has a major impact on CO₂ emissions. In Switzerland and France, where the majority of electricity is generated from low-carbon sources, taking the train, particularly the TGV, is the most environmentally-friendly option. On the other hand, in countries like Germany and Poland, where electricity is partly generated by coal-fired power stations and some lines are not electrified, coaches can sometimes have a lesser impact than trains. (2)
At first glance, according to the graph, the car seems more harmful than the plane in terms of CO₂ emissions per passenger per 1'000 km. We often hear that a plane consumes around 3L per passenger per 100 kilometers, whereas the car rarely exceeds 5L per 100. So we might think that the plane is more frugal, but is this really the case?
3. Why are airplanes such a nuisance?
Carbone4's article "Les idées reçues sur l'aviation et le climat " helped us understand a little more about why airplanes are harmful, beyond their CO₂ emissions. (3)
Firstly, aviation is a major contributor to global warming, not only because of CO₂, but also through other so-called "non-CO₂" effects. In addition to carbon dioxide (CO₂), aircraft emit nitrogen oxides (NOₓ) and water vapor, which is a greenhouse gas (GHG). We have to imagine that these effects react in the atmosphere and increase the ozone (O3) content, in the stratosphere. At high altitude, these emissions of water vapour and sulphur particles (present in the fuel) lead to the formation of condensation trails. By reflecting and trapping heat, these contrails amplify global warming.
What makes these emissions even more problematic is that, at thousands of meters in the atmosphere, they have a far more harmful effect than those released on the ground. At this altitude, gases and particles remain longer and have a more direct impact on the climate. In fact, recent studies show that non-CO₂ effects, such as contrails and NOₓ, could triple the climatic impact of aircraft.

So if we compare them with gases excluding CO2 and with the actual load factor of transport modes, what does that say?
Fuel consumption is not enough to assess the carbon footprint of a mode of transport. If we include non-CO₂ emissions, the plane emits around 260 gCO₂e per passenger per kilometer, compared with 196 gCO₂e for a car with a single passenger. And to be even more precise, we know that on long journeys, the passenger rate per vehicle is 2.2 people. This means that traveling with several people in a car considerably reduces your carbon impact.
In addition, calculations for public transport, such as air travel, already include average occupancy rates (e.g. 30 people for a coach, 10 for a thermal bus, 101-220 passengers for a short-haul aircraft, etc.).
To go further and calculate the carbon impact of different means of transport, you can use the online tool ImpactCO₂, which details the methodology behind each calculation: impactco2
4. The impact of transport infrastructures
The other argument often discussed, especially when talking about trains, is the impact of infrastructure. Here, we're talking about the grey energy associated with the construction of transport, airports, rails etc...
Of course, this dimension is important, but it really comes into its own in the long term, when new infrastructures are built. In the short term, whether it's rails or airports, these structures won't disappear until your next trip. Even taking this aspect into account, the carbon footprint of air transport remains the highest.
The bottom line: when everything is taken into account, the plane loses hands down.

5. Will the new planes improve the situation?
Since 1990, airlines have been seeking to reduce their fuel consumption, partly because of the rising price of kerosene. Technological advances, such as aircraft automation, have also contributed to this efficiency, with techniques like eco-piloting and weight reduction on board. These efforts have resulted in a more than 2-fold reduction in fuel consumption per passenger and per kilometer between 1990 and 2018.
Aircraft, it has to be said, remain impressive technological feats, yet despite this progress, as traffic has increased by a factor of 4.6 over the same period, total emissions have more than doubled. This kind of phenomenon is known asthe "rebound effect". By saving fuel, flight costs fall, so we fly more. What's more, the airline industry benefits from tax advantages, such as exemption from kerosene taxes and the absence of VAT, not to mention public subsidies for airport infrastructure, which keeps prices down.
6. Air travel: a privilege for the elite
Air transport also reveals a profound climate inequality. Around 80% of the world's population has never flown, while the richest 1% generate almost half of all air transport emissions. This inequality underlines the fact that air travel remains a privilege, often reserved for the wealthiest, while having a disproportionate impact on the climate.

7. What solutions for equitable access to air transport?
- The Frequent Flyer Tax: This progressive tax would increase with each additional flight by the same individual over a given period. This approach aims to make those who fly frequently, often the wealthy elites responsible for a significant proportion of emissions, pay more.
- Flight quotas: These would limit the number of kilometers flown or flights made by an individual over several years. This measure aims to guarantee equal access to aviation for all citizens, regardless of their financial situation, while limiting the environmental impact.
8. Change of habit or wait for green kerosene?
Beyond the technical improvements, it's a change in our perception of travel: taking a plane to cross continents in a few hours has become a normalized, almost banal gesture. The problem with aviation is the possibility of covering gigantic distances, which were unthinkable before. We're encouraged to go further and further, and repeatedly. In the end, it's not so much a question of infrastructure or green kerosene, but rather the choice of destination. It's the distance that makes our carbon budget explode.
It's obvious that, to reduce the climate impact of air transport, reducing or even stopping air travel is the solution. Even if air travel is quick and easy, especially when it's the price of a parmigiana. In Switzerland, almost three quarters of all flights are for leisure and personal travel, nothing really vital. So why not opt for less polluting modes of transport, such as train or coach, for our little escapades? We're right in the heart of Europe, so it's easier than you might think!
Unlike the car, the airplane is not electrifiable, at least not for mass operation. Green kerosene, produced from water and CO₂ using renewable energies, isn't just around the corner either.
So even if planes are becoming greener and more efficient, the short-term solution is still to reduce the number of flights. If you really can't avoid flying, choose economy class (to maximize the number of passengers), travel light to reduce fuel consumption, and take direct flights, since it's take-offs and landings that generate the most greenhouse gases.