Your thesis is about the ways in which the French travel industry can meet the 2050 carbon neutral targets. Can you tell us about the situation for air travel as it currently stands?
Aurélien Bigo. Over the past few decades, the number of passengers has doubled every fifteen years. We have also seen an increase in medium-haul flights. Average fuel consumption per passenger has decreased fourfold since 1960, due to technological advances and a higher load factor for planes. However, this progress has been balanced out – and then some – by the increase in traffic. This means that the greenhouse gas emissions of the aviation industry are continuously on the rise. This growth has only been hindered, for a while, in times of crisis, such as the post 9/11 period and the current Coronavirus-related economic crisis.
Is the aviation industry capable of reducing its carbon footprint?
For this, we will need disruptive innovation so that the sector may one day shake its reliance on fossil fuels. These innovations should be assessed according to several different criteria: environmental impact (on CO2, but not exclusively), cost, and potential roll-out date. According to these criteria, no current technology is compatible with the French Climate Plan’s goal of reaching carbon neutrality by 2050, or with the target of limiting global warming to 2°C. The risk is that efforts may shift to other industries.
What about biofuels?
On average, the current, first-generation biofuels emit just as much greenhouse gases as petrol does, if we look at their life cycle assessment (LCA)1. This is mostly due to changes in land use – areas are deforested to make place for biofuel crops, which themselves emit greenhouse gases. Second-generation biofuels, made from crop residue and biowaste, emit much less greenhouse gas. However, they are in limited supply. Their potential is insufficient to replace fossil fuels across the entire aerospace industry. And let us not forget that other industries, such as road and sea travel, are also invested in these kinds of fuels.
Is hydrogen the solution?
The French government recently announced a national strategy to develop decarbonised hydrogen2. The objective is for the first hydrogen planes to be launched by 2035, but the problem is that fleets are only replaced every 20 years, at best. This plan would also not comply with the Paris Climate Agreement. To stay within 2°C of global warming, we would have to reduce our greenhouse gas emissions by at least 2.7% every year, which will be impossible.
What’s more, hydrogen has a major disadvantage – it is very hard to store. That means it can only be used for short- and medium-distance flights, whereas it is long-haul flights that contribute the majority of the industry’s carbon emissions. Finally, the cost of hydrogen is very likely too high for this fuel source to be viable. In any case, greenhouse gas emissions are not the aviation industry’s only problem when it comes to the climate. NOx emissions, condensation trails and induced cirrus 3 also have a negative impact, and neither biofuels nor hydrogen would solve that.
What are the solutions?
Technological solutions are not necessarily the answer. We have to think differently. The aviation industry often emphasises that planes do not use more fuel per passenger and kilometre than cars do. But if we look at CO2 emissions per hour, it is a completely different story. The history of mobility shows that travel times have stayed the same – one hour per day on average.
Our mobility has been shaped by the speed of modes of transport. We have a seen the rise in faster methods, which can take us 40–50 km per day on average, compared to the 4–5 km commute from a century or two ago. For longer distances, the same reasoning applies. If we look at emissions per transport time, planes pollute way more than other transport methods – we are talking about 90kg CO2/h, versus 7kg CO2/h for cars, and 0.6kg CO2/h for trains. When we look at it in terms of transport time, we see that planes are the most polluting means of transport, both due to high emissions per kilometre, and by promoting travelling the longest distances.
So, what can be done to make the aviation industry to drastically reduce its emissions?
Only by reducing air traffic will we be able to limit our emissions. But this solution is clearly taboo in the current climate, as politicians are counting on future growth, with airport extensions planned for Paris-Charles de Gaulle Terminal 4, Nice, Caen and Lille. The simplest way would be to take further action on domestic flights by closing the routes that are least used and can be travelled by train. The current measure of eliminating domestic flights that can be replaced by 2.5 hour-long train trips is not having a big enough impact. For international flights, measures should be considered on a global level to have a significant effect. A fuel tax could be an option. Companies could also opt to travel by rail for trips under 4 or 5 hours and use video conference tools to reduce the number of long journeys. That being said, 75% of trips are made for personal, not business, reasons.
Thesis defense on 23 November 2020. Thesis available here.
To learn more about this topic, see Aurélien Bigo’s article in The Conversation (available in French only).
