Carbon labelling for flights

Carbon labels on flights are a specific form of eco-labelling. Carbon labels clearly show the carbon footprint of products to 'nudge' people into changing consumption habits. They are a soft policy measure that encourages people to choose the itinerary with the lowest carbon footprint when purchasing a flight, without actively limiting consumer choices. Studies show significant differences in emissions for flights between the same destinations. Carbon labels give visibility to these differences and influence consumer choices.

As a soft measure that does not actively constrain choices, the success of the carbon labels depends on their ability to change behaviour. Often, those most likely to be influenced by carbon labels are "environmentally minded". However, the extent to which even they are affected varies (Juvan and Dolnicar, 2014b). To date, the impact of such soft measures on consumer behaviour has not been shown to be significant. Soft measures cannot be considered alternatives to policies like carbon pricing, or technology-based regulations on fuel and aircraft type, which have a known quantifiable impact.

For carbon labels to be most effective, people need to understand the information provided and its significance, trust it, and understand how to change their behaviour in response. It is important to ensure consistency in presenting the information, the methodology sued in calculating emissions, and the input data used.

Currently, there is no universally accepted format for carbon labels, though the presentation of the information determines how effective it is in nudging behaviour. Some existing labels are aircraft-specific or airline-specific rather than flight-specific, which does not help consumers choose between different flight options.

• The methodology and input data used for calculations also differ. Data required for flight-specific labels include distance, aircraft type, freight and passenger load factors, seating configuration and fuel consumption. Fuel consumption data is typically not available to the public, and emissions calculators furthermore tend to provide estimates based on a "typical" flight rather than a specific aircraft and actual load factors. Many existing emissions calculators, therefore, vary widely in calculated CO2 emissions for the same flight, some by as much as 540% (Baumeister, 2018; Juvan and Dolnicar, 2014a).

Many existing carbon labelling practices are not effective due to poor communication and lack of standardisation. For carbon labels to be more effective, studies indicate a variety of best practices:

• Carbon labels should have a single globally recognised system and cover all commercial passenger flights, making them easily comparable.
• Carbon labels should be enforced by an independent authority and be mandatory for all flights.
• Simply presenting kilograms of CO2 emitted by a flight is too abstract. Only 5% of respondents of a survey of environmentally-minded tourists felt it would help decision-making (Gössling and Buckley, 2016). Emissions set in contrast to an annual climate budget may build more awareness (Baumeister 2018).
• The use of colour coding in carbon labels has been reportedly more successful in influencing behaviour, likely due to its similarity to the EU appliance energy rating system. The previously mentioned survey of environmentally-minded tourists showed that 26% would be influenced by a colour-coded label, though only 2% would be strongly influenced by one (Gössling and Buckley, 2016). Most studies that use a colour scale rely on the familiar green to red spectrum (green for the lowest carbon footprint, and red for the highest). However, studies to date do not provide firm guidance on how its upper and lower bounds should be determined in the context of aviation.
• Providing information on the labels about the purpose and goals of the label has been shown to increase preference for lower-emission flights significantly over labels that did not provide additional context.

Evidence from other eco-labelling initiatives, such as energy efficiency ratings on appliances, may be relevant in designing the most effective labels and estimating their impact. For example, a study of Chinese refrigerator purchasing habits showed that energy efficiency labelling had little impact on purchases on the lower end of the price range, but had greater influence at the higher end (Wang, et al., 2021). An EU study of energy efficiency labels found that letter grades are more easily understood and more influential than numeric scales (London Economics, 2014). 

• ravellers are generally very price elastic, which means there is limited evidence to suggest that carbon labels could significantly shift the behaviour of the general public. However, with time, if there is a standard, globally recognised system in place, it may increase the transparency of the environmental impact of flying. As a result, carbon labelling may interact with other decarbonisation measures. For example, it may incentivise airlines to undertake other decarbonisation initiatives such as voluntarily renewing fleets and demonstrating this improvement via the carbon labels.