A British study reveals that although long-distance trips represent only about 2.7% of journeys, they are responsible for 69.3% of carbon emissions related to passenger transport. And while international travel accounts for only 0.4% of trips, it is responsible for 59.1% of emissions. This concerning finding highlights the need for regulatory efforts focused on long-distance travel.
Transportation is responsible for 30% of global energy consumption and 37% of anthropogenic carbon emissions. However, despite this significant share of greenhouse gas emissions, it is one of the most difficult sectors to decarbonize. For instance, most sectors of activity in the UK reduced their total CO2 emissions by an average of 44% between 1990 and 2019, with the exception of transport, which only recorded a 5% reduction. The majority of these emissions come from passenger travel.
On the other hand, decarbonization efforts are mainly concentrated on green transition technologies, such as electricity and the use of biofuels (like green hydrogen). However, these technologies are not sufficient to offset travel-related emissions and achieve net zero emissions.
Moreover, while the number of national car trips has on average decreased significantly in Europe, international flights have increased considerably. For an airplane trip, each passenger can emit nearly 37 kilograms of CO2 every 1.5 kilometers. In comparison, a car journey emits between 25 and 31 kilograms of CO2 per passenger for an equivalent distance.
Apart from adopting green transition technologies, a reduction in passenger transport demand is essential to reducing travel carbon emissions. However, although long-distance trips constitute a significant part of passenger carbon emissions, surveys concerning their true extent are rare. Furthermore, air travel is generally considered separately in the assessment of transportation’s carbon footprint.
The new case study, conducted in the UK, aimed to fill the gaps by combining several surveys to characterize the CO2 emissions related to residents’ travel. “Even if efforts to shift local travel to more sustainable modes of transport are really positive, omitting aviation emissions from national statistics—as is currently the case in almost all countries—we are not getting a comprehensive picture and are ignoring a large part of the problem,” explains Muhammad Adeel of the University of the West of England, co-lead author of the study, in a statement from the University of Leeds. Most Western countries could apply the results detailed in the journal Nature Energy.
International Travel Responsible for 59% of CO2 Emissions
The researchers used data from the National Travel Survey (NTS) and the International Passenger Survey (IPS) (between 1997 and 2017). Unlike previous studies, which focused specifically on factors such as demand numbers and daily travel, the new survey has a dual objective. The first is to analyze the correlation between passenger travel (all modes of transport combined), the resulting CO2 emissions, kilometers traveled, and travel purposes.
The second objective of the study involves a new measure: sensitivity to emission reduction. This allows for evaluating the decarbonization potential for each trip according to distance and is expressed as the ratio between the rate of emission reduction and the rate of modified trips. To put it another way, the technique evaluates which travel types can undergo modifications to optimize carbon emission reduction, while minimizing the impact on individuals and trips.
The researchers found that although they account for less than 2.7% of trips, journeys of more than 80 kilometers (one way) are responsible for 69.3% of carbon emissions from passenger travel (all modes of transport combined). The disparity is even greater for international travel: they are responsible for 59.1% of emissions while representing only 0.4% of trips. These results show that, although constantly increasing, the adoption of green transition technologies is far from sufficient to reduce transport-related emissions.
Estimates of sensitivity to emission reduction showed that targeting long-distance travel could be a more effective way to reduce emissions than current efforts focused on local and home-to-work travel. “It’s concerning to see that long-distance travel, especially flights, has increased, but they also offer opportunities,” says Zia Wadud of the University of Leeds, lead author of the study.
Walking or cycling could replace car trips of less than 13 kilometers, resulting in a 9.3% reduction in carbon emissions. However, this rate would only be achieved if 59.1% of all local car trips were replaced. This corresponds to a sensitivity to emission reduction of 0.17 units.
In contrast, transferring all flights under 1600 kilometers to rail transport would result in a 5.6% reduction in carbon emissions. Moreover, only 0.17% of trips would need to be modified, thus giving a sensitivity to emission reduction of 33.2 units. Furthermore, this figure would rise to 158.3 units if international flights were limited to one per year.
The team hopes that these results can contribute to raising awareness about the need to reduce long-distance travel. The study notably offers an insight into the positive impacts that could be obtained through a simple change in behavior. This data could also help inform policy decisions on reducing the climate impacts of transport.
