Which mode of transportation is best for the earth? A study, published in the journal Environmental Science and Technologyby researchers at IIASA and Center for International Climate and Environmental Research (CICERO) calculates the climate impact for passenger trips of 500-1000 km — typical distances for business or holiday trips. It shows that while air travel continues to have the biggest climate impact per distance travelled, the choices that people make about how they drive or take public transport make a big difference in how much they contribute to climate change.
A coach bus typically carries nearly 38 passengers — making it over 70% full, according to the American Bus Association. This is partly why bus travel is so cheap, and it has helped fuel a boom in express city-to-city bus service from the likes of Megabus and Bolt. These new bus companies have doubled their trips since 2010 and now serve nearly every major U.S. city.
Planes get 50 mpg per passenger. Improvements in engine technology, aerodynamics, and putting more people on each flight has made taking a plane a much greener choice. Solo car travel is the biggest culprit when it comes to emissions, producing nearly twice that per passenger of trains and three to four times that of buses. Traveling alone in a large car can be as bad for the climate as flying, but driving with three in a small car could have an equally low impact as a train ride. A 1000 km trip alone in a big car could emit as much as 250 kg of carbon dioxide (CO2), the researchers calculate, while a train trip or carpooling in a small car could emit as little as 50 kg of CO2 for each traveler.
Air travel has by far the biggest impact on climate per distance traveled, because it can lead to contrails and formation of cirrus clouds that have a strong climate impact, as well as ozone. These mechanisms have a strong effect on the climate, but cause warming over much shorter periods of time than CO2.
Previous work and publicly available carbon footprint calculators estimate only averages for the whole transport system, at best. That means that they can miss big differences in climate impact that come from other pollutants, personal choices, and local mitigation measures.
Technologies to control air pollutant emissions from cars, buses, power plants, and trains effectively minimizes their climate impact, the study also shows — benefiting not just air quality but also climate change mitigation efforts. The researchers say that mitigation efforts should concentrate on improving fuel efficiency and developing low-carbon fuels. While this is also important for aircraft, they say, more needs to be done to avoid the contrail and cirrus clouds.
For people wanting to minimize their climate impact, try to avoid flying, driving alone, and driving big cars. Instead, when you can, choose the train, bus, or carpool with 2 to 3 people.