A new study of the individual carbon footprint from leisure or business travel reveals that while air travel continues to have the largest environmental impact, people's terrestrial transportation preference can still make a big difference in how much individual actions contribute to climate change.

Researchers at the International Institute for Applied Systems Analysis (IIASA) and the Center for International Climate and Environmental Research (CICERO) studied the impact of passenger trips of 500-1,000 kilometers (310 - 621 miles), which it said are the typical distances traveled during business or holiday trips.

One takeaway from the research was that the overall environmental impact of carpooling can match traveling by train.

"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," IIASA's Jens Borken-Kleefeld said in a statement.

Researchers reported a 1,000 km trip by an individual in a large car could emit as much as 250 kg of carbon dioxide (CO2), while a train ride or carpool in a small car could emit as little as 50 kg of CO2 for each traveler.

Because of the contrails and formation of  climate-impacting cirrus clouds and emission of ozone, air travel has the largest impact on climate per distance traveled, though other, lesser factors must still be taken into account when accounting for the overall climate impact, the researchers report. Their study focused on the short-lived greenhouse gases and aerosols emitted by ground transportation and airplanes. The study also accounted for vehicle occupancy and efficiency, which Terje Berntsen, climate researcher at CICERO, said can be overlooked because they are not regulated in the Kyoto Protocol.

The researchers say it's possible that because previous work and publically available carbon footprint calculations only give estimated averages for the environmental impact of the entire transportation system, climate factors coming from other pollutants, personal choices and local mitigation measures may become overlooked.

Emissions control technology in cars, buses and trains can minimize climate impact, the researchers report, adding that mitigation efforts should concentrate on improving fuel efficiency and developing low-carbon fuels.

Technologies to control air pollutant emissions from cars, buses, power plants and trains effectively minimize their climate impact, the study also shows -- benefiting not just air quality but also climate change mitigation efforts.

For people wanting to minimize their climate impact, Borken-Kleefeld suggests,"Try to avoid flying, driving alone, and driving big cars. Instead, when you can, choose the train, bus, or carpool with two to three people."

The study was published in the journal Environmental Science and Technology