Flying v Driving
The simple answer is that driving in a relatively fuel-efficient car (25-30 miles per gallon) usually generates fewer greenhouse-gas emissions than flying. In assessing the global warming impact of a trip from Philadelphia to Boston (about 300 miles), the environmental news website Grist.org calculates that driving would generate about 104 kilograms of carbon dioxide (CO2)—a leading greenhouse gas—per typical medium-sized car, regardless of the number of passengers, while flying on a commercial jet would produce some 184 kilograms of CO2 per passenger.
Flying vs Driving: Carpooling Generates Fewest Greenhouse Gases Per Passenger
What this also means, of course, is that while even driving alone would be slightly better from the standpoint of greenhouse-gas emissions, carpooling really makes environmental sense. Four people sharing a car would collectively be responsible for emitting only 104 kilograms of CO2, while the same four people taking up four seats on a plane would generate some 736 kilograms of carbon dioxide.
Flying vs Driving: Cross-Country Calculations Show Stark Contrasts
Journalist Pablo Päster of Salon.com extends the comparison further, to a cross-country trip, and comes to similar conclusions. (Differences in the math are attributable to the use of slightly varying assumptions regarding fuel usage and source equations.) Flying from San Francisco to Boston, for example, would generate some 1,300 kilograms of greenhouse gases per passenger each way, while driving would account for only 930 kilograms per vehicle. So, again, sharing the drive with one or more people would lower each individual’s carbon footprint from the experience accordingly.