Now that I could have seen coming.
Typical CO2 emissions of passenger cars per km.
For new passengers cars an emission value of about 140 g carbon dioxide per km shall be achieved soon.
At the moment such values may still range between 180 and 210 g/km. In the figure on the left additional energy consumers like air conditioners and seat heating are not included, so that the real world values are a bit higher. If we consider that there are about 1.4 people in average sitting in one car, this means that a typical car passenger emits around 120 - 150 g CO2 per km with the future trend going towards 100 g.
This emission is a bit lower for a typical passenger in an aircraft. Scandinavian Airlines gives for example the following information: On a flight from Oslo in Norway to Rome in Italy (2000 km) in an aircraft for 176 passengers the emission is 85 g CO2 per person. On a flight from Oslo to Atlanta in the USA (7000 km) in a plane for 250 passengers it is 117 g per person. If you consider that the is also cargo freight on board the amount is even a bit lower.
Information about the emissions of an airplane for the flight Oslo - Rome. Please click the image for the full view. Calculate your own flights at: www.sasems.port.se (Scandinavian Airlines)
But we need to consider that in a car there is usually enough space for 4 persons. This capacity is seldom used. Aircrafts do usually not fly half empty but work with capacity use in the range of 70 - 90%. Low cost airlines in Europe usually reach 80% use of capacity. Therefore for example car sharing could improve the values of per capita emissions for cars, while this is hardly possible for airplanes.
A major difference is that the CO2 is released in a much shorter time, since an airplane travels nearly 900 km per hour and a car on a longer distance maybe 90 km per hour.
...
The most important difference is the altitude in which the emissions are released. The air in the typical flight altitude of about 9 to 11 km. Has completely different properties than the air next to the ground.
It is much colder and it is much drier. Temperatures between -40 and -50 degrees are not unusual, also in summer. The water content drops to a few ppm. This means, maybe 3 - 10 molecules among one million are water. Next to the ground there is typically about 1% water or even more in humid climates, this means 10,000 of one million molecules are water. So if water comes out of the car the atmosphere does not care, since there is already so much water around.
...
