Various substances that affect the climate are emitted during a flight. The quantity of greenhouse gases emitted during a flight depends on various factors, specifically:
- the quantity of fuel that is burned
- the type of engine

In turn, the quantity of fuel that is burned depends on the distance flown, the flying altitude, the weather, and the aircraft's aerodynamics and load.

The emission of greenhouse gases is normally calculated per passenger and kilometer. The emission of CO2 per passenger kilometer is between about 90g (for long flights) and 150g (short). As we have already said, it is not only CO2 that affects the climate - in 1999, the IPCC (Intergovernmental Panel on Climate Change) published its report on Aviation and the Global Atmosphere, in which it estimated the total 'climate-effectiveness' of emissions during flight. The report concluded that the overall effect is 2 to 4 times greater than the effect of CO2 on its own.