Isn’t it true that emissions at altitude have a far greater impact on the environment?
Carbon dioxide, CO2, the most important greenhouse gas – has the same effect on the environment, whatever the source and wherever it is emitted. However, aircraft engines, like cars, trucks, ships and trains, emit other gases too. Some of these may also affect the climate, and some may have a greater effect at altitude than at ground level. Soot is an example, but soot emissions from jet engines have been largely eliminated in the last 20 years. Oxides of nitrogen (NOx) are another example, but they can have both warming and cooling effects. Water vapour in the form of contrails can lead to cloud formation, which is recognised as a challenge for the industry. Essentially, CO2 effects are well known and understood, other emissions much less so. There is an additional effect at altitude, but it has not been adequately quantified. However, it is not of a magnitude that justifies diversion of attention away from the main focus, which is CO2.
