The two combustion products which future technology will be unable to eliminate from present day jet engines are carbon dioxide and water vapor. The potential climatic change effects of carbon dioxide are considered to be a small part of a larger CO2 problem. Water vapor added to the troposphere forms contrails. The paper will assess the non-conclusive evidence of increased cirrus cloudiness at certain locations. Finally the potential climatic effects of added water vapor in the stratosphere on the radiation budget, the small decrease in ozone, and polar night cloudiness is evaluated in the light of future commercial aviation injections of water vapor.