The most obvious environmental consequences of a transition to hydrogen-fueled aircraft are reduction of emissions of air pollutants from the aircraft itself. The problem of air pollution from operation of transport aircraft can be conveniently divided into two categories: operation on or near the airport, and operation at altitude under cruise conditions. The pollutant emissions from subsonic aircraft while in cruise flight make a relatively insignificant impact on overall air quality. The various products emitted from aircraft gas turbine engines have different effects on conditions which influence temperatures in the atmosphere and on the surface of the earth. Noise in the vicinity of airports has long been a source of bitter complaints from residents and businesses in the vicinity. Production of large quantities of hydrogen will require considerable acreage for production of the raw material with attendant fertilizer and water supply problems.