Actually, there is none. Although high-flying jet airplanes emit a large amount of it, the CO2 in the exhaust is not at all responsible for the white streaks. They are called contrails, which is short for condensation trail.
Contrails are clouds that form when water vapor condenses and freezes around small particles (aerosols) in aircraft exhaust at high altitudes.
Water vapor is a byproduct of all combustion processes. It is part of the exhaust that your car emits. Normally you don’t see it. In cold temperatures you might once in a while experience it.
So, while CO2 is certainly hurting the environment, it has nothing to do with contrails. However, they seem to have a negative influence on the climate as well. Getting rid of CO2 in the exhaust does not automatically mean that there will be no contrails.
Although a turbine engine burning hydrogen emits no CO2 at all, there might still be some contrails. But we can expect there would be significantly less of the harmful persistent ones. The small particles (aerosols) needed for condensation will be far less than when burning jet fuel.
