Quote Originally Posted by Johanna
I am not aware of any clean low emission way of flying. Can you tell me about it?
How much cleaner is it than, say, a normal Boeing 707?
Basically, the only by-product (=the pollution) of the hydrogen oxidation is water. Can it be any more clean?

However, the total environmental footprint depends on the way this hydrogen was obtained. It is yet to be proved (=unknown) that hydrogen could be mined from the certain geological formations. Presently, the most common way to produce hydrogen is to extract it from water by means of electricity. So, technically, hydrogen is more like an energy carrier. If the clean energy (solar, wind, geothermal, etc.) is used for the extraction, the environmental impact of operating such plane is very low (i.e. there are other factors unrelated to fuel emissions).