The thickness of the Earth's atmosphere, compared with the size of the Earth, is in about the same ratio as the thickness of a coat of shellac on a schoolroom globe is to the diameter of the globe. That's the air that nurtures us and protects us from deadly ultraviolet light from the sun. We are pumping all kinds of stuff into it. Who knows what other challenges we are posing to this vulnerable layer of air that we haven't been wise enough to foresee.