UK: Self-driving Car Completes Autonomous Long Journey

Interesting concept that of thin air. How does one know if the air is thick or thin and does air have to be sent to a slimming clinic regularly to be assessed? Does thick air contain more Nitrogen or greater concentrations of CO2? Is that why the worry about CO2 is so profound, not a heating problem but an obesity problem?

Would thin air look thinner than thick air, that is if we could see it, mind you I have been in the desert where the air was too thin to take off in propeller airplanes until the day had cooled. So does that mean every time I took a flight I vanished into thin air or not quite as thick air?

Or is this a slur on the mental capacity of air with the division into thin and thick air being used as an artificial barrier to air. How would an oxygen thief handle an intake of thin air? There are plenty of oxygen thieves around these days but surely they absorb thick air and it imbues them with its properties?

Too many questions here so I will leave it to others to decide if thin air only occurs in the rarefied tropo fears.