To the author - where did you get your information?  China is doubling the number of planes in the air every 3 years, and nobody else is reducing.  And more dense air makes it EASIER for planes to take off, not harder.  Perhaps you've heard of a place called Mumbai.  50 degrees Celsius and you can't see a kilometer through the pollution.  Extremely dense air with pollution and humidity, and one of the busiest airports in the world.  Conversely, when we tried to take off from Calgary last year and it was -45 Celsius at 2:00 am, and they delayed the flight until 9:00 am so that it would warm up a bit and the plane could get lift.