Recently I visited Leh in Ladakh area of India and the places around.
When we reach Leh, which is at altitude of 11,500 ft, we do feel that we have some difficulty in breathing. This experience is even more obvious when we visit some higher altitudes like Khardunga La, which is at 18380 ft. (See me at this point of highest motorable road of the world)
But few years back, I visited some other place "Hemkund" in India, which is at 14000 ft, where, I did not experience any difficulty in breathing.
Why is this difference? Is it because of green coverage of the areas. The valley of flowers and Hemkund area has better green coverage, as compared to Leh, which is desert at this altitude.
