Highaltitude

High altitude refers to elevations where the atmosphere is noticeably thinner than at sea level. There is no single universal boundary; the term is used differently in aviation, medicine, and mountaineering. In general, high altitude begins around 2,000–3,000 meters (about 6,500–9,800 feet) above sea level, where air density and oxygen partial pressure decline markedly. In aviation, high-altitude flight commonly denotes operations at flight levels of about 18,000 feet (roughly 5,500 meters) and above, with pressurized cabins and supplemental oxygen for occupants.

Atmospheric conditions at high altitude include lower air pressure, reduced humidity, and cooler temperatures. The transition from the troposphere to the lower stratosphere occurs near 8–12 kilometers, though the exact boundary varies with latitude and season. Weather and winds can be more extreme and variable than at sea level.

Humans experience hypoxia as altitude increases, leading to altitude sickness and, at higher elevations, risk of high-altitude cerebral or pulmonary edema. Acclimatization—slower ascent, rest days, and sometimes supplemental oxygen—improves tolerance and safety. The rate of acclimatization depends on the individual and the target altitude.

Applications of high-altitude study include aviation design, mountaineering safety, physiology and medicine, atmospheric science, and ecology of alpine environments. Research at high altitude informs understanding of human limits, flight performance, weather dynamics, and the effects of low-oxygen environments on organisms.