Mountains have an irresistible appeal to most flatland folks. Some mountaintops are jagged, or dome-like, and you can’t tell where exactly the summit is. But Mt Everest, the tallest peak in the world, is different. Its clearly defined crest is about the size of a small dining table with barely room for five people. The view from it is incredible: on a clear day, you can see more than 300 miles to the north and admire Earth’s full curvature, looking across the Tibetan plateau with its rounded rolling hills and snow-capped mountains. To the east and west, the jagged peaks of the Himalayas stretch out, and to the south lies India, with its thick cloud cover of pollution and haze.
But this panoramic view has a price. For humans evolved at sea level where the air pressing down is thickest, and the air pressure greatest. As you climb, the air grows thinner, and air pressure falls. It’s not that there’s less oxygen at high altitudes — just that air molecules spread out more, so that each breath pulls in less air, ergo, less oxygen. By 18,000 feet, you are above half of the atmosphere, where pressure and density are half that at sea level. Here, each breath contains half as many molecules — and half as many oxygen molecules. (On 29,035-ft Everest, air pressure is just one- third that of sea level).
So climbers often suffer symptoms of Acute Mountain Sickness, like headache, dizziness, shortness of breath, nausea, and disturbed sleep. Above 25,000 feet, the risk of dying from hypothermia and frostbite is highest. Sometimes, you can’t get your breath even when resting, because of High Altitude Pulmonary Edema (HAPE) — fluid buildup in the lungs. Even scarier is High Altitude Cerebral Edema (HACE), caused by the swelling of brain tissue. The increasing number of red blood cells makes blood thicker, which could lead to heart attacks. Still, the single most deadly problem is hypoxia: lack of oxygen in the brain. Although the brain makes up only three per cent of the body’s mass, it uses 20 per cent of the oxygen supply. So without oxygen, judgment is impaired, and you become, well, dim-witted, but still on top of the world!