Put Mt. Everest (28 deg North) at the latitude of Mt. McKinley (63 deg North)
in the United States and it is likely that no climber would ever have been able
to reach the summit breathing the natural air. Everest would feel,
physiologically, as if it were an additional 3,000 feet higher. The air would
be so thin that even the best climber would have no choice but to use
supplemental oxygen. Why? Because of the many factors which affect
Pioneering scientists discovered atmospheric pressure (also known as barometric
or air pressure) in the 17th century, and
determined a startling new fact—that air actually has weight. Evangelista
Torricelli, one of the first to discover atmospheric pressure, once said, "We
live submerged at the bottom of an ocean of the element air." The Earth's
gravitational field is pulling on air, and this pull, or "pressure" of air, is
called atmospheric pressure. Toriccelli also went on to develop the mercury
barometer, an instrument used to measure atmospheric pressure.
A barometer also monitors variations in atmospheric pressure. As air becomes
thinner, the density of air decreases, and so too does the pressure of air.
Many different factors affect the density of air. Most measurably, as altitude
increases, air becomes less dense, decreasing atmospheric pressure. Standard
altitude-pressure tables allow mountaineers and aviators to determine their
approximate height by measuring atmospheric pressure. This relationship also
works inversely. The height of a mountain determines, approximately, the
density of air on its summit. As air becomes less dense, it contains less
gases per unit of volume, and therefore less oxygen. Physiologists use this
information to predict the oxygen deprivation a mountaineer faces at high
For the most part, this relationship works quite well. But factors other than
altitude also effect the density of air. For one thing, water molecules have
less mass than other gas molecules in air; so as water vapor increases, the
density of air decreases. Temperature also changes the density of air. As air
gets warmer it expands and becomes less dense, causing atmospheric pressure to
In addition, air within the atmosphere can rise and fall, changing the
atmospheric pressure. In fact, meteorologists monitor atmospheric pressure at
the Earth's surface in order to determine whether the pressure is rising or
falling, which helps to predict weather patterns.
High pressure often
represents stable air, while low pressure can signify instability. On a cold,
sunny day there will be a significantly higher atmospheric pressure than when a
big storm is moving in on a hot and humid day.
But the density of the atmosphere varies at different points around the globe
as well. At the poles, the atmosphere is much thinner than at the equator.
Because of these variations, two mountaineers climbing at the same altitude but
on different mountains could experience different atmospheric pressures and
therefore different physiological effects.
One climber might have no trouble breathing, while the other can
barely pull in enough oxygen to survive. The small amount of oxygen on the top
of Everest puts this peak near if not at human's physiological limit. And this
is why Everest, if it were at a higher latitude, could very well be beyond the
physiological limits of someone trying to climb without oxygen.
Only one direct measurement of atmospheric pressure has ever been made on the
summit of Mt. Everest, in 1981. The present expedition has a small hand-held
barometer and we hope it may be possible for them to make the second