May 25, 2004

High winds suck oxygen from Everest

Predicting pressure lows could protect climbers.

by Mark Peplow
Nature News

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Climbers on Mount Everest could die because of sudden drops in air pressure triggered by high winds, according to scientists who have analysed weather patterns around the summit. Better forecasting of these events could save lives, they say.

Mountaineers are already advised not to make attempts on the summit in high winds. But Kent Moore, a physicist from the University of Toronto, believes that they should also watch out for the changing wind systems that rob the air around the peak of vital oxygen.

Moore became interested in the problem after reading Into Thin Air, a book that details the deaths of eight Everest climbers during storms in May 1996. He says the deaths were probably precipitated by a lack of oxygen, which would have made the climbers confused and disoriented.

The top of Mount Everest sits in the upper troposphere, a part of the atmosphere where winds travelling at 110 km an hour can pummel climbers. This region is also affected by jet streaks, extra fast bursts of wind within the jet streams that race around the Earth from west to east. The book describes how the mountaineers waited until a lull in the weather, and then began climbing to Everest's peak. But when a jet streak passed by shortly afterwards, the climbers found themselves in trouble.

Moore explains that these jet streaks can drag a huge draught of air up the side of the mountain, lowering the air pressure. He calculates that this typically reduces the partial pressure of oxygen in the air by about 6%, which translates to a 14% reduction in oxygen uptake for the climbers. Air at that altitude already contains only one third as much oxygen as sea-level air. "At these altitudes climbers are already at the limits of endurance," says Moore. "The sudden drop in pressure could have driven some of these climbers into severe physiological distress."

Pressure at the top

To verify the link between jet streaks and a sudden pressure drop, Moore used data from the highest weather station in the world: a probe left by Massachusetts Institute of Technology researchers to record barometric pressure at the South Col in 1998. Moore and his colleague John Semple, a doctor from the Sunnybrook and Women's College Hospital in Toronto, worked out how this pressure change would affect climbers. The work was presented last week at the Joint Assembly of the American and Canadian Geophysical Unions.

Climbers currently rely on wind-speed information to decide whether it is safe to make the final ascent. But they do not take into account jet streaks, says Moore, even though streaks would be easy to predict with standard weather forecasting techniques. "When the winds up there are changing, that's the danger point, and they don't look at that."

Intrepid mountaineers usually start their ascent of the world's highest mountain from a base camp at about 5000 m, trekking to the South Col at a height of around 8000 m. From there it is a full day's climb to the summit at 8850 m.

On 8 May 1978, Reinhold Messner and Peter Habeler achieved the first ascent of Mount Everest without an oxygen supply. Since then, more and more climbers have opted to go to the highest place in the world without the support of oxygen cylinders.

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