Doctor warns over Everest deaths

Andrew Sutherland of the Nuffield Department of Surgery in Oxford, England, said the unofficial death toll on Mount Everest had already reached 15 this year -- the highest since 1996 when 16 people died, eight in one night after an unexpected storm.

Writing in the latest edition of the British Medical Journal, Sutherland said climbers often confused fitness with their ability to survive at high altitudes.

"In my view, climbers are not climbing beyond their ability but instead beyond their altitude ability," he said.

Despite better understanding of acclimatization, improved climbing equipment and established routes, the death rate on Everest remains alarmingly high, with about one death for every 10 successful ascents.

Many climbers die from high altitude cerebral edema (HACE) and high altitude pulmonary edema (HAPE) - two kinds of altitude sickness that can cause a fatal accumulation of fluid in the brain or lungs.