Global warming, El Nino and Mount Everest. Consequences for mountaineers caught in high impact weather then and now

The 20th century was bracketed by two high profile events on Mount Everest, the 1924 Mallory and Irvine disappearance and the 1996 “Into Thin Air” storm, in which a loss of life occurred high on the mountain during deteriorating weather conditions. Although there have been dramatic improvements in our knowledge of the mountain and the technology used on it; an unappreciated change that has also occurred, as a result of warming in the region, has been an increase in summit barometric pressure. Here we use a unique set of meteorological data collected during the 1924 expedition as well as modern datasets to compare and contrast conditions during the two storms and the two climbing seasons. We show that both storms were associated with a drop in summit barometric pressure sufficient to have induced hypoxia. We furthermore show that the Mallory and Irvine attempt occurred later than typically occurs now and that this was most likely the result of a concurrent El Nino event.