We make use of the NCEP Reanalysis that has been validated against observations made at the South Col of Mount Everest. We also make use of direct measurements of surface ozone, a tracer for pollution as well as the presence of stratospheric air, that we have collected near Mount Everest since 2005.
We show that the warming has resulted in a thickening of the atmosphere in the Mount Everest region. Since 1948 this warming has led to an increase in the annual mean summit barometric pressure of ~1.5 mb. We furthermore show that ozone concentrations in the Mount Everest region during the spring climbing season tend to increase with altitude and above 3500m, they typically exceed exposure guidelines established by the World Health Organization. We have identified two distinct sources for this ozone. The first being stratospheric in origin and the second source was identified as long-range transport of polluted air masses from the Indian subcontinent and South East Asia.
The increase in summit barometric pressure is of a magnitude to be of physiological importance suggesting that it is becoming easier to climb Mount Everest without the use of supplementary oxygen. Given that the warming that gives rise to this increase has been ongoing since the 1850s, it follows that that early climbers were also exposed to lower barometric pressures as compared to modern climbers thus making their accomplishments all that more impressive. The ozone data shows contributions from both the stratosphere and the long-range transport of pollution. At present, the stratosphere is dominant source as a result of the high elevations in the region that places the surface in proximity to this source. However the contribution from long-range transport is expected in increase as the industrialization of the Indian subcontinent continues. The high values we observe suggest that ozone exposure at extreme altitude may therefore represent a new health risk for mountaineers and indigenous populations in the Himalaya.