This section explains the cause of altitude problems and how to prevent or minimise their effects.

Everyone knows that the air becomes thinner the higher you go. This is why jet aircraft are pressurised, and why Alpine mountaineers become breathless as they climb.

Altitude in the context of high mountains refers to heights above sea level of between about 2,500 metres (a low Alpine peak) and 8,848 metres (the height of Mount Everest). It should be remembered that the effects of climate and weather can make a significant difference to the apparent height, as for example on the Equator the air pressure is higher than at the Poles, and so the thinning of the air at altitude is slightly less apparent. In contrast, a high sub-Arctic mountain such as Denali (Mount McKinley) presents a lower than expected pressure at its summit, as well as extreme cold, and for these reasons alone it is potentially a more dangerous summit than some much higher ones that are nearer the Equator