What effect does climate and geography have on human health?

This is a very interesting and intelligent question, but don't you want to consider the several kinds of climates all over the world ? Taking your question on a general sense, human tissues are affected by temperature and humidity variations, becoming people vulnerable to common and to serious diseases as well. Clothes protect people against bad weather.
Considering a naked person, climate variations would be much more dangerous, because we do not have thick hair like animals subjected to extreme levels of temperature and humidity. Geography, when concerned to human health, is related to the distance above sea level which increases or decreases air pressure and this also affects human health, but this is a different condition because people who are living on those places are adapted to them.