Andean uplift and climate change

Sedimentological data indicate that a semi-arid/arid climate prevailed across the Central Andes from 15 Ma to 4 Ma. Between 4 and 3 Ma a switch to hyperaridity occurred along the western margin of South America. Palaeoaltitude data suggest that a substantial proto-Central Andean mountain range was in place between 15 and 9 Ma. These data support the idea that the Andean rain shadow existed by 15 Ma and that it reinforced the preexisting climatic regime rather than changing it. The change to hyperaridity in western South America is attributed to a combination of global climate cooling and enhanced upwelling of the Humboldt current generated by closure of the Central American Seaway between 3.5 and 3 Ma, and not to the Andean rain shadow.