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Located along the west coast of subtropical South America, the Atacama Desert features an extremely dry climate in sharp contrast with relatively wet conditions over the Central Andes and farther east. The Atacama’s hyperaridity has been attributed to its subtropical location, the cold waters over the adjacent southeast Pacific Ocean and the presence of the Andes Cordillera. Although geological evidence reveals less dry conditions in the remote past, the timing of the arid-to-hyperarid transition is a matter of controversy. Several studies suggest that such transition occurred between 19 and 13 Ma fostered by the concurrent uplift of the Andes during the lower-middle Miocene. Other studies, however, suggest a much earlier (similar to 25 Ma) or later (2-1 Ma) transition associated with global or regional ocean cooling. Here we use PLASIM, a simple global climate model, to study the effect of the Andean surface uplift and sea surface temperature changes upon Atacama aridity. In one set of experiments, the continental topography was scaled by a factor ranging from 0.9 to 0.1. Decreasing the height of the Andes did not increase precipitation over the Atacama region, but rather decrease the precipitation over the Central Andes and the interior of the continent. These results, consistent with previous modeling studies, suggest that the Andean uplift was not an important ingredient in the onset of Atacama hyperaridity, even if both events overlapped in time. A globally uniform sea surface warming does not result in a significant increase of precipitation over the Atacama. In contrast, a regional warming over the subtropical southeast Pacific very effectively increase precipitation along the west coast of South America by decreasing the subsidence and the dry advection at low levels. It suggested that a reinforcement of the Humboldt Current since the late Miocene and particularly during the Pliocene/Pleistocene transition was crucial in the drying of the Atacama Desert that culminated with the present day hyperarid conditions. (c) 2010 Elsevier B.V. All rights reserved.