Population models seeking climate as a triggering factor for the extinction of Neandertals and the colonisation of Europe by Anatomically Modern Humans are contradictory due to uncertainties in the dating methods, in the cultural attribution of archaeological layers and to the lack of terrestrial continuous and well-dated palaeoclimatic sequences. This is particularly the case for the Iberian Peninsula where Neandertal populations seem to have survived later than in other regions of Europe. A review of the available palaeoclimatic evidence for OIS3 of Iberia reveals that this mainly consists of low resolution, fragmentary, ill-dated and often ill-interpreted records. Correlation between palaeoenvironmental sequences from two IMAGES pollen-rich deep sea cores and archaeological data from western Europe (the electronic archive of the radiocarbon dates is available at QSR website http://www.elsevier.nl/locate/quascirev) indicates that Aurignacian moderns colonised France and the north of Iberia at the onset of the H4 event. During this cold episode a probable contraction of Neandertal populations is recorded in southern Iberia where no Aurignacian settlements are detected. Such a decline in population density is correlated with the particular desert-steppe-like environments, made up of Artemisia, Chenopodiaceae and Ephedra, characterising the H4 of this area. While reducing the size of Neandertal populations, this inhospitable environment may have favoured their persistence in this region. Mainly exploiting herds of herbivores adapted to Graminees-rich grasslands, the Aurignacian moderns were probably not interested in colonising these arid Mediterranean biotopes, and did that only after the H4 event.