Global warming and biological invasions are leading to a major reconfiguration of biogeographic provinces. Past intervals of warm climates in Earth's history provide windows into how species have responded to warming and can help predict future biogeographic configurations. We modeled the suitability of the Mediterranean for West African tropical species that occurred in the basin during the last interglacial period (135 to 116 ka) and connectivity along northwest Africa, where a large upwelling system currently delays poleward range expansion. tropical species. We show that this barrier can weaken even under moderate climate scenarios, contributing to the emergence of a new ecosystem throughout the Mediterranean, a process already initiated by biological invasion through the Suez Canal. ( Paolo G. Albano,  Lotta Schultz, Johannes Wessely, Silvia Danis, more at pnas.org)