The Green Sahara as a Driver of Holocene Climate Dynamics

Past warm climate intervals provide critical opportunities to evaluate the ability of climate models to simulate the processes that govern future hydroclimate change. During the Holocene, enhanced summer insolation strengthened the West African Monsoon, producing the African Humid Period, when much of the Sahara was vegetated and hosted extensive lakes and river systems. Despite strong geological and archaeological evidence, climate models do not reproduce these “Green Sahara” conditions. This limitation has important implications for understanding past hydroclimate variability and for projecting future monsoon behavior. In this talk, I present two test cases demonstrating that Saharan vegetation acted as an active climate forcing during the Holocene, with impacts extending far beyond North Africa. First, using an ensemble of climate simulations with prescribed “Green Sahara” vegetation, I show that Saharan greening reorganized large-scale atmospheric circulation and forced persistent North Pacific sea surface temperature anomalies, contributing to drought conditions in the southwestern United States. Second, combining the same modeling framework with a new network of stable isotope proxy records, I demonstrate that Saharan vegetation weakened the South American Monsoon, producing reduced precipitation and enriched isotopic signatures across the tropical Andes. I conclude by outlining future work aimed at identifying the missing processes that limit current models’ ability to simulate a Green Sahara.