African monsoon changes in the Late Cenozoic from the climate modelling perspective

Africa's climate underwent significant hydroclimate changes in the Late Cenozoic. For instance, the repeated phases of aridification across the continent played a crucial role in shaping the regions biodiversity and hominid evolution. Consequently, understanding the historical climate variations in the region becomes essential for reconstructing its paleoenvironment and paleobiological history. Moreover, past climates can be used as analogues for potential future climates and thus help us understand the implications of future climate scenarios. The precipitation seasonality and variability in the region are predominantly driven by the African monsoons, which exhibit intricate climate dynamics controlled by both regional and large-scale atmospheric teleconnections. However, due to the complexity of these dynamics and teleconnections, even state-of-the-art General Circulation Models (GCMs) still struggle to accurately reconstruct its past climate variability and provide reliable future projections. Here, we simulate the response of the African monsoons to different late Cenozoic paleoenvironmental changes, such as atmospheric CO2 concentration (pCO2), orbital forcing, palaeogeography, vegetation, and orography (including the topographic evolution of the East African Rift System (EARS)). We performed time-specific simulations with a high-resolution setup of the GCM ECHAM5-wiso and the paleoenvironmental boundary conditions for the Middle Miocene climate optimum (MMCO; 16.9-14.7 Ma), Middle Miocene climate transition (MMCT; 14.7-13.8 Ma), Mid-Pliocene (MP; ~3 Ma), the Last Glacial Maximum (LGM; ~21 ka), the Mid-Holocene (MH; ~6 ka), and the pre-industrial (PI; the reference year 1850). Furthermore, we conducted topographic sensitivity experiments of the EARS under the MMC and MMCT conditions to understand the role of tectonics in the evolution of Africas climate and atmospheric dynamics. We focused our analysis on disentangling the thermodynamic effects (e.g., water vapour content changes) and dynamic effects (e.g., Hadley circulation) on the monsoon changes and associated atmospheric dynamics (e.g., African Easterly Jet, Somalia Jet, Tropical Easterly Jets, low-level westerlies). Overall, the study provides an overview of hydroclimate and climate dynamics changes over Africa for the past 20 Ma, contributing to the understanding of the feedback between changes in pCO2, orbital forcing, and tectonic events that are relevant for improving future climate prediction.