| Summary: | <jats:title>Abstract</jats:title><jats:p>Savanna ecosystems were the landscapes for human evolution and are vital to modern Sub-Saharan African food security, yet the fundamental drivers of climate and ecology in these ecosystems remain unclear. Here we generate plant-wax isotope and dust flux records to explore the mechanistic drivers of the Northwest African monsoon, and to assess ecosystem responses to changes in monsoon rainfall and atmospheric pCO<jats:sub>2</jats:sub>. We show that monsoon rainfall is controlled by low-latitude insolation gradients and that while increases in precipitation are associated with expansion of grasslands into desert landscapes, changes in pCO<jats:sub>2</jats:sub> predominantly drive the C<jats:sub>3</jats:sub>/C<jats:sub>4</jats:sub> composition of savanna ecosystems.</jats:p>
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