Abstract
The effect of CO2 fertilization on tropical forests is uncertain due to a lack of direct data and confounding effects of climate variability. Long-term proxy records could help understand the impact of elevated CO2 on tropical vegetation. We provide observationally inferred evidence that the evolution of the Atlantic Forest in SE Brazil between ~ 150 and 65 ka was influenced by CO2 variability rather than temperature or precipitation on both precessional and millennial time scales. Plant wax n-alkanes in a marine core were used to trace forest cover uctuations and compared with continental records of fossil pollen, revealing a strong correlation with CO2 levels. This highlights CO2 fertilization as a key driver of the past Atlantic Forest evolution, emphasizing the need for protection initiatives to preserve its longterm capacity in carbon storage. Further research is needed to understand the long-term effects of CO2 on tropical forests at the ecosystem scale.