Global climate and vegetation changes during the Eocene-Oligocene Transition: a review of recent progress

Wang, Nan

CHINESE SCIENCE BULLETIN-CHINESE

2026

71

3

Li, SF

The Eocene-Oligocene transition (EOT) represents a critical period in Earth's climate system, marked by a shift from a warmhouse to a coolhouse climate. This critical interval, spanning approximately 34 million years ago, was primarily characterised by a rapid decline in atmospheric CO2 concentrations. This decline ultimately triggered pronounced global cooling, aridification and the initial development and growth of the Antarctic ice sheet, all of which profoundly influenced the evolution, distribution, and diversity of vegetation. While there is a consensus regarding the decline in sea surface temperatures during the EOT, the terrestrial temperature response to the EOT remains a subject of ongoing debate, particularly concerning spatial heterogeneity and latitudinal gradients. The primary drivers of the EOT are also under active investigation. Although various hypotheses-including orbital forcing, a drop in CO2 concentrations, and thermal isolation-have been supported by numerical simulations, a single dominant forcing factor has yet to be identified. The global vegetation response to the EOT is evident in the retreat of forests, a decrease in thermophilic flora, and the expansion of drought-tolerant species. However, significant regional variations exist in species diversity. Currently, systematic research is still relatively sparse regarding how EOT global climate change comprehensively drove the co-evolution of terrestrial ecosystems across broader spatial and continuous temporal scales. Currently, spatiotemporal uncertainty in palaeovegetation data makes it difficult to link the co-evolution of ecosystems with climate change across the EOT. To better resolve this, we integrate palaeo-vegetation proxies with palaeoclimate simulations from HadCM3 with interactive vegetation, as well as an offline vegetation model (SDGVM). Our analysis indicates that consistent global terrestrial cooling across all latitudes (high, mid, and low) during the EOT drove changes in ecosystem development, with high latitudes experiencing more pronounced seasonal temperature variations. The vegetation simulations reveal trends of forest opening and the expansion of C-4 grasses, although these findings occasionally show local inconsistencies with fossil records. To bridge these gaps, future research should integrate big data with numerical simulations, establish high-precision spatiotemporal frameworks, and develop more reliable climate and vegetation models. This approach will enhance our understanding of the co-evolutionary mechanisms between climate and vegetation during the EOT. This review offers a deep-time perspective for predicting how terrestrial ecosystems may respond to future climate change. By integrating multi-source data and models, we can unravel the complexities of climate-biosphere interactions, thereby providing crucial theoretical support for global change research.