Late Paleozoic climate transition from a long-term climate modelling perspective

The Late Paleozoic Ice Age (LPIA) represents Earth's longest icehouse period in the Phanerozoic and the only recorded greenhouse–icehouse–greenhouse cycle on a vegetated Earth. Sedimentary archives provide evidence of glaciation events, but the mechanisms driving the LPIA's onset (~330 Ma) and end (~260 Ma) remain debated. Here we investigate the climatic transitions associated with the LPIA using both non-dimensional (COPSE) and spatially resolved climate models, emphasizing the interplay between paleogeography, silicate weathering, and solid Earth degassing. By integrating new paleogeographic reconstructions constrained by fossil and lithological climatic paleo-indicators, we identify high-weatherability zones and assess their evolving influence on carbon fluxes. Additionally, the Variscan orogeny's role is examined to evaluate how physical erosion enhances chemical weathering and CO₂ drawdown.

Simulations highlight that maintaining icehouse conditions required not only a decrease in solid Earth degassing but also an enhancement in silicate weathering driven by the combined effects of increased topography and runoff. These processes amplified the consumption of CO₂, supporting the initiation of a widespread glaciation. In contrast, the transition back to greenhouse conditions appears driven by a progressive decrease in exposed land for high intensity weathering. Climate sensitivity played a significant role in modulating these transitions, and model adjustments to this parameter improved alignment with CO₂ proxy data.

Our findings provide new insights into the interactions between tectonics, paleogeography, and biogeochemical processes in shaping Earth's climatic history. By leveraging geological evidence to refine long-term carbon cycle models, this work underscores the critical importance of accurately representing the paleogeography to understand ancient climate transitions and inform projections of future climate change.