Tim Lenton, Exeter University: this collaboration involves modelling the climatic response and recovery from climate perturbations. “Earth system modelling” is a powerful method for understanding how temperatures and CO2 concentrations varied due to changes in the parameters that control long-term climate. We have modelled the climate system through the 2nd largest mass extinction in Earth history (at the end of the Ordovician, 445 million years ago), which coincided with a significant cooling and glaciation. In particular, we were studying how the climate recovered from this abrupt cooling.
Global climate stabilisation by chemical weathering during the Hirnantian glaciation
Chemical weathering of silicate rocks is a primary drawdown mechanism of atmospheric carbon dioxide. The processes that affect weathering are therefore central in controlling global climate. A temperature-controlled “weathering thermostat” has long been proposed in stabilising long-term climate, but without definitive evidence from the geologic record. Here we use lithium isotopes (δ7Li) to assess the impact of silicate weathering across a significant climate-cooling period, the end-Ordovician Hirnantian glaciation (~445 Ma). We find a positive δ7Li excursion, suggestive of a silicate weathering decline.