The climate change caused by the land plant invasion in the Devonian

Land plants invaded continents during the Mid-Paleozoic. Their spreading and diversification have been compared to the Cambrian explosion in terms of intensity and impact on the diversification of life on Earth. Whereas prior studies were focused on the evolution of the root system and its weathering contribution, here we used a coupled climate/carbon/vegetation model to investigate the biophysical impacts of plant colonization on the surface climate through changes in continental albedo, roughness, thermal properties, and potential evaporation. From the Early to the Late Devonian, our model simulates a significant atmospheric CO2 drop from 6300 to 2100 ppmv that is due to an increase in the consumption of CO2 though continental silicate weathering. The continental drift and the climatic changes promoted by land plants explain this trend. The simulated CO2 drawdown is paradoxically associated with unchanged temperatures. We show here that the CO2 drop is counteracted by a large warming resulting from the surface albedo reduction caused by the appearance of an extended plant-cover. If CO2 is consensually assumed as the main driver of the Phanerozoic climate, this paper demonstrates that, during land-plant invasion, the modifications of soil properties could have played in the opposite direction of the carbon dioxide fall, hence maintaining warm temperatures during part of the Devonian. (C) 2011 Elsevier B.V. All rights reserved.