By Late Cretaceous or early Tertiary time, the diversification and proliferation of angiosperm-deciduous ecosystems resulted in higher rates of mineral weathering. This increase in the global average weathering rate would have caused a decrease in atmospheric carbon dioxide and, hence, global cooling. The magnitude of this decrease is quantitatively explored here by developing a formulation for global weathering which combines ecosystems that differ in their fractional global coverage and intrinsic rates of weathering. Incorporating this formulation into models—specifically, several previously developed global steady-state models of the geochemical cycle of carbon between the atmosphere and carbonate rocks—gives results that show signifi-cant global cooling from the evolution of the angiosperm-deciduous ecosystems. This cooling may vary from a few degrees up to 10°C. In this way, deciduous ecosystems with high rates of mineral weathering could have contributed to the evolution during the past 100 m.y. of a cooler Earth and thus were a factor in producing conditions that enhanced their global proliferation.