A greenhouse warming produced by increased emissions of mantle volatiles (CO₂, SO₂, HC1), particularly from the Deccan Traps flood basalt eruptions in India, has been suggested as a cause of the terminal Cretaceous extinctions. In order to quantify some of the possible climatological effects of an injection of volcanic volatiles into the ocean-atmosphere system, we have developed a global biogeochemical carbon-cycle model that emphasizes the roles of ocean chemistry and the chemical weathering of terrestrial carbonate and silicate rocks. Model results indicate that Deccan Traps degassing would have produced variations in atmospheric CO₂, leading to a sustained global warming of less than 2 °C—too weak a climatic effect to be associated with mass extinctions. The calculated global warming is at a rate two orders of magnitude slower and less than half the absolute amount experienced during the Holocene.