Climate Change and Extinction Events

Abstract

Extinction rates remain fairly constant over time, but there are occasions during which a large number of species are lost in a short time. These events are known as mass extinctions. Estimates of the number of major mass extinctions that occurred in the Phanerozoic range from as few as five to more than 20. Climate change (global cooling and warming) is a recurrent factor in triggering mass extinction events. We are particularly interested in those associated with global warming due to the direction of current climate change. Warming alone has been sufficient to bring about the mass extinction of tropical marine species by affecting ocean ecosystem functioning. Past global warming conditions promoted anoxia in ocean water, which may have triggered mass extinctions in marine organisms. Anoxia is frequently associated with eutrophication. This is another factor triggering extinction of marine organisms and it is an important aspect of current pollution problems. Past global warming conditions were closely associated with increased atmospheric concentrations of carbon dioxide, which is the greenhouse gas most responsible for the current climate change. High atmospheric concentration of carbon dioxide also leads to ocean acidification, which has been identified as the cause of mass extinctions of organisms with calcareous body parts. Postextinction communities were usually dominated by species with broad ecological tolerances and wide distributions. This supports the current strategy of giving conservation priority to specialized and rare species. The study of past mass extinction events also illustrates the importance of coextinction processes in the collapse of ecosystems.