Abrupt Impacts of Climate Change: Anticipating Surprises by Committee on Understanding & Monitoring Abrupt Climate Change & Its Impacts

Author:Committee on Understanding & Monitoring Abrupt Climate Change & Its Impacts
Language: eng
Format: epub
Tags: ebook
Publisher: The National Academies Press
Published: 2013-12-31T00:00:00+00:00

BOX 2.4 MASS EXTINCTIONS

Mass extinctions are generally defined as times when more than 75 percent of the known species of animals with fossilizable hard parts (shells, scales, bones, teeth, and so on) become extinct in a geologically short period of time (Barnosky et al., 2011; Harnik et al., 2012; Raup and Sepkoski, 1982). Several authors suggest that the extinction crisis is already so severe, even without climate change included as a driver, that a mass extinction of species is plausible within decades to centuries. This possible extinction event is commonly called the “Sixth Mass Extinction,” because biodiversity crashes of similar magnitude have happened previously only five times in the 550 million years that multi-cellular life has been abundant on Earth: near the end of the Ordovician (~443 million years ago), Devonian (~359 million years ago), Permian (251 million years ago), Triassic (~200 million years ago), and Cretaceous (~66 million years ago) Periods. Only one of the past “Big Five” mass extinctions (the dinosaur extinction event at the end of the Cretaceous) is thought to have occurred as rapidly as would be the case if currently observed extinctions rates were to continue at their present high rate (Alvarez et al., 1980; Barnosky et al., 2011; Robertson et al., 2004; Schulte et al., 2010), but the minimal span of time over which past mass extinctions actually took place is impossible to determine, because geological dating typically has error bars of tens of thousands to hundreds of thousands of years. After each mass extinction, it took hundreds of thousands to millions of years for biodiversity to build back up to pre-crash levels.

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