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Figure 1.8. Species Extinction Rates"Fossil Record" refers to average extinction rates as estimated from the fossil record. "Past Century-Known Species" refers to extinction rates calculated from known extinctions of species (lower estimate) or known extinctions plus "possibly extinct" species (upper bound). A species is considered to be "possibly extinct" if it is believed by experts to be extinct but extensive surveys have not yet been undertaken to confirm its disappearance. "Projected" extinctions are model-derived estimates using a variety of techniques, including species-area models, rates at which species are shifting to increasingly more threatened categories, extinction probabilities associated with the IUCN categories of threat, impacts of projected habitat loss on species currently threatened with habitat loss, and correlation of species loss with energy consumption. The time frame and species groups involved differ among the "projected" estimates, but in general refer to either future loss of species based on the level of threat that exists today or current and future loss of species as a result of habitat changes taking place over the period of roughly 1970 to 2050. Estimates based on the fossil record are low certainty; lower-bound estimates for known extinctions are high certainty and upper-bound estimates are medium certainty; lower-bound estimates for projected extinctions are low certainty and upper bound estimates are speculative. The rate of known extinctions of species in the past century is roughly 50-500 times greater than the extinction rate calculated from the fossil record (0.1-1 extinctions per thousand species per thousand years). The rate is up to 1,000 times higher than the background extinction rates if possibly extinct species are included."  Source:
Millennium Ecosystem Assessment |
