Accelerated Modern Human-Induced Species Losses: Entering the Sixth Mass Extinction. Ceballos, G., Ehrlich, P. R., Barnosky, A. D., Garćıa, A., Pringle, R. M., & Palmer, T. M.
Accelerated Modern Human-Induced Species Losses: Entering the Sixth Mass Extinction [link]Paper  doi  abstract   bibtex   
The oft-repeated claim that Earth's biota is entering a sixth ” mass extinction” depends on clearly demonstrating that current extinction rates are far above the ” background” rates prevailing in the five previous mass extinctions. Earlier estimates of extinction rates have been criticized for using assumptions that might overestimate the severity of the extinction crisis. We assess, using extremely conservative assumptions, whether human activities are causing a mass extinction. First, we use a recent estimate of a background rate of 2 mammal extinctions per 10,000 species per 100 years (that is, 2 E/MSY), which is twice as high as widely used previous estimates. We then compare this rate with the current rate of mammal and vertebrate extinctions. The latter is conservatively low because listing a species as extinct requires meeting stringent criteria. Even under our assumptions, which would tend to minimize evidence of an incipient mass extinction, the average rate of vertebrate species loss over the last century is up to 114 times higher than the background rate. Under the 2 E/MSY background rate, the number of species that have gone extinct in the last century would have taken, depending on the vertebrate taxon, between 800 and 10,000 years to disappear. These estimates reveal an exceptionally rapid loss of biodiversity over the last few centuries, indicating that a sixth mass extinction is already under way. Averting a dramatic decay of biodiversity and the subsequent loss of ecosystem services is still possible through intensified conservation efforts, but that window of opportunity is rapidly closing. [Excerpt: Discussion] Arguably the most serious aspect of the environmental crisis is the loss of biodiversity – the other living things with which we share Earth. This affects human well-being by interfering with crucial ecosystem services such as crop pollination and water purification and by destroying humanity's beautiful, fascinating, and culturally important living companions (4, 5, 15, 27-30). [\n] Our analysis shows that current extinction rates vastly exceed natural average background rates, even when (i) the background rate is considered to be double previous estimates and when (ii) data on modern vertebrate extinctions are treated in the most conservative plausible way. We emphasize that our calculations very likely underestimate the severity of the extinction crisis because our aim was to place a realistic ” lower bound” on humanity's impact on biodiversity. Therefore, although biologists cannot say precisely how many species there are, or exactly how many have gone extinct in any time interval, we can confidently conclude that modern extinction rates are exceptionally high, that they are increasing, and that they suggest a mass extinction under way – the sixth of its kind in Earth's 4.5 billion years of history. [\n] A final important point is that we focus exclusively on species, ignoring the extirpation of populations – the units relevant to ecological functioning and the delivery of ecosystem services (4, 5, 29). Population extinction cannot be reliably assessed from the fossil record, precluding any analysis along the lines of that presented here. Also, although it is clear that there are high rates of population extinction (18), existing data are much less reliable and far harder to obtain than those for species, which will remain true for the foreseeable future. Likewise, we have not considered animals other than vertebrates because of data deficiencies. [\n] The evidence is incontrovertible that recent extinction rates are unprecedented in human history and highly unusual in Earth's history. Our analysis emphasizes that our global society has started to destroy species of other organisms at an accelerating rate, initiating a mass extinction episode unparalleled for 65 million years. If the currently elevated extinction pace is allowed to continue, humans will soon (in as little as three human lifetimes) be deprived of many biodiversity benefits. On human time scales, this loss would be effectively permanent because in the aftermath of past mass extinctions, the living world took hundreds of thousands to millions of years to rediversify. Avoiding a true sixth mass extinction will require rapid, greatly intensified efforts to conserve already threatened species and to alleviate pressures on their populations – notably habitat loss, overexploitation for economic gain, and climate change (31-33). All of these are related to human population size and growth, which increases consumption (especially among the rich), and economic inequity (6). However, the window of opportunity is rapidly closing. [...]
@article{ceballosAcceleratedModernHumaninduced2015,
  title = {Accelerated Modern Human-Induced Species Losses: {{Entering}} the Sixth Mass Extinction},
  author = {Ceballos, Gerardo and Ehrlich, Paul R. and Barnosky, Anthony D. and Garćıa, Andrés and Pringle, Robert M. and Palmer, Todd M.},
  date = {2015-06},
  journaltitle = {Science Advances},
  volume = {1},
  issn = {2375-2548},
  doi = {10.1126/sciadv.1400253},
  url = {https://doi.org/10.1126/sciadv.1400253},
  abstract = {The oft-repeated claim that Earth's biota is entering a sixth ” mass extinction” depends on clearly demonstrating that current extinction rates are far above the ” background” rates prevailing in the five previous mass extinctions. Earlier estimates of extinction rates have been criticized for using assumptions that might overestimate the severity of the extinction crisis. We assess, using extremely conservative assumptions, whether human activities are causing a mass extinction. First, we use a recent estimate of a background rate of 2 mammal extinctions per 10,000 species per 100 years (that is, 2 E/MSY), which is twice as high as widely used previous estimates. We then compare this rate with the current rate of mammal and vertebrate extinctions. The latter is conservatively low because listing a species as extinct requires meeting stringent criteria. Even under our assumptions, which would tend to minimize evidence of an incipient mass extinction, the average rate of vertebrate species loss over the last century is up to 114 times higher than the background rate. Under the 2 E/MSY background rate, the number of species that have gone extinct in the last century would have taken, depending on the vertebrate taxon, between 800 and 10,000 years to disappear. These estimates reveal an exceptionally rapid loss of biodiversity over the last few centuries, indicating that a sixth mass extinction is already under way. Averting a dramatic decay of biodiversity and the subsequent loss of ecosystem services is still possible through intensified conservation efforts, but that window of opportunity is rapidly closing.

[Excerpt: Discussion] Arguably the most serious aspect of the environmental crisis is the loss of biodiversity -- the other living things with which we share Earth. This affects human well-being by interfering with crucial ecosystem services such as crop pollination and water purification and by destroying humanity's beautiful, fascinating, and culturally important living companions (4, 5, 15, 27-30).

[\textbackslash n] Our analysis shows that current extinction rates vastly exceed natural average background rates, even when (i) the background rate is considered to be double previous estimates and when (ii) data on modern vertebrate extinctions are treated in the most conservative plausible way. We emphasize that our calculations very likely underestimate the severity of the extinction crisis because our aim was to place a realistic ” lower bound” on humanity's impact on biodiversity. Therefore, although biologists cannot say precisely how many species there are, or exactly how many have gone extinct in any time interval, we can confidently conclude that modern extinction rates are exceptionally high, that they are increasing, and that they suggest a mass extinction under way -- the sixth of its kind in Earth's 4.5 billion years of history.

[\textbackslash n] A final important point is that we focus exclusively on species, ignoring the extirpation of populations -- the units relevant to ecological functioning and the delivery of ecosystem services (4, 5, 29). Population extinction cannot be reliably assessed from the fossil record, precluding any analysis along the lines of that presented here. Also, although it is clear that there are high rates of population extinction (18), existing data are much less reliable and far harder to obtain than those for species, which will remain true for the foreseeable future. Likewise, we have not considered animals other than vertebrates because of data deficiencies.

[\textbackslash n] The evidence is incontrovertible that recent extinction rates are unprecedented in human history and highly unusual in Earth's history. Our analysis emphasizes that our global society has started to destroy species of other organisms at an accelerating rate, initiating a mass extinction episode unparalleled for 65 million years. If the currently elevated extinction pace is allowed to continue, humans will soon (in as little as three human lifetimes) be deprived of many biodiversity benefits. On human time scales, this loss would be effectively permanent because in the aftermath of past mass extinctions, the living world took hundreds of thousands to millions of years to rediversify. Avoiding a true sixth mass extinction will require rapid, greatly intensified efforts to conserve already threatened species and to alleviate pressures on their populations -- notably habitat loss, overexploitation for economic gain, and climate change (31-33). All of these are related to human population size and growth, which increases consumption (especially among the rich), and economic inequity (6). However, the window of opportunity is rapidly closing. [...]},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-13653291,~to-add-doi-URL,anthropocene,anthropogenic-impacts,biodiversity,mass-extinction,species-extinction,system-catastrophe,vertebrate},
  number = {5}
}

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