By James D. Agresti
November 28, 2011
“Overall, species loss is now occurring at a rate 1,000 times greater than the natural background rate,” warns Al Gore in the Academy Award-winning documentary, An Inconvenient Truth (see clip below). Similarly, Michael J. Novacek of the American Museum of Natural History wrote in a 2007 book (page 46) that “species are going extinct at thousands of times the background extinction rate,” and we are “thus likely to lose 30 to 50 percent of all living species within this century.”
Such dire portrayals are incompatible with concrete data on species extinctions. In a recently published paper in the journal Diversity and Distributions, the authors analyzed the “actual historical record of extinctions” and found that a total of 190 birds and land-dwelling mammals have gone extinct since the year 1500. The data also showed that only three of these mammals and six of these birds lived on continents. The rest lived on islands, where populations are small and geographically restricted. As the authors explain:
The three extinct mammals represent approximately 0.08% of the continental species pool. Even if we assume that all three went extinct in the past 100 years (vs. 500 year), it would take, at this rate, 1235 years for 1% of continental mammals to go extinct. Similarly for birds, the six species represent 0.062% of the 9672 species pool and it would take 1613 years to lose 1% of extant species at current rates even if the recorded extinctions all took place over the last 100 years.
This is a far cry from Novacek’s claim that we are “likely to lose 30 to 50 percent of all living species within this century.” Gore, Novacek, and many other environmentalists either don’t understand or neglect to mention that this “natural background rate” they speak of is a fossil-based estimate burdened with so many assumptions that a 2005 Cambridge University Press book on biodiversity (page 139) states that no “serious” attempt has been made to “judge the reliability” of this figure because the “uncertainties at each stage of the calculation” would make the effort worthless. The book goes on to explain, “Probably no one will be surprised if this estimate is off by a factor of 10 or even 100.”
Based upon the data above, it may be off by even more than this. For more details, see my commentary on this subject in American Thinker.