So what did they find?

First of all, they determined that 25% of all mammals for which adequate data are available are threatened with extinction, with the percentage for marine mammals rising to 36%. These figures include 188 critically endangered species that face what they call "a very high probability of extinction," as well as 29 species for which they say "it may already be too late."

What are the primary causes of the possible near-term mammal extinctions?

The international team of experts states that "worldwide, habitat loss and degradation (affecting 40% of species assessed) and harvesting (hunting or gathering for food, medicine, fuel and materials, which affect 17%) are by far [our italics] the main threats to [land] mammals." With respect to marine mammals, however, they say "the dominant threat is accidental mortality (which affects 78% of species), particularly through fisheries by-catch and vessel strike," while "pollution (60% of species) is the second most prevalent threat."

So what factor is most important to maintaining mammal species richness and preventing wholesale extinctions?

As stated in the table of contents tag line to the article, the comprehensive assessment of the 130 researchers "shows that primary productivity [our italics] drives species richness on land and sea," while in the article itself the authors write that "as with land species, marine richness seems to be associated with primary productivity," noting that "whereas land species' richness peaks toward the equator, marine richness peaks at around 40°N and S, corresponding to belts of high oceanic productivity."

Shipper et al. conclude their review by stating that their results "paint a bleak picture of the global status of mammals worldwide." And so they do. However, we can reduce the loss and degradation of habitat and animal harvesting on land, as well as accidents and pollution at sea, but only if we truly dedicate ourselves to doing so. On the other hand, attempting to prevent catastrophic mammal extinctions by trying to change the world's climate, as Al Gore, James Hansen and others claim we must do by restricting CO2 emissions, is even worse than wishful thinking, for it simply cannot be done. What is more, fully half of all the archived content of our website is a testament to the fact that atmospheric CO2 enrichment significantly increases primary productivity, both on land and at sea; and this phenomenon is the greatest known force for maintaining earth's mammal species richness.

Clearly, the combination of these elements of the problem's solution -- protecting mammal habitat from loss, degradation and pollution, while curtailing willful and accidental animal harvesting, plus allowing the atmosphere's CO2 content to pursue its historical upward course without overt curtailment -- is the only hope we really have of saving what yet remains of earth's endangered mammals.

Sherwood, Keith and Craig Idso

Reference
Schipper, J. and 129 coauthors. 2008. The status of the world's land and marine mammals: Diversity, threat, and knowledge. Science 322: 225-230.