Why This Mass Extinction is Different

Scientists believe we are in the sixth major mass extinction of the planet. As Wired reports:

Earth may be in the midst of the greatest extinction ever, according to a new mass extinction scoring system.

Their system, published today in the Proceedings of the National Academy of Sciences, attempts to quantify those periods when more than half of all species disappeared. In addition to the current mass extinction, this has happened at least five times: the End Ordovician, Late Devonian, End Permian, End Triassic and End Cretaceous. The latter -- marking the end of the Age of Dinosaurs -- receives the most attention, but scientists have been unable to decide which extinction was most significant.

By multiplying the number of organismal groups that went extinct with the time it took, they arrived at a metric called "greatness." According to this, the dinosaur-ending End Cretaceous event, possibly caused when asteroid strikes or volcanic explosions sheathed the Earth in ash, was twice as great as any previous extinction.

The Permian extinction event, caused 250 million years ago by the formation of the Pangea supercontinent and volcano-induced oceanic poisoning, placed third on the researchers' rankings -- and it still encompassed the loss of 96 percent of Earthly life.

The International Union for the Conservation of Nature estimates that 800 plant and animal species have gone extinct in the last 500 years, with more than 16,000 currently threatened with extinction -- and those lost or threatened organisms come the from mere 41,000 species so far assessed by science. More than a million have been described but remain unstudied.

The most troubling figures, however, come not from the total species lost but the rate at which they're vanishing: 1,000 times faster than usual. But even that alarming rate may be too conservative.

There is a major difference between the previous mass extinctions and this one.

The previous ones were were caused by traumatic events such as asteroids colliding with the Earth or major volcanic eruptions. This greatly reduced the amount of life that the Earth could support. Not only did most species go extinct, but also the population size of all species fell dramatically.

In the current mass extinction, the total amount of life that the Earth can support is not declining. One way to measure this is net primary productivity (NPP) which tells how much biomass is being created by plants on land and phytoplankton in the ocean. More NPP means more biomass at the bottom of the food chain. This in turn allows the Earth to support larger populations of animals all the way up the food chain. NASA satellites have recorded a 6% increase in net primary productivity (NPP) from 1982-1999. One study suggests that NPP is likely to increase by 40% over the next 100 years due to global warming.

In business terms, this current mass extinction could be thought of as a consolidation. There may be fewer species, but there will be larger populations of the ones that remain.

For example, most primate species populations have been dwindling fast and 48% of primate species are threatened with extinction. But, one specific primate species has done so well (better than any large mammal species has ever done, with a population of over 6 billion) that the total population of all primates has never been higher.

Another example is Hawaii, which is a verdant tropical paradise. In terms of the amount of life it supports, it is doing better than any other state in the US. And yet it is also home to nearly 1/2 of the 114 species extinctions in the US in the last 20 years and currently has 344 endangered species, more than any other state in the nation. As one scientist writes:

''Not a single plant, none of the lowland birds in Hawaii are native.'' We are turning the world into ''a McDonald's ecosystem,'' with the same species living roughly the same way everywhere.

I think the phrase "McDonald's ecosystem" is a good way to look at this current mass extinction. While loss of biodiversity is not a good thing, it is a much smaller problem than the Earth losing its ability to support life. While the previous mass extinctions had both species extinctions and smaller populations of life, the current one just has species extinctions.