Last week the science fiction pop-culture blog io9 published an article asking the question, are we in the middle of a mass extinction? To answer that question, they interviewed Ross MacPhee, a paleontologist, curator at the American Museum of Natural History, and an expert on mass extinction. You can read that article for yourself, but in brief, he argued that we are not in the middle of a mass extinction event because 1). in order for it to be a mass extinction you have to lose species from every level of the biosphere, from top predators to micro-flora, and 2). statistical estimates of the modern loss of species based on E. O. Wilson’s work have not been put to empirical test. Furthermore, loss of local populations of animal and severely reduced populations of species do not equate actual extinctions.
There’s no reason to doubt MacPhee’s expertise. He’s had a long and esteemed career, and contributed significantly to his discipline. However, it’s important to remember that by discipline he is a paleontologist. As such he is an expert in past extinction events, not current or future events. Asking a paleontologist about a current extinction event is a little like asking a sports historian to predict next year’s Super Bowl. The beginning of a mass extinction event is probably going to look a lot different from the middle. The truth is, we can’t know if we’re in the middle of a mass extinction event until we’re in the middle of a mass extinction event, and by then it’s too late.
So instead of looking at what is happening now, and measuring it against a hard-coded definition, it would probably be more helpful to ask ourselves, “are things happening now which left unchecked could result in a mass extinction?”
News of one such mass-extinction precursor came across my feeds today. An article in Nature by Siegel and Franz suggests that our current level of climate change is resulting in about a 1% a year drop in the population density of phytoplanktons, the bottom-most element of the marine food chain. Specifically, they note a 40% decrease in population from 1950 to the present. While MacPhee’s assessment that it’s not a mass extinction until species at the top and bottom of the biosphere have been effected, it doesn’t take much of an intuitive leap to say that if the thing that krill feed on goes extinct, or at very least is driven to the brink of extinction, a lot of other species will disappear too. So, while I don’t fault MacPhee for answering the question asked of him, I do think that there was a more responsible way of answering it than this, “My point is that people are speculating about extinction with arm-waving. I don’t see evidence of mass extinction or extinctions of large effect. Doubtless humans are endangering species – but how many gravestones are we talking about? I don’t know, and I don’t think anybody else does either.” As he notes earlier, when extinctions happen, they happen quickly. Otherwise life has a chance to adapt. By the time we can show him the cemetery, we’ll be living in it. So the best question is not, “Are we living through a mass extinction event” instead it is, “Are we doing everything we can to promote resiliency in the form of rich biodiversity while we can?”
David A. Siegel & Bryan A. Franz. Oceanography: Century of phytoplankton change. Nature, July 28, 2010; p569