Image above from the paper by Hull et al. "rarity in mass extinctions and the future of ecosystems" Nature 528, 345–351 (17 December 2015). Notice how the decline in the fossil abundance, takes the shape of a "Seneca Cliff". The article examines the current situation of the Earths's ecosystem and concludes that we are not yet falling down the cliff, but we might be in the future.
Sometimes, my colleagues make me think of the old joke, "I wouldn't want to belong to a club that accepts people like me as members." That happened to me once more when I read an interview to Smithsonian paleontologist Doug Erwin that was published with the title "We are NOT in the sixth mass extinction", ("The Atlantic," June 13, 2017). Here, Erwin states that the idea that we are in the sixth extinction is just "junk science".
If you wanted further proof that scientists are a bunch of unreliable nerds who live in a world of their own, you need to go no further. How can it be that the "sixth extinction" had become accepted science and then, suddenly, another one of those silly scientists comes up and says that it is not true? How can you believe a single word coming from them?
So. let's try to understand what this whole story is about. First, where does the idea of the sixth extinction come from? Perhaps it was popularized for the first time in a 2011 paper by Barnosky et al on Nature that dealt mainly with the megafauna extinction during the Holocene. Of course, the idea is older than that. If you look on "Google Scholar," the term "sixth extinction" produces more than 174,000 hits. If this is junk science, surely plenty of scientists seem to like this kind of junk.
So, why does Dr. Erwin defines as junk science a subject of study that looks perfectly legitimate and widely explored? The article in "The Atlantic" is just baffling. It starts with an image of the asteroid that's supposed to have killed the dinosaurs; then the title says "we are NOT in a mass extinction," then there follows a long review of all the ongoing extinctions, and then we read that "Erwin says no."
So, what are you supposed to understand from all this? Twice we are told that, yes, extinctions are ongoing, and twice that they are not. To add to the confusion, later in the article we are treated with paragraphs such as "“If we’re really in a mass extinction—if we’re in the [End- Permian mass extinction 252 million years ago]—go get a case of scotch,” he said." What in the world do you think could that mean?
Oh, boy, that life is complicated. Let's quit the silly article in "The Atlantic" and go see the original article in Nature where Erwin and his coauthors explain what they have in mind. And there, unlike in the Atlantic, we have an understandable text. Here are some excerpts from the article.
To date, the majority of extinction studies have been biased towards terrestrial species and charismatic megafauna and we know relatively little about changes in the abundance and ranges of the shelly marine invertebrates that would provide a direct link to mass extinctions in the fossil record.
From custodians of deep time, we need quantitative assessments of the fossil record of the present and future earth in order to accurately size up current biotic changes with the same filter through which we see the past.
Although extinctions are rare, the ecological ghosts of oceans past already swim in emptied seas.
You see the point? So far, we have focussed on the extinction of "charismatic" species, from the past one of mammoths, giant sloths, and the like to the ongoing ones of Elephants, tigers, cheetahs, and others. However, a true mass extinction sees the disappearance, or at least the the near disappearance of common species such as marine invertebrates. But that doesn't appear to be happening, yet.
There follows that, if someone in a remote future were to examine the fossil record for our times, he/she/it wouldn't see, not yet at least, the same kind of disastrous "Seneca Collapse" of the most common species that we see for the "big five" mass extinctions. Once a true "End-Permian-like" extinction were to start, it would be so rapid and destructive that nobody would be alive, discussing it.
That's it, folks: the title "We are NOT in the sixth mass extinction" simply means "we are not YET in the sixth mass extinction", but there are plenty of ongoing extinctions that prefigurate a true mass extinction ("emptied seas") for a non-remote future. That's because we know that most of the past mass extinctions (and perhaps all of them) were caused by the same phenomenon that's ongoing nowadays: the release of large amounts of greenhouse gases in the atmosphere.
Said in other words, imagine you are falling from the 10th floor. You are not yet splattered on the sidewalk and, if you really want to be precise, you shouldn't say that you are in the same condition of other people who fell from the same window in the past. Who knows? You might fall on something soft, or maybe learn how to fly while en route. Precision is precision, right?
So, the position taken by Dr. Erwin is scientifically correct, although it doesn't change what we know about the ongoing extinctions (and, as a personal opinion, I normally avoid branding the work of my colleagues as "junk science," even though I may not agree with them). We didn't go through a mass extinction, yet, because it is just beginning. The problem is that the meaning of the article in The Atlantic, and in particular its title, will NOT be generally understood. On the contrary, it will give plenty of ammunition to the throngs of those who claim that "CO2 is plant food," "the Earth is getting greener," "global warming is good for people"; and the like. It is already happening. As usual, when scientists say something that some people judge unpalatable, they are cheaters and liars. When a scientist says the opposite, he is suddenly defined as reliable.
I don't think Erwin is to be faulted in particular for this disaster in scientific communication. It happens all the time and especially when you stumble on journalists who tend to sensationalize what you tell them. Unfortunately, as scientists, we haven't yet learned how to communicate science to the public.
