We’re In The Sixth Mass Extinction Event
The urgency behind the most recent IPCC report has thankfully garnered it a lot of attention worldwide*. It’s a report that was very frank in its desperation for people to take this threat as seriously as possible. Yet both this report and the one that hit us in February also made mention of one other key factor that has been swept under the rug – the ability of functioning ecosystems to both mediate and mitigate the impact of climate change.
Alongside a wealth of other benefits we gain from biodiversity, ecosystems play vital roles in helping us withstand the rigours of climate change. Wetlands and rivers protect us from increased flooding. Forests help mitigate extreme heat waves. Peatlands, mires, and permafrost are all crucial carbon sinks. Yet as species disappear, these ecosystems deteriorate, as pieces of the complicated web that they’re made up of disappear. It’s why the concept of mass extinction is so frightening.
But what is mass extinction? We often hear about the concept of a mass extinction, and the question of whether we’re currently in the sixth mass extinction is constantly thrown around. So let’s have a quick look at exactly what extinction itself means, what a mass extinction is, and why it’s increasingly obvious that we’re in one.
Extinction itself seems like a pretty set term – it occurs when every individual of a species is no longer alive, right? Well yes, on the surface that’s it. The IUCN’s definition simply states that there is ‘no reasonable doubt’ that the last individual has died.
Figuring out whether that last individual has died is a problem though. Some species are easy to track, so it’s easy to know where they are and how many of them there are. It’s why, sadly, we’re so certain that the white rhino has done its dash. But other species are more difficult to survey, which makes the concept of ‘reasonable doubt’ a tricky one. Often these species populations are already low, which makes knowing enough about their range and chances of survival difficult.
It’s why with some species we declare extinction after we haven’t had any evidence of their presence for a certain number of years. Yet differing lifespans, as well as their likelihood of being seen in the first place, make setting a common threshold across species almost nonsensical.
The problem isn’t helped by our inability to accept the demise of certain charismatic species. Take the thylacine (also known as the Tasmanian tiger). It was declared extinct in the early 1900s, but it’s such an Australian icon that every few years a new spate of ‘sightings’ (one of these was a pademelon, pictured below) pique public interest and ecologists spend weeks tampering everyone’s hopes. The Ivory-Billed Woodpecker is also thought to be extinct, but thanks to its important cultural status, people will not give up hope. Just last week a new preprint was popularised, suggesting that the bird is still out there somewhere.
Regardless of whether or not a few stragglers are holding on in the wild, the function that these species once held in their respective ecosystems is gone. And when this happens on a large scale, ecosystems start to deteriorate. But how large does that scale need to be before we start talking about mass extinctions?
There have been five mass extinctions in earth’s history. The one most people are most familiar with is the most recent of those, the KT extinction. It occurred at the end of the Cretaceous period, wiping out the majority of non-avian dinosaurs as well as a huge range of other species. Before that came the Permian extinction, which is thought to have wiped out 96% of all marine species, and is often referred to simply as the ‘Great Dying’. We define periods of mass extinction as occurring when extinction rates are significantly above ‘background levels’ – ie. the normal levels of extinction we’d see if everything was fine and dandy.
So does that mean we’re in a mass extinction event? Absolutely. Already in 1995, Science published an article by Stuart Pimm which claimed that extinction levels were between 100 and 1,000 times what they should be. A more recent paper took a background level of two mammals species going extinct per 10,000 species over a one hundred year period (which is twice the estimated rate), and suggested that the number of extinctions occurring over the last century would normally take between 800 and 20,000 years.
So yes, it seems clear that this is a sixth mass extinction event. We may only be at the start of it, but it’s certainly happening. And the further it goes, the harder it will be to reverse. If species continue to disappear, the ecosystems that simultaneously house and depend on them will disappear too, and many of our main allies in the fight against climate change will vanish.
Dr. Sam Perrin is a freshwater ecologist who completed his PhD at the Norwegian University of Science and Technology who is very much annoyed that with all these species going extinct the duck is still hanging around like it deserves its place here. You can read more about his research and the rest of the Ecology for the Masses writers here, see more of his work at Ecology for the Masses here, or follow him on Twitter here.
* Though probably still not as much as it deserves