It’s no secret that wildlife around the world is under severe stress. The most recent Red List from the International Union for the Conservation of Nature estimated that 33% of the species evaluated by the group are at least threatened. The causes are many—hunting, disease, habitat loss, invasive species, even climate change—but they mostly boil down to one main reason: us.
The good news is that we have confirmed extinction for just a handful of species that we know of—though scientists have only been able to formally assess less than 3% of the world’s 1.9 million named species. (And keep in mind that the actual number of species on the planet is certainly far greater than that.) That’s where the good news ends. Conservationists increasingly believe that a warmer, more crowded planet could be headed for a great extinction wave, one that could wipe out more than three-quarters of the species on the planet. And according to a new study published in Nature, that extinction wave could occur in as little as 300 years.
A little history is in order first. Over the course of more than 4.5 billion years, the world has seen five great extinction events—defined as the loss of more than 75% of estimated species. The greatest (or worst) of all was the Permian event, also known as the Great Dying, which ended 451 million years ago and resulted in the loss of 96% of estimated species. The most recent event was the death of the dinosaurs 65 million years ago. All the great extinction events are believed to be due to rapid climate change—perhaps from massive volcanic activity during the Permian event, or an asteroid collision leading to global cooling, which seems likely to have killed off the dinosaurs.
Great extinction events are, by their definition, extremely rare—those five disasters are the only ones to occur over the past 540 million. The Nature study—led by Anthony Baronsky, a professor of integrative biology at the University of California-Berkeley—looked at the rate of historical extinction in the fossil record for mammals and found that less than two species go extinct per million years. That can be considered the normal or background rate. The problem is that in the modern age, mammals have been going extinct at a much faster rate—at least 80 over the past 500 years, out of an estimated 5,570 mammal species. That’s a rate that looks a lot closer to what likely happened during the mass extinction events, which means we seem to be losing species much faster than they disappeared before modern humans came on the scene. In the decades and centuries to come, if the extinction rates hold, we could be entering another great extinction wave without even knowing it, as Barnosky said:
If you look only at the critically endangered mammals – those where the risk of extinction is at least 50 percent within three of their generations – and assume that their time will run out, and they will be extinct in 1,000 years, that puts us clearly outside any range of normal, and tells us that we are moving into the mass extinction realm.
If currently threatened species – those officially classed as critically endangered, endangered and vulnerable – actually went extinct, and that rate of extinction continued, the sixth mass extinction could arrive within as little as 3 to 22 centuries.
The researchers point out that since we’ve only lost a small percentage of total species so far, we do have the chance to turn things around—if we try hard enough. But we’re facing an uphill battle, thanks mostly to the presence of human beings, as the authors write:
It may be of particular concern that this extinction trajectory would play out under conditions that resemble the ‘perfect storm’ that coincided with past mass extinctions: multiple, atypical high-intensity ecological stressors, including rapid, unusual climate change and highly elevated atmospheric CO2. The huge difference between where we are now, and where we could easily be within a few generations, reveals the urgency of relieving the pressures that are pushing today’s species towards extinction.
Can we get there? While some progress has been made—including the agreement by governments around the world last year to reduce the rate of species loss—a warming planet headed towards 9 billion richer human beings is one that may be hostile to most species. (Right on cue, federal wildlife officials yesterday declared that the Eastern mountain cougar was almost certainly extinct.) Our could be to preside over a planet that is fit for human beings, and very little else.
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