Studies have shown time and again that humans are pretty effective at driving other animals to extinction — but a new study published in Science this week suggests that when it comes to some species, that blame might have been misplaced.
The study — conducted by researchers at the University of Adelaide — claims that a series of abrupt climatic events, not humans, led to the extinction of certain megafauna, including mammoths, giant sloths, and other giant mammals. And while that might take away some of the historic blame humans have faced for hunting these animals to extinction, the authors warn that it’s actually bad news for humans, because if the current warming pattern isn’t abated, humans could face the same fate as the long-gone giants.
Human interest in megafauna like mammoths began more than two centuries ago with the discovery of their fossilized remains, and those fossils have long served as the primary tool scientists used to study the extinct animals. But researchers at the University of Adelaide, led by paleogeneticist Alan Cooper, decided to study the animals using a different tool: ancient DNA extracted from fossils. By figuring out how diverse a species’ DNA was for any one place, the researchers were able to figure out about how many animals from a given species existed at a specific time.
Using data from thousands of sites across America, Europe, and Asia, Cooper and his colleagues were able to map when and where different species began to disappear. They then turned to the climate record, using ice cores from Greenland and marine sediments from Venezuela to map temperature changes. They found that some 50,000 years ago, the Earth began going through periods of sudden warming — called interstadials — where the Earth’s average temperature increased by as much as 28.8 degrees Fahrenheit over a decade. Then, the Earth would cool — sometimes just as abruptly.
Scientists previously thought that the cooling periods were most likely linked with megafauna extinction, but Cooper and his colleagues’ findings refute that idea. Instead, they found that during the colder periods, the giant mammals did fine — it was only during the abrupt warming periods that megafauna populations underwent rapid declines.
Humans were likely the nail in the coffin for many of these species, but the study argues that humans weren’t always necessary for a megafauna species to go extinct. It points specifically to the short-faced bear, a giant bear that once roamed North America but went extinct, the study claims, well before humans migrated to the area.
Cooper isn’t sure what particular aspect of the warming period might have triggered extinctions, something he told the Washington Post would be the subject of more study.
“We can see the relationship between the warming periods and the extinctions,” Cooper said, “but can’t tell whether its the warming or the pace of change. It’s one of the two.”
Something that concerns climate scientists about current global warming trends is the rate at which climate change is unfolding — a rate that NASA says is “unprecedented in the past 1,300 years.” If a rapid series of warming 50,000 years ago led to the disappearance of some megafauna, the study warns, that could spell trouble for the future. Previous studies have already warned of the extinction that could occur if climate change goes unabated — one 2013 study found that species will have to evolve 10,000 times faster than they have in the past in order to keep up with the Earth’s warming.
“The study suggests that current warming trends are a major concern, as in many ways the rise of atmospheric CO2 levels and resulting warming effects are expected to have a similar rate of change to the onset of past interstadials, heralding another major phase of large mammal extinctions,” Cooper told the Conversation.
In an interview with Science, David Steadman, a paleontologist at the Florida Museum of Natural History, raised some concerns about the study’s conclusions, worrying that it relied too much on the fossil record to determine when the animals had gone extinct. He also said that the study might lean to heavily on climate change as the driving force behind the extinctions — other warming events, he said, took place while the animals were alive and did not drive them to extinction. To Steadman, the fact that so many extinctions began to occur when humans arrived in the areas where the animals lived suggests that humans really were the driving factor.