Climate Change Likely Drove Extinction of Mammoths and Other Large Animals

New study suggests that overhunting wasn't the reason they disappeared.

Close up of mammoth skeleton on dark background
Mammoth skeleton at a museum in Zurich. Kubu / Getty Images

A new study suggests that it wasn’t hunting that drove mammoths, ground sloths, and other gigantic animals to extinction in North America. Instead, researchers suggest that climate change likely caused populations of these massive creatures to plummet.

Thousands of years ago, there were large animals including mastodons, massive beavers, and armadillo-like creatures called glyptodons on the continent. But by about 10,000 years ago, most of these animals weighing more than 44 kilograms (97 pounds) — called megafauna — had vanished.

For years, researchers hotly debated whether human hunting or a major climate event (or a combination) of the two had caused the animals to disappear.

In a new study published in the journal Nature Communications, findings showed that drastic decreases of temperatures around 13,000 years ago were the reason so many of these animals died out. Scientists from the Max Planck Extreme Events Research Group in Jena, Germany, used a new statistical modeling approach to find the connection.

“Our group, the Extreme Events Research Group, is, as the name suggests, interested in studying past extreme events. And while not our sole focus, we are particularly interested in past extreme events and their relationship to humans,” Mathew Stewart, co-lead author of the study, tells Treehugger.

To study how extreme events may have had an impact on humans, archaeologists and paleontologists typically use the radiocarbon record. That’s the measurement of radiocarbon content in organic objects, like bone fragments or wood chips, to determine when the plant or animal died.

The rationale is that the more animals and humans there are, the more carbon is left behind when they are gone. And that is reflected in the fossil and archaeological records.

“There are, however, a number of issues with this method. The main issue is that it blends together the process you are trying to identify with chronological uncertainty – that is, the errors associated with radiocarbon dates,” Stewart says. “This makes it an unsuitable tool for reconstructing through-time population changes, as has been shown in numerous simulation studies.”

To get around those issues, researchers used a novel statistical approach developed by the study’s other lead author W. Christopher Carleton. The new method better accounts for uncertainty in fossil dates.

The team used this new approach to investigate whether the North American extinction of megafauna could be explained by human overhunting, climate change, or some combination of the two.

Population and Changing Temperatures

When the researchers appalled this new method to megafauna extinction, their findings suggested that population levels fluctuated due to changing temperature.

"Megafauna populations appear to have been increasing as North American began to warm around 14,700 years ago," says Stewart. "But we then see a shift in this trend around 12,900 years ago as North America began to drastically cool, and shortly after this we begin to see the extinctions of megafauna occur."

Specifically, they found that increases in temperatures correlated to increases in population of these large animals, and decreases in temperatures with decreases in their numbers.

“And when we look at the timing of the final decline in megafauna numbers and the approximate extinction, it suggests that the return to near-glacial conditions around 13,000 years ago and associated ecological changes played a key role in the megafauna extinction event,” Stewart says.

Although the findings suggest that the change in climate was the main cause of extinctions, the answer likely isn’t that straightforward. The researchers found no support for overhunting as the simple reason for population loss.

“However, that is not to say humans played no role whatsoever,” Stewart says. “They may have been involved in more complicated and indirect ways than simple overkill models suggest. For example, they may have facilitated habitat and population fragmentation, or provided the ‘final blow’ to megafauna populations already on their way to extinction.”

View Article Sources
  1. Stewart, Mathew, et al. "Climate Change, Not Human Population Growth, Correlates With Late Quaternary Megafauna Declines in North America." Nature Communications, vol. 12, no. 1, 2021, doi:10.1038/s41467-021-21201-8

  2. "Radiocarbon Dating." American Chemical Society.