Abrupt climate warming, not cold snaps, kicked off megafauna extinction: study

Patterns of extreme warming events are linked to the extinction of megafauna such as mammoths, new research has found.

The findings, published today in Science, challenge previously held views that cold snaps or hunting by humans were the key drivers behind the disappearance of large animals like giant sloths and mammoths.

The research team, led by Dr Alan Cooper from the University of Adelaide and Professor Chris Turney from the University of NSW used ancient DNA analysis and radiocarbon dating to demonstrate a direct link between abrupt, decadal-long warming events known as interstadials and sharp declines in megafaunal populations.

These short, rapid warming events with temperature increases of about 4-16C occurred during the late Pleistocene era, which ended around 12,000 years ago, and caused marked shifts in global rainfall and vegetation patterns, said Cooper.

Humans finished what climate change began

The mysterious disappearance of megafauna such as the mammoth and the giant ground sloth has been the subject of scientific fascination for centuries, dating to when Charles Darwin discovered remains in South America.

Fellow author Turney said humans still played a major role in the cluster of extinction events at the end of the Ice Age.

“Similar wholesale ecosystem changes did not occur earlier in the climate record when interstadials were common but humans were not. However, climate shifts appear to be the major driver in megafaunal extinction events,” he said.

“By concentrating on prime hunting spots along dispersal routes, humans could have killed the few bold individuals moving out to re-establish an extinct population – and thereby caused localised extinctions.”

The next step, he said, is to resolve how and why warming events are so destructive, and warned that the research may provide an insight into expected impacts of today’s warming climate.

“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,” he said.

Strong evidence on role of climate

Chris Johnson, Professor of Wildlife Conservation at the University of Tasmania, said it was important to recognise that many of the extinctions documented by this study were of genetically distinct populations, not species.

“In most cases, the species themselves persisted, and what happened was that populations that went extinct were replaced by migration of animals of the same species (but with different genetics) from other parts of the species’ ranges,” he said.

That may help explain why, until now, the pattern had not been easily recognisable.

“It was necessary to get genes out of fossil material to realise that anything had happened, because otherwise the continuity of the fossils suggests no change.”

According to Johnson, the research provided “evidence for climate having strong effects on the dynamics of megafaunal populations and causing rapid distribution change and disappearance, and then restoration of populations.”

“That is very important information,” he said. “It is also clear that something quite different happened when humans came along: lots of big animals disappeared everywhere, and were not replaced by animals moving in from somewhere else.”

Tim Cohen, Senior Lecturer in the School of Earth and Environmental Sciences at the University of Wollongong, described the finding as a unique contribution to a long standing debate as to the relative role of climate and humans in megafaunal decline.

“Unlike in the past when many studies lacked both extinction and climate data, this piece presents a very convincing set of high resolution climate records for the northern hemisphere as well as a raft of new DNA data. Going against what we have perceived in the past, which is that the earth’s coldest periods were those that impacted species the most, this research shows that rapid warming periods in the last glacial cycle have been critical in driving ecological responses and extinctions,” he said.

“Until recently we have assumed that the climate was stable throughout the period when humans first arrived on the Australian continent and some of the megafauna became extinct but maybe a similar story will unfold down under, where past climatic variability drove widespread ecological responses.”

Professor Chris Turney and Dr Alan Cooper has written an analysis of their findings for The Conversation here.