Hunting and habitat destruction by humans only delivered the “death blow” to animals whose fate was probably already sealed, new evidence suggests.
Experts combined ancient DNA from museum specimen collections, radiocarbon dating and climate data covering 31 time periods and stretching back 56,000 years.
The team from the University of Adelaide and the University of New South Wales expected to learn that intense cold snaps had contributed to extinctions. Instead they found the opposite - the most powerful factor involved in the death of megafauna turned out to be short, rapid warming events known as interstadials.
Lead researcher Professor Alan Cooper, director of the Australian Centre for Ancient DNA, said: “This abrupt warming had a profound impact on climate that caused marked shifts in global rainfall and vegetation patterns.
“Even without the presence of humans we saw mass extinctions. When you add the modern addition of human pressures and fragmenting of the environment to the rapid changes brought by global warming, it raises serious concerns about the future of our environment.”
Scientists have long debated whether the disappearance of the mammoth, woolly rhino, giant sloth, short-faced bear and other large ice-age species was primarily due to environmental influences or human activity.
The new evidence, published in the journal Science, provides strong support for the former theory.
Repeated interstadial warming events were linked to the loss of megafauna species, with or without human help.
Researchers showed that interstadials, recorded during the last Ice Age or Pleistocene (60,000-12,000 years ago) coincided with major extinction events even before the appearance of man. One animal, the North American short-faced bear, had already vanished before humans arrived in the New World about 13,000 years ago.
In Eurasia, the woolly mammoths and other big animals persisted for thousands of years after modern humans showed up in this region 44,000 years ago, and then disappeared during a series of warm spells.
Co-author Professor Chris Turney, from the University of New South Wales, Australia, said: “It is important to recognise that man still played an important role in the disappearance of the major megafauna species.
“The abrupt warming of the climate caused massive changes to the environment that set the extinction events in motion.
“But the rise of humans applied the coup-de-grace to a population that was already under stress.”
Prof Turney added: “During the last Ice Age, Scotland would have been home to a cornucopia of large-bodied mammals long-extinct today and often more popularly associated with foreign climes.
“Woolly rhinos, giant deer, cave lions, brown bears all would have called the Lowlands home at some time.
“The big question is what caused their extinction in Scotland and across Europe as a whole?”