Abrupt episodes of warming, not unlike the rapid man-made global warming the world is undergoing today, have, in the past, played a key role in mass extinction events of large animals such as mammoths, researchers say.
Short but rapid warming episodes called interstadials during the last ice age or Pleistocene era 60,000 to 12,000 years ago can be associated with major extinction events even before the appearance of man, researchers at two Australian universities say.
Extreme cold episodes such as glacial maximums occurring in the same time periods don't appear to be linked with such extinctions, scientists at the University of Adelaide and the University of New South Wales report in the journal Science.
The researchers say they came to those conclusions after detecting patterns revealed in studies of ancient DNA, suggesting rapid disappearances of large species known as megafauna.
The timing of those extinctions suggests they were tied to warm periods, not sudden cold snaps as had long been believed.
"This abrupt warming had a profound impact on climate that caused marked shifts in global rainfall and vegetation patterns," says lead study author Alan Cooper of the University of Adelaide.
"Even without the presence of humans we saw mass extinctions."
That's not to say humans are entirely blameless, the researchers emphasize.
"It is important to recognize that man still played an important role in the disappearance of the major megafauna species," says study co-author Chris Turney from the University of New South Wales.
The extinction events were set in motion by abrupt episodes of climate warming that caused massive changes to the environment, he says, but the rise of humans was the coup de grâce for species that were already under stress.
The new findings can help explain the sudden disappearance of mammoths and giant sloths that went extinct at the end of the last ice age around 11,000 years ago, other experts say.
"There are still people who are putting all the blame on humans, and some blame climate," says Adrian Lister, an evolutionary paleontologist at the Natural History Museum in London who was not involved in the Australian study. "But a growing number see it as it a synergistic effect, a powerful combination of those two factors happening at once."
The findings of the new study should be a warning today that the current trend of global warming, if not stopped or at least slowed, could drive many more species to extinction, the researchers say.
"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," Cooper says.
