Bad news: Climate change helped kill the woolly mammoth

The Cambridge group compiled dates from previous studies for the arrival of humans and the extinction of megafauna on each landmass: Australia, Eurasia, New Zealand, North America, and South America. And they took the temperature record locked in an Antarctic ice core as a guide to global climate change. Then they compared how well climate change and human arrivals, alone or in combination, could predict the timing and severity of extinctions on the five landmasses. To sort out the importance of timing uncertainties, they tested 320,000 different extinction scenarios. “We tested a lot of models across a huge range of human arrival times and extinction times,” Prescott says. “It seems likely that both climate and human factors played a role” in most cases.

“What they found makes sense,” says mammalian paleoecologist Anthony Barnosky of the University of California, Berkeley. “It makes a clear case for there being an interaction. It shows what happens when two bad things happen at once.” Barnosky and environmental scientist Barry Brook of the University of Adelaide in Australia have found such a human-climate synergy operating in megafaunal extinctions when severe climate change coincided with human arrivals. A similar synergy is happening today, they say, as global warming intensifies and the human population continues to grow.