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Rapid temperature spikes of as much as 16 degrees Celsius may have been more to blame for the extinction of wooly mammoths, giant sloths, and other megafauna around 11,000 years ago than overhunting by humans, a new study in the journal Science suggests.
But the new research, conducted by scientists from the United States and Australia, emphasizes that the combination of the two forces may have delivered a devastating one-two punch on Earth's large creatures.
"A lot of people try to shift the blame to either humans or climate, but we're showing that both are really important," Alan Cooper, the study's lead author and a professor at the University of Adelaide, told VICE News. "It's a double-edged sword. Species are already surviving in the face of climate change, and suddenly humans are on the landscape, because humans tend to move to new areas when it's warm. And when humans show up, they really disrupt."
And today both factors, a changing climate and a heavy, widespread human footprint on ecosystems across the globe, are at play, making the study an insightful lesson in history.
"Now we've got the perfect storm," Cooper told VICE News. "The worry is that we're setting up conditions now that are starting to look quite similar to the onset of those [warm spikes] in the past which have caused all the damage."
Cooper and his colleagues focused on the end of the Pleistocene epoch and the dawn of the Holocene, which occurred about 11,000 years ago. The period was characterized by a shift from mostly icy conditions around the world to warmer temperatures, which allowed for human societies to flourish.
"It's the stability of the Holocene that's responsible for agriculture, for societies. Everything we think about with civilization is dependent on that consistency," Cooper told VICE News. "The last thing we should be doing right now is poking the global climate system with a stick, which is effectively what we're doing by pumping all that carbon dioxide and methane into the atmosphere."
We might still be in the Holocene, but in recent years, as the effects of human-driven climate change have become more and more apparent, a growing — and vocal — contingent of scientists argue we've entered a whole new geologic epoch called the Anthropocene. This new epoch — the "Age of Man" — is characterized by human-generated carbon emissions, plastics, nuclear fall-out, and chemical-infused fertilizers, all of which are radically changing the chemical and biological composition of the atmosphere, soil, and oceans.
And, according to a June study published in Science Advances, humans may be causing the sixth great extinction in half a billion years. Think of it as humans achieving what only massive meteor strikes or epic volcanic activity could do — wiping out extraordinary numbers of plant and animals species.
"The evidence is incontrovertible that recent extinction rates are unprecedented in human history and highly unusual in Earth's history," the scientists said. "Our analysis emphasizes that our global society has started to destroy species of other organisms at an accelerating rate, initiating a mass extinction episode unparalleled for 65 million years."
The number of species that have gone extinct in the last century, they say, is on pace with what has typically taken between 800 and 10,000 years to disappear.
Last year was the hottest on record and 2015 is on pace to top it. Ten of planet's warmest years on record have occurred since 1998.
And that's got Cooper very concerned.
"[Relatively recent] climate disruptions are nothing versus what the planet can do when its equilibrium is shifted," Cooper told VICE News. "And the great danger, of course, is that we have no bloody idea when that kicks in, how much you have to disturb it before you do change some of these ocean currents, or other heat distribution systems of the planet" that could lead to rapid warming.
"What our record shows is that, when you do, it's nasty," Cooper said.
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