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Climate Change, Not Human Hunting, Killed Off Ancient Australian Megafauna

Between direct man-made causes like habitat loss and climate change at large, this mass extinction is moving quickly.
Photo: Karora/Wikipedia

Human activity may be responsible for the demise of many animal species in both historic and prehistoric times—remember, we're in the middle of the sixth great extinction now—but in ancient Australia it was climate change that did in most of the huge animals that lived there before humans even arrived.

New research published in the Proceedings of the National Academy of Sciences shows that on the ancient continent of Sahul (modern day Australia, New Guinea, Tasmania, and nearby islands) most of the region's amazing megafauna were already extinct by the time humans arrived 45,000-50,000 years ago. Of the 90 giant animal species that once lived on the ancient landmass, just eight to 14 species were still around by the time people started hunting. Over 50 species are entirely absent from the fossil record for the past 130,000 years.

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The conventional view is that human activity killed off these remarkable animals, but this latest review, based on analysis of Antarctic ice cores and other environmental indicators, finds that Sahul became increasingly arid, with an erratic climate over the past 450,000 years. The extinction of these animals probably occurred over "tens, if not hundreds, of millennia," study lead author Stephen Wroe says, "under the influence of inexorable, albeit erratic, climatic deterioration."

Wroe adds, despite the assertion that humans were to blame for the extinction of so many of these animals, "There has never been any direct evidence of humans preying on extinct megafauna in Sahul, or even of a tool-kit that was appropriate for big game hunting."

Before taking a leap forward to the obvious connection to events of today, check out the type of amazing animals that lived in Sahul. I don't use the word amazing lightly, but Professor Wroe's description of them really is just that:

These leviathans included the largest marsupial that ever lived—the rhinoceros-sized Diprotodon—and short-faced kangaroos so big we can't even be sure they could hop. Preying on them were goannas [Australian monitor lizards] the size of large saltwater crocodiles, with toxic saliva and bizarre but deadly marsupial lions with flick-blades on their thumbs and bolt cutters for teeth.

There's no doubt that today's climate is changing rapidly, with human activity to blame. Both direct human activity, creating habitat loss and directly killing animals (as is the case of overfishing), as well as indirect human activity, in the form of climate change, is the primary cause, full stop.

It's a huge topic, what accelerating climate change will do to extinction rates globally, but here's what may be in store in a nutshell: Computer models show that 15 to 37 percent of all species on the planet will be "committed to extinction" by mid-century due to the effects of climate change.

Looking at extinction rates and the causes of extinction and extrapolating forward, within 300 years 75 percent of all animal species currently alive could be extinct. That's a similar amount to the Cretaceous-Tertiary extinction of 65.5 million years ago, which wiped out the dinosaurs, as well as the Late Devonian extinction of 360 million years ago, but happening at a much, much faster rate.

For the past 65 million years scientists have calculated that the average extinction rate was less than two species per million years. In the past 500 years alone, conservatively, 80 of the roughly 5500 species of mammals have gone extinct. Between direct man-made causes like habitat loss and climate change at large, this mass extinction is moving quickly.