Two new studies take a questioning look at our species mythology of Man the Mighty Hunter. Long-held theories have attributed massive megafauna die-offs in prehistoric Australia--the extinctions of big beasts like the marsupial lion, "immense, wombat-like" Diprotodon optatum and a 900 lb (400 kg) lizard called Megalania prisca--solely to the arrival of humans. But this might just be guilt by association. Researchers in the UK and Australia took a look at the fossil record, and say that it was a little more complicated than that: a transition to a colder, drier climate at about the same time humans arrived transformed woodlands and scrublands into grasslands. Many beasts large and small did not survive the changes in their habitat. "You try taking out a two-to-three-tonne wombat with a pointy stick," said Dr Stephen Wroe, from the University of Sydney. "I don't doubt the first Aboriginals did hunt megafauna but the argument that they did it with the efficiency required to effect near-instantaneous extinction is not, in my view, credible."
I think climate played a role in the late Quaternary extinctions, but I also think that in North America humans played a large role as well. The finds of the massive kill zones where herds of horses, etc were chased into chasms and slaughter raises the question of early humans "living in tuned with the natural balance" dogma.
The rapid changes in climate after the last Glacial max. of the Laurentian Ice Sheet did cause sweeping changes in the grasslands of Central North America, but I think that human push really was the straw that broke the mammoth's back.
Yes; the linked article does refer to the similar timing on both continents, but as one of the researchers points out, there are no stone spear points in the Australian fossil record until well after the die-off is thought to have happened--unlike North America at roughly the same time.