Are we causing the next mass extinction?

Sad news in this Yahoo! article:

Mankind may have unleashed the sixth known mass extinction in Earth's history, according to a paper released by the science journal Nature.

Over the past 540 million years, five mega-wipeouts of species have occurred through naturally-induced events.

But the new threat is man-made, inflicted by habitation loss, over-hunting, over-fishing, the spread of germs and viruses and introduced species, and by climate change caused by fossil-fuel greenhouse gases, says the study.

Evidence from fossils suggests that in the "Big Five" extinctions, at least 75 percent of all animal species were destroyed.

Palaeobiologists at the University of California at Berkeley looked at the state of biodiversity today, using the world's mammal species as a barometer.

Until mankind's big expansion some 500 years ago, mammal extinctions were very rare: on average, just two species died out every million years.

But in the last five centuries, at least 80 out of 5,570 mammal species have bitten the dust, providing a clear warning of the peril to biodiversity.

[…]

On the assumption that these species are wiped out and biodiversity loss continues unchecked, "the sixth mass extinction could arrive within as little as three to 22 centuries," said Barnosky.

Compared with nearly all the previous extinctions this would be fast-track.

Four of the "Big Five" events unfolded on scales estimated at hundreds of thousands to millions of years, inflicted in the main by naturally-caused global warming or cooling.

[…]

The authors admitted to weaknesses in the study. They acknowledged that the fossil record is far from complete, that mammals provide an imperfect benchmark of Earth's biodiversity and further work is needed to confirm their suspicions.

But they described their estimates as conservative and warned a large-scale extinction would have an impact on a timescale beyond human imagining.

"Recovery of biodiversity will not occur on any timeframe meaningful to people," said the study.

"Evolution of new species typically takes at least hundreds of thousands of years, and recovery from mass extinction episodes probably occurs on timescales encompassing millions of years."

Even so, they stressed, there is room for hope.

"So far, only one to two percent of all species have gone gone extinct in the groups we can look at clearly, so by those numbers, it looks like we are not far down the road to extinction. We still have a lot of Earth's biota to save," Barnosky said.

Even so, "it's very important to devote resources and legislation toward species conservation if we don't want to be the species whose activity caused a mass extinction."

“Room for hope” sounds good, but given how low biodiversity conservation scores on politicians’ radars, I personally don’t have much.

And a scientist mentions in the article how, given current trends, “by the end of this century, we may well have wiped out half of [all species], especially in tropical forests and coral reefs.”