2011 March 2. Has the Earth's sixth mass extinction already arrived? By Robert Sanders, UC Berkeley News Center. Excerpt: …In a study to be published in the March 3 issue of the journal Nature, University of California, Berkeley, paleobiologists assess where mammals and other species stand today in terms of possible extinction, compared with the past 540 million years, and they find cause for hope as well as alarm….
…“So far, only 1 to 2 percent of all species have 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,” [Professor Anthony] Barnosky said. “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.”….
…The study originated in a graduate seminar Barnosky organized in 2009 to bring biologists and paleontologists together in an attempt to compare the extinction rate seen in the fossil record with today’s extinction record....
[See also Multitude of Species Face Climate Threat, by Carl Zimmer, The NY Times.]

2009 June 19. Sudden Collapse In Ancient Biodiversity: Was Global Warming The Culprit? ScienceDaily. Excerpt: Scientists have unearthed striking evidence for a sudden ancient collapse in plant biodiversity. A trove of 200 million-year-old fossil leaves collected in East Greenland tells the story, carrying its message across time to us today.
...The researchers were surprised to find that a likely candidate responsible for the loss of plant life was a small rise in the greenhouse gas carbon dioxide, which caused Earth's temperature to rise.
Global warming has long been considered as the culprit for extinctions--the surprise is that much less carbon dioxide gas in the atmosphere may be needed to drive an ecosystem beyond its tipping point than previously thought.
...Until this research, the pace of the extinctions was thought to have been gradual, taking place over millions of years.
It has been notoriously difficult to tease out details about the pace of extinction using fossils, scientists say, because fossils can provide only snap-shots or glimpses of organisms that once lived.
Using a technique developed by scientist Peter Wagner of the Smithsonian Institution National Museum of Natural History in Washington, D.C., the researchers were able to detect, for the first time, very early signs that these ancient ecosystems were already deteriorating--before plants started going extinct.
The method reveals early warning signs that an ecosystem is in trouble in terms of extinction risk.
...By the year 2100, it's expected that the level of carbon dioxide in the modern atmosphere may reach as high as two and a half times today's level.
"This is of course a 'worst case scenario,'" says Jennifer McElwain of University College Dublin, the paper's lead author. "But it's at exactly this level [900 parts per million] at which we detected the ancient biodiversity crash.
"We must take heed of the early warning signs of deterioration in modern ecosystems. We've learned from the past that high levels of species extinctions--as high as 80 percent--can occur very suddenly, but they are preceded by long interval of ecological change."...

2006 February. Affecting Evolution and Extinction. By David Pescovitz. ScienceMatters@Berkeley, Volume 3, Issue 18. Every so often, a huge number of species on Earth are wiped out relatively quickly. The last time a large extinction event occurred, between 50,000 and 10,000 years ago, two-thirds of large mammals were swept into the dustbin of history. Why? UC Berkeley paleontologist Anthony Barnosky sifts through the fossil record to understand how environmental changes can cause mammals to move, evolve, and sometimes die off. His research could even help reveal whether we're headed for another mass extinction. ...The aim... is to differentiate between effects of climate change that are natural, and those that could be harbingers of a bigger problem.... "Is part of being a species the fact that you move around in response to climate change and it's no big deal?" Barnosky says. "I'm trying to establish a natural baseline of how much communities change in response to climate change in the past." ... Barnosky ... investigate[d] the cause of large mammal extinctions in the late Pleistocene period, 50,000 to 10,000 years ago. Historically, scientists have thought that human populations of the time over-hunted, killing off animals such as mammoths, ground sloths, native American horses, and camels. However, Barnosky and his colleagues discovered that human impact wasn't the sole cause of the extinctions. Rather, climate change combined with the over-hunting was a "one-two punch" leading to the extinction, he says. The big concern, Barnosky says, is that the state of the planet then is not so different from today. "We've ramped everything up," he says. "Global warming has never been faster and human populations are exploding exponentially. Realistically, I think the ecosystem will change pretty dramatically.