Global Warming = Mass Extinction?

I've been looking at a rather sensationalist news story from the Guardian back in 2003, where the first line states that:

"Rising global temperatures over the next century could trigger a catastrophe to rival the worst mass extinction in the history of the planet"

My first reaction was skeptical, but on inspection of next few lines it seems this bold statement was actually based on some logic. Bristol based scientists had found that the Permian mass extinction 250 MYA, which saw 95% of Earth's species go extinct, was caused by only 6º C of warming. Worryingly, 6º C is the maximum warming predicted by the Intergovernmental Panel on Climate Change for a business as usual scenario... !

However, if you continue reading it turns out that the Permian extinctions were caused by massive volcanic activity, the greenhouse gas emissions of which triggered the warming. This seems rather misleading; what about the effects of huge eruptions and giant ash clouds upon dinosaur death? Don't volcanic eruptions cool the planet anyway, as the dust filled atmosphere reflects the Sun's energy back out to space? While it's arguable that reporting a "looming catastrophe" for biodiversity because of climate change will stir preventative action, I consider articles like these to simply erode public trust in climate change scientists. The article did get me thinking though - is there past evidence of climate change causing significant biodiversity loss, preferably without volcanoes muddying the waters?