Reply #4: The species is threatened

[cprise]

And here is one possible scenario published in 2006 by Scientific American:

http://www.chicagocleanpower.org/ward.pdf

Summary: Increasing anoxia from global warming results in an explosion of anoxic bacteria that take over the oceans, spewing hydrogen sulfide gas that kills most animal life on the planet. Seems its happened naturally in the very distant past (pronounced global warming -> H2S extinction) and I don't see why a man-made global warming trend wouldn't trigger the same thing.