Global warming now percieved as global ecological tipping

Scientists are seeing yet another level of global change: A "tipping point." "earth-approaching-tipping-point-say-scientists#comments"

And a news release pointing to a group of scientific papers:

First, I recommend reading the comments associated with the Slashdot post above. The comment-ors on Slashdot typically provide a wonderful parsing of the problem with many voices and viewpoints.