Yup, scary stuff. I've become irritated at how people use the term "tipping point," though... a recent bunch of press has started using it to mean "if we stop increasing our anual CO2 production now, we won't stop or reverse global warming," which, while true, is more because the climate effects are caused by the amount that's currently there, not the amount that we add every year, so this is not new or particularly deep. Maybe I should be OK with the phrase, because at least it gets the attention of people who don't understand what I just described, but it bugs me because there may be something a lot worse in terms of what I call a tipping point: once things get to a certain point, there may be a self-sustaining "runaway" chain reaction.
Several worrisome things could happen if greenhouse gasses and global warming hit a certain threshold: Disolved CO2 in the oceans could be released to the air as the water temperature goes up, increasing the atmospheric greenhouse gasses further, raising the temperature more, releasing more CO2, ad infinitum. Also, as the glaciers shrink, there is less sunlight reflected by the white snow, and more absorbed by the dark ground and water, so the amount the planet is heated by the sun goes up.
Of course, there may be mitigating effects as well as accelerating effects-- unfortunately, we don't really understand (for example, more desert, different cloud cover, ...) However, if we hit a "tipping point" where we're in a vicious circle, we're in big trouble, much more so than the kind of "tipping point" they're talking about in the news a lot.