Presumably you've gotten your answer from the follow-ups, the system 'tips over' the edge and goes from being stable (always returning to the mean when the stimulus is removed) to unstable (removing the stimulus doesn't increase stability of the system).

The problem with it as a theme is that we really don't have a good idea of how the climate system operates long term, and by long term I mean geologically long term, not human long term. Even if we had pre-recorded satellite views of the planet and detailed measurements for the last 2,000 years that would be 2.6% of the 75 ky Ice Age cycle, and less than 0.0004% of the 50 My extinction cycle, or .000005% of the planet lifecycle.

For reference, 2.6% of a solar year is 9 days.

Humans measure time in terms of lifetime, its a very natural thing to do and since they typically live 70+ years, if you were to come to someone 9 days after you have first shown up on the planet and said "Can't you see, the temperature is a full 5 degrees warmer than it was when I started taking measurements!" And that human would pat them on the head and say, "Yes, you will see much bigger changes than that as the year goes by, it will get so hot you will will die of heat exhaustion if you stand outside all day without protection, and then later it will get so cold that you would freeze to death." And they aren't afraid and they consider it normal, because they have seen it many times before, over their whole life. But when the same person comes to them and says "The temperature is full 5 degrees warmer than it has been in 2000 years!", the fact that 2,000 years represents 100 - 200 generations of people (depending on how you choose a 'generation') it fills them with fear because nobody they know has ever experienced anything like that, its different, its scary, and its unknown.

Back in the day (we're talking the 60's) climate scientists would say "Gee, all of these geological records show that the climate changes in cycles, from very warm to very cold. And they noticed we were coming up on a time when the cycles suggest the end of the inter-glacial period was nigh and we should be looking for the leading edge of the next ice age.

Anyway, the planet has been warmer than it is now, its been colder, and it has changed with people present and without them present. The tipping point models have the climate becoming irreversibly destabilized after we pass it, what they don't say is what that means. Does it mean the planet gets really hot? does it mean an ice age starts? Nobody knows and the models don't help.