The term "tipping point" has entered the modern household vocabulary. It is being applied to a wide range of phenomena, ranging from social networks on the internet, to the spread of diseases, to climate change. These phenomena, from a technical scientific standpoint, are both different and the same. What I mean is that the underlying stories, causes and consequences are quite different, but they do share some intriguing mechanistic similarities. Let's indulge in a little science for a moment. A tipping point is perhaps better understood as a surprise, that is, an incremental (or "smooth") change in some input to a system at some point results in a sudden or discontinuous change in the state of the system. Let me demonstrate. Imagine that you have a small model boat with you in the bathtub. You roll the ship a wee bit to the left. When you release it, the boat promptly rights itself. You roll it again, but this time a little bit more to the left. Once again, the boat will right itself. You can continue to do this, with each time the boat righting itself. At some point, however, the little increase in roll will cause the boat to TIP over! The system, as we say, has entered a new stable state (much to the discomfort of the crew unfortunately).IPCC warming models

Now why is all this relevant to climate change? A common hallmark of systems that exhibit tipping points, or surprises, is that they are complex; they tend to have many semi-independently interacting parts. These parts influence each other directly or indirectly, often amplifying or reinforcing perturbations or changes to the system. The amplifications, or positive feedbacks, can literally seem to blow a small change all out of proportion. A tipping point can be reached when these feedbacks cause the system to restructure itself, or unravel, to the point where the interactions are quite different, or the interactors are themselves changed. The tricky part, for us, is that complex systems are often very difficult to understand, and almost impossible to predict. Tipping points, surprises, catastrophes, etc. occur in these systems when external disturbances push the interactions to the point where internal dynamics and feedbacks take over control of the outcome. So does Earth's climate have a tipping point? Will global warming result in gradual increases in temperature over the next century as predicted by IPCC models? Or will there be surprises along the way? Will ice sheets collapse instead of melting away with whimpers? I don't know, but everything that I do know about complex systems tells me that we must be wary. If the ship that you are about to board is tossing about on the waves, and you're not sure whether it can weather the storm, my best advice to you is to postpone your journey.

I'll have a lot more to say about tipping points and complex systems in the next several postings. Stay tuned!

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