A tipping point is a point in time when a small thing can make a big change happen. The term was popularized in sociology in recent decades, but really comes from physics where is refers to adding a small amount of weight to a balanced object causing it to topple over.
Two years ago, NASA reported that the sea ice surrounding Antarctica reached a new record high extent, surpassing levels mapped since the late 1970s. This seemed to be quite contrary to the global warming trend that is leading to the melting of the Arctic and glaciers worldwide. And in fact, it does seem rather puzzling.