Tipping point theory, historical examples
Tipping point events have occurred throughout earth's history and parts of the earth system are currently being monitored for signs of abrupt change. Past earth system tipping points include The Great Oxygenation which brought molecular oxygen (O2) into the atmosphere and Snowball Earth events where the earth's surface became ice-covered. Tipping points can occur on a planetary scale, as in the previous examples. These events can also occur on a regional  scale. For example, the West Antarctic Ice Sheet is a regional feature that is currently being monitored for signs of collapse.