Now that the uniformitarian model of planetary development is pretty well discredited, it would make sense for me that this be reflected in Civ. Some of the possibilities we could think about: 1 - Supervolcanic Eruption (or "Ultra-Plinian" eruption) Very rare & given the timescales we currently understand these events to occur on such an event should only happen once in every fifty or so starts, but when it does hit it should have global effects. Historical equivalent would be the Santorini eruption that devastated the entire mediterranean & caused the Egyptian civilization to collapse along with the Minoans. 2 - Impact Event. These should certainly be included, and ranging in severity from planet killers through Tunguska type events down to a single city devastated (if it hits on a city tile, that is). This could also lead to a planetary wonder of an Asteroid Shield/Net. 3 - Tsunami. As we know all too well, these happen more often than we might like to think. Effects should vary. 4 - Climate. Before I start I need it said up front I do not subscribe to the Anthropogenic Warming theory - I believe it to be a cyclic event that has happened as recently as the 8th century BC, with a definite warming in the Mediaeval period followed by the so-called "Mini Ice-Age" in Europe, and there seems to be a great deal of evidence for a catastrophic global event that all but wiped from the map a global civilization at around 8,000 BCE, maybe later (the dating is very difficult but the event was literally earth-shaking) and it also seems there could well have been another at around 2500BCE and previously at around 5,000BCE. Our world is not nearly as stable as we thought.......and global; events could be a fun mod. They should not happen too often & not necessarily in every game either.....but when they do happen their effects should be felt. Imagine another Carrington Event happening now?