Pariah
Outside Influence

There should be some sort of "Global Disasters" list in the Cheats, allowing you to inflict massive damage to all civilizations without knowing the ultimate result. On the harder levels of the game, these global disasters would occasionally happen unannounced - maybe once per game, at a random turn. (Yes - I know there's a thread on random events

The specific disasters could include:
Giant impact (continent-wide fires, mass extinction, cosmic winter etc);
Supervolcano (similar global winter, lots of pollution, huge lava flows);
Geopocalypse (gigantic earthquakes worldwide: most cities flattened, random terrain changes, social breakdown leads to barbarian proliferation).
New ice age (glaciers expand, sea level drops, farmlands lost)
Alien invasion (superadvanced barbarian-type units appear everywhere);
GM virus breakout (populations crash in all civs, many cities deserted);
Judgement Day (someone builds a wonder called GlobeSat, or AI Defence... or even Skynet... and it becomes self-aware, nukes cirties in all nations, then becomes a new AI civ with a very powerful military bent on conquering the world. No-one can negotiate with it, either).
The Alien invasion disaster would have to be restricted to the later stages of the game, when the human & AI civs would be advanced enough to have at least some chance of defeating the invaders.
Any thoughts, folks?