There are a few ideas for eco system threatening catastrophes that the players are working toward averting- a strike by an asteroid or comet is one scenario.
Although like life the other players are the disaster waiting to happen to the environment I imagine.
Trying to have devastation that is spectacular but survivable is tricky- also a strike would probably set everything on fire/blast/vapourise everything on a little planetoid- from the ground the light would be blotted out by the cloud- from the air the ground would be blotted out but you'd see all of the eject/planet blasted back into space (I suppose).
Also trying to think of disaster thar is "do-able" is hard- but things like voxel tidal waves or chunks being blown away and chunks flying through the sky and landing/breaking up seems doable- or at least procedurally so- not sure about the computing available.
I guess a lot of game programming is sleight of hand- "what you thought you saw"- a mix of procedural and canned.
