I believe that having an option for a slowly increasing or decreasing temperature over time would be quite fun. For example, you could emulate your planet slowly drifting away from it's host star, the temperature decreasing by a few degrees per season. If possible, this could be part of the new scenario system. I think this would be preferable to having the ColdSnap trigger at shortening intervals.
I'm sure that it is in new scenario system.
Winter is coming ;)
Suggested that long ago in a "Themed Storyteller" way, look like will have the equivalent in Alpha14
Tynan specifically mentions this as a feature of the scenario system, so you've got your wish.