Seeing that we have seasons already, maybe we should consider adding in random events as well. What this would be is a game-wide global modifier to a specific resource production.
Example:
Unexpected Dry Season: Only fires during the Summer season, -50% farm output
Warm Winter: Food debuff from winter season is halved
Nuclear Reactor Meltdown: Radiation increased by [nukes x 10] on every continent
[Resource] Rush: [Any raw resource other than food] output increased by 10