- Background pollution, no effect, every city starts with this amount of pollution
- Minor health effects, happiness lowered
- Potentially Hazardous, happiness lowered more, rain more common, flood chance very lightly increased
- Major health effects, population growth decreased, rain slightly more common, happiness lowered
- Severe health effects, population growth severely crippled/or straight out stops, happiness is very low, snow is rarer and rain more common
- Biologically unlivable, population starts to decrease, happiness 0.
Unless specifically activated by the owner of the region, pollution will not spread to other regions. If activated, it will spread much slower.
With 3 new buildings, you will be able to slow down/stop/decrease pollution.
- Tree farm, the cheapest method to combat pollution. Unlocked at the start of the game, and makes a tiny bit of extra profit
- Moss farm, a more expensive, but still very cheap way to combat pollution. Better than the tree farm, unlocked at Small Town.
- Carbon harvester, INCREDIBLY EXPENSIVE to keep up, needs LOADS of energy and water, but completely limits pollution at tier II. It harvests carbon from the carbon dioxide and carbon monoxide and turns them into coal, which is then shipped by Santa. Hovewer, it leaves trace amounts of carbon dioxide in the air to make sure people don't perish due to oxygen poisoning, and some small amounts of carbon monoxide may also slip through.
Double Down, a scenario with 2 massive coal plants that each cost 1 mil to remove and always keep pollution level at Tier IV, but give a lot of energy early game. Scenario ends when pollution goes back down to Tier I (Background level). Pandemics and floods can and WILL happen haphazardly.
Acid Rain, a disaster that looks exactly like normal rain but decreases population. Only possible above tier IV pollution.