Global Warming is caused by cities creating excessive amounts of Pollution.
Effects
Each time global warming advances, the entire world loses coastal land for jungles and swamps, and inland squares are lost to desert. This tends to devastate cities and leads to global impoverishment.
Is it possible to reverse this?
- The effects of Global Warming can be reduced by cleaning up Pollution and reducing the amount each city pollutes.
- Although you can perform a converse operation with Nuclear Winter, this tends to mess things up more than help (areas all become extremes), just like in real life.
Math
Clicking '(Click for more info)' displays, among other things, the line:
Global warming chance: X% (Y%/turn)
For a new game this will look something like:
Global warming chance: 0% (-4%/turn)
This means that there is no chance of warming, of course. As pollution is generated (by any player), each polluted tile increases Y by 1%. This effect takes place on the turn following the pollution itself. Also, each turn Y is added to X; if Y is negative then X will decrease (but X can never be less than 0). If a polluted tile is cleaned then Y is decreased.
For example, if 3 tiles become polluted then next turn, there will still be a 0% chance of warming. If next 2 more tiles become polluted (total 5) then Y will be +1% and each turn thereafter X will increase. If, on the other hand, X is, say, 4% and some pollution is cleaned up so that Y is, say, -2%, then in 2 turns the chance of warming will drop to zero.
If warming does occur then X is reset to 0% and 2% is subtracted from Y. Therefore, warming will not occur repeatedly, turn after turn. Also, it becomes more difficult for warming to occur each time. However, with sufficient pollution, it's quite possible to have several rounds of warming.
Eco-terrorism
It is possible to war on other players with pollution. Increase production with Factories and Power Plants; and increase population (people pollute too). Don't build pollution-reducing improvements and avoid cleaning up polluted tiles. Eventually, you will force global warming; if you are persistent, several rounds of it.
All players will suffer in the same fashion but not equally. Ocean tiles cannot become polluted or be changed to another terrain type by warming. Hills and Mountains will not change terrain type although they can be polluted. (You may need to clean up the occasional high-value Iron Mountain or Coal Hill Railroad Mine tile.) So, before committing eco-terror, be sure to build Harbors and Offshore Platforms. If your cities are largely coastal, your land may turn largely into worthless Swamp and Jungle but you will still retain a good measure of food, production, and tile-trade. You should keep a large number of Engineers handy and put teams of them to work Irrigating the odd Swamp back up to Grassland.
Your enemies may well be caught short by eco-terrorism if they lack the necessary technologies to compensate or have not invested in the required improvements. AI deals particularly poorly with eco-terror, rarely building Offshore Platforms and being more concerned with producing military units than sufficient Engineers. It's common to invade a city and find that food production is stalled, supported units nearly equal production, and the AI player is hopelessly trying to pump out another 100-shield AEGIS Cruiser.