From the book "Rome on 640K a Day":

Each city has a "tolerance" for 20 Smokestack Points per turn. Each point generated beyond that become a smokestack on the city display, representing a 1% chance per turn that a square around the city will become polluted.

  • Smokestack Points = Industrial Pollution + Pop. Pollution

  • Industrial Pollution = # of shields generated by city.
  • Divide by 2 if city has hydro or nuclear Plant; OR
  • Divide by 3 if city has a Recycling Center.

  • Population Pollution = City Size * Pollution Modifier.

    • Pollution Modifiers = 0.25 with Industrialization;
      • 0.50 with Automobile;
      • 0.75 with Mass Production;
      • 1.00 with Plastics;
      • 0.00 with Mass Transit.
    • Note: Mass Transit eliminates Population Pollution.

City PollutionEdit

Pollution city screen (Civ1)

Pollution may be caused by large resource production in cities, large city populations, nuclear weapons, or the meltdown of a Nuclear Power Plant. If a city has a potential pollution problem, smokestacks in the city display information window indicate the probability that a nearby map square may become polluted.

Map PollutionEdit

Pollution map (Civ1)

The pollution in a map square may be cleaned up by a Settler. Move the Settler into the square and press the Pollution key (P key) or choose the Pollution option from the Orders menu. It takes four turns of work to clean up pollution. If pollution gets out of control, Global warming may occur.

Undocumented Bugs/Features Edit

After the player discovers a high number (depending on difficulty level among other factors) of Future Tech, pollution begins to spawn near cities without relation to city pollution. With each subsequent turn, the amount of pollution spawned per turn continues to increase (regardless of further Future Tech research). Due to the high rate of pollution, a permanent cycle of global warming becomes inevitable.

Players playing on Emperor should expect to encounter this pollution event around Tech Level 64.

It has been theorized that this is an undocumented feature that the game developers put in to signal the player has gotten a "high enough" score.

For discussion on this bug, see this thread.