Towards the end of the game the civs should start suffering from serious environmental problems and overpopulation. Especially large cities would grow very fast without proper investments(sanitation, public transport, water supply, schools, etc.). This should be a real challenge to overcome, maybe building a Wonder would reduce it.

The fossil fuels should also be an ending resource. Maybe the civs should discover a new resource by science??

There should also be some state or level of pollution or greenhouse gases where the icecaps would start melting. Or maybe some natural disasters could randomly destroy cities. But the civs could overcome these problems by foresting and new techs.

In CivII the environmental impacts where modeled well causing the changes in terrain! But the overgrowth or ending of resources was never a problem!

Just ideas, maybe too complicated to put in a game but would make it very interesting towards the end!

Civ4 will have all that environmental stuff removed, instead a health system will be in place.
And I am glad that they did that, pollution was way overdone, and not realistic anymore.

Because it was random. Firaxis should devise more complicated model that would fit real world. The same applies to natural disasters like earthquakes, volcano eruptions, huragans or tsunamis, if there will be any.

Such things should never be random. Earthquakes should happen close to large mountain chains, huragans should appear in the areas with appropriate weather conditions (generally, in the ocean), etc.

That way, founding a city on the ocean coast next to mountains, you already know the risk you are taking.

Because it was random. Firaxis should devise more complicated model that would fit real world. The same applies to natural disasters like earthquakes, volcano eruptions, huragans or tsunamis, if there will be any.

Such things should never be random. Earthquakes should happen close to large mountain chains, huragans should appear in the areas with appropriate weather conditions (generally, in the ocean), etc.

That way, founding a city on the ocean coast next to mountains, you already know the risk you are taking.

It wasn't complete random. Heavy polluting cities did suffer more from pollution. Though it didn't make any sense. It is not so that a whole country the size of the Netherlands (or a US state) is so spoiled nothing can be gained from there.

Regarding earthquakes....they are not related to mountains. The lines where earthtquakes appear to happen more frequently are also on non-mountain areas.

A lot of these issues were discussed recently here. (http://forums.civfanatics.com/showthread.php?t=126168&page=1&pp=20)