The game tiles are too large and theres not enough detail in the game to include accurate terraforming (including canals, they are really minor) other than massive deforestation, and thats included.
I am still for Terraforming just because workers get bored easily. They need to change plains into grassland back and forth, need to change rivers and hills and build vacuum tubes trough the oceans (yeah i liked some aspects of 'Call to powers').
Desertification is included (poorly).
I am really disapointed that the effect of global warming and pollution gets weaker every civ game (even if it was overexaggerated in civ1, now its basically nonexistant in civ4).
drkodos is messing up causes and timescales.
The Bering Land Bridge from Asia to America disappeared 8000 years BP. Civ4 starts 6000 BP (BP means years before ~1950 measured by radioactive decay).
And It has nothing to do with terraforming, only a declining ice age (actually speed up by some deforestation, but civ is not simearth).
http://en.wikipedia.org/wiki/Image:Beringia_land_bridge-noaagov.gif
Youre right that this thread is NOT about topography.
Youre silly if you argument that civ doesn't represent Oceans or deserts and your examples are not terraforming (you might have had a slim chance with the sahara desert though, there have been more trees and PLAINS ~4000 BC).
Civ4 doesnt include large scale terraforming, and that doesnt exist today in a large enough scale to be 1 tile big on a huge map. Name a Dam that stores enough water to turn one tile into 'coast'. Suggest a way to implement canals in a correct significant scale of impact (its included in roads and trade routes).