This is an interesting subject which will undoubtedly be discussed at length amongst the players. Many will want to start turning Mars into Earth (which is to say, making it warm enough for liquid water on the surface, and with a breathable atmosphere) - a process called terraforming.

Terraforming is a large-scale project which will take anywhere from hundreds to thousands of years. However, let's say that we develop and operate the game for ten years, and that game time passes at about the same rate as Earth time. It is fairly probable that no significant terraforming of Mars can be achieved in just 10 years.

However players may still wish to see things like: factories for producing greenhouse gasses; black dust sprinkled on the polar ice caps; orbiting mirrors; etc., within the game environment. Even though these things may not have a noticeable effect on the atmosphere of Mars, they will add to the realism of the game, as they may be projects that colonists want to undertake.

It is probably best to wait for the players to provide guidance in this matter. I know from ROM that debates about such things can go forever, but if they do really want to have things like this on Mars, then it will be up to the developers to decide if and when and how to introduce them in a realistic way.

It would also be good to provide information about the current state of the terraforming process, i.e. the current and desired atmospheric pressure, temperature, and constituents. Even though these parameters are unlikely to change during the game's lifetime, it will still be interesting and educational to show this information.

SolSys Developers' Site