Mars terraforming is a hypothetical process by which the climate, the surface and the known characteristics of the red planet would be deliberately changed in order to make the planet habitable by humans and other terrestrial life forms, thereby providing the possibility of a safe and sustainable colonization of large areas of the planet.
In a not too distant future the demographic increasing and the growing demand for resources could create a strong pressure to colonize new habitats such as the surface of Earth’s oceans, seas floor, and space around the Earth, the Moon or other planets of the Solar System. Furthermore projecting us in a distant future (of the order of hundreds of millions years), some scientists believe that the Sun may become too warm to maintain the life on our planet, even before our star passes through the Red Giant stage.
When this happens, it is assumed that it will be imperative for humans to migrate to space regions further away from the Sun, in order to have a chance to survive. By means terraforming processes might be possible to set the Red Planet in the range of habitable planets and thereby allow humans to earn a few thousand more years. So it will possible to gain other time for developing new space travel technologies.
Only by this way should be possible to reach the capabilities for colonize extrasolar systems, when also Mars will become inhospitable.
For example should be possible manipulate martian environment, by releasing large amounts of greenhouse gases into the atmosphere of the planet, raising the temperature. This would cause the evaporation of carbon dioxide from the polar caps, that further increasing the greenhouse effect should melt any ice in its subsurface.
This will give disponibility of liquid water, a climate more similar to the Earth and a more dense atmosphere, based on carbon dioxide. Finally, implantation of plants would enrich the atmosphere in oxygen, throught the photosynthesis.