It Would Take Millions of Years With Today’s Technology
It's not as straightforward as having Matt Damon plant some potatoes and hoping for the best to terraform Mars. According to a common notion, all we have to do is melt the Martian ice, release CO2, and then watch as it gradually becomes subtropical.
Even if it makes sense on paper, there are certain problems with the practical use, according to NASA. For instance, there isn't enough CO2 trapped on Mars to accomplish that. Right present, Mars' atmosphere is too thin to be useful. It would be useless to even release water because it would either freeze or evaporate. The air must have density. Currently, the atmospheric pressure on Mars is less than 1% of that on Earth.
Liquid water requires pressure similar to that on Earth, which is impossible to achieve given the gases presently present on Mars. If we want to bring it up to par, we'd need to erect some plants straight out of the Industrial Revolution that would spew pollution into the atmosphere. If it doesn't work, we'll have to delve very far beneath the Martian surface to find what we need. NASA calculated that it would take roughly 10 million years to make Mars habitable and Earth-like at our current technological level.
