If I recall correctly, the atmosphre of Mars is composed largely of Carbon Dioxide...
What plants do we have that survive cold weather well?
According to Elton John, it’s cold as hell on Mars.
Plant a LOT of them on Mars and wait a while. You’ll hava a “shirt-sleeve atmosphere.”
Bring a few comets in at a shallow re-entry angle, and you can have all the water you want —assuming the “Fountains Of The Deep” may be too hard to stimulate...
The atmosphere of mars is largely composed of. Nothing. It’s 2% of our atmosphere. So. Nothing. But the tiny parts that are there do contain CO2