Umm, akshually. The Martian atmosphere is already 95℅ CO2. Its cold because the atmosphere is so thin. Its thin because Mars does not have a strong magnetic field like Earth does, so solar winds can strip away bits of the atmosphere. Also, Mars only has about 0.38 times the gravity of Earth, making it easier for gases to escape.
Akshually akshually atmospheric escape is a very slow process and would take even a large atmosphere thousands or maybe even millions of years to disappear. You could add the atmosphere first and have plenty of time to figure out how to keep it second.
The atmosphere would still be a CO2 toxic hellscape, so we could only send billionaires there for a long time.
What if the second solution is some technology - godlike to people from our time - that could start spinning the core of Mars to create a magnetosphere? That might be more difficult with people already living there.
I’ve seen people restart core spinning on earth with nukes, might work on Mars too!
https://m.imdb.com/title/tt0298814/?ref_=nv_sr_srsg_0_tt_2_nm_6_in_0_q_core
Wait… So if we just get rid of Earth’s magnetic field, solar winds will solve global warming?
They may not be depicted accurately, but they do happen.
https://www.nasa.gov/solar-system/the-fact-and-fiction-of-martian-dust-storms/
But that is an easily solved problem. Take the design of the James Webb, substitute the super cooled infrared camera and replace it with a superconducting magnet setup. Fly this setup to L1 of mars and start global warming.
I didn’t come up with that. Someone at NASA did. Years ago: https://astrobiology.nasa.gov/news/how-to-give-mars-an-atmosphere-maybe/
