system
Given the following post, respond as if you're commenting on Reddit:
human
Do you think with current science and technology, that we could start a colony on another planet?

Mars is ALMOST like earth, minus water and plants, but do you think it could be possible to shape our red neighbor into a livable planet, without the use of re-breathers/space suits?
EDIT: Astrokiwi is very knowledgeable and has kindly explained that Mars is much more different than  i thought. Thank you!
gpt
Mars is pretty different to Earth. The atmosphere is about 1% of the thickness of Earth's - it would basically feel like a vacuum to any Earth organism. It also gets less than half the heat the Earth does. So you would need to pump in a lot of gas to make the air breathable, and to trap the heat in.

It is easy to underestimate the scale of this endeavour. All of the total sum of all of the carbon dioxide emission from all of the industry in the history of the Earth *has* made an effect on the atmosphere, but it's still on the order of hundreds of parts per million (though of course, this is affected by the natural processing of CO2).

We can use this as an estimate of the scale of the project. What would happen if this scale of industry was producing oxygen and nitrogen instead of CO2? While dedicated machinery might produce air more efficiently, it's unlikely we'll get that scale of dedicated machinery on Mars without already terraforming it already, so this is still a good estimate of an upper limit. We're talking about the effects of 7 billion people here...

According to wikipedia, the sum of all of our CO2 emissions is 29,888,121,000 tonnes per year (let's say 3x10^10 ) , while Mars's atmosphere is 25,000,000,000,000 tonnes (25 x 10^12 tonnes). To multiply this by 100 (roughly what we need) would require 2.5 x 10^15 tonnes. So if we had the equivalent of Earth's entire industry on Mars, but producing air instead, it would take about 100,000 years to get an Earth-like atmosphere.

So even with an unrealistically large-scale industry on Mars producing air, it is not going to happen any time soon.

Edit: No need to downvote the people responding to me - they're just follow-up questions!