>“If we want to warm up the atmosphere of Mars, what if we use global warming?”

but we can't even pluck the CO2 out of Earth's already incredibly useful atmosphere.

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trying to make something useful out of "nothing" is much much harder.

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https://en.wikipedia.org/wiki/Terraforming

Terraforming or terraformation ("Earth-shaping") is the hypothetical process of deliberately modifying the atmosphere, temperature, surface topography or ecology of a planet, moon, or other body to be similar to the environment of Earth to make it habitable for humans to live on.