Methane is lighter than most atmospheric gases. It rises up in the atmosphere and gets blown away by the solar wind never to be seen again. It is only a greenhouse gas for a short time. There is probably some math by which you can calculate how long it takes for a molecule of methane to rise up into the sky. At any rate, carbon is the fourth most abundant element in the universe but only the 14th most abundant element in the earth’s crust. This is because carbon forms methane quite readily and the methane volatilizes and floats away. If anything we should be alarmed that all the useful carbon is getting blown away into space.
Interestingly, something like 12 % of carbon in the air is carbon 14, which is produced by interactions between nitrogen and cosmic rays in the upper layers of the atmosphere.
If co2 gets low enough (around 140 ppm) plants start to die.
And in space it’ll cause vacuum-al warming. It might even get sucked into the sun! Run! The sky is falling! The sun is warming! Icebergs are floating around the South Pole! Heeeelp!