I would not survive with CO2... they would cost me too much,... just got another flat today

As to the chemistry question... I too am a chemistry major (as also a phyisics major)

All atoms have unstable isotopes, nuclotides do decay with time, depending on the half life. Generally we think that molcules that follow the line of stability (nuclotide chart) do not or decay very very slowly (as if a half life of 200 years+ is not slow). We would not see the decay of stable CO2 molecule in our lifetimes if never.