Well, according to the Cambridge Encyclopedia of Astronomy ( 1977 ) Mars has 700 kg/m2 of atmospheric CO2, compared to 10 kg/m2 for Earth. That is, Mars has 70 times the amount, in absolute terms, of CO2 in its atmosphere, than does the Earth. And yet, this doesn’t keep Mars warm.
It’s a puzzle.
That’s because CO2 doesn’t keep our planet warm, N2 and O2 do that. The CO2 does capture outgoing IR and transfer it to the N2 and O2. Mars is missing the N2 and O2.