Okay, bear with me; some very rough calculations here, and they're hardly what you'd call scientific. But here goes:
I took the minimum distance of Earth from the sun - 147,098,074 km - and the maximum distance of Mars from the sun - 249,228,730 km (using the minimum for Earth and the maximum for Mars so it would not be skewed in favour of what I'm trying to prove) and used those figures to get a relative figure for the amount of light each gets from the sun.
Basically, as light radiates from the sun in a sphere, the amount of energy at any two points are related by the equation for the surface area of a sphere: a=4r2, where r is the radius of the sphere. I did this for both figures and got (sorry for Excel's crappy version of standard form here): 8.65514E+16 for Earth and 2.4846E+17 for Mars. To get the relative amount, I divided the figure for Mars by the figure for Earth. So Mars gets about 2.870663161 times less energy from the sun than Earth.
Then, I set about calculating the effect of warming as a result of CO2 in Mars' atmosphere. I couldn't find any figures for the volume of Mars' atmosphere - only its scale height, which, to be honest, I don't really know how to use in this calculation, but Mars has a higher scale height of atmosphere than Earth's, whatever that means. It's not a huge difference though.
Anyway, the pressure of Mars' atmosphere is, on average, at the surface, 0.6kPa. This is a lot less than Earth's - at 101.3kPa. However, Earth only has 0.038% carbon dioxide by volume, compared to Mars' huge 95.3%. To get a relative arbitrary figure for the mass of CO2, I multiplied the measurement of pressure against the proportion of carbon dioxide by volume, to get 57.18 for Mars and 3.8494 for Earth. So Mars has, in relative terms, 14.854263 times more carbon dioxide per litre of air than Earth, even if the air is a lot thinner.
Now, combining those two relative figures - 14.854263 and 2.870662161 - I got a figure for how much of a difference CO2 should have in climate change on Mars compared to Earth (by dividing the relative mass of carbon dioxide by the lowered energy from the sun) per litre of air. Incredibly, it would CO2 related warming would be 5.174505739 times greater on Mars than Earth.
So, yeah, you'd expect the temperature to rise much more on Mars than Earth as a result of this; and it throws a LOT of doubt onto the "olo global warming is fake" argument you guys are throwing around.