"It seems to me that since mars' atmosphere is pretty much a vacuum that it would not have that much of an effect on the temperature no matter what gas it was made of. I'm also skeptical of your statement that mars has as much CO2 as earth."

Well, I figured it out a while ago, and don't have the numbers, but I'll show you a quick dirty which I don't claim is accurate but it's fast.

CO2 on Earth is 380 ppm, or 1,000,000 to 380 and this ratio is about volume instead of weight/mass, so for every cubic meter of liquid CO2 you would have 380 million cubic meters of Oxygen and Nitrogen, and other parts of Earth's atmosphere.
As fraction it is less than 1/1000th of the Earth atmosphere- roughly, a 1/3 of this.

Mars is about 1/100th of Earth's atmosphere- in terms of pressure. So very roughly, 30 times more CO2 in Mars atmosphere than Earth's atmosphere- NOT talking comparing the total mass of these atmospheres, or being very accurate.

So, much for quick and dirty.

I'll see if I can get something more accurate:

"Martian Atmosphere

Surface pressure: 6.36 mb at mean radius (variable from 4.0 to 8.7 mb depending on season)
[6.9 mb to 9 mb (Viking 1 Lander site)]
Surface density: ~0.020 kg/m3
Scale height: 11.1 km
Total mass of atmosphere: ~2.5 x 10^16 kg
Average temperature: ~210 K (-63 C)"
http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html

So, 25,000,000,000,000,000 kgs and 95.32% is CO2

Earth atmosphere is:
Total mass of atmosphere: 5.1 x 1018 kg
http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html

So, Earth atmosphere's total Mass is roughly 200 times more than Mars' atmosphere.
And according above references:
Earth: Mean molecular weight: 28.97 g/mole
And for Mars, Mean molecular weight: 43.34 g/mole

CO2 is: One mole CO2 = 44.0g

If Earth's Atmosphere was mostly CO2 instead of it's atmosphere weighing 5.1 x 10^18 kg, it would weigh: 7.75 x 10^18 kg. And 380 ppm of it would weigh 2.93 x 10^15.

So Earth has 2.93 x 10^15 kg of CO2
And Mars' atmosphere which 95.32% CO2 has mass of
~2.5 x 10^16 kg
And around 2.38 10^16 kg of pure CO2

So Mars has around 8.1 times more CO2 than Earth's Atmosphere in terms of comparing the total atmospheres.

Now, Earth has surface are of 510,100,000 sq km.
Mars has "144,100,000 km2, 0.282 that of Earth"
http://www.vrmars.com/The-Planet-Mars.htm

So, per each square kilometer of Mars there 28.8 times more CO2 above it than compare to each square kilometer on Earth.
Or another way to say this is if Earth had 10,960 ppm of CO2 it would a similar greenhouse affect from the CO2 as compared to Mars. Though of course, Earth receives far sunlight than Mars- Mars gets about 40% of Earth's sunlight.

Anyways, my very rough number was fairly close.