Your argument is completely spurious - the relative weight of our emission is not what determines if we change the climate.
It would be like saying the average human weighs 70Kg so 500micrograms of LSD will do nothing as it is only 7.14^-7% of the body mass.
I'm sorry you understood it that way. I wanted to point out that it is in fact a pretty big deal! Human produced CO2 (mainly from fossil fuel burning) is changing the global environment pretty dramatically. nathannecro wanted to see evidence that we're doing something on the macro scale, here it is.
Atmosphere weighs 5.1 . 10^18 [2] so the CO2 we produce is 1/100000 (or 0.001%) of the total weight.
Atmosphere contains 0.046% CO2 by weight [3]. So, next year, it's going to be 0.047%
[1] http://www.epa.gov/climatechange/ghgemissions/global.html
[2] http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.htm...
[3] http://www.engineeringtoolbox.com/air-composition-d_212.html