I would question whether our activities are the sole or even the primary cause of the growth in CO2. However, you leave out one thing I can question as well, which is do the fact that the CO2 concentrations are rising and temperatures are rising even imply that the CO2 rise is the cause of the temperature rise? Correlation does not imply causation, you know.
The Earth has been here a lot longer than the 100 years since mankind has started producing mass quantities of CO2. CO2 levels have been much higher than they are right now in the geologic history of the Earth. Further, a lot of the climate change proponent scientists have been proven to have been knowingly using bad science to scare people into an agenda.
When will Slashdot stop drinking the climate change Kool-Aid?