The "Inconvenient Truth" is that the earth has been gradually warming for about 20,000 years, and since the end of the last ice age 10-12,000 years ago there have been warmer and cooler periods of varying lengths of time. If we got to live long enough we'd eventually see another ice age.
Could our activities raise the global temperature? Sure, maybe by a few tenths of a degree over a few hundred years. But one moderate sized volcanic eruption pumps more gases into the atmosphere than all of our SUVs, power plants and trash burning for a year. No matter what we do, nature will have her way.
The current rate of warming is projected to be 1.8 degrees Celsius this century -- more if fossil fuel burning increases.
Volcanoes do not emit more CO2 than man's activities; in an average year, the C02 emission from human activities is about 150 times more than volcanic CO2 emissions.