Right, but ten thousand years ago (or whenever), volcanoes were going off and forests were burning too, I think, and the carbon they contributed to the atmosphere is reflected in the fossil record. It's the change over the last couple of hundred years (not just the last couple of decades) that's of concern, and there is no notion that the natural sources are solely responsible.
Regarding "millions of tons of greenhouse gases": consider that
a mid-sized 30 mpg car driving 12,000 miles/year will create about 3.55 tons of CO2/year, multiply by the number of cars on the road, and I think we can take on a few volcano's-worth of emissions ourselves.