Also, during past periods of high volcanic activity, and certainly before humans, I'm sure the statistic of humans emitting more C02 than volcanoes would not be correct. That snapshot may only apply to today. Tomorrow it may not. In the past, it certainly didn't. Also, water vapor is a more effective greenhouse gas than co2, and has consistently been around in larger, but variable, quantities. During glacial periods, less c02 is consumed by plants and absorbed by frozen oceans. But, less water vapor consumed and emitted (available) too. As glaciers retreat, more co2 and water vapor are released, but also consumed. More questions about where we actually are today...