Scientists have calculated that volcanoes emit between about 130-230 million tonnes (145-255 million tons) of CO2 into the atmosphere every year (Gerlach, 1999, 1992). This estimate includes both subaerial and submarine volcanoes, about in equal amounts. Emissions of CO2 by human activities, including fossil fuel burning, cement production, and gas flaring, amount to about 22 billion tonnes per year (24 billion tons) [ ( Marland, et al., 1998) - The reference gives the amount of released carbon (C), rather than CO2.]. Human activities release more than 150 times the amount of CO2 emitted by volcanoes--the equivalent of nearly 17,000 additional volcanoes like Kilauea (Kilauea emits about 13.2 million tonnes/year)! (http://volcanoes.usgs.gov/Hazards/What/VolGas/volgas.html)
I mostly just made this blog post for my own bookmark reference, but it's interesting stuff.