Comparison of CO2 emissions from volcanoes vs. human activities.
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)!
When you look at the figure above you see that CO2 rises continuously, and the seasonal cycle is clearly visible. There are no spikes, although there have been several major eruptions in that time. This figure from the British Antarctic Survey makes is even more clear:
CO2 from ice cores (Law Dome, Antarctica, from papers by Etheridge et al 1996 and by MacFarling Meure et al 2006) and from atmospheric measurements (Mauna Loa, Hawaii, courtesy of NOAA CMDL). The arrows indicate the dates of selected major volcanic eruptions (U = unknown 1258, T = Tambora 1815, K = Krakatau 1883, A = Agung 1963, P = Pinatubo 1991).
And another thing: why should all the volcanoes in the world suddenly decide to emit carbon dioxide at the same time we start burning fossil fuels? And then, where is all the carbon dioxide that we emit going?