Continuing interest in the effects of carbon dioxide on climate has been promoted by the exponentially increasing anthropogenic
production of CO
2. Volcanoes are also a major source of carbon dioxide, but their average input to the atmosphere is generally considered minor
relative to anthropogenic input. This study examines eruption chronologies to determine a new estimate of the volcanic CO
2 input and to test if temporal fluctuations may be resolved. Employing representative average values of 2.7 g cm
−3 as density of erupted material, 0.2 wt percent CO
2 in the original melt, 60 percent degassing during eruption, and an average volume of 0.1 km
3 for each of the eruptions in the recently published eruption chronology of Hirschboeck (1980), a volcanic input of about
1.5 · 10
11 moles CO
2 yr
−1 was determined for the period 1800–1969. The period 1800–1899 had a somewhat lower input than 1900–1969, which could well
be related more to completeness of observational data than to a real increase in volcanic CO
2. This input is well below man's current CO
2 production of 4–5 · 10
14 moles CO
2 yr
−1.
The average values above together with specific volumetric estimates were employed to calculate CO2 input from individual historic eruptions, massive flood basalts, and ash-flow eruptions. Total CO2 release from the largest of flood basalt and ash-flow sequences was 1015-1016 moles of CO2. The impact of these sources on global atmospheric CO2 and climate, however, will be limited by the duration and spacing of the major individual eruptive periods in the sequences.