Annual volcanic carbon dioxide emission: An estimate from eruption chronologies

Continuing interest in the effects of carbon dioxide on climate has been promoted by the exponentially increasing anthropogenic production of CO₂. 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 CO₂ 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 CO₂ in the original melt, 60 percent degassing during eruption, and an average volume of 0.1 km³ for each of the eruptions in the recently published eruption chronology of Hirschboeck (1980), a volcanic input of about 1.5 · 10¹¹ moles CO₂ 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 CO₂. This input is well below man's current CO₂ production of 4-5 · 10¹⁴ moles CO₂ 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.