ANTHROPOGENIC VERSUS VOLCANIC CO2: MYTHS AND MISREPRESENTATIONS

Climate change skeptics and deniers often promote the wholly false perception in print, websites and blogs that volcanoes outdo humans in adding CO₂ to the atmosphere and oceans. Ian Plimer’s 2009 bestseller Heaven and Earth: Global Warming — the Missing Science is a prime example: “Volcanoes add far more carbon dioxide to the oceans and atmosphere than humans.” … “Volcanoes produce more carbon dioxide than the world’s cars and industries combined.” … “One [submarine] hot spring can release far more carbon dioxide than a 1,000-megawatt coal-fired power station…” Plimer never offers, nor does he cite sources that offer, supporting evidence for such claims. And he does not provide published estimates of the present-day global volcanic CO₂ emission rate. Although studies containing these estimates are among Heaven and Earth’s 2,311 references, the estimates themselves are not divulged. Ironically, these estimates are missing in a book alleged to rectify supposed excesses of missing science. Published estimates from research findings over 30 years for present-day global emission rates of CO₂ from subaerial and submarine volcanoes range from 132 million (minimum) to 378 million (maximum) metric tons per year (Mt_CO2 y^-1). Estimate medians and author-preferred estimates reduce outlier spread and give a ~150-270 Mt_CO2 y^-1 range. These global volcanic estimates are dwarfed by CO₂ emissions from fossil fuel burning, cement production, gas flaring and land use changes, accounting for some 36,300 Mt_CO2 in 2008. This anthropogenic CO₂ emission rate is ~100-300 times larger than the estimate ranges for annual global volcanic CO₂ release. Light-duty vehicles and industry contribute ~9,000 Mt_CO2 y^-1, or ~25-70 times more than estimated global volcanic CO₂ emissions. At full capacity, a 1,000-megawatt coal-fired power station releases ~9 Mt_CO2 y^-1, or ~3 times the annual baseline output of Kilauea Volcano, which surely exceeds a submarine hot spring’s output. Scaling up volcanic CO₂ output to the anthropogenic level requires adding on the order of 10,000 volcanoes to the 50-60 normally active volcanoes of the subaerial landscape and more than 100 mid-ocean ridge systems to the seafloor. It clearly would be a very different world if volcanoes added far more CO₂ to the atmosphere and oceans than we do.