Not even 1 per cent of the Earth’s carbon reserves are above surface
NOT EVEN one per cent of the Earth’s total carbon— about 43,500 gigatonnes (Gt)—is above surface, in the oceans, on land and in the atmosphere. The rest—an estimated 1.85 billion gigatonnes—is stored inside the Earth, according to the Deep Carbon Observatory (DCO), a 10-year-long collaboration of over 1,000 scientists across the world who were studying the quantities, movements, forms and origins of carbon in the Earth.
“For over billions of years, carbon from the interior of the Earth has been released into the atmosphere via prominently visible volcanoes and from less visible emissions along the oceanic ridges where new oceanic plates are formed,” says Balz S Kamber, professor of Petrology at Queensland University of Technology in Brisbane, Australia and a DCO collaborator. The Earth needs carbon dioxide (CO2) in its atmosphere to sustain the natural greenhouse effect that prevents us from freezing. At the same time, roughly equal amounts of atmospheric carbon returns to the Earth through the downward subduction of tectonic plates and other processes, keeping the carbon cycle in equilibrium. “However, anthropogenic combustion of fossil fuels has completely overwhelmed the natural emissions,” adds Kamber. The researchers found that volcanoes emit 280 to 360 million tonnes of CO2 each year, and that this is 40 to 100 times less than CO2 emissions due to human activities. This is worrying because in the past 500 million years, the period when complex life forms arrived on Earth, the carbon equilibrium has been disrupted four times and they resulted in mass extinctions. “In the future, the 20th and 21st centuries will be seen as a period that recorded the extinction of a large number of species,” says Kamber.