Humans are responsible for releasing up to 100 times more carbon dioxide into Earth's atmosphere every year than all the volcanoes in the world combined, scientists have announced.
This is one of the key findings of a decade-long study into the planet's carbon reserves, results of which have been published in a series of papers in the journal Elements.
In their research, the team from the Deep Carbon Observatory (DCO) program in the U.S. calculated that Earth has approximately 1.85 billion gigatonnes of carbon. It comes in various forms of solids, gas, and liquids. CO2 that is above ground—in the atmosphere, oceans and on land—accounts for about 1 percent of the total carbon, making up 43,500 gigatonnes.
Marie Edmonds, a scientist with the DCO from the U.K.'s University of Cambridge, said in a statement: "Carbon, the basis of all life and the energy source vital to humanity, moves through this planet from its mantle to the atmosphere. To secure a sustainable future, it is of utmost importance that we understand Earth's entire carbon cycle."
One of the ways carbon enters Earth's atmosphere is through volcanic eruptions. Magma contains dissolved gasses—including CO2—and when a volcano erupts, these are released into the atmosphere. It can also seep out of volcanoes through porous rocks, soils and vents.
In their report, the DCO team found that annual atmospheric CO2 from manmade sources, such as the burning of fossil fuels, is between 40 and 100 times greater than what is produced by all the world's volcanoes put together. They estimate the annual amount of CO2 released from volcanoes and other magma-driven geological processes is between 300 and 400 million metric tonnes. Of this, volcanoes are responsible for 280-360 million tonnes. These include super-regions where large amounts of CO2 are released—including Yellowstone, The East Africa Rift valley and the Technong volcanic province in China.
Previously, large scale volcanic eruptions have been linked to mass extinctions—including the Great Dying event 252 million years ago, which wiped out 96 percent of all marine species on Earth.
Researchers found that over the last 500 million years, there have been five instances of "carbon catastrophes"—where huge amounts of CO2 were released into the atmosphere in a short period. This included the dinosaur-killing asteroid, which released between 425 and 1,400 gigatonnes of CO2. During these carbon catastrophes, the atmosphere got warmer, the oceans became more acidic and mass extinctions took place.
In June, scientists with the NOAA announced that atmospheric concentrations had reached their highest level ever recorded, reaching 414.7 parts per million. The last time CO2 concentrations were higher than this was over three million years ago, when sea levels were between 50 and 80 feet higher than they are now, according to NOAA.
Experts with the DCO are now trying to better understand the carbon cycle and how it may change in the future.
"For billions of years, Earth seems to have found a balance between carbon subducted deep into the interior and carbon emitted from volcanoes—processes that help to stabilize climate and environment," Cin-Ty Lee, from Rice University, said in a statement.
"But how stable is that incessant cycling? No natural law requires that the amount of carbon going down…must exactly equal the carbon returned to the surface by volcanoes and other less violent means. No question is more central to the Deep Carbon Observatory than this balance between what goes down and what comes back up."
