Washington, May 22 : Scientists have determined that the Earth's crust might hold a lethal cache of carbon, which could ultimately determine the fate of our planet's atmosphere.
Carbon is locked away down in the Earth's crust in magma and old carbonate rocks buried by plate tectonics, in fossil fuels like coal and oil, and in ice lattices beneath the ocean bed.
It has long been assumed that this carbon was largely cut off from the surface, and could safely be ignored when analyzing the effect of greenhouse gases on climate.
But now, it seems there may be much more "deep carbon" ready to spew out than we thought, according to the conclusion of a meeting at the Carnegie institution's Geophysical Laboratory in Washington DC.
The meeting determined that the greatest threat of an unexpected release of carbon from the deep comes probably from an indirect effect of human-made CO2 (Carbon dioxide).
Global warming could destabilise some deep carbon reserves, notably in clathrates - ice lattices that are found beneath the ocean floor and continental permafrost, and even under freshwater lakes like Lake Baikal in Siberia.
These ice structures may hold trillions of tonnes of methane.
"We are extremely concerned that clathrates are the largest single source of greenhouse gases that could be added to the atmosphere," said Robert Hazen of the Carnegie Institution. "If you raise temperatures even slightly, they could be released," he added.
According to Hazen, though the deep carbon cycle could theoretically absorb human-made emissions, this would take millions of years. On the other hand, catastrophic methane emissions could happen over just a few decades.
Natural processes such as volcanism are also known to bring carbon to the surface, but there may be other mechanisms to release buried carbon that have not been considered by mainstream climate science.
For example, there is growing evidence that microbes living deep in the crust may be converting carbon into forms that can migrate to the surface - notably methane.
Unknown non-biological chemical reactions may also be able to produce methane or hydrocarbons that seep up through the crust, according to Vladimir Kutcherov of the Royal Institute of Technology in Stockholm, Sweden.
For example, methane or petroleum might be produced when carbonate rocks react with water and iron upon being subducted into the mantle.