With rare exceptions the quantity of carbon dioxide (CO2) released from under the earth's surface, in its mantle, has been roughly in balance with that returned via subduction of tectonic plates and other processes. That's not the case for the past 100 years, however: human CO2 emissions have ranged between 40 and 100 times greater than that from geologic sources, such as volcanoes, according to the results of a 10-year study from the Deep Carbon Observatory.
An online platform that brings together research scientists worldwide to conduct long-term studies of the Earth's carbon cycle, Total Carbon Observatory's latest research results estimate the Earth's total carbon at 1.85 billion metric gigatons (1.8 billion billion). Just two-tenths are above the surface. The rest lies below, including in the Earth's crust, mantle and core.
A tremendous volume of geologic events taking place during the past 500 million years, such as magmatic, volcanic eruptions and meteor impacts, have released "catastrophic volumes of carbon out-gassing," according to the research report. That has lead to warming of the atmosphere, ocean acidification and mass extinctions.
Volcanoes, carbon imbalances and climate warming
Imbalances in the Earth's carbon cycle can cause rapid global warming, changes to the weathering of silicates, changes to the hydrologic cycle, and rapid changes in habitat that can themselves cause mass extinctions, according to Deep Carbon's research team. Similar carbon catastrophes have been caused by asteroids and meteors (bolides), such as the massive Chixculub impact in the Yucatan area of Central America 65 million years ago, which led to the extinction of the dinosaurs and most other plants and animals existent at the time.
"The Chicxulub event ... greatly disrupted the budget of climate-active gases in the atmosphere, leading to short-term abrupt cooling and medium-term strong warming. Thus, some large bolide impacts are comparable to those observed in the Anthropocene in terms of rapidly disrupting the C (carbon) cycle and potentially exceeding a critical size of perturbation," according to Australian researchers Balz Kamber and Joseph Petrus.
Volcanoes, the collision and separation of continental and oceanic tectonic plates and reexamination of other geologic phenomena with the latest high-tech tools have produced new, important insights regarding the Earth's inner workings over a time span from billions of years ago to the present, from the Earth's core to its atmosphere and from individual volcanoes to the five continents in scale, according the 500-member Reservoirs and Fluxes team at Deep Carbon Observatory, which is getting ready to celebrate its 10-year anniversary at the National Academy of Sciences in Washington, D.C.
Deep Carbon's new, annual estimate of out-gassing of CO2 via volcanoes and through other geological processes, such as the heating of limestone in mountain belts, came in at roughly 300 to 400 million metric tonnes (0.3-0.4 metric gigatons). Volcanoes and volcanic regions alone outgas an estimated 280-360 million tonnes (0.28 to 0.36 Gt) of CO2 per year. This includes the CO2 contributions from active volcanic vents, from the diffuse, widespread release of CO2 through soils, faults, and fractures in volcanic regions, volcanic lakes, and from the mid-ocean ridge system, Deep Carbon elaborates.
Carbon outgassing and climate change
In many world regions, tectonic outgassing— emissions from mountain belts and other plate boundaries— particularly in cool night temperatures, can cause dangerous levels of CO2 close to the ground -- "enough to suffocate livestock," according to the research results.
Large volcanic events have upset the Earth's carbon balance about four times over the past 500 million year. In total, 1 million or more square kilometers of magma, equivalent to Canada's area, has been released within a time frame of a few tens of thousands of years up to as much as 1 million years. These "large igneous provinces degassed enormous volumes of carbon (estimated at up to 30,000 Gt— equal to about 70% of the estimated 43,500 Gt of carbon above the surface today," Deep Carbon highlights in a news release.
More broadly, Deep Carbon zoomed in on the following key findings:
- Humanity's annual carbon emissions through the burning of fossil fuels and forests, etc., are 40 to 100 times greater than all volcanic emissions Just two-tenths of 1 percnet of Earth's total carbon, about 43,500 metric gigatons, lies above surface in the oceans, on land, and in the atmosphere. The rest is subsurface, including the crust, mantle and core, an estimated 1.85 billion metic gigatons in total
- CO2 out-gassed to the atmosphere and oceans today from volcanoes and other magmatically active regions is estimated at 280 to 360 million tonnes (0.28 to 0.36 Gt) per year, including that released into the oceans from mid-ocean ridges
- Earth's deep carbon cycle through deep time reveals balanced, long-term stability of atmospheric CO2, punctuated by large disturbances, including immense, catastrophic releases of magma that occurred at least five times in the past 500 million years. During these events, huge volumes of carbon were outgassed, leading to a warmer atmosphere, acidified oceans. and mass extinctions
- Similarly, a giant meteor impact 66 million years ago, the Chicxulub bolide strike on Mexico's Yucatan peninsula, released between 425 and 1,400 Gt of CO2, rapidly warmed the planet and coincided with the mass (>75%) extinction of plants and animals -- including the dinosaurs. Over the past 100 years, emissions from anthropogenic activities such as burning fossil fuels have been 40 to 100 times greater than our planet's geologic carbon emissions
- A shift in the composition of volcanic gases from smelly (akin to burnt matches) sulfur dioxide (SO2) to a gas richer in odorless, colorless CO2 can be sniffed out by monitoring stations or drones to forewarn of an eruption -- sometimes hours, sometimes months in advance. Eruption early warning systems with real-time monitoring are moving ahead to exploit the CO2 to SO2 ratio discovery, first recognized with certainty in 2014
"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. Key to unraveling the planet's natural carbon cycle is quantifying how much carbon there is and where, how much moves—the flux — and how quickly, from Deep Earth reservoirs to the surface and back again," DCO scientist Marie Edmonds of the University of Cambridge, UK was quoted as saying.