An Estimate of Earth's Total Carbon

Environmental & Science Education

STEM

Earth Science

Earth Systems

Geology

Edward Hessler

In the National Research Council's, A Framework for K-12 Science Education, it is recommended that K-12 science education be organized around three major dimensions: scientific and engineering practices, crosscutting concepts that unify the study of science and engineering, and core ideas in the four standard disciplinary areas (physical, life and earth sciences; and engineering (applications of science). 

The focus here is on just one part of one of the crosscutting concepts: energy and matter: flows, cycles, and conservation--the carbon cycle which you have seen in textbooks. Such diagrams are used to describe the way a part of the world works. They simplify and organize a complex system. 

The movements of carbon are well understood but until recently the amount of carbon found above the Earth's surface (ocean, land, and atmosphere) and the Earth's subsurface (crust, mantle and core) has not been well understood. 

A large 10-year project, the Deep Carbon Observatory (DCO), recently released its findings documenting the numbers on the amount of carbon found in the various compartments represented in a diagram of the carbon cycle, just one cycle that humans have been very active in destabilizing. The study included 504 scientists, 39 countries, 102 projects, and resulted in 372 publications.

In the press release from DCO announcing the findings, Marie Edmonds of the University of Cambridge, UK says , “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.” 

The press release includes six of the main findings, the best current estimates, carbon catastrophes, and some comments. Here are three of the main findings:

• Just two-one thousandths* of 1% (0.0002) of Earth's total carbon—about 43,500 gigatonnes (Gt)—is 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 Gt in all. (This means that more than 99 percent is underground.)
• 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
• Humanity’s annual carbon emissions through the burning of fossil fuels and forests, etc., are 40 to 100 times greater than all volcanic emissions

These numbers are staggeringly large. The press release includes this assist to coming to grips with them. A single gigaton (Gt) equal 1 billion metric tonnes, greater than the weight of water in 400,000 Olympic-sized pools--enough pools to cover 85 percent of Chicago (234 square miles or ~606 square kilometers).

This comment by Sami Mikhail, University of St. Andrews, UK provides a perspective on the significance of this study but please read the other comments.

"Earth is unique among the planets in our solar system in that it has liquid water at its surface, fosters life, and has active plate tectonics. Identifying all linkages between these phenomena serve as important steps in humanities enduring quest to understand the origins of Earth-like habitability. One absolute certainly, however, is that carbon plays a governing role. For example, Earth's clement environment is related to atmospheric chemistry, which is warm enough to stabilize liquid water at its surface but cold enough to permit plate tectonics, and it is an incontrovertible fact that the carbon content of our atmosphere and oceans are directly linked with Earth’s climate.”