Mystery Carbon Hidden Under Grass?
By Don Comis
October 30, 2002
Could a missing 2 billion tons of
carbon be hidden below the world's grasslands and rangelands?
Reports from an 11-state Agricultural
Research Service carbon dioxide monitoring network in the central and
western United States show that rangeland soils could be storing at least a
sizeable share of it.
The network, formed in 1995, had its roots in a mystery announced by global
modelers in the 1980s: They couldn't account for 2 billion tons of carbon
emitted annually in carbon dioxide from fossil fuel burning, deforestation and
Network scientists wondered if rangelands were the missing sink where the
carbon was being stored. After all, rangelands are the largest type of natural
landscape in the world, comprising about half of the Earth's land
surface--including 824 million U.S. acres.
Network results so far show that just the 126 million acres of grassland in
the Great Plains alone could be storing 9 million metric tons of carbon
annually. ARS scientists estimate that U.S. rangeland soils have the potential
to store a total of 30 to 110 million metric tons of carbon a year. That is
about 5 percent of the annual U.S. emissions of carbon.
Each of the 11 sites has samplers on towers taking readings at three and six
feet above the ground, every 20 minutes, around the clock.
Knowing where the missing sink is will help to manage it so it will keep
performing its valuable carbon storage function. Network research shows that
ranchers can do this as well with grazing as without, as long as they don't
overgraze the land.
Rangeland has an advantage over forests for storing carbon because most of
the carbon in rangeland is stored below ground, where fire won't release it.
For more on the ARS carbon dioxide rangeland monitoring network, see the
October issue of
Agricultural Research magazine.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.