Nutrient-rich topsoil is being eroded much faster than it can be replenished, experts say.
While many worry about the potential consequences of atmospheric warming, a few experts are trying to call attention to another global crisis quietly taking place under our feet.
Call it the thin brown line. Dirt. On average, the planet is covered with little more than three feet of topsoil -- the shallow skin of nutrient-rich matter that sustains most of our food and also appears to play a critical role in supporting life on Earth.
"We're losing more and more of it every day," said David Montgomery, a geologist at the University of Washington. "The estimate is that we are now losing about 1 percent of our topsoil every year to erosion, most of this caused by agriculture."
"It's just crazy," fumed John Aeschliman, a fifth-generation farmer who grows wheat and other grains on the Palouse near the tiny town of Almota, just west of Pullman.
"We're tearing up the soil and watching tons of it wash away every year," Aeschliman said. He's one of a growing number of farmers trying to convince others to adopt "no-till" methods, which involve no tilling of the land between plantings, leaving crop stubble to reduce erosion and planting new seeds between the stubble rows. Montgomery has written a popular book, "Dirt," to call public attention to what he believes is a neglected environmental catastrophe. A geomorphologist who studies how landscapes form, Montgomery describes modern agricultural practices as "soil mining" to emphasize that we are rapidly outstripping the Earth's natural rate of restoring topsoil. "Globally, it's clear we are eroding soils at a rate much faster than they can form," said John Reganold, a soils scientist at Washington State University. "It's hard to get people to pay much attention to this because, frankly, most of us take soil for granted."
The National Academy of Sciences has determined that cropland in the U.S. is being eroded at least 10 times faster than the time it takes for lost soil to be replaced.
The United Nations has warned of worldwide soil degradation -- especially in sub-Saharan Africa, where soil loss has contributed to the rapidly increasing number of malnourished people. Healthy topsoil is a biological matrix, a housing complex for an incredibly diverse community of organisms -- billions of beneficial microbes per handful, nitrogen-fixing fungi, nutrients and earthworms whose digestive tracts transform the fine grains of sterile rock and plant detritus into the fertile excrement that gave rise to the word itself ("drit," in Old Norse).
As such, true living topsoil cannot be made overnight, Montgomery emphasized. Topsoil grows back at a rate of an inch or two over hundreds of years.
"Globally, it's pretty clear we're running out of dirt," Montgomery said. Ron Myhrum, state soil scientist with the U.S. Department of Agriculture's office in Spokane, Wash., agreed that global soil loss is a huge problem. But Myhrum said erosion rates in the Northwest region have improved recently because of better conservation farming practices.
"We don't have the kind of dust storms here we used to have," Myhrum said. "What's more alarming to me than erosion is conversion of farmland to urban use."