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NO TILL?: By avoiding tillage, seen here, farmers can both increase the quality of their soil and sequester greenhouse gases.
USDA

Saving the trees could slow climate change, new research shows. Each year, nearly 33 million acres of forestland around the world is cut down, according to the Food and Agriculture Organization of the United Nations. Tropical felling alone contributes 1.5 billion metric tons of carbon—some 20 percent of all man-made greenhouse gas (GHG) emissions—to the atmosphere annually. If such losses were cut in half, it could save 500 million metric tons of carbon annually and contribute 12 percent of the total reductions in GHG emissions required to avoid unpleasant global warming, researchers recently reported in Science.

Forest depletion ultimately contributes more GHG emissions than all the cars and trucks in use worldwide, says Werner Kurz, a forest ecologist with Natural Resources Canada, who was not involved with the study. "What we are doing in these tropical forests is really a massive problem."

Changes in forest management and agricultural practices could significantly reduce the threat of global warming much more quickly than can technological solutions such as carbon capture and storage (CCS) from coal-fired power plants, according to experts. "We don't know how to do CCS. These are things we could do today," says Bruce McCarl, an agricultural economist at Texas A&M University in College Station. "They are a bridge to the future."

Among proposed changes: more widespread adoption of so-called no-till farming, a practice that involves leaving unharvested crop stalks and other plant matter behind in the field undisturbed by plows and other soil-agitating instruments. "Anything that reduces soil disturbance increases carbon storage," McCarl notes.

Basically, the carbon stored inside the remains sinks into the soil instead of being stirred up and into the atmosphere when the soil is prepared for planting using conventional means. Such no-till farming provides a double benefit for farmers: improved soils and reduced fuel use, because it negates the need to harvest the stalks with tractors and other equipment (although it can lead to short-term reductions in crop yields) says Chuck Rice, a soil scientist at Kansas State University in Manhattan, Kan.

The opportunity to pour carbon back into the soil exists because farming over the past century has depleted its levels of organic carbon, Rice notes. But, as with water, the soil can only hold so much carbon before it is saturated. "Sequestration could be provided for the next 30 to 50 years," before the soil will reach its limit and other actions will be needed, he says.

Growing crops for fuel—known as biofuels—represents another potential way of cutting GHGs by replacing fossil fuels (biofuels created underground by nature over millions of years). "Biofuel production also shows promise for directly offsetting some reliance on fossil fuels," says Stephen Ogle, an ecosystem research scientist at Colorado State University in Fort Collins. "This represents a direct reduction in emissions from the current trends, because dedicated energy crops will reassimilate some of the carbon dioxide emitted by energy use."

Such changes, however, are not without peril. They could lead to higher food prices as well as to converting marginal lands back into crop production, which would, in turn, lead to GHG emissions. Further, pursuing cellulosic ethanol (a biofuel brewed from stalks and other leftover plant material) could eliminate the same remnants—and, therefore, their carbon storage potential—that no-till practices would otherwise sequester, Rice adds, noting that the risks and benefits of any solutions must be carefully weighed.

There are some radical (and less likely) solutions as well, given that more than half of U.S. acreage is used to produce animal feed. "If we really want to solve the world greenhouse gas problem, we will all become vegetarians," McCarl says, pointing out that it takes seven pounds of feed to raise a pound of beef, 1.4 pounds for chickens and three pounds of feed per pound of hog. "If everyone was a vegetarian," he says, "then you could farm a lot less acreage."