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."
If adopted, this significant lifestyle change would also cut down on another animal problem: waste. Cow, pig and chicken excrement fester in lagoons, emitting methane—a short-lived but potent GHG. On the other hand, capturing that methane also offers an opportunity to create electricity. Biodigesters (covered tanks that employ bacteria to break down animal waste) produce abundant methane, says Albert Morales, executive vice president of Environmental Power, a purveyor of such systems. "The gas goes to a generator,'' he explains, "that generates power for the [electricity] grid."
Economists and other experts argue that offsetting coal-fired electricity generation may be the most promising use of such agricultural and forestry biofuels. While roughly 20 percent of the carbon in corn, for example, is recycled if turned into the motor fuel ethanol, as much as 95 percent of the carbon in the whole corn plant can be recycled if burned in electric power plants, McCarl says.
The pulp and paper industry, which creates large amounts of waste, is already utilizing such carbon recycling and generation. In fact, such manufacturers have become net exporters of energy in Canada by burning residue wood. This kind of efficiency could reduce GHG emissions in the U.S. alone "in the neighborhood of 300 million metric tons on an annual basis," McCarl says, "principally from burning biofuels for electricity and [from] forest management."
Forest management is the linchpin of any effort to combat climate change in these sectors, contributing the largest share of greenhouse gases. And it will not be as simple as building a fence around the world's forests. "We need to understand the dual role of forests of storing carbon and providing carbon to serve society's needs," Natural Resources Canada's Kurz says. "Choosing wood-based products has a much lower fossil fuel footprint than using some other building materials," such as concrete.
In Scandinavia, for example, forests cover more land now than in the previous century—thus increasing their carbon storage—while still being regularly harvested. "The more we can prolong the storage of wood products in human structures, the longer the carbon is kept out of the atmosphere. When we do get rid of it, we should burn it to offset fossil fuels, part of a cascading system of multiple uses," Kurz says. "Good forest management is typically also good carbon management."