"Carbon Sinks" Could Help Fight Climate Change, Report Says

by Katherine Stapp

(IPS) -- Undaunted by their government's refusal to get on board an international push to reduce emissions of so-called greenhouse gases, many U.S. scientists are urging new strategies to contain carbon dioxide, the leading culprit in global warming.

Much of their attention has been focused on cleaner fuels and enhanced energy efficiency. But a report released Jan. 19 by the Washington-based Pew Center on Global Climate Change says that carbon sequestration -- using forests and farmland as "biological scrubbers" or "sinks" to store excess carbon dioxide -- is just as feasible.

"The cost estimates of addressing climate change would be overly pessimistic without factoring in carbon sequestration," said Robert Stavins, a Harvard University economist who co-authored the report with Kenneth Richards of Indiana University.

"It is potentially very important for climate change policy, especially for the United States," he said.

Their report, titled "The Cost of U.S. Forest-based Carbon Sequestration", synthesized nearly a dozen previous studies and concluded that 500 million tons could be safely disposed of each year for 30 to 90 dollars per ton, depending on the region and the method used.

Over the last century and half, scientists around the world have measured a steady increase in greenhouse gas emissions from fossil fuel combustion, with the most dramatic rise in the United States.

While emissions due to deforestation have also been growing, that process has been slower here. Still, the country's carbon absorption steadily declined since the 1960s, even as its emissions continue to accelerate.

Too much carbon dioxide in the upper atmosphere creates a blanket effect that traps solar radiation and causes the planet to warm -- in turn sparking disease epidemics and extreme weather patterns.

President George W. Bush has refused to submit the treaty to Congress for ratification because he says industrialized nations are unfairly singled out, and that Kyoto would cost the United States upwards of five million jobs.

Although the U.S. Environmental Protection Agency says on its website that "sequestration activities can be carried out immediately, appear to present relatively cost-effective emission reduction opportunities, and may generate environmental co-benefits," the agency refused to comment on the report.

But if and when the United States does join the treaty, experts say, it will need strategies to comply with Kyoto's emissions caps -- and a key one could be boosting sequestration.

The amount of agricultural land involved would be huge, the Pew report underlined. To sequester 300 million tons of carbon each year -- about one-fifth of U.S. emissions -- would require 148 million acres, at a total annual cost of $7.2 billion.

"When you think of it as an area the size of Texas, it's really striking, but this would be spread around the United States," Stavins explained. "Every region has land that would be a good candidate for conversion."

"To put this in perspective, total cropland, pasture and range in the United States is on order of one billion acres," he added.

Carbon dioxide circulates in a continuous flow through the atmosphere, the oceans, and the earth's ecosystems. The main culprits behind the slow but steady increase in atmospheric carbon are the burning of fossil fuels, which adds 5.5 billion metric tons of carbon per year, and land-use changes, which account for another 1.1 billion tons.

The earth's natural carbon "sinks" -- the oceans and forests -- absorb an impressive 3.2 billion tons of carbon, but that still leaves 3.4 billion tons of excess carbon in the atmosphere every year.

Examples of agricultural sequestration practices include planting grasses or trees along streams and croplands to prevent soil erosion, better management of grazing land, using a tillage system in which at least 30 percent of the crop residue remains on the soil after planting, and substituting biomass for fossil fuels.

Land could also be turned over for forestation, which would incur maintenance costs associated with fertilization, thinning, security, and other activities, but would also mean a loss of agricultural production.

"We call it the 'opportunity cost' -- what must be sacrificed beyond the accountant's measure of monetary outlays," Richards said.

Tree species in different regions also absorb carbon at different rates, scientists have found. For example, the loblolly pine in the southern plains states takes in the most carbon early in its life cycle, peaking in the second decade of growth and declining rapidly thereafter.

The ponderosa pine, on the other hand, which grows in central mountain states, has a gradually increasing rate of carbon sequestration over 70 years, peaking at about three tons per acre per year, and declining gradually over the succeeding century.

Stavins and Richards list several ways the government could encourage sequestration, including giving subsidies to private landowners for adopting practices that are known to increase carbon stocks; taxing undesirable land-use changes; expanding forest plantations on public lands; and establishing a carbon trading system.

"In fact, the costs of carbon sequestration could end up being below carbon trading (share prices) if the United States becomes a party to Kyoto, because demand would push the prices up," Stavins said.