Are landfills a major threat to climate?

Are landfills a major threat to climate?

Most people associate an increase inchlorofluorocarbons and carbon dioxide with such climate-altering changes as ozone destruction and global "greenhouse' warming. However, other trace gas pollutants--including methane--can also affect ozone and warming (SN: 5/18/85, p.308). A new study suggests solid-waste landfills are a substantial source of atmospheric methane right now, and may grow dramatically to become one of the world's largest sources, as developing countries establish more and more waste dumps.

The study, by Paul J. Crutzen and H.G.Bingemer at the Max Planck Institute for Chemistry in Mainz, West Germany, challenges the conclusions of a recently distributed report compiled by the Department of Energy. The Department of Energy report, a five-volume survey of the scientific literature on effects of climate-altering emissions, concludes that sources of atmospheric methane resulting from human activities "seem to be having only a minor influence on the [atmospheric] methane budget.'

But the German calculations--basedon estimates of the quantity and types of urban wastes disposed in landfills throughout the world--indicate that the anaerobic decay of organic material buried in municipal- and industrial-waste dumps may be contributing between 30 million and 70 million tons of methane per year. If true, that would represent 6 to 18 percent of the methane annually released into the atmosphere, they say, rivaling emissions from such leading natural methane sources as domestic animals, forest burning and wetlands (including rice paddies). In making their calculations, Crutzen and Bingemer ignored wastes generated in rural areas, under the assumption that most of those wastes ultimately are used as fodder or fuel, rather than being dumped.

According to Aslam Khalil, an atmosphericscientist with the Oregon Graduate Center in Beaverton, these landfill estimates "are not inconsistent with any measurements we have made.' In fact, he notes, his own tally of source estimates for atmospheric methane, published in 1983, came up about 50 million to 70 million tons short of what could be accounted for in the atmosphere. Landfills might well account for part of that earlier gap, he says.

Writing in the Feb. 20 JOURNAL OFGEOPHYSICAL RESEARCH, the German researchers note that although industrialized countries are the main source of landfill-generated methane today, "very large increases in methane production from waste dumps are expected in the coming decades from the developing world. Consequently, methane production from municipal and industrial wastes could become one of the main contributors to the global atmospheric methane budget.'

One way to limit methane emissionsfrom these dumps is to collect the gas before it escapes from a landfill. This will "not only provide an economical energy source, but will also reduce global air pollution significantly,' the German researchers say.

Crutzen and Bingemer's thesis "makessense to me,' says Pat Zimmerman, an atmospheric scientist studying methane sources at the National Center for Atmospheric Research in Boulder, Colo. However, he says, the significance of their paper is not in the magnitude of its landfill-methane estimates, which still are subject to large uncertainties. Rather, it may focus researchers' attention on quantifying a new facet of the methane problem, he says.

Zimmerman also cautions againstdownplaying the contribution of other methane sources. His own work suggests that termites may account for an even higher percentage of methane release (SN: 11/6/82, p.295). "There are a lot of uncertainties throughout this whole problem,' he says.