Magazine article Science News

Runaway Greenhouse Gas Losing Its Steam

Magazine article Science News

Runaway Greenhouse Gas Losing Its Steam

Article excerpt

Although the international community missed its opportunity in Brazil last month to set limits on carbon dioxide emissions, not all the news under the greenhouse is bad. Without even trying, humans have apparently succeeded in slowing the atmospheric buildup of methane, another powerful greenhouse gas, scientists reported this week.

Measurements made around the world reveal that while concentrations of methane continue to increase, they are not rising as quickly now as they were almost a decade ago. In 1983, methane levels were climbing at 13.3 parts per billion per year. But by 1990, the rate of increase had dropped to 9.5 parts per billion per year, according to researchers with the National Oceanic and Atmospheric Administration (NOAA), the University of Colorado at Boulder, and the Australian Commonwealth Scientific and Industrial Research Organization, based in Mordialloc, Victoria. They describe their findings in the July 23 NATURE.

Climate experts worry about rising methane levels because the buildup of this gas accounts for roughly 15 to 20 percent of the greenhouse warming power added to the atmosphere each year. Methane comes from natural sources as well as from human activities such as cattle rearing, rice farming, and the mining of fossil fuels.

The researchers analyzed a data set of roughly 10,000 air samples, collected at 37 sites scattered around the world, mostly on islands. While the scientists cannot pinpoint what has put the brakes on the methane buildup, the pattern of recent changes offers some clues. …

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