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Although there is much less methane in the atmosphere -- about 1800 parts per billion -- methane is 25 times more potent a greenhouse gas than CO2, because it absorbs more of the sun's energy. "People really aren't sure why methane leveled off" in past years, said Ed Dlugokincky at NOAA. A number of factors probably contributed to a decline in methane emissions beginning in the early 1990s, including a decline in production of fossil fuels in the former Soviet Union accompanying its economic collapse, he said, and efforts to reduce methane emissions from landfills and other human sources in Western Europe. The 2007 rise is equally mysterious. "We're pretty sure it's not the result of biomass burning," Dlugokincky said, because the researchers did not detect an increase in carbon monoxide levels, which would be present if burning were the culprit. The measurements -- weekly samples from about 60 stations around the world -- suggest that methane increases may come from tropical and Arctic latitudes. This may mean that warmer, wetter weather over wetlands in these regions allowed bacteria there to produce more methane, Dlugokincky said. Another possibility is that the increase marks the beginning of methane releases from the thawing of Arctic permafrost, a potentially huge source of greenhouse gases. Permafrost holds about the same amount of carbon as is present in all of the world's recoverable coal, he said. "It's way too soon to answer a question like that," he cautioned. Longer term monitoring and more measurement stations in the Arctic will be needed to tell whether this is just a blip in the methane record caused by the right weather conditions, or whether this is a longer term trend. "We are on the lookout in case something happens in the Arctic," Tans said. Related Links: |
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