Carbon dioxide isn't the only greenhouse gas that worries climate scientists. Airborne levels of two other potent gases — one from ancient plants, the other from flat-panel screen technology — are on the rise, too.
And that's got scientists concerned about accelerated global warming.
The gases are methane and nitrogen trifluoride. Both pale in comparison to the global warming effects of carbon dioxide, produced by the burning of coal, oil and other fossil fuels. In the past couple of years, however, these other two gases have been on the rise, according to two new studies. The increase is not accounted for in predictions for future global warming and comes as a nasty surprise to climate watchers.
Methane is by far the bigger worry. It is considered the No. 2 greenhouse gas based on the amount of warming it causes and the amount in the atmosphere. The total effect of methane on global warming is about one-third that of man-made carbon dioxide.
Methane comes from landfills, natural gas, coal mining, animal waste, and decaying plants. But it's the decaying plants that worry scientists most. That's because thousands of years ago billions of tons of methane were created by decaying Arctic plants. It lies frozen in permafrost wetlands and trapped in the ocean floor. As the Arctic warms, the concern is this methane will be freed and worsen warming.
It's still early and the data are far from conclusive, but scientists say they are concerned that what they are seeing could be the start of the release of the Arctic methane.
After almost eight years of stability, atmospheric methane levels — measured every 40 minutes by monitors near remote coastal cliffs — suddenly started rising in 2006. The amount of methane in the air has jumped by nearly 28 million tons from June 2006 to October 2007. There is now more than 5.6 billion tons of methane in the air.
“If it's sustained, it's bad news,” said MIT atmospheric scientist Ron Prinn, lead author of the methane study, which will be published in the journal Geophysical Research Letters on Oct. 31. “This is a heads-up.” By contrast, nitrogen trifluoride has been considered such a small problem that it has generally been ignored. The gas is used as a cleaning agent during the manufacture of liquid crystal display television and computer monitors and for thin-film solar panels.
Earlier efforts to determine how much nitrogen trifluoride is in the air dramatically underestimated the amounts, said Ray Weiss, a geochemistry professor with Scripps Institution of Oceanography and lead author on a nitrogen trifluoride paper
Nitrogen trifluoride levels in the air — measured in parts per trillion — have quadrupled in the last decade and increased 30-fold since 1978, according to Weiss, who is also a co-author of the methane paper.
It contributes only 0.04 percent of the total global warming effect that man-made carbon dioxide does from the burning of fossil fuels.