2 Greenhouse Gases on the rise worry scientists

WASHINGTON (AP) -- 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. Scientists have been trying to figure out how they would know if this process is starting.

By contrast, nitrogen trifluoride has been considered such a small problem that it's 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. It is set to be published in Geophysical Letters in November.

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.

But nitrogen trifluoride is one of the more potent gases, thousands of times stronger at trapping heat than carbon dioxide. Methane is more than 20 times more potent than carbon dioxide on a per molecule basis. Carbon dioxide remains the most important gas because of its huge levels and rapid growth.

Still, methane and the potential of future increases is a worry, Weiss and others say.