entist in the climate program at the Massachusetts Institute of Technology. She published a study last month in The Journal of Geophysical Research -- Atmospheres in which she and several colleagues concluded that future trends for ozone and methane would largely cancel each other out.
Generally, she said, models show that although ozone should increase in cities, on average around the globe levels should drop, and this will allow methane to persist longer in the air because there will be fewer hydroxyl radicals there to destroy it.
The effects of all of this on climate, she concluded in the paper, are likely to be a wash.
Dr. Ralph J. Cicerone, an atmospheric scientist and chancellor of the University of California at Irvine, said he agreed with Dr. Hansen that the complexity of chemistry in the atmosphere should not deter efforts to cut ozone, methane and other substances that contribute both to pollution and climate problems.
He pointed to recent work showing that although levels of ozone and nitrogen oxides, which help create ozone, have been dropping over the United States and western Europe, they are relentlessly rising elsewhere.
One study, Dr. Cicerone said, showed that nitrogen oxide concentrations in China, South Korea, Taiwan and Japan rose 60 percent from 1997 to 1998. There is plenty of concrete benefit to be gained, with little of the potential pain that might come from putting the same effort into reducing carbon dioxide emissions.
But other scientists fear that any shift away from reducing burning of coal and oil would only impede long-term progress toward limiting the human influence on climate.
''The most important thing is to stabilize all these emissions,'' said Dr. Thomas P. Ackerman, chief scientist in the Energy Department's atmospheric radiation measurement program in Richland, Wash. ''And there's no way you're going to do that without attacking the fossil-fuel problem. We're a society that likes to have simple solutions, but there are no easy answers here.''
For his part, Dr. Hansen seems satisfied simply to have nudged the climate debate toward considering partial, common-sense solutions that he feels have been neglected.
He added that one way to spur interest would be to illustrate the other harmful qualities of the greenhouse ingredients on his list up close and personal.
Maybe, he said, it would make sense to ''lock people in a room with a good bit of ozone and black carbon in the air until they come up with some positive ideas.''
Correction: October 4, 2000, Wednesday An article in Science Times yesterday about efforts to stave off global warming misstated the period in which emissions of nitrogen oxides from four Asian countries rose 60 percent. It was 1987 to 1998, not 1997 to 1998.Continue reading the main story