A sharp new debate has sprung up among atmospheric scientists over where to aim efforts to stave off the prospect of global warming from the buildup of heat-trapping greenhouse gases in the atmosphere. Some say the main target should be carbon dioxide, the most common greenhouse gas, while others say the most practical solution is to focus first on less common, but more powerful, substances possibly influencing climate, like methane, ozone and soot.
The debate comes just as negotiators from more than 150 countries are preparing to head to The Hague next month to put flesh on the bones of the 1997 Kyoto Protocol, a treaty outlining commitments by industrialized countries to reduce their greenhouse emissions and help poor countries avoid new emissions as their economies grow.
The argument for attacking the less common greenhouse ingredients is mainly based on the idea that these substances contribute to harmful air pollution as well as climate change -- and so an easier case can be made to policy makers and the public to clean them up.
They are also relatively easy to attack with existing or developing technologies, whereas carbon dioxide can still generally be reduced only by burning less fuel.
Proponents of this strategy, most notably Dr. James E. Hansen, an influential NASA climate expert, say that cutting carbon dioxide, at least in the short term, is a far more daunting task because it is a basic byproduct of burning coal and oil. In other words it is a basic byproduct of almost every aspect of modern life.Continue reading the main story
But there are problems with focusing on other heat-trapping substances, as well, other scientists say. Soot and the other greenhouse gases, they argue, constitute an extraordinarily complex brew whose influence on climate and interactions with each other and with clouds and other atmospheric ingredients are still poorly understood.
''When you add in their chemical interactions, most scientists' eyes glaze over, it's so complicated,'' said Dr. Michael Oppenheimer, an atmospheric chemist who is chief scientist of Environmental Defense, a private conservation group.
The debate was spurred last August, when Dr. Hansen and a team of his colleagues at NASA's Goddard Institute for Space Studies, which is based in Manhattan, published ''Global Warming in the 21st Century: An Alternative Scenario,'' in The Proceedings of the National Academy of Sciences.
In the paper, they said that deep cuts in carbon dioxide emissions were probably impossible in the short run, while the other gases and soot were already targets because of their contribution to old-fashioned pollution. In its conclusion, the team used a word rarely found in studies of global warming: ''optimistic.''
The analysis has since been criticized by some longtime colleagues of Dr. Hansen and embraced by industry groups and elected officials who have long voiced doubt about the science behind climate change and the need for big cuts in fossil fuel use.
Just last Thursday, for example, Dr. Hansen's findings were repeatedly cited by Republican senators holding a hearing questioning the need for the Kyoto Protocol, which has been signed by more than 100 countries but has yet to be ratified by any industrial powers. Many of the treaty's provisions focus on cutting carbon dioxide.
Dr. Hansen's critics, including many influential experts on the atmosphere and climate, say that emissions of all of the gases should be curtailed wherever this is possible and not too expensive but that cutting carbon dioxide must still be a top priority.
For his part, Dr. Hansen said that both sides in the debate had largely either misrepresented or misinterpreted his study. He said the fundamental goal was simply to find the most efficient -- and politically and economically palatable -- way to cleanse the atmosphere of human effluents that have the biggest impact on climate.
He said he still hoped that once the dust settled, policy makers from all parts of the spectrum might find merit in the proposal.
''I think it may be possible to get conservatives and libe